Understanding infrared thermography reading 7 part 1 of 2 by charlie Chong

Infrared Thermal Testing Reading VII Part 1 of 2 My ASNT Level III, Pre-Exam Preparatory Self Study Notes 12 June 2015

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Military Applications

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Military Applications

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Military Applications

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Military Applications

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The Magical Book of Infrared Thermography

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ASNT Certification Guide NDT Level III / PdM Level III IR - Thermal/Infrared Testing Length: 4 hours Questions: 135 1. Principles/Theory • Conduction • Convection • Radiation • The nature of heat and heat flow • Temperature measurement principles • Proper selection of Thermal/Infrared testing 2. Equipment/Materials • Temperature measurement equipment • Heat flux indicators • Performance parameters of non-contact devices

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3. Techniques • Contact temperature indicators • Non-contact pyrometers • Infrared line scanners • Thermal/Infrared imaging • Heat flux indicators • Exothermic or endothermic investigations • Friction investigations • Fluid Flow investigations • Thermal resistance (steady state heat flow) • Thermal capacitance investigations 4. Interpretation/Evaluation • Exothermic or endothermic investigation • Friction investigations • Fluid flow investigations • Differences in thermal resistance • Thermal capacitance investigations

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5. Procedures • Existing codes and standards • Job procedure development 6. Safety and health • Safety responsibility and authority • Safety for personnel • Safety for client and facilities • Safety for testing equipment Reference Catalog Number NDT Handbook, Third Edition: Volume 3, Infrared and Thermal Testing 143 Fundamentals of Heat and Mass Transfer 952 ASNT Level III Study Guide: Infrared and Thermal Testing 2265

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Fion Zhang at Shanghai 12th June 2015

http://meilishouxihu.blog.163.com/

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http://greekhouseoffonts.com/

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Notation: h σ α ε ρ τ

= Plank’s constant = Stephen-Boltzmann constant = absorptivity = emissivity = reflectivity = transmissivity

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Infrared Spectrum

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IVONA TTS Capable.

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Assorted Reading

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Subject matters approaches

Reading VII Content  Reading One: Thermocouples: The Operating Principle  Reading Two: Facilities Instructions, Standards, & Techniques Vol.4~11+2 “Thermal Analysis”  Reading Three: Infrared Thermography Guide-R3  Reading Four: Emissivity: Understand the difference between apparent and actual IR temperatures

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Reading: One Thermocouples: The Operating Principle

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

â&#x2013; THERMOCOUPLES: THE OPERATING PRINCIPLE A thermocouple is a device made by two different wires joined at one end, called junction end or measuring end. The two wires are called thermo elements or legs of the thermocouple: the two thermo elements are distinguished as positive and negative ones. The other end of the thermocouple is called tail end or reference end (Figure 1). The junction end is immersed in the environment whose temperature T2 has to be measured, which can be for instance the temperature of a furnace at about 500Â°C, while the tail end is held at a different temperature T1, e.g. at ambient temperature.

Figure 1: Schematic drawing of a thermocouple

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

Because of the temperature difference between junction end and tail end a voltage difference can be measured between the two thermo elements at the tail end: so the thermocouple is a temperature-voltage transducer. The temperature versus voltage relationship is given by:

where Emf is the Electro-Motive Force or Voltage produced by the thermocople at the tail end, T1 and T2 are the temperatures of reference and measuring end respectively, S1,2 is called Seebeck coefficient of the thermocouple and S1 and S2 are the Seebeck coefficient of the two thermoelements; the Seebeck coefficient depends on the material the thermoelement is made of.

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

Looking at Equation1 it can be noticed that: 1. a null voltage is measured if the two thermoelements are made of the same materials: different materials are needed to make a temperature sensing device, 2. a null voltage is measured if no temperature difference exists between the tail end and the junction end: a temperature difference is needed to operate the thermocouple, 3. the Seebeck coefficient is temperature dependent. In order to clarify the first point let us consider the following example (Figure 2): when a temperature difference is applied between the two ends of a single Ni wire a voltage drop is developed across the wire itself. The end of the wire at the highest temperature, T2, is called hot end, while the end at the lowest temperature, T1, is called cold end.

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

Figure 2: Emf produced by a single wire

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

When a voltmeter, with Cu connection wires, is used to measure the voltage drop across the Ni wire, two junctions need to be made at the hot and cold ends between the Cu wire and the Ni wire; assuming that the voltmeter is at room temperature T1, one of the Cu wires of the voltmeter will experience along it the same temperature drop from T2 to T1 the Ni wire is experiencing. In the attempt to measure the voltage drop on the Ni wire a Ni-Cu thermocouple has been made and so the measured voltage is in reality the voltage drop along the Ni wire plus the voltage drop along the Cu wire. The Emf along a single thermoelement cannot be measured: the Emf measured at the tail end in Figure1 is the sum of the voltage drop along each of the thermoelements. As two thermoelements are needed, the temperature measurement with thermocuoples is a differential measurement. Note: if the wire in Figure 2 was a Cu wire a null voltage would have been measured at the voltmeter.

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

The temperature measurement with thermocouples is also a differential measurement because two different temperatures, T1 and T2, are involved. The desired temperature is the one at the junction end, T2. In order to have a useful transducer for measurement, a monotonic Emf versus junction end temperature T2 relationship is needed, so that for each temperature at the junction end a unique voltage is produced at the tail end. However, from the integral in Equation1 it can be understood that the Emf depends on both T1 and T2: as T1 and T2 can change independently, a monotonic Emf versus T2 relationship cannot be defined if the tail end temperature is not constant. For this reason the tail end is maintained in an ice bath made by crushed ice and water in a Dewar flask: this produces a reference temperature of 0째C. All the voltage versus temperature relationships for thermocouples are referenced to 0째C. The resulting measuring system required for a thermocople is shown in Figure 3.

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

Figure 3: A measuring system for thermocouples

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

In order to measure the voltage at the tail end, two copper wires are connected between the thermoelements and the voltmeter: both the Cu wires experience the same temperature difference and as a result the voltage drops along each of them are equal to each other and cancel out in the measurement at the voltmeter. The ice bath is usually replaced in industrial application with an integrated circuit called cold junction compensator: in this case the tail end is at ambient temperature and the temperature fluctuations at the tail end are tolerated; in fact the cold junction compensator produces a voltage equal to the thermocouple voltage between 0째C and ambient temperature, which can be added to the voltage of the thermocouple at the tail end to reproduce the voltage versus temperature relationship of the thermocouple. A sketch of a thermocouple with cold junction compensation is reported in Figure 4.

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

Figure 4: An example of Cold Junction Compensation

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

It should be underlined that the cold junction compensation cannot reproduce exactly the voltage versus temperature relationship of the thermocouple, but can only approximate it: for this reason the cold junction compensation introduces an error in the temperature measurement. Figure4 shows also the filtering and amplification of the thermocouple. Being the thermocouple voltage a DC signal, removal of AC noise through filtering is beneficial; furthermore the thermocouples produce voltage of few tens of mV and for this reason amplification is required. The small voltage range for some of the most common thermocouples (letter designated thermocouples) is shown in Figure5, where their voltage versus temperature relationship is reported. Type R, S and B thermocouples use Pt-base thermoelements and they can operate at temperatures up to 1700째C; however they are more expensive and their voltage output is lower than type K and type N thermocouples, which use Ni-base thermoelements. However, Ni base thermocouples can operate at lower temperatures than the Pt-base ones. Table1 reports the approximate compositions for positive and negative thermoelements of the letter designated thermocouples. Charlie Chong/ Fion Zhang

http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

Figure 5: Voltage vs Temperature relationship for letter-designated thermocouples

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

Table 1: Approximate composition for thermoelements of letter-designated thermocouples

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

All the voltage-temperature relationships of the letter designated thermocouples are monotonic, but not linear. For instance the type N thermocouple voltage output is defined by the following 10 degree polynomials, where t is the temperature in degree Celsius:

The coefficients Ci are reported in Table2. In order to have a linear voltage-temperature relationship the Seebeck coefficient should be constant with temperature (see Equation1); however the Seebeck coefficient is temperature dependent, as shown for instance for type K thermocouple in Figure6. Additional details on the voltage-temperature relationships for letter designated thermocouple can be found at: http://srdata.nist.gov/its90/main/ Charlie Chong/ Fion Zhang

http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

Table 2: Type N thermocouple coefficients

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

Figure 6: Type K Seebeck coefficient versus Temperature

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http://www.msm.cam.ac.uk/utc/thermocouple/pages/ThermocouplesOperatingPrinciples.html

â&#x2013; Thermocouple Basics

Let's start with T. J. Seebeck, who in 1821 discovered what is now termed the thermoelectric effect. He noted that when two lengths of dissimilar metal wires (such as iron and Constantan) are connected at both ends to form a complete electric circuit, an emf is developed when one junction of the two wires is at a different temperature than the other junction. Basically, the developed emf (actually a small millivoltage) is dependent upon two conditions: (1) the difference in temperature between the hot junction T2 and the cold junctionT1, Î&#x201D;T. Note that any change in either junction temperature can affect the emf value and Î&#x201D;V (2) the metallurgical composition of the two wires. S1, S2, Seebeck coefficient of the two thermoelements

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Although a ‘thermocouple’ is often pictured as two wires joined at one end, with the other ends not connected, it is important to remember that it is not a true thermocouple unless the other end is also connected! It is well for the user to remember this axiom 公理 : 'Where there is a hot junction there is always a cold or reference junction ' (even though it may seem hidden inside an instrument 1,000 feet away from the hot junction). Still in Seebeck's century, two other scientists delved deeper into how the emf is developed in a thermoelectric circuit. Attached to their names are two phenomena they observed: ■ The Peltier effect (for Jean Peltier in 1834) and ■ The Thompson effect (for Sir William Thompson a.k.a Lord Kelvin in 1851).

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Without getting into the theories involved, we can state that: “the Peltier effect is the emf resulting solely from the contact of the two dissimilar wires. Its magnitude varies with the temperature at the juncture.” Similarly, ‘the Thompson effect can be summarized as having to do with emf's produced by a temperature gradient along a metal conductor.” Since there are two points of contact and two different metals or alloys in any thermocouple, there are two Peltier and two Thompson emfs. The net emf acting in the circuit is the result of all the above named effects. Read more on Peltier and Thompson effects http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20Word%20%20Class%206_Temperature%20Measurements%20using%20Thermocouples.pdf

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Polarity of the net emf is determined by: (a) the particular metal or alloy pair that is used (such as iron/ constantan) and (b) the relationship of the temperatures at the two junctions. The value of the emf can be measured by a potentiometer, connected into the circuit at any point. In summary, the net emf is a function primarily of the temperature difference between the two junctions and the kinds of materials used. If the temperature of the cold junction is maintained constant, or variations in that temperature are compensated for, then the net emf is a function of the hot junction temperature. (cold junction either at constant known temperature of compensated) In most installations, it is not practical to maintain the cold junction at a constant temperature. The usual standard temperature for the junction (referred to as the 'reference junction') is 32 ยบ F (0 ยบC). This is the basis for published tables of emf versus temperature for the various types of thermocouples.

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The Law of Intermediate Temperatures provides a means of relating the emf generated under ordinary conditions to what it should be for the standardized constant temperature (e.g., 32 ยบ F). Referring to Figure 4-1, which shows thermocouples 1 and 2 made of the same two dissimilar metals; this diagram will provide an example of how the law works.

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Figure 4-1: Thermocouple Operation mV 8 Thermocouple 3

Thermocouple 2

Thermocouple 1

0 0 Charlie Chong/ Fion Zhang

200

400

600

800 ยบ F

Thermocouple 1 has its cold junction at the standard reference temperature of 32 º F and its hot junction at some arbitrary intermediate reference temperature (in this case, 300 º F). It generates 2.68 mv. Thermocouple 2 has its cold junction at the intermediate reference point of 300 º F and its hot junction at the temperature being measured (700 º F). It generates 4.00 mv. The Law of Intermediate Temperatures states the sum of the emfs generated by thermocouples 1 and 2 will equal the emf that would be generated by a single thermocouple (3, shown dotted) with its cold junction at 32 º F and its hot junction at 700 º F, the measured temperature. That is, it would hypothetically read 6.68 mv and represent the 'true' emf according to the thermocouple's emf vs. temperature calibration curve.

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Based upon this law, the manufacturer of an infrared thermocouple need only provide some means of substituting for the function of thermocouple 1 to provide readings referenced to the standard 32 ยบ F cold junction. Many instruments accomplish this with a temperature-sensitive resistor which measures the variations in temperature at the cold unction (usually caused by ambient conditions) and automatically develops the proper voltage correction. Another use of this law shows that extension wires having the same thermoelectric characteristics as those of the thermocouple can be introduced into the thermocouple circuit without affecting the net emf of the thermocouple. In practice, additional metals are usually introduced into the thermocouple circuit. The measuring instrument, for example, may have junctures that are soldered or welded. Such metals as copper, manganin, lead, tin, and nickel may be introduced.

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Would not additional metals like this modify the thermocouple's emf? Not so, according to the Law of Intermediate Metals. It states that the introduction of additional metals will have no effect upon the emf generated so long as the junctions of these metals with the two thermocouple wires are at the same temperature. This effect is illustrated in Figure 4-2, with A and B representing the thermocouple wires. A practical example of this law is found in the basic thermoelectric system shown in Figure 4-3. The instrument can be located at some distance from the point of measurement where the thermocouple is located. Several very basic and practical points are illustrated in this elementary circuit diagram: Quite often the most convenient place to provide the cold junction compensation is in the instrument, remote from the process. With the compensation means located in the instrument, in effect, the thermoelectric circuit is extended from the thermocouple hot junction to the reference (cold) junction in the instrument. The actual thermocouple wires normally terminate relatively near the hot junction.

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Conventional couples have what is called a 'terminal head' at which point interconnecting wires, known as 'extension wires' are required as shown. Since these wires are in the thermoelectric circuit, they must essentially match the emf vs. temperature characteristics of the thermocouple. With the cold junction located inside the instrument, internal extension wires of the proper materials must be used between the instrument terminals and the cold junction. With this set-up, there are in effect three added thermocouples in the circuit: one in the thermocouple assembly, one in the external extension wire, and in the internal extension wire. However, according to the Law of Intermediate Temperatures, the actual temperatures at the terminal head and at the instrument terminals is of no consequence: the net effect of the three thermocouples is as if one thermocouple ran from the hot junction to the cold junction.

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Figure 4-2: Equivalent Thermocouple Circuits

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Figure 4-3: Typical Thermocouple Installation

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The Law of Intermediate temperatures The law of intermediate temperatures indicates that the electromotive forces are additive for temperature intervals The sum of two electromotive forces, generated by two thermocouples:  E1 with its junctions between T1 and T2  E2 with its junctions between T2 and T3  Eequivalent to emf generated by one thermocouple with its junctions between T1 and T3

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http://www.energy.kth.se/compedu/webcompedu/WebHelp/S3_Measuring_Techniques/B7_Temperature_Me asurements/C2_Practical_Thermometers/S3B7C2_files/Intermediate_temperatures.htm

Law of Homogeneous Materials A thermoelectric current cannot be sustained in a circuit of a single homogeneous material by the application of heat alone, regardless of how it might vary in cross section. Law of Intermediate Materials The algebraic sum of the thermoelectric forces in a circuit composed of any number of dissimilar materials is zero if all of the circuit is at a uniform temperature. Law of Successive or Intermediate Temperatures If two dissimilar homogeneous materials produce thermal emf1 when the junctions are at T1 and T2 and produce thermal emf2 when the junctions are at T2 and T3, the emf generated when the junctions are at T1 and T3 will be emf1 + emf 2. Could somebody talk about intermediate connecting 3rd material?

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What is the law of intermediate metals? According to the Thermocoupleâ&#x20AC;&#x2122;s Law of Intermediate Metals, illustrated in the figure, inserting any type of wire into a thermocouple circuit has no effect on the output as long as both ends of that wire are the same temperature, or isothermal. Consider the circuit in the next figure. Both circuits are quite similar but a short length of constantan wire has been inserted just before junction J3 and the junctions are assumed to be held at identical temperatures. Assuming that junctions J3 and J4 are the same temperature, the Thermocouple Law of Intermediate Metals indicates that the circuit in the figure on left is electrically equivalent to the circuit of the figure on right. Consequently, any result taken from the circuit in the figure on left also applies to the circuit illustrated in the figure on right.

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http://www.thermibel.be/documents/thermocouples/thermoocuple-law-metals.xml?lang=en

Mtls-A

Mtls-B

Mtls-A

Isothermal Region

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Mtls-C

Mtls-B

The Law of Intermediate temperatures The law of intermediate temperatures indicates that the electromotive forces are additive for temperature intervals The sum of two electromotive forces, generated by two thermocouples:  E1 with its junctions between T1 and T2  E2 with its junctions between T2 and T3  Eeqv Equivalent to emf generated by one thermocouple with its junctions between T1 and T3

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http://www.energy.kth.se/compedu/webcompedu/WebHelp/S3_Measuring_Techniques/B7_Temperature_ Measurements/C2_Practical_Thermometers/S3B7C2_files/Intermediate_temperatures.htm

Peltier effect The Peltier heat is the quantity of heat in addition to the quantity I2R that must be removed from the junction to maintain the junction at a constant temperature. This amount of energy is proportional to the current flowing through the junction; the proportionality constant is the Peltier coefficient πAB , and the heat transfer required to maintain a constant temperature is:

Qπ = πAB∙I

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caused by the Peltier effect alone. This behavior was discovered by Jean Charles Athanase Peltier (1785-1845) during experiments with Seebeck’s thermocouple. He observed that passing a current through a thermocouple circuit having two junctions, as in Figure 4, raised the temperature at one junction, while lowering the temperature at the other junction.

http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20Word%20%20Class%206_Temperature%20Measurements%20using%20Thermocouples.pdf

Thomson effect Consider the conductor shown in Figure 5, which is subjected to a longitudinal temperature gradient and also subject to a potential difference, such that there is a flow of current and heat in the conductor.

Qσ = σ∙I(T2-T1) where σ is the Thomson coefficient

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http://www.me.uprm.edu/laboratories/inme4031/pdf_Documents/Classes/Microsoft%20Word%20%20Class%206_Temperature%20Measurements%20using%20Thermocouples.pdf

End Of Reading One

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Reading: Two Facilities Instructions, Standards, & Techniques Vol.4~11+2 â&#x20AC;&#x153;Thermal Analysisâ&#x20AC;? (abstract)

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U.S. Department of the Interior Technical Service Center Bureau of Reclamation Denver, Colorado

1.1 Infrared Thermogram Image Quality Image quality is affected by many factors, as shown in figure 7: Image quality contributors.

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1.1.1 Spot Size (IFOV) The thermal analysis equipment will record the temperature of a “spot” in the image and display this temperature. The size of the spot is critical since the temperature recorded is the average of the temperatures of the pixels within the spot. If the spot is too large, the average may “water down” a hot spot pixel, giving the false impression that the temperature is lower (or higher) than the pixel centered on the hot spot. Ideally, the spot size will be as small as possible, but there are practical limits. The spot size is partially determined by how close the device is to the target; and, in some cases, the approach distance must be relatively large for safety or physical obstructions or because the target is in the air. Using a telephoto lens on IR cameras will reduce the spot size of distant targets. Even though these can be expensive, they should be used where quantitative measurement is needed.

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When using hand-held radiation thermometers, it is critical to understand and take into account the spot size for your specific equipment. Hand-held radiation thermometers typically have a spot size ratio ranging from 6:1 to 110:1. For comparison, thermal imaging cameras have a spot size ratio ranging from 63:1 to 889:1 with the typical spot size being approximately 250:1. The spot size of a thermal imaging camera can be changed depending on work to be performed by using different lenses. Figure 8 is an example of how the actual spot size changes based on spot size ratio and the distance from the target. Assuming the employee is 6 feet from the equipment under test, the actual spot size can vary from 0.65 inch to 12 inches. If the actual target size is 0.5 inch, then with a spot size ratio of 110:1, the employee would need to be within 55 inches of the target to only measure the temperature of the target. If the spot size ratio was 12:1, then the employee would need to be within 6 inches of the target to only measure the temperature of the target.

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Figure 8. Spot size of hand-held radiation thermometer.

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It is important to understand the device’s spot size ratio, sometimes called the distance-to-spot ratio or instantaneous measurement field of view (IFOV), which determines the maximum distance the thermographer can be from the target and still get a good reading. For example, a spot size ratio of 250 to 1 means that, at 250 inches (about 21 feet), the spot size to be measured must be a minimum of 1 inch (the projected spot will cover 1” by the individual sensing pixel, should the target of interest is smaller than 1”, the reading will be the averaging of the adjacent areas of interest covered by the projected spot?) . If the thermographer cannot get within 21 feet, a telephoto lens should be used. If the spot size or target is less than 1 inch (for example, ½ inch), the device would need to be closer than approximately 10½ feet for accurate temperature readings, or a telephoto lens would be required. For ¼ inch, the device would need to be closer still. The target should be larger than the spot size to ensure accurate data.

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The realtionship between IFOVgeo and IFOVmeas IFOVmeas = 3 x IFOVgeo Where IFOVgeo = is the theoretical spot size base on angle subtended by the pixel in mRad. IFOVmeas is the practical spot size for correct measurement. The area of interest should not be larger than IFOVmeas for meaningful measurement. (to be verified!)

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1.1.2 Distance The physical distance of the IR thermal equipment to the target is one parameter that cannot be corrected after the image is taken and saved. The distance to the target is an important variable in determining apparent temperatures. The distance should be measured or estimated and entered into the camera. Using a laser distance device is an easy way to measure the distances between the thermographer and equipment. Never use a metal tape measure to determine the distance between the thermographer and equipment when working near energized equipment. The discussion above on spot size shows that the correct distance is very important to obtain quality IR images and proper analysis. The distance from the IR thermal equipment to the target needs to be reported on the PM forms. To simplify the process, it is possible to mark the floor in front of the equipment so the thermographer always maintains the same distance from the target, allowing for repeatable measurements.

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1.1.3 Field of View and Instantaneous Field of View The definition of field of view depends on the type of instrument used. For a hand-held radiation thermometer, the field of view (or instantaneous field of view [IFOV]) is the target spot size. (as there is only one sensor FOV=IFOV?) In a scanner, imager, or radiometer, the field of view is the scan angle, picture size, or total field of view. This can be related to a regular 35-millimeter (mm) camera; a 50-mm lens will provide a certain picture size. If the lens size is doubled to 100 mm (a basic telephoto lens), at the same distance, the overall field of view is reduced, but the items in the picture appear closer and clearer in detail. In IR thermography, the lenses are designated using angular notations. As the lens angle increases, so does the field of view. A â&#x20AC;&#x153;standardâ&#x20AC;? 24-degree lens will have a larger field of view than a 12-degree telephoto lens. IFOV relates directly to spatial resolution of the instrument used. IFOV is the smallest area that can be accurately seen at a given instance. Figure 9 illustrates the field of view and the relation to the instantaneous field of view when using a thermal imaging camera.

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Figure 9. Field of view of an IR camera.

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1.1.4 Estimating Emissivity Îľ

Before inspection of any component, it is essential that the emissivity of that component be estimated and set in the IR thermal inspection equipment. Otherwise, inaccurate temperatures will be recorded. For qualitative inspections, the starting emissivity may be estimated at 0.9â&#x20AC;&#x201C;0.95. It is a good practice for a facility to establish a uniform starting emissivity for consistent results. Hand-held radiation thermometers may or may not allow the user to change the emissivity of the instrument. If the instrument does not allow the user to change the emissivity, then it will only provide accurate results for objects with the preprogrammed emissivity. Coatings may be added to equipment included in the thermal analysis program that will change the emissivity of the object.

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Some cameras and the associated analyzing software programs can adjust emissivity after the image is saved. However, if the emissivity is set prior to imaging, quicker analysis may be made in the field as to the severity of any anomalies found. Emissivity tables are provided in many publications and also can be found in appendix F. These tables should be used sparingly and with caution. The best emissivity value for a given target is established in the field using accepted practices for determining the targetâ&#x20AC;&#x2122;s emissivity. See appendix E.

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1.1.5 Background Sources Heat energy from sources of radiation other than the target must be estimated and entered into the camera for a more accurate temperature measurement. There are specific procedures for using the camera to determine the background temperature. Once obtained, these values should be inputted into the camera. (The reflectivity Ď ? or Tamb only? without the Ď , the ambient contributions could not be quantified?)

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1.1.6 Pointing, Aiming, and Ambient Reflections Viewing angles can affect the amount of IR radiation gathered by the thermal analysis instrumentation. The optimum angle of the instrument to the target is 90° (perpendicular) to the plane of the target. Effort should be made to ensure the best possible viewing of the target. The optimum angle cannot always be achieved or maintained. Therefore, the temperature recorded from a target on an angle other than 90° may not be as accurate. Generally, shiny surfaces do not emit radiation energy efficiently and can be hot while appearing cool in an IR thermographic image or on the readout of the hand-held radiation thermometer. Likewise, direct reflections of sun rays from shiny surfaces into the camera can be misread as hot spots. One method of determining if the spot observed in a camera is an anomaly or is the result of a reflection is to move around the target when possible. Usually, when conducting outdoor inspections, if the “hot” spot goes away or diminishes significantly, then the “hot” spot was probably a reflection. If the hot spot remains, measure it.

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Do not rely on this technique for all targets. Targets may be large or shaped so that hot spots on the front side may be completely obscured when viewed from the back side. The technique of moving around then will not accurately locate all anomalies. The thermographer must be aware of unusual conditions that may influence the IR radiation measured by the test instrument. This points out the need for training and experience. It also emphasizes the need to have the thermographer familiar with the workings of the equipment being inspected.

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1.1.7 Calibration Have the thermal analysis instrumentation calibrated periodically, according to the manufacturerâ&#x20AC;&#x2122;s recommendations. This will help ensure the instruments are working properly and recording accurate thermograms and/or temperatures.

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2.1.8 Reference Photos It is very helpful when analyzing thermograms to have a visual reference photo taken with a standard camera of the equipment at the same time and point of view as the thermogram. The reference photo will make it easier to identify components that might not be obvious in the thermogram. When using hand-held radiation thermometers, reference photos are critical to identify locations of hot spots. Since hand-held radiation thermometers do not capture data, extensive notes and reference photos are the only way to document the location of temperature data for future reference.

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1.2 Methods of Determining or Enhancing the Emittance of a Target Thermographers calculate or determine the emissivity of different targets in a number of ways. Accurate emissivity values are needed if quantitative temperature measurements are required. If possible, emissivity enhancement coatings can be applied to target areas. Coatings, usually in the form of paint, have known emissivities. These coatings are usually applied to shiny or reflective surfaces to provide a higher known emissivity and to provide accurate temperature measurements. Most of the coatings today have emissivities at or near 0.95. Black electrical tape (3M Scotch 33â&#x201E;˘) can be used to determine the emissivity of targets. This tape has been measured and is used as a reference by many thermographers. Emissivity of the tape is 0.95. This technique requires the tape to be placed on the target material prior to energizing, loading, or heating the equipment to be monitored. For the following technique to work properly, the measured target or component temperature must be raised 20 degrees Fahrenheit (Â°F) or higher above ambient temperature. This technique will not work if the target is at ambient temperature. Charlie Chong/ Fion Zhang

Place a Â˝- to 1-inch square of the electrical tape on the target. Measure the background temperature by setting the emissivity to 1.0 in the infrared (IR) camera and pointing the camera away from the target. In most cases, defusing the focus will give an average background temperature. The background temperature also can be measured by using a piece of cardboard with an aluminum foil cover set next to the target. Again, set the camera emissivity to 1.0 and the camera slightly out of focus. Measure the temperature at the center of the cardboard/aluminum foil. The background temperature should be entered into the camera if the camera being used allows this. The correct distance to the target should be added to the camera settings. The thermographer needs to recognize the spot size and ensure that the target size is adequate and is in focus. (the target should be 3x the instrument spot size) Set the camera to an emissivity of 0.95. Once the target is at temperature, measure the temperature of the taped (or emissivity enhanced) area.

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Note the temperature. Move the measuring spot just off of the tape and on to the surface for which emissivity is to be determined. Adjust the emissivity in the camera, until the temperature of this spot matches the temperature measured on the tape. Once the temperatures match, read and record the emissivity. This emissivity now can be used in the future for this particular equipment and perhaps similar equipment. Other techniques for increasing emissivity of targets include using the geometry of the components. For instance, the intersection where a lug or nut meets the connection surface will form a small cavity that, when viewed in the IR camera, will have an increased emissivity. ( if the depth to width ration is 7, the emissivity could be assume to be 0.98?) All types of cavities will tend to have higher emissivities and should be used whenever possible. Other techniques or formulas for calculating emissivity can be found in numerous publications and are usually included in most training classes. Cavity radiatorâ&#x20AC;&#x201D;â&#x20AC;&#x201D;A hole, crack, scratch, or cavity that will have a higher emissivity that the surrounding surface because reflectivity is reduced. A cavity seven times deeper than wide will have an emissivity approaching 0.98. Charlie Chong/ Fion Zhang

Thermograms

Figure 1. Transformer bushing with incorrect washer that does not allow correct connection. Connection spot 1 (52.4 degrees Celsius [째C]), is greater than (>) 30 째C hotter than spot 2 (22.2 째C) on similar bushing under same load.

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Thermograms

Figure 2. High-side connection from transformer, illustrating a â&#x20AC;&#x153;barber poleâ&#x20AC;? effect where only part of the cable strands carry the current. This qualitative image prompted immediate remedial action.

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Thermograms

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Thermograms

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End Of Reading Two

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Reading: Three Infrared Thermography Guide-R3 Electric Power Research Institute

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ABSTRACT This guide is a valuable reference for the development of infrared thermography (IR) capabilities as part of a plant predictive maintenance program. The guide includes IR theory, a summary of IR inspection applications, and the technical information necessary to develop an effective in-house program. The body of the guide is structured for the general user of IR, and the appendices provide a more in-depth look at this technology for the advanced user. This third revision of Infrared Thermography Guide contains updated information on IR equipment technology, IR inspection applications, and training and certification criteria.

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INTRODUCTION Many electric generating stations and utilities have integrated the non-contact, nondestructive capabilities of infrared thermography (IR) for condition monitoring and diagnostics in their predictive maintenance program. The purpose of this guide is to assist the nuclear industry in its efforts to factor IR into its predictive maintenance program. This guide provides the theory of IR, a summary of existing and potential applications, and the technical information necessary to develop an effective in-house program. Also included is a matrix that lists all of the known manufacturers of IR instruments for a broad range of applications.

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IR has been used in commercial applications since the early 1970s. In the early 1990s, at the time this guide was first completed, the most frequent applications centered on building energy losses, roof moisture detection, and inspections of major electric equipment. Applications have since expanded to almost all areas of plant predictive maintenance (PdM), product and process control, and nondestructive testing of materials. The wide and growing selection of thermal imagers and viewers available for these applications provides both qualitative and quantitative displays of temperature distribution patterns.

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The manufacturers of modern thermal imagers and viewers have kept pace as detector and microprocessor technologies have advanced. The capabilities of today.s IR thermal imagers and viewers have yet to be fully explored and developed for commercial applications. In addition, computer software programs are now available to store, retrieve, analyze and compare infrared images. Much of the information presented in the original guide was developed as a result of a demonstration project at a U.S. nuclear utility. In addition to information gathered through this demonstration project, all Nuclear Maintenance Applications Center (NMAC) members were surveyed to provide data on the implementation status of IR technology at their facilities. This latest revision of the guide (Revision 3) was undertaken to correct text errors, to update the information on IR products vendors, certification, training, and techniques, and to restructure the guide so that it can become a living document, able to be readily updated to reflect technology changes. The body of the guide is structured for the general user of IR, and the appendices provide an in-depth look at this technology designed for the more advanced user. Charlie Chong/ Fion Zhang

Basic IR Concepts A target at any temperature above absolute zero will emit infrared radiation in proportion to its temperature. Thermal imagers develop an electronic image by converting the invisible heat radiation emitted by that target into electrical signals that can be displayed on a monitor and/or recorded on a variety of electronic storage media. By monitoring these targets with thermal imaging equipment, a visual image of their temperature differentials can be displayed. The variations in intensities of the blacks, grays, and whites (or color variations) provide an indication of the temperature differences. Areas of higher temperatures will appear brighter and the areas at lower temperatures will appear darker (or appear as different colors). The quantity and wavelength distribution of the energy that is radiated depends upon the temperature and spectral characteristics of the material, and on that materials radiation efficiency (emissivity). Thermal imagers convert the invisible heat radiation (thermal detector?) into visible images while spot radiometers convert the heat radiation from a single spot into a number indication on a meter. (the photon detector not addressed?)

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The thermographer views the target through an IR instrument, while looking for unexpected or unusual temperature patterns. A qualitative examination compares the apparent temperature pattern of one component to that of an identical or similar component under the same or similar operating conditions. Temperature differences can be measured quantitatively as well. The achievement of accurate temperature indications, however, is dependent upon many factors and extreme care must be taken in the selection of variables used in temperature calculations. The thermal images obtained can be stored on memory sticks, PCMCIA cards, computer hard drives, floppy disks, CDs, ZIP disks, or video tape. An advantage of infrared monitoring or testing is that it can be performed with the equipment in service at normal operating conditions (that is, it will not interfere with normal plant operations).

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CONTENTS 1. 2. 3. 4. 5. 6. 7.

Thermography overview A compendium of commercial infrared sensing and imaging instrument The measurement mission Inspection techniques Examples of infrared applications Basic elements of an in-house program Training and certification

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1. THERMOGRAPHY OVERVIEW Temperature and thermal behavior of plant machinery, power generation and distribution equipment, control systems, and related materials are the most critical factors in the maintenance of operations. For this reason, temperature is frequently considered the key to successful plant maintenance and is, by far, the most measured quantity. Although conventional methods of temperature measurement using thermometers and thermocouples are still commonly used for many applications, infrared thermography (IR) sensors have become less expensive, more reliable, and electrically interchangeable with conventional thermistors and thermocouples. Noncontact measurement using infrared sensors has become an increasingly desirable alternative over conventional methods. Now, with the proliferation of innovative computer hardware and software, computer-aided predictive maintenance (PDM?) is feasible and efficient.

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1.1 Advantages of Non-Contact Thermal Measurement The four most commonly stated advantages of non-contact thermal infrared measurement over contact measurement are that it is non-intrusive, remote, much faster than conventional methods, and that it measures the temperature at the surface of the target (test subject) not the surrounding air. Any one, or a combination of the following conditions, warrants the consideration of a noncontact sensor: •

• • •

Target in motion . When the target to be measured is moving, it is usually impractical to have a temperature sensor in contact with its surface. Bouncing, rolling, or friction can cause measurement errors and the sensor might interfere with the process. Target electrically hot . Current-conducting equipment and components present a hazard to personnel and instruments alike. Infrared sensors place both out of harm’s way. Target fragile . When thin webs or delicate materials are measured, a contacting sensor can often damage the product. Target very small . The mass of a contacting sensor that is large with respect to the target being measured will usually conduct thermal energy away from the target surface, thus reducing the temperature and producing erroneous results.

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• Target remote . If a target is very far away from, or inaccessible to, contacting sensors, infrared measurement is the only option. • Target temperature changing . Infrared sensors are much faster than thermocouples. Infrared radiant energy travels from the target to the sensor at the speed of light. A rapidly changing temperature can be monitored by infrared sensors, with a millisecond response or faster. • Target destructive to thermocouples . When the high mortality rate of thermocouples due to jarring, burning, or erosion becomes a serious factor, an infrared sensor is a far more cost effective alternative. • Multiple measurements required . When many points on a target need to be measured, it is usually more practical to re-aim an infrared sensor (IR Scanner, Line scanner) than it is to reposition a thermocouple or to deploy a great number of thermocouples. The fast response of the infrared sensor is important. There are, of course, limitations to the non-contact approach conditions that might make it impractical or ineffective. These will be covered as the discussion progresses.

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1.2 Heat Transfer and Infrared Radiation Basics Infrared thermography is based on measuring the distribution of radiant thermal energy (heat) emitted from a target surface and converting this to a surface temperature map or thermogram. The thermographer requires an understanding of heat, temperature, and the various types of heat transfer as an essential prerequisite in preparing to undertake a program of IR thermography. This section is an overview discussion to provide the reader with a basic understanding of how heat transfer phenomena affect noncontact infrared thermal sensing and thermographic measurements. For a more detailed discussion of temperature and heat transfer basics, see Appendix A. Comments: The differences in detecting principle by thermal detectors and photon detector were not addressed Thermal detector â&#x20AC;&#x201C; heat sensitive? Photon detector â&#x20AC;&#x201C; spectral sensitive?

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1.2.1 Heat and Temperature Heat is defined as thermal energy in transition, flowing from one place or object to another as a result of temperature difference, with the flow of heat changing the energy levels in the objects. All of the energy must be taken into account because energy can neither be created nor destroyed. What we often refer to as a heat source (like an oil furnace or an electric heater) is really one form or another of energy conversion; the energy stored in one object is converted to heat and flows to another object. Temperature is a property of matter and not a complete measurement of internal energy. It defines the direction of heat flow when another temperature is known. Heat always flows from the object that is at the higher temperature to the object that is at the lower temperature. As a result of heat transfer, hotter objects tend to become cooler and cooler objects become hotter, approaching thermal equilibrium. To maintain a steadystate condition, energy needs to be continuously supplied to the hotter object by some means of energy conversion so that the temperatures and, hence, the heat flow, remain constant.

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1.2.2 Instruments for Temperature Measurement (Contact and NonContact) Conventional temperature measuring instruments use various contact sensors. A mercury thermometer works on the principle of expansion with heat: the mercury expansion is calibrated based on its known characteristics and the reading is an indication of the temperature at the site of the mercury reservoir. Thermometers using thermocouples, thermopiles, and thermistors are based on the electrical-thermal characteristics of these sensors and produce a reading based on the temperature of the object with which the sensor is in contact. Infrared thermal instruments are non-contact devices and produce readings based on the surface temperature of objects at which the instrument is pointed.

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1.2.3 Converting Temperature Units Temperature is expressed in either absolute or relative terms. ■ There are two absolute scales called º Rankine (English system) and Kelvin (metric system). ■ There are two corresponding relative scales called º Fahrenheit (English system) and º Celsius or Centigrade (metric system). For a detailed discussion of temperature units and formulas for converting from one scale to another, see Appendix A. Table 1-1 is a conversion table to facilitate the rapid conversion of temperature between Fahrenheit and Celsius values. Instructions for the use of the table are shown at the top. For convenience, Table 1-1 is repeated in Appendix A (Table A-1). For quick reference, the conversion factors are summarized in Appendix C, Plate 1.

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1.2.4 The Three Modes of Heat Transfer There are three modes of heat transfer: (1) conduction, (2) convection, and (3) radiation. All heat transfer processes occur by one or more of these three modes. IR, Infrared thermography is based on the measurement of radiative heat flow and is, therefore, most closely related to the radiation mode of heat transfer. For a detailed discussion of heat transfer modes and the relationship between infrared measurements and radiative heat flow, see Appendix A.

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1.3 Measuring and Mapping Temperature Without Contact All targets radiate energy in the infrared spectrum. The hotter the target, the more energy that is radiated. Very hot targets radiate in the visible spectrum as well as in the infrared. As targets cool, they no longer glow but they continue to radiate. The radiation can be felt on a hand placed near the targetâ&#x20AC;&#x2122;s surface, but the glow canâ&#x20AC;&#x2122;t be seen because the energy has shifted from red to infrared. Infrared detectors can sense infrared radiant energy and produce useful electrical signals proportional to the temperature of target surfaces. Instruments using infrared detectors allow a fast and highly sensitive target surface temperature measurement without contact. Instruments that combine this measurement capability with the capability of scanning a target surface area are called infrared thermal imagers. They produce thermal maps, or thermograms, where the brightness intensity or color of any spot on the map is representative of the surface temperature of that spot. In other words, they extend non-contact point temperature measurements to non-contact thermography.

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1.3.1 The Three Elements of a Non-Contact Temperature Measurement In using infrared instruments for making non-contact temperature measurements, three sets of characteristics need to be considered: â&#x20AC;˘ Target surface â&#x20AC;˘ Transmitting medium between the target and the instrument â&#x20AC;˘ Measuring instrument Figure 1-1 shows how the instrument is aimed at the target and makes the measurement through the medium.

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Figure 1-1- Categories of Conditions for Infrared Thermal Measurements

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Every target surface above absolute zero radiates energy in the infrared. The hotter the target, the more radiant infrared energy is emitted. The physical laws that define this behavior are discussed in detail in Appendix A, along with a detailed discussion of medium and instrument characteristics. Emissivity is a very important characteristic of a target surface and must be known in order to make accurate non-contact temperature measurements. Methods for estimating and measuring emissivity are discussed throughout this guide, and the emissivity setting that is needed to dial into the instrument can usually be estimated from available tables and charts. The proper setting needed to make the instrument produce the correct temperature reading can be learned experimentally by using samples of the actual target material. This more practical setting value is called effective emissivity.

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Although the transmitting medium is usually air, non-contact temperature measurements can be made through a vacuum, gas, or certain solid materials. The characteristics of the medium need consideration and a detailed explanation of this is included in Appendix A. Figure 1-2 shows the necessary components of an infrared radiation thermometer that makes a single point non-contact temperature measurement on the target surface. Collecting optics (that is, infrared lenses, etc.) is necessary in order to focus the energy radiated from the target onto the sensitive surface of an infrared detector. The detector converts this energy into an electrical signal that is representative of the temperature of a spot on the target. Adding scanning elements between the target and the detector (also shown in Figure 1-2) allows the instrument to scan the target surface and to produce a thermogram. Most currently available infrared thermal imagers incorporate multi-detector focal plane array (FPA) sensors that are electronically scanned and that eliminate the requirement for an opto-mechanical scanning mechanism (single sensor type?) .

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When an infrared radiation thermometer (point-sensing instrument) is aimed at a target, it collects energy within a collecting beam, the shape of which is determined by the configuration of the optics and the detector. The crosssection of this collecting beam is called the field of view (FOV) of the instrument and it determines the size of the area (spot size) on the target surface that is measured by the instrument. On scanning and imaging instruments this is called the instantaneous field of view (IFOV) and becomes one picture element on the thermogram.

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Figure 1-2 Components of an Infrared Sensing Instrument (non FPA?)

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1.4 Performance Parameters of Thermal Sensing Instruments This section previews the performance parameters of point-sensing instruments and scanning and imaging instruments. For a detailed discussion of these parameters and how to specify and test the performance of instruments, please refer to Appendix A. 1.4.1 Point-Sensing Instruments Point-sensing instruments are defined by the following performance parameters: â&#x20AC;˘ Temperature range . The high and low limits over which the target temperature might vary â&#x20AC;˘ Absolute accuracy . As related to the NIST (National Institute of Standards and Technology) standard â&#x20AC;˘ Repeatability . How faithfully a reading is repeated for the same target

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• Temperature sensitivity . The smallest target temperature change that the instrument needs to detect • Speed of response . How fast the instrument responds to a temperature change at the target surface • Target spot size and working distance . The size of the spot on the target to be measured and its distance from the instrument • Output requirements . How the output signal is to be utilized • Spectral range . The portion of the infrared spectrum over which the instrument will operate • Sensor environment . The ambient conditions under which the instrument will operate

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1.4.2 Line Scanners and Imagers - Qualitative and Quantitative The parameters used for assessing the performance of infrared thermal line scanners and imagers are more complex because a thermal line-scan or image is made up of a great number of discrete point measurements. Many of the performance parameters of infrared thermal line-scanners and imagers, such as accuracy, repeatability, and spectral range, however, are the same as those of radiation thermometers. Others are derived from, or are extensions of, radiation thermometer performance parameters. Some types of thermal imagers show comparative temperatures and not actual temperature measurements. For users of these thermal viewers (see section 3), parameters dealing with accuracy and repeatability do not apply. Parameters exclusive to thermal line-scanners and imagers are as follows:

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1. Total field of view (TFOV) . The thermogram image size, in terms of scanning angle. (example: TFOV=20° Vertical x 30° Horizontal) The TFOV of a line scanner is considered to be the TFOV of one scan line. 2. field of view (IFOV) . The spot size represented by one detector element at the target plane: Imaging spatial resolution. (example: IFOV= 2 milliradians) (1° = 35 milliradians) 3. Measurement spatial resolution: (IFOVmeas) . The spatial resolution that describes the minimum target spot size on which an accurate temperature measurement can be made. (example: IFOVmeas = 5 milliradians) 4. Frame (or line) repetition rate . The number of times every point on the target is scanned in one second. (example: Frame rate = 30/second or 30 Hz; Scan rate = 60 lines/second) 5. Minimum resolvable temperature (MRT) . The smallest blackbody equivalent target temperature difference that can be observed: Temperature sensitivity. (example: MRT=0.1°C @ 30°C target temperature) 6. Other parameters such as spectral ranges, target temperature ranges, accuracy and repeatability, and focusing distances are essentially the same as those for point-measuring instruments. Charlie Chong/ Fion Zhang

1.4.3 Thermal Imaging Software In order to optimize the effectiveness of thermographic measurement programs, the thermographer needs a basic understanding of the thermal image processing techniques. The following is a list of broad categories of thermal image processing and diagnostics currently available. A discussion of each of these categories is included in Appendix A. A detailed description of currently available thermal imaging and diagnostic software is provided in section 2. Thermal imaging software can be categorized into the following groups: • • • • •

Quantitative thermal measurements of targets Detailed processing and image diagnostics Image recording, storage, and recovery Image comparison Archiving and database*

*Although data and image database development is not an exclusive characteristic of thermal imaging software, it should be considered an important part of the thermographer’s tool kit. Charlie Chong/ Fion Zhang

2. A compendiumć&#x2018;&#x2DC;čŚ of commercial infrared sensing and imaging instruments This chapter begins with a classification of infrared sensing and imaging instruments by type and application. The list includes commercially available instruments, from singlepoint thermal probes to on-line control sensors, to high-speed, highresolution thermal imaging (thermography) systems. A detailed overview of performance characteristics and features follows, along with a discussion of the typical thermographic display approaches that are used by various imager manufacturers. This is followed by a discussion of currently available thermographic image processing software and image hard-copy recording accessories. Finally, a tabulation of currently available instruments by category and manufacturer is appended, including a digest of performance characteristics and features. A current index of manufacturersâ&#x20AC;&#x2122; addresses, phone numbers, Web sites (where available), and/or e-mail addresses is also included.

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2.1 Classification of Instruments Infrared sensing instruments are traditionally classified into three groups: â&#x2013; point-sensing, â&#x2013; linescanning, and â&#x2013; thermographic (two-dimensional scanning). Point-sensing devices (commonly called Infrared Radiation Thermometers) collect radiant energy from a spot or area on the surface of an object to be measured (the target) and provide an output indication, usually in terms of target temperature. Line-scanning instruments provide an output, generally an analog trace, of the radiant energy (or, in ideal cases, temperature) distribution along a single straightline projection from the target surface. Thermographic instruments (imagers) provide an image of the energy distribution over a scanned area on the target surface. This is presented in the form of an intensity-modulated black and white picture or a synthesized color display called a thermogram.

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Point sensors, line scanners, and imagers can be further divided into subgroups. This section will review commercially available instruments along the lines of this breakdown: Point-Sensing • Probes and IR thermocouples • Portable (hand-held) • On-line monitoring and control • Specials Line-Scanning • Opto-mechanically scanned • Focal plane array (FPA), electronically scanned Thermographic • Opto-mechanically scanned imagers (single element, mechanical manipulated) • Electronically scanned pyrovidicon imagers (?) • Electronically scanned FPA focal plane array imagers (multi-elements array)

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2.2 Instrument Manufacturers Particularly in the point-sensing category, there are many companies offering the same instrument under different private label arrangements. In order to avoid duplication, the original manufacturer or prime (U.S.) distributor will be listed in the material that follows. At the end of Section 2, a comprehensive list of instruments is included (Table 2-1), for which descriptive literature was available at the time of the preparation of this text. The performance characteristics are summarized rather than presented in detail. The listed manufacturer should be contacted for detailed performance information. A listing of current addresses, phone numbers, Web sites, and/or e-mail addresses, for the listed equipment manufacturers, is included in a separate table (Table 2-2) at the end of Section 2. In addition, a third table is included, which summarizes proven industrial applications for thermal imaging instruments (Table 2-3). The information that follows will highlight the applications for which each instrument category and group is particularly suited, based on configuration or performance characteristics.

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2.3 Discussion of Instruments ■ 2.3.1 Point Sensors (Radiation Thermometers) 2.3.1.1 Probes Temperature probes are characterized by low price (from less than $100 to about $1,000), pocket-portability, and wide-collecting angle. They are batterypowered and are generally optically pre-adjusted for minimum spot size at a short working distance (a 1/4" (6.35 mm) spot at a 3/4" (19.05 mm) working distance is typical). Some models are designed to operate into a conventional multi-meter and some incorporate their own readout box with a liquid crystal diode (LCD) display. They usually feature disposable batteries and some models have ac adapters. Temperature ranges are from about 0°F, or slightly below, to 600°F, and a sensitivity of +/- 1°F is easily achieved. Emissivity adjustments are available on some models. Probes are ideal for close-up measurements and are used in circuit board analysis, troubleshooting of electrical connections, the inspection of plumbing systems, and in application to biological and medical studies.

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2.3.1.2 Portable Hand-Held With few exceptions, these instruments are pistol-shaped and designed for middle-distance measurements. They are usually optically pre-adjusted for infinity focus. A typical 2Â° field of view resolves a 7.5-cm (3-inch) spot at a 150-cm (60-inch) working distance, and a 30-cm (1- foot) spot at a 9-m (30oot) working distance. Prices range from about $100 to more than $3,500. Sighting and aiming methods vary from simple aiming notches to enclosed illuminated reticles. There are instruments with extremely narrow fields of view (0.5Â°) that include a rifle stock and telescopic sight. Most instruments in this group incorporate emissivity adjustments and some include microcomputers with limited memory and data-logging capabilities. Most are available with a recorder output, although this feature is seldom used. A meter is always provided and, with one exception that reads in BTU/ftÂ˛-h, the readout is always in temperature units. Analog displays are still available, although they are decreasing in popularity. Digital readouts featuring light emitting diodes (LEDs) were introduced first but the LCD display, introduced more recently, is now used almost universally because its tiny power drain extends battery life.

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For this reason, the more recent instruments offer replaceable rather than rechargeable batteries and battery life approaches one year. Some instruments in this group have zeroing adjustments, but all of the newer instruments include auto-zeroing features. Temperature ranges are, typically, from 0°C to 1500°C. Temperature sensitivity and readability are usually 1°C (or °F) or 1% of scale, although sensitivities on the order of 0.1°C (or °F) are achievable. This instrument group is particularly suited to applications where spotchecking of target temperatures is sufficient and continuous monitoring is not required. A typical use would be for periodic maintenance checks of rotating machinery to detect whether or not bearings are beginning to overheat. These instruments, over the past few years, have become an important part of many plant energy conservation programs. Although many of these instruments provide extremely accurate readings, accuracy, like the recorder output, is less important to most users than repeatability, ruggedness, portability, reliability, and ease of use. Some newer models incorporate microcomputers with special features such as a data-logger, which has the capability to store as many as 60 readings for future retrieval and printout.

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2.3.1.3 On-Line Monitoring and Control These instruments are primarily used for monitoring and control of manufacturing processes. The one feature that distinguishes this instrument group from the others is dedicated use. The instrument is generally mounted where it can measure the temperature of one specific target, and it remains there for the life of the instrument or the process. With few exceptions, these instruments operate on line power. The output signal of the instrument can be observed on a meter, used to operate a switch or relay, feed a simple or sophisticated process control loop, or it can be used in any combination of these functions. Early on-line instruments consisted of an optical sensing head and an electronics/control readout unit at the other end of an interconnecting cable. This configuration still exists to some extent, but most of the newer units feature sensing heads that are more stable electronically and, hence, more independent of the remote control units.

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The trend is for these new sensors to mate with universal indicator/control units that accept input from various types of industrial sensors. This instrument group is selected to perform a specific task, so the manufacturer provides a shopping list ordering format to the customer, enabling them to purchase all required features. Manufacturers offer sensing head features such as variable or fixed focus, sighting tubes, light pipes, water-coolable housings, air purge fittings, air curtain devices, and see-through aiming with target-defining reticles. The shopping list for the indicator/controller unit might include digital readout, binary coded decimal (BCD) output, analog output, single, double, or proportional set point, rate signals, sample and hold, peak or valley sensor, and data-logger interface. Emissivity controls, located in a prominent place on a general-purpose instrument, are more likely to be located behind a bezel ç&#x17D;ť ç&#x2019;&#x192;ć&#x;&#x153;on the sensor on these dedicated units, where they are set one time and locked.

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Spectral characteristics are worth mentioning separately, although, technically, they are part of the sensing head shopping list. The spectral interval over which the sensing head operates is selected to optimize the signal from the target, to reduce or eliminate the effect of an interfering energy source, or to enable the instrument to measure the surface temperature of thin films of material that are largely transparent to infrared energy. This last application has made these instruments important factors in the manufacture of thin film plastics and also of glass. Exercise: What is the spectral filter need to measure the surface temperature of PU.

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2.3.1.4 Specials There are several special categories of spot-measuring instruments that are worth mentioning, although they might, by strict definition, fit into one or more of the above categories. (1) Two-color or ratio pyrometers are one special case of an on-line instrument. These are particularly useful in high-temperature applications and in measuring small targets. The effective emissivity of the target need not be known, providing that it is constant and that reflections are controlled. The target need not fill the field of view, provided that the background is cool, constant, and uniform. Impurities in the optical path that result in broadband absorption, do not affect the measurement because the measurement is based on the ratio of energy in two spectral bands. Ratio pyrometers are, generally, not applicable to measurements below 500째F.

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Another special case is the (2) fiber optic-coupled thermometer. With this instrument, inaccessible targets can be measured by replacing the optic with a flexible or rigid fiber optic bundle. This, of course, limits the spectral performance and, hence the temperature range, to the higher values, but it has allowed temperature measurements to be made when none were possible.

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Fiber Optic-coupled Thermometer

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(3) The infrared microscope is a third special case. This instrument is configured like a conventional microscope. Through the use of reflective microscope objectives and beam splitters, it enables the operator to simultaneously view and measure targets down to 0.0003" (.00762 mm) in diameter with an accuracy and resolution of about 0.5째F. Another special case, known as the (4) laser pyrometer, has also become available. This instrument uses the reflected energy of an active laser to measure target reflectance. A built-in microcomputer calculates target effective emissivity and uses this to provide a corrected true temperature reading. The laser pyrometer is useful for high temperature diffuse target surfaces. Prices of instruments in the on-line control instrument group vary from less than $1,000 for an infrared switch, to more than $15,000 for infrared microscopes and on-line instruments equipped with many control features. Generally speaking, the price goes up when sensitivity, small spot size, and speed of response are all required and, of course, when many shopping list items, or additional features, are added.

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â&#x2013; 2.3.2 Line Scanners The purpose of spatial scanning is to derive information concerning the distribution of radiant energy over a target scene. Quite often, a single straight line scanned on the target is all that is necessary to locate a critical thermal anomaly. In the newer line scanners, the single-element detector is replaced by a multi-element single-line focal plane array (FPA) and the optomechanical scanning element is eliminated. Probably the first approach to line scanning that was adopted commercially was in an aerial-type thermal mapper in which the line scanner was mounted on a moving aircraft and scanned lines normal to the direction of motion. The outputs representing these individual scan lines were intensity-modulated and serially displayed in shades of gray on a strip map. This display represented the thermal map of the surface being overflown by the vehicle.

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2.3.2.1 Opto-Mechanically Scanned Line Scanners The earliest process-monitoring line scanners (many of which are still in use) employed a single element detector and a single scanning element, usually a mirror. The instantaneous position of the scanning element is usually controlled or sensed by an encoder or potentiometer so that the radiometric output signal can be accompanied by a position signal output and be displayed on a chart recorder, an oscilloscope, or some other recording device. One portable, battery-powered line scanner, still used commercially, scans a single line on target, develops a visible temperature trace using light emitting diodes and, by means of optical beamsplitting techniques, superimposes this trace over the visible scene viewed by the operator. The operator selects the line to be scanned by aiming the instrumentâ&#x20AC;&#x2122;s horizontal centerline.

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Photorecording of the composite scene is accomplished by aiming a conventional instant color camera through the eyepiece of the scanner. This instrument has no recorder output and is, therefore, not suited for process control applications. Unlike most thermal viewers, however, absolute temperatures are obtainable with this device. Good applications for this line scanner include electrical switchgear and transmission lines, the troubleshooting of plumbing systems, and webprocess profiling.

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2.3.2.2 Electronically Scanned Focal Plane Array FPA Line Scanners The newest high-speed on-line commercial line scanners employ linear focal plane detector arrays that are electronically scanned. They develop high resolution thermal maps by orienting the linear array along an axis normal to the motion of a moving target such as a paper web, a rotating kiln, or a strip steel process. The output signal information is in real-time computer compatible format and can be used to monitor, control, or predict the behavior of the target. The best applications for this scanner are in on-line real-time process monitoring and control. In significant recent developments, families of line cameras have been made available with a wide selection of linear focal plane array detectors based on the speed, resolution, and spectral sensitivity requirements of the process being monitored.

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â&#x2013; 2.3.3 Thermographic Instruments An important advantage of radiation thermometers over contact thermometers is their speed of response. The measured energy travels from the target to the sensor at the speed of light. The response of the instrument can then be in milliseconds or even microseconds. This important feature has allowed the field of infrared radiation thermometry to expand into real-time thermal scanning and thermal mapping. When problems in temperature monitoring and control cannot be solved by the measurement of one or several discrete points on a target surface, it becomes necessary to spatially scan (that is, to move the collecting beam (instantaneous field of view) of the instrument relative to the target). The detector output is intensity-modulated in proportion to the total exitant radiant energy at each point scanned on the target surface. The image produced is presented in monochrome or color, where the gray shades or color hue are intended to represent a thermal level at the target surface.

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These thermal images are called thermograms. The purpose of spatial scanning is to derive information concerning the distribution of infrared radiant energy over a target scene. Scanning can be accomplished either optomechanically or electronically. Opto-mechanical scanning can be done by moving the target with the instrument fixed, or by moving (translating or panning) the instrument, but is most practically accomplished by inserting movable optical elements into the collected beam. Although an almost infinite variety of scanning patterns can be generated using two moving elements, the most common pattern is rectilinear. This is most often accomplished by two elements that each scan a line normal to the other. A typical rectilinear scanner employs two rotating prisms behind the primary lens system (refractive scanning). An alternate configuration uses two oscillating mirrors behind the primary lens (reflective scanning).

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This is also commonly used in commercially available scanners, as are combinations of reflective and refractive scanning elements. Electronic scanning involves no mechanical scanning elements, the thermal pattern of the surface is scanned electronically. The earliest method of electronically scanned thermal imaging is the pyrovidicon (pyroelectric vidicon) or thermal video system. With this method, charge proportional to target temperature is collected on a single pyroelectric detector surface, within an electronic picture tube. Scanning is accomplished by an electronic scanning beam. Although offering them in favor of instruments based on solid-state focal plane array technology. Most recently, electronically scanned thermal imaging is accomplished by means of an infrared focal plane array (IRFPA), whereby a two-dimensional staring array of detectors collects radiant energy from the target and is digitally scanned to produce the thermogram. All of the above approaches to producing an infrared thermogram will be discussed.

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Commercial thermal imaging systems fall into the following categories and sub-categories: • • • •

Thermal viewers, opto-mechanically scanned Imaging radiometers, opto-mechanically scanned Thermal viewers, electronically scanned (pyrovidicon imagers) Focal plane array (FPA) imagers, qualitative (thermal viewers), and quantitative (imaging radiometers)

Keywords: Thermal viewers (thermal detector) - qualitative Imaging radiometer (photon detector) – quantitative (radiometric)

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A comprehensive list (Table 2-1) of all known, commercially available thermal-imaging instruments, on which descriptive literature was available at the time of the preparation of this document, is included at the end of Section 2. Performance characteristics are also briefly summarized. A listing of current addresses, phone numbers, Web sites, and/or e-mail addresses, of the listed equipment manufacturers, is included in a separate table (Table 2-2) at the end of Section 2. In addition, a third table is included, which summarizes proven industrial applications for thermal imaging instruments (Table 2-3). The information that follows will highlight the applications for which each instrument category and group is particularly suited, based on configuration or performance characteristics.

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Infrared (IR) thermography is a well established technique for remotely measuring the temperature of a surface where it is impractical or impossible to do so by a contact means. The term thermography denotes an imaging capability, but the concepts are the same for non-imaging sensors. IR thermography exploits the correlation between the temperature of a surface and the IR energy emitted by the surface. This relationship is described by Stefan’s Law:

where σ is the Stephan-Boltzmann constant (= 5.67×10-8 W/(m2·K4)) and T is the temperature of the surface. The spectrum of the IR light is described by Planck’s blackbody function.

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2.3.3.1 Thermal Viewers, Opto-Mechanically Scanned Opto-mechanically scanned thermal viewers are inexpensive battery-powered scanning instruments producing a qualitative image of the (thermally associated) radiant exitance distribution over the surface of a target. The battery packs are rechargeable and usually provide 2 ~ 3 hours of continuous operation. These are one-piece, lightweight instruments, designed to be simple to operate. The first viewers required cryogenic cooling of the detector elements, which was accomplished by means of a small tank of compressed argon. These early units, while still in use, are no longer manufactured. Newer units feature thermoelectric detector cooling provided by a battery-powered cooler. (and sterling cooler?) Note: Although they are being replaced gradually by focal plane array imagers (see section 2.3.3.4), at the time of this writing, opto-mechanically scanned thermal viewers are still in wide use commercially. For this reason, the following operational description is provided.

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Thermal viewers are not designed for absolute temperature measurements, but they can demonstrably sense temperature differences in tenths of degrees. Some manufacturers have modified these viewers and introduced absolute temperature references so that absolute measurements are possible in certain applications. (discuss this statement, on how this pseudo absolute temperature measurement is accomplished?) This generally requires an additional box, however, and diminishes the portability that defines the instrument group. (It also increases the price.) Thermal viewers operate most effectively with cooler targets (0°C.150°C) but, through the use of optical attenuators, they can be used for targets of up to 1500°C. Typically, the area scanned (field of view) with thermal imagers is from 6° to 8° high and from 12° to 18° wide, with spatial resolution (instantaneous spot size) of 2 mRad (1 cm at 2 m). (? – see next page) Although a hard copy of the thermal image can be acquired by through-theeyepiece recording using either conventional or instant film, currently available units offer direct video recording by means of a conventional VCR output jack and camcorder accessories. Charlie Chong/ Fion Zhang

Applications for thermal viewers are found throughout the industrial environment but are generally limited to those in which the temperature measurements are not critical and the recording quality does not need to be optimum. The combination of a thermal viewer (to locate thermal anomalies) and a handheld thermometer (to quantify them) is powerful and cost effective. Thermal viewers are particularly useful industrially in tight spaces or, conversely, when a sizable area must be traversed and user fatigue becomes a factor. Exercise: From text: 2 mRad (1 cm at 2 m). (?) Calculation: D = Îąâ&#x2C6;&#x2122;d, D = 2 x 10-3 x 2 = 4 x10-3 = 4mm# Q? (4mm or 2mm?)

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2.3.3.2 Opto-Mechanically Scanned Imaging Radiometers Opto-mechanically scanned imaging radiometers provide potentially quantitative temperature measuring capability and high-resolution image quality. Detector cooling is almost always required and this is done using any of several means including thermoelectric (Peltier effect) coolers, compressed argon, refillable liquid nitrogen containers, and, most recently, electricpowered Stirling cycle nitrogen coolers. Most commercial imaging radiometers use a single detector, but some manufacturers offer dualdetector or multi-detector (linear array) instruments. All provide a means of measuring target surface temperature. Note: Although they are being replaced gradually by focal plane array imagers (see Section 2.3.3.4), at the time of this writing, opto-mechanically scanned imagers are still in wide use commercially. For this reason, the following operational description is provided. (Could be misleading note, 未必-里根星球计划)

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These imagers use refractive, reflective, or hybrid scanning systems and operate in either the 3.5 µm (MWIR) or the 8.14 µm (LWIR) atmospheric window. In addition to quantitative temperature measuring capability (Radiometers) in idealized circumstances, these instruments feature excellent capabilities for both spatial resolution (about 1 mRad) and minimum resolvable temperature (0.05°C to 0.1°C). Most manufacturers offer isotherm graphics features, spectral filtering, interchangeable optics for different total fields of view (FOVtotal) , color or monochrome (black and white) displays, flexible video recording capabilities, and computer compatibility. Most general-purpose systems in use today feature compact, field-portable, battery-operable sensing heads and control/display units, some of which are integrated into camcorder configurations. A complete system, including battery and video recorder, can usually be handled by one person, by either mounting the components on a cart or assembling them on a harness. Detector cooling for all newer models that are intended for field operation is accomplished by means of thermoelectric or Stirling-cycle cooler, thus eliminating the inconvenience of liquid nitrogen refills in the field. Charlie Chong/ Fion Zhang

Thermoelectric Cooling - Figure

below The operating principle of thermoelectric devices is depicted above which demonstrate that it is possible to convert temperature gradients into electrical currents (or vice versa) and that thermoelectric devices can be used for both cooling and recovery of waste heat.

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http://www.nano.ucf.edu/research/compsim_masunov1.php

Sterling Cooling â&#x20AC;&#x201C; Electromechanical Cooling

Sterling Cooling

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http://www.robertstirlingengine.com/cold.php

DIY Temperature Chamber – Thermoelectric Cooling / Peltier Cooler

■ https://www.youtube.com/embed/XApTATLNEcQ

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https://www.youtube.com/watch?v=XApTATLNEcQ

Stirling Cycle Engine, Two-Cylinder Alpha Type

â&#x2013; https://www.youtube.com/embed/aPxRB6JNfCw

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https://www.youtube.com/watch?v=aPxRB6JNfCw

Stirling Engines - How They Work

â&#x2013; https://www.youtube.com/embed/gQb2sN6UWkA

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https://www.youtube.com/watch?v=gQb2sN6UWkA

Ultra-Low Temperature Cooler - A Product of Precision Manufacture

â&#x2013; https://www.youtube.com/embed/-B2VcNy8dNs

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https://www.youtube.com/watch?v=-B2VcNy8dNs

Ronald Regent Star War

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Ronald Regent Star War

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2.3.3.3 Thermal Viewers, Electronically Scanned (Pyrovidicon Imagers) Pyrovidicon imaging systems are not unlike home video-recording systems except that the camera tube is a pyroelectric vidicon (pyrovidicon) rather than a conventional vidicon. It records target radiation in the infrared rather than the visible spectrum. The significant difference is that the pyrovidicon has no dc response; that is, if the camera is not continuously panned over the target or the collecting beam is optically chopped, the image fades from the screen (pyroelectric elements) . This behavior is caused by the fundamental photoelectric response characteristics of the detector material. Aside from the tube, which is costly, and the lens, which is generally made of germanium and also costly, these systems use commercially available television equipment and recording accessories. Note: Although they are being replaced gradually by focal plane array imagers (see section 2.3.3.4), at the time of this writing, pyrovidicon imagers are still in wide use commercially. For this reason, the following operational description is provided.

Charlie Chong/ Fion Zhang

By comparison with other infrared imaging systems, the picture quality and resolution are good, approaching conventional television format. The thermal image can be viewed or videotaped with equal convenience and no cooling is required. The requirement for continuous target panning can be made less objectionable by the ability to play back an image and freeze the frame for detailed image inspection. Compact synchronous choppers that provide flicker-free performance and enhance image quality are incorporated in most instruments. Pyrovidicon systems do not intrinsically offer absolute measurement capability, but a thermal profile feature, available on some units, provides an analog of the center scan line displayed to the side of the image. Some models incorporate a spot-measuring sensor (addition photon detector sensor?) boresighted with the scanner and its measurement superimposed on the video display, along with a defining reticle in the center of the display. Software packages are offered that are specified to provide quantitative measurements by compensating for field variations and introducing temperature references.

Charlie Chong/ Fion Zhang

Thermal resolution of pyrovidicon instruments is between 0.1°C and 0.2°C in panned mode (?) and between 0.2°C and 0.4°C (half as good) in chopped mode. Another useful feature available on some models integrates a video camera into the viewing channel so that simultaneous visual and thermal images can be seen on a split-screen or in a fade in, fade out format. Although pyrovidicon displays are monochrome (black and white), some models incorporate colorizer accessories and image-processing software packages. Pyrovidicon systems are particularly suited to moving targets, airborne scanning, and distant measurements. They operate well in the 8.4 µm atmospheric transmission window. They are susceptible to a momentary loss of sensitivity from saturation phenomena, known as depoling, when suddenly aimed at very hot targets with the aperture improperly open. The automatic repoling circuits require about a 30-second restoration time, resulting in some operator inconvenience. Operating costs are very low because no coolant is required, and common erasable videocassettes are used for recording purposes. Videotapes can be monitored on conventional television receivers.

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2.3.3.4 Focal Plane Array (FPA) Imagers - Qualitative and Quantitative. In the mid 1980s, detector mosaics, or staring infrared focal plane arrays, were used successfully for military night vision Forward Looking InfraRed (FLIR) viewers and have since been made widely available for use in commercial thermal-imaging instruments. In an IRFPA imager, each detector element is assigned one display picture element and mechanical scanning is eliminated altogether. IR focal plane array (IRFPA) radiometers are adaptations of military and aerospace FLIRs but, unlike FLIRs, they are designed to allow measurement of the apparent temperature at the target surface and to produce quantitative as well as qualitative thermograms. They represent the most recent developments in FPA imagers. Although measurement-capable IRFPA imagers were promised as early as 1987, these capabilities were slow in arriving because of the complexity of the task. It was well into the 1990s before good quality measurement capabilities became available.

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At the present time, most commercial manufacturers offer a wide choice of high-resolution IRFPA imagers and radiometers. Today.s IRFPA imagers offer thermal resolution that is comparable to opto-mechanically scanned imagers (0.05°C to 0.2°C) and spatial resolution that is considerably better (1 mRad or better with standard optics). With inherently faster response, no moving parts, and superior spatial resolution, IRFPA imagers and radiometers have all but completely replaced opto-mechanically scanned imagers throughout the user community. Keywords: ■ IRFPA imagers and radiometers ■ IRFPA (1) imagers and (2) radiometers ■ Qualitative & Quantitative

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Currently, most commercially available (1) measuring and (2) non-measuring IRFPA cameras use uncooled focal plane arrays of bolometric or pyroelectric/ferroelectric thermal detectors. Although detector cooling is not required, the detector arrays are temperature-stabilized by means of low power thermoelectric devices to ensure instrument stability. (Bolometric, pyroelectric and ferroelectric are thermal detectors â&#x2030; photon detectors?) Although there are no scanning elements, pyroelectric FPAs require a mechanical chopper because they have no DC response.

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For special applications where high speed, improved sensitivity, or spectral selectivity is required, cooled photo- detector arrays are used. These include platinum silicide (PtSi), indium antimonide (InSb), mercury-cadmium-telluride (HgCdTe) and, most recently, gallium arsenide (GaAs) quantum well infrared photo-detectors (QWIP), all of which require cooling. Detector cooling can be accomplished by any of several means, including TE (thermoelectric Peltier effect) coolers, compressed argon, refillable liquid nitrogen containers and, most recently, electric-powered Stirling-cycle nitrogen or helium coolers. Most of today.s commercially available cooled imagers are equipped with either a TE cooler or a compact, high-efficiency Stirling-cycle cooler. The Stirlingcycle cooler operates like a micro-miniaturized electric refrigerator.

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Discussion Subject: For special applications where high speed, improved sensitivity, or spectral selectivity is required, cooled photo- detector arrays are used. Question: Does thermal detector (â&#x2030; photon detector) applicable to spectral selectivity?

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IRFPA imagers and radiometers.

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2.3.3.5 FPA Imager Performance Comparisons Most application needs can be fulfilled by means of selecting from among five categories of instruments available in today.s commercial thermal imager market. These include: 1. Un-Cooled FPAs (the general purpose choice) 2. Mid-Range Infrared (MWIR) Indium Antimonide (InSb) or Platinum Silicide (PtSi) FPAs 3. High-speed, high-sensitivity photo-detector FPAs (for special applications) 4. NIR (near-infrared) FPAs (for telecommunications, fiber optic, and laser profiling applications) 5. Special High-Temperature FPA Imaging Pyrometers (for special hightemperature applications, such as furnace temperature monitoring)

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■ Un-Cooled FPAs (the general purpose choice) (Bolometric, pyroelectric and ferroelectric are thermal detectors ≠photon detectors?)

Un-cooled IRFPA imagers, operating within the 7.14 µm region, are suitable for most applications in: • Predictive maintenance, condition monitoring • Buildings, roofs, and infrastructure • Process monitoring and control (except where there are high-speed or spectral considerations) • Medical and biological studies • Materials evaluation and nondestructive testing (except for high-speed or high-resolution applications) • Security, surveillance, night vision, search and rescue, firefighting Typical performance characteristics of imagers in this category are: • Temperature sensitivity (noise-equivalent temperature difference [NETD]): 0.08°C (80 milliKelvins) @ 30°C • Spectral range: 7.5 ~ 13 µm • Spatial resolution: 1.3 milliradian (320x240 element micro-bolometric FPA) • Frame repetition rate: 50/60 Hz Charlie Chong/ Fion Zhang

■ Mid-Range Infrared (MWIR) Indium Antimonide (InSb) or Platinum Silicide (PtSi) FPAs (these are photon detector?) Cooled platinum silicide (PtSi) or indium antimonide (InSb) imagers are preferable where spectral selectivity at shorter wavelengths is important (such as in some manufacturing processes) or for high-temperature applications (such as furnace measurements). A typical imager in this category could have the following performance characteristics: • • • •

Temperature sensitivity (NETD): 0.07°C (70 milliKelvins) @ 30°C Spectral range: 3.4.5 µm Spatial resolution: 1.2 milliradian (256x256 element PtSi FPA) Frame repetition rate: 50/60 Hz

InSb-based imagers have somewhat better thermal sensitivity than PtSibased imagers and are somewhat more expensive.

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■ High-speed, high-sensitivity photo-detector FPAs (for special applications) For special applications involving high-speed phenomena, high thermal sensitivity, and processing flexibility at longer wavelengths, the detector of choice has become the gallium arsenide (GaAs) QWIP FPA. A typical imager in this category could have the following performance characteristics: • • • •

Temperature sensitivity (NETD): 0.02°C (2 milliKelvins) @ 30°C Spectral range: 8.9 µm Spatial resolution: 1.1 milliradian (320x240 element GaAs QWIP FPA) Frame repetition rate: selectable from 50/60 Hz to 750/900 Hz

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Discussion Subject: MWIR: Cooled platinum silicide (PtSi) or indium antimonide (InSb) imagers are preferable where spectral selectivity at shorter wavelengths is important (such as in some manufacturing processes) or for hightemperature applications (such as furnace measurements). LWIR: For special applications involving high-speed phenomena, high thermal sensitivity, and processing flexibility at longer wavelengths, the detector of choice has become the gallium arsenide (GaAs) QWIP FPA.

Could the reasons for preferences/ selections for/ of SWIR be: ■ Manufacturing processes requirements? (selective transmissivity or specific temperature measurements) ■ High temperature applications? What are the others? Could the reasons for preferences/ selections for/ of LWIR be: ■ Manufacturing processes requirements? (selective transmissivity or specific temperature measurements) ■ High thermal sensitivity? ■ High responsivity?

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Figure 3.2: Response Curves of Various Infrared Detectors

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IR detector spectral detectivity

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IR detector spectral detectivity

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http://www.intechopen.com/books/advances-in-optical-fiber-technology-fundamental-optical-phenomenaand-applications/sige-based-visible-nir-photodetector-technology-for-optoelectronic-applications

IR detector spectral detectivity

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IR detector spectral detectivity

Charlie Chong/ Fion Zhang

http://pe2bz.philpem.me.uk/Lights/-%20Laser/Info-999-LaserCourse/C04-M08-OpticalDetectors/mod04_08.htm

IR detector spectral detectivity

Charlie Chong/ Fion Zhang

http://www.intechopen.com/books/optoelectronics-advanced-materials-and-devices/advances-in-infrared-detector-array-technology

■ NIR (near-infrared) FPAs (for telecommunications, fiber optic, and laser- profiling applications) A typical imager in this category could have the following performance characteristics: • Radiant sensitivity Noise Equivalent Irradiance (NEI): 1x1010 ph/cm2/sec (Because the applications for this type of instrument are concerned with measuring radiant power rather than temperature, sensitivity is expressed in NEI rather than NETD.) • Spectral range: 900 - 1700 nm (0.9 - 1.7 µm) • Spatial resolution: 1.2 - 1.6 milliradian (320 x 256 element InGaAs FPA) • Frame repetition rate: 30 Hz

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■ Special High-Temperature FPA Imaging Pyrometers (for special high-temperature applications, such as furnace temperature monitoring) A typical imager in this category could have the following performance characteristics: • Temperature sensitivity (NETD): • Spectral range: 700.1100 nm (0.7.1.1 µm) selected filters for ranges from 600°C to 2400°C • Spatial resolution: 1.2.1.6 milliradian (776x484 near-infrared FPA detector) • Frame repetition rate: 30 Hz

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2.4 Thermal Imaging Diagnostic Software The new generation of thermal imagers features image processing capabilities that can be generally categorized into four groups. Applications for thermal imaging often require the use of more than one of these four groups: • Quantitative thermal measurements of targets • Detailed processing and image diagnostics • Image recording, storage, and recovery • Image comparison

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2.4.1 Quantitative Thermal Measurements of Targets This is the temperature value of any point (or all points) on the target surface. For true radiance measurements, the system throughput attenuation must be taken into consideration as well as losses through the measurement medium (atmosphere, in most cases). For true temperature measurement, the target effective emissivity must also be considered. In order to provide true radiance values, the system calibration constants are fed into the computer on initial setup and a system of prompts assures the operator that changes in aperture settings, target distance, interchangeable lenses, etc. are fed into the keyboard each time a change in operating condition occurs. For true temperature values, it is necessary for an effective emissivity value to be inserted by the operator. The temperature readings that are then displayed assume that the entire target surface effective emissivity is equal to this inserted value. In operation, a color scale (or monochrome gray scale) is provided along one edge of the display with a temperature shown corresponding to each color or gray level.

Charlie Chong/ Fion Zhang

The operator can also place one or more spots or cross hairs on the image and the temperature value of that pixel will appear in an appropriate location on the display. Some systems allow the assignment of several different effective emissivities to different areas of the target, as selected by the operator, with the resulting temperature correction. One system, developed for the thermal imaging of semi-conductor devices and other micro-targets, offers a spatial effective emissivity correction based on the actual measurement of the surface effective emissivity of the target. By means of a precision-controlled heated sub-stage, the operator heats the unpowered device to two known temperatures in sequence. At each temperature, a radiance image is recorded. Using the known temperature and the known radiance for two temperatures, the effective emissivity matrix is computed, pixel by pixel, and stored. This matrix is subsequently used to correct the powered radiance image of that specific device and to provide a true temperature thermogram.

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2.4.2 Detailed Processing and Image Diagnostics Detailed processing and image diagnostics is a phrase that describes the capability of the computer to analyze each pixel of the thermal image and to present information in a wide variety of qualitative and quantitative forms for the convenience of the user. Some (by no means all) of these forms are discussed below. In addition to the spot meter capability discussed previously, the operator might call for profile displays. The analog trace (in x, y, or both) of the lines on the image that intersects at the selected spot will then appear at the edge of the display. Some systems allow the operator to display as many as seven sets of profiles simultaneously. Profiles of skew lines can also be displayed on some systems. The operator can draw areas on the display in the form of circles, rectangles, or point-to-point free forms. These areas can be shifted, expanded, shrunken, or rotated. They can be used to blank out or analyze portions of the image. On command, the computer will provide a detailed analysis of the entire image or the pixels within the area including maximum, minimum, and average values, number of pixels, or even a frequency histogram of the values within the area. Charlie Chong/ Fion Zhang

Although a standard (default) color scale is usually provided by the manufacturer, color scales can be created by the operator in almost infinite variety from as many as 256 colors stored within the computer. Zoom features allow the operator to expand a small area on the display for closer examination, or to expand the colors for a small measurement range. Autocale features provide the optimum display settings for any image that is selected. 3-D features provide an isometric thermal contour map of the target for enhanced recognition of thermal anomalies.

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2.4.3 Image Recording, Storage, and Recovery This is the capability to index, record, and retrieve images and data. Most commercial thermal imaging systems offer limited image storage by means of on-board removable floppy disks, PCMCIA cards, or other reusable storage devices. Limited image analysis software can also be incorporated into the field-portable instrument. Images can be stored from a frozen-frame thermogram of a live target on operator command, or the operator can set up an automatic sequence and a pre-set number of images will be stored at preet time intervals. Most systems also offer VCR options so that an entire measurement program can be recorded on videotape. These videotapes can then be played back into the system and images can be stored on playback from videotapes. Stored images can be retrieved from storage and displayed at the operator.s command.

Charlie Chong/ Fion Zhang

Diagnostic software is generally offered separately from the basic imaging instrument, although some limited diagnostic software is usually included in the basic package for on-site analysis. The current trend by manufacturers is to offer more and more onboard image analysis capabilities but, for extensive image storage and analysis, the images are more often downloaded from the cards to computers with large storage capacities and memory. The extensive image and data analysis software is resident on the computer hard drive.

Charlie Chong/ Fion Zhang

2.4.4 Image Comparison Image comparison is a very significant capability in that it allows the automatic comparison of images taken at different times. The computer allows the operator to display two images, sideby- side or in sequence, and to subtract one image from another, or one area from another, and to display a pixel-by-pixel difference thermogram. This provides the capability for archiving thermal images of acceptable components, assemblies, and mechanisms, and for using them as models for comparison to items produced subsequently. Subtractive routines produce differential images illustrating the deviation of each pixel (picture element) from its corresponding model. Image averaging allows the computer to accumulate several scan frames and to display the average of these frames. Comparison (subtraction) of images can be derived from two real-time images, two stored images, or a real-time and a stored image.

Charlie Chong/ Fion Zhang

2.5 Recording, Hard Copy & Storage of Images and Data Thermal image recording and storage has evolved dramatically from Polaroid速 instant photos of the display screen, to magnetic storage and archiving of images and data (such as labels, dates, conditions of measurement, and instrument settings), to the instant digital image storage capabilities incorporated into most of today.s thermal imagers. Hundreds of images can be recorded in the field and stored on removable, reusable memory cards. The problem of making a hard copy of the displayed image has also been solved with the advent of miniaturized digital cameras and photo-quality color printers that can print high-resolution images directly from camera outputs or from downloaded images and process them on the computer. Thermal images are saved in any one of several digital image formats such as .bmp, .tif, and .jpeg for archiving and future analysis. Corresponding visible reference images of the same targets can be recorded in the same format by digital cameras. Some manufacturers have integrated digital visible photo-recording capabilities into their new models of thermal imagers. Both thermal and visible images can be printed independently or as part of a detailed report, as described in Section 2.6.

Charlie Chong/ Fion Zhang

2.6 Report Preparation Stimulated by the demand of the predictive maintenance community for timely and comprehensive reporting of the findings of IR surveys, most manufacturers of thermal imagers have developed comprehensive report preparation software. These packages provide templates that allow the thermographer to prepare reports in standard word processor formats (such as Word for Windows速), into which digital thermal images and visible images imported from various imaging radiometers and digital cameras, can be directly incorporated. Additional diagnostic software is customarily provided in these packages so that post-analysis and trending can be added to the report.

Charlie Chong/ Fion Zhang

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing Probes and IR Thermocouples

2-16

Dickson

D161

Various models -40°C to +500°C, hold button LCD display, laser pointer, emissivity control (e set).

Exergen

SnakeEye and Smart IRt/c series

Wide range of infrared thermocouples with standard and custom configurations.

Horiba

IT580

32°F to 572°F, 0–300°C, LCD display, e set, hold button.

Ircon

Ultimax Jr

-40°C to +500°C, e set, LCD display, laser aiming spectral range: 8–14 µm.

Linear

QuickTEMP, C500, C1600, and C1700 series

-18°C to +315°C, QuickTEMP has LCD display and optional laser pointer, C500 connects to a multi-meter, C1600 has multiple models with various ranges, some models have e set. C1700 reads heat flow in BTU/sq ft/hr.

Mikron

Model M50, M500 IR thermocouples

Various temperature ranges from 0°C –500°C.

Omega

OS36, OS37, and OS38 series IR thermocouples

Modular and hand-held infrared thermocouples, various ranges.

OS200, 500, 600, 88000 and OS20 series

Close-focus probes with LCD readouts.

Raytek

Raynger IP series

A family of plug-in accessory probes that convert a digital multi-meter (DMM) or thermocouple meter into a close focus, non-contact IR thermometer. -18°C to 250°C, 8–14 µm.

Telatemp

TH1-440S and TemptestR

Ranges from -50°C to +500°C, LCD display, LED aiming available e set.

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing, Hand-Held Dickson

D160 series

Various models -40°F to +950°F, -45°C to +538°C, hold button LCD display, laser pointer, emissivity control (e set).

Everest

Model 100.3ZL and ZH

Two models from -30°C to +1100°C, LCD display, analog output, aiming light, peak sampler, differential available. Rechargeable battery.

Exergen

E series Microscanner

-50°F to +550°F or -5°C to +285°C, one piece with LED bar graph and numerical scale, high- and low- hold feature, audio alarm.

DX series

Close-up sensor with reflective cone for target emissivity correction; ranges from -4.5°C to +871°C, digital read-out.

Ircon

ULTIMAX series

Various models from -30°C to +3000°C, thru-the-lens sighting, spectral ranges 0.65, 0.96–1.06, and 8–13 µm (some models are ratio-pyrometers), LCD display, analog and RS-232 outputs, replaceable batteries.

Irtronics

Sniper series

Laser or visual sights, 8 wavelengths, 0–3000°F/C.

Land

Cyclops series (Minolta), 33, 41, 52, Compac 3

High- and low-temperature (to 5500°C), small targets, variable focus, reticle display, Compac 3 has low-temperature, fixed-focus, thru-lens sight.

Linear

LT, LTL, and LTS series

-29°C to 1093°C, 30:1 or 60:1 optics, laser pointer or non-parallax sight available, 1% accuracy. F-C switch, LCD display.

Mikron

M90, M100, M101, M102, and M103 series

Various models, including ratio pyrometers, from -40°C to +3000°C, LCD displays, options: laser aiming light, telescope, e set, various FOVs.

Omega

HHM, OS520, OS631, OS900 series, others.

Wide range of models with ranges from -18°C to 2482°C, options include laser aiming, through-the-lens viewing, BTU read-out.

Palmer-Wahl

Heat Spy DHS-100 series, DHS-200 series, DHS-20 series, DHS-34 series, DHS53 series, HAS-201 series

Various models from -40°C to +1760°C, analog, LCD, and LED displays. Series DHS has e set, peak-hold, and various FOVs, including telescopic. Through-the-lens sighting and laser aiming features are available.

2-17

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing, Hand-Held (cont.) Pyrometer

Pyrolaser laser pyrometer

Ranges from 600°C–3000°C, uses laser to measure reflectance and correct for emissivity, thru-lens sight, rechargeable battery.

Pyrofiber series

Fiber-optic-coupled, ranges from 600°C–3000°C, uses laser to measure reflectance and correct for emissivity, thru-lens sights, rechargeable battery.

Raytek

Raynger MiniTemp, MX, 3I, IP, ST series

Various models from -30°C to 900°C, dual LCD display, hi-lo alarms, RS232/analog output, datalogger, max-min-mean, differential, laser aiming available.

Teletemp

INFRAPRO 3 and 4

Various models from -32°C to +760°C, rechargeable battery, e set, LED display. Laser aiming and scope available.

Williamson

600, Viewtemp, Truetemp

Viewtemp is 25°C to 1650°C, LED inside reticle, e set, and rechargeable battery. Truetemp is 2-color, 550°C to 2200°C. 600 has analog display, various ranges from 75°F to 3000°F.

E2 Technology (now part of Mikron)

Heat switch (Solar TD100 and Meteor 300), Pulsar and Quasar Series Photon, Nova, Comet, other models

Various heat pulse switches and ruggedized models from 260°C–1650°C, including ratio pyrometers.

Everest

3000 series, 4000 series

Ranges from -40°C to +1100°C, spot size available down to 0.01". Multiplexes up to 8 heads through electronics.

Horiba

IT-230

0°C–300°C, multiple ranges, digital output with e set, multiple control features.

Ircon

Modline 3 and 4 series, SA, SR, and 1100 Series, Javelin, Mirage and MiniIRT series, others.

Various models and accessories, -18°C to +1375°C, integrated, fixed-focus, two-wire transmitters, spectral selection. Various models of two-piece, -18°C to 3600°C with thru-lens sights, LCD display, spectral selection (including ratio pyrometers), and control and output options. IR pulse switches and fiber opticcoupled heads.

Irtronics

Argosy, Spartan, others

Various ranges from 30°C to 3000°C, spectral selection, telephoto, multizones, fiber-optic-coupled heads available.

Point-Sensing On-line

2-18

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing On-line (cont.) Land

System 4, SOLO, UNO, CF series

Wide selection of instruments, 120°C to 2600°C, two-color, spectral selection, fiber optic, telephoto lens option, modular, many accessories. SOLO is a line of two-wire thermometers.

Linear

TM1000 series, M series, MX series

TM 1000 series are modular sensors, ranges from 0°C–2000°C, spectral selection, thru-lens sights, linearized outputs, many control options. M series are lower cost, fewer options. MX series are customized units with hightemperature and high-resolution options.

Mikron

M67 series

Modular, ranges from 0°C–1650°C, spectral selection, fixed- and variablefocus, thru-lens sights, many accessories.

M68, M668, M600, M680 series

Fiber optic, one color and ratio pyrometers, ranges from 250°C–3500°C.

M190 series

Two-piece, 0°C–3000°C, spectral selection, fixed- and variable-focus, thrulens sights, many accessories.

M77/78

M77 is two-color, M78 is two-color, fiber-optic-coupled.

Omega

OS36, 39, 42, 65, 101, 1592 series, many others

Wide range of sensors including fiber-optic-coupled, ranges from -45°C to +3700°C.

Raytek

Thermalert IT series Thermalert ET series

Various models, -15°C to +538°C, two-piece, small sensing head. Various models, -15°C to +1650°C, integrated sensing head, e set, spectral selections, processing options.

Thermalert III series

Various models, -15°C to +3000°C, two-piece, LED display, e set, spectral selections, processing options.

Thermalert IV series

Various models, -15°C to +3000°C, two-piece, dual LED display, set points, e set, processing options, spectral selections.

Compact Series

Intended for low-cost, multiple-sensor applications.

2-19

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Point-Sensing On-line (cont.) Raytek (cont.)

Marathon Series

For high-temperature applications, up to 3000°C, 1 µm spectral region, include ratio pyrometer and fiber-optic-coupled models.

Quantum Focus

RM2

Infrared microscope. Spot size down to 0.0003".

Williamson

PRO 80, PRO 90, PRO 100, PRO 200

Various models including two-color, fiber-optic-coupled, 30°C–2500°C, spectral selections, many accessories.

TempMatic 4000, FiberView 5000, 500, 700, and 1000 series

Various models, ranges from 30°C–2500°C, two-wire, fixed-focus transmitters and two-wire, fixed-focus single wavelength and ratio pyrometers, some fiberoptic-coupled models.

HGH (France)

ATL-100 narrow angle (6 deg) ATL-020 wide angle (90 deg)

Modular thermoelectrically cooled, high-resolution analog and digital outputs, operates with control system host computer.

Ircon

ScanIR II series

Modular thermoelectrically cooled and un-cooled detectors for various spectral bands from 1 to 5.1 µm, high-resolution analog and digital outputs, visible laser alignment feature, operates with host computer.

Infrared Solutions

IR ScanPro 1000

Scanner based on no moving parts, un-cooled 120-element thermoelectric linear array. Extensive computer interface.

Land

Landscan LS Series optomechanically scanned

Modular, adjustable scan rate, six models with wavelengths from 1 to 5 µm, temperature ranges from 70°C–1400°C, high-resolution analog and digital outputs, operates with control system host computer.

ScanTemp ST Series optomechanically scanned

Low cost, adjustable scan rate, eight models with wavelengths from 1 to 14 µm, temperature ranges from 0°C–1400°C, analog and digital outputs, operates with control system host computer.

Line Scanners

2-20

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Mikron

MikroLine series, 250, 2128, 2256

128-, 160-, or 256-element arrays of PbSe, pyroelectric or GaAs and other detectors, temperature ranges of 0°C–1300°C, spectral ranges of 1.4–1.8 µm, 3-5 µm, 4.8–5.2 µm, and 8–14 µm, frame rates up to 18 kHz, full-processanalysis software.

Pyrometer

ThermATrace

Un-cooled, provides composite visual image and IR scan line superimposed, portable, rechargeable battery, photo-recording only.

Raytek

CS-100, GS-100, TF-100, TIP-450 (all using the MP-50 Thermalert line scanner)

Each system for a different process application, modular thermoelectrically cooled, high-resolution analog and digital outputs, various wavelengths, operate with integral control system or host computer.

Line Scanners (cont.)

Thermographic Opto-Mechanically Scanned Imaging Radiometers Bales

BSI TIP

Very high-resolution desk-top imager with liquid nitrogen cooling, 2–12 µm, TFOV 20x30 deg, extensive on-board, real-time diagnostic software, advanced capability for variable frame rate, multiple simultaneous images. Part of pulsed multi-mode inspection system.

Compix

PC2000 and 2000/e

TE-cooled single-element PbSe (3–5 µm) with PC card module to convert IBM-based desktop and notebook computers to thermal imagers, slow scan (10 seconds and 15 seconds per frame) 244x193 pixel image. 2100 series has magnifier lens for microscope resolution down to 0.002 inch.

PC2100 and 2100/e CMC-Cincinnati Electronics (also markets AVIO)

AVIO TVS Series

TE-cooled and Stirling-cycle cooled models featuring 10-element InSb, 3–5 µm, 10degVx15degH TFOV, lightweight and portable with on-board LCD color monitor, accessories.

Infrared Solutions

IR SnapShot (also sold by Ircon as DIGICAM-IR)

120-element, un-cooled thermoelectric array for 8–12 µm operation, mounted on slide-mechanism for single image one-second frame. Extensive diagnostic software, remote operation capability.

2-21

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

Opto-Mechanically Scanned Imaging Radiometers (cont.) Jenoptik

Varioscan series

Stirling-cycle cooled, liquid nitrogen cooled, and TE-cooled HgCdTe detector models for 8–12 µm and 3–5 µm performance, 30°x20° FOV slow-scan, highsensitivity, extensive diagnostic software.

Land

Cyclops T135

Camcorder-configured reflective scanner using TE-cooled, 12-element HgCdTe, 3–5 µm, 25 f/s, 16x16deg TFOV, monochrome viewer, separate image processor available.

FPA Thermal Viewers (Non-Measuring) AIM

µ Cam, FS, and FL FLIR families

Modular, building block cameras using cooled HgCdTe, GaAs QWIP and PtSi FPAs from 128x128 element to 640x486 element.

BAE

MicroIR

Un-cooled 320x240 element micro-bolometric FPA imager module in a weatherproof, ruggedized housing.

CMC-Cincinnati Electronics

Nightmaster, Night Conqueror, others

Many models of Stirling-cycle cooled 160x120, 256x256, and 640x512 element InSb FPA imagers (3–5 µm) for a wide variety of military, search, and surveillance applications.

Electrophysics

PV-320

Un-cooled barium-strontium-titanate (BST) IRFPA imager, 2–14 µm or 0.6–20 µm 320x240 element array, 60 Hz frame rate, quantifiable option.

FLIR

ThermaCAM E series

Un-cooled miniaturized (less than 1.5 lbs) 160(H)x120(V) element microbolometer FPA, portable, battery-powered, 7.5–13 µm, laser aimer, nonmeasuring version.

ThermoVision 1000, Sentry and Ranger; MilCAM SAFIRE, UltraFORCE, SeaFLIR, others

High-resolution, Stirling-cycle cooled InSb and PtSi, (3–5 µm) QWIP (8–9 µm) selectable TFOV-thermal viewers for military, law enforcement, air and sea, and other security and surveillance applications.

SAT – HY600

Un-cooled amorphous silicon micro-bolometer 320(H)x240(V) element FPA, 8–14 µm.

Guangzhou SAT

2-22

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Thermal Viewers (Non-Measuring) (cont.) Indigo

Alpha NIR

Miniaturized, 320x256 element InGaAs FPA, 900–1700 nm, for telecommunication, fiber optic, and laser-profiling applications.

Alpha

Miniaturized, 160x128 element micro-bolometer FPA, 7.7–13.5 µm.

Merlin

Family of imagers offering 320x256 element FPAs in four spectral bands: InGaAs (0.9–1.68 µm un-cooled), InSb (1.0–5.4 µm Stirling-cycle cooled), GaAs QWIP (8–9 µm Stirling-cycle cooled), and micro-bolometer (7.5–13.5 µm un-cooled).

Phoenix

Family of imagers offering 320x256 and 640x512 element FPAs in three spectral bands: InGaAs (0.9–1.7 µm un-cooled), InSb (2–5 µm and GaAs QWIP (8–9.2 µm Stirling-cycle cooled).

Omega

Miniaturized, 160x128 element micro-bolometer FPA, 7.7–13.5 µm.

Infrared Solutions

Modular 160

120x160 pixel un-cooled micro-bolometer FPA in miniaturized (three-inch cube) module for 8–14 µm operation.

IRISYS

IXS 9004

Very low-cost portable, battery-powered viewer using un-cooled 16x16 element pyroelectric FPA, 8–14 µm spectral region, connects to IBM PC and includes image and color display software.

Marconi

Argus Series

Firefighter thermal imagers.

Mine Safety Appliance Corp.

VideoTherm 2000

Un-cooled 320x240 element pyroelectric FPA hand-held viewer with added measurement capability by means of boresighted radiation thermometer, monochrome or color display (8–14 µm).

Raytheon

PalmIR-250

Un-cooled ferroelectric 320x240 FPA, 7–14 µm, battery-powered portable viewer, monochrome display.

2-23

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Thermal Viewers (Non-Measuring) (cont.) Raytheon (cont.)

Sentinal

Un-cooled micro-bolometer 320x240 element FPA 8–14 µm, battery-powered portable viewer, monochrome display.

Santa Barbara Focal Plane

Various Models

High-resolution front-end detector and optics for integration into user's system, based on liquid nitrogen-cooled, 128x128 element 256x256, 320x240, 320x256, 640x480, and 512x512 element InSb FPA (focal plane array) detectors, 1–5 µm.

US Infrared

THERMOviewer

Portable, battery-powered, un-cooled barium-strontium-titanate (BST) 320x240 element IRFPA imager, 2–14 µm spectral range, 60 Hz frame rate, boresighted IR thermometer provides spot measurement reference, color display, aimed at low-cost PdM applications.

Wuhan

IR920, 922, and 923

Un-cooled micro-bolometer 320(H)x240(V) element FPA, 920 has image radio transmitter and receiver. 922 is helmet-mount, 923 is long-range monitoring/surveillance camera.

FPA Imaging Radiometers (Measuring) Cedip

Jade MW Jade LW Jade UC

Stirling-cycle cooled 320x256 element FPA MCT or InSb, 3–5 µm, extensive diagnostic software. Stirling-cycle cooled 320x256 element FPA MCT, 7.5–9.6 µm, extensive diagnostic software. Un-cooled 320x240 micro-bolometer FPA, 8–14 µm, extensive diagnostic software.

CMC-Cincinnati Electronics

2-24

TVS8500

Stirling-cycle cooled 256x256 element InSb FPA, 3–5 µ, 13.7degVx14.6degH TFOV, multiple-temperature measurement on multiple-selected pixels, emissivity compensation, lightweight and portable with on-board LCD color monitor, accessories.

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Imaging Radiometers (Measuring) (cont.) FLIR

ThermaCAM PM390

Stirling-cycle cooled PtSi 256x256 element FPA, portable battery-powered, 3.4–5 µm, integral display, extensive diagnostic software.

ThermaCAM E2

Un-cooled miniaturized (less than 1.5 lbs) 160(H)x120(V) element microbolometer FPA, portable, battery-powered, 7.5–13 µm, LCD display, laser aimer, extensive diagnostic software.

ThermaCAM P40 ThermaCAM P60

Un-cooled high-sensitivity micro-bolometer 320(H)x240(V) element FPA, portable, battery-powered, 7.5–13 µm, integral or LCD display, extensive diagnostic software. P60 has improved sensitivity, laser aimer, added LCD color display.

ThermaCAM PM545

Un-cooled micro-bolometer 320(H)x240(V) element FPA, portable, batterypowered, 7.5–13 µm, integral or LCD display, extensive diagnostic software.

ThermaCAM PM675 ThermaCAM PM695 ThermaCAM SC300

Un-cooled micro-bolometer 160(H)x120(V) element FPA, 7.5–13 µm, extensive diagnostic software, low-cost research camera.

ThermaCAM SC500

Un-cooled micro-bolometer 320(H)x240(V) element FPA, 7.5–13 µm, extensive diagnostic software, for high-performance scientific applications.

ThermaCAM SC1000

Stirling-cycle cooled PtSi 256x256 element FPA, portable battery-powered, 3.4–5 µm, integral display, extensive diagnostic software, for high-performance scientific applications.

ThermaCAM SC2000

Un-cooled micro-bolometer 320(H)x240(V) element FPA, portable, batterypowered, 7.5–13 µm, integral display, extensive diagnostic software, for highperformance scientific applications.

ThermaCAM SC3000

Stirling-cycle cooled GaAs QWIP 320(H)x240(V) element FPA, 8–9 µm spectral response, high-speed, up to 900 Hz, high-sensitivity, broad dynamic range, extensive diagnostic software, for high-performance scientific applications.

2-25

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Imaging Radiometers (Measuring) (cont.) FLIR (cont.)

2-26

ThermoVision 160M

Un-cooled micro-bolometer 160(H)x120(V) element FPA, 7.5–13 µm, extensive diagnostic software, many lenses available, including microscope, low-cost industrial automation camera.

Thermovision 320 series

Un-cooled micro-bolometer 320(H)x240(V) element FPA, 7.5–13 µm, extensive diagnostic software, for multiple-process monitoring and machine vision applications, high-performance industrial automation cameras.

Guangzhou SAT

SAT – HY6000 and 6800

Un-cooled micro-bolometer 320(H)x240(V) element FPA, 8–14 µm, extensive diagnostic software, and wide selection of field-interchangeable lenses.

Indigo

Alpha

Miniaturized, 160x128 element micro-bolometer FPA, 7.7–13.5 µm. Measuring capability by means of added diagnostic software.

Merlin

Phoenix

Family of imagers offering 320x256 and 640x512 element FPAs in three spectral bands: InGaAs (0.9–1.7 µm un-cooled), InSb (2–5 µm Stirling-cycle cooled) and GaAs QWIP (8–9.2 µm Stirling-cycle cooled). Measuring capability by means of added diagnostic software.

TVS-620

Un-cooled, 320x240 element micro-bolometer FPA, 8–14 µm, portable handheld unit with integrated display, software, removable PC card image storage.

IRISYS

IRI 1001

Very low-cost portable, battery-powered using un-cooled 16x16 element pyroelectric FPA, 8–14 µm spectral region, connects to IBM PC and includes measurement and color display software.

Infrared Solutions

Modular 160

120x160 pixel un-cooled micro-bolometer FPA in miniaturized (three-inch cube) module for 8–14 µm operation.

Ircon

Stinger

Un-cooled pyroelectric 320(H)x240(V) element FPA, spectral range: 8–14 µm, extensive diagnostic software, for multiple-process monitoring and machine vision applications.

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Imaging Radiometers (Measuring) (cont.) HGH

Source of AVIO and CMC Cincinnati Cameras.

Jenoptik

VarioTHERM series

Stirling-cycle cooled, 256x256 PtSi FPA. 3.4–7 µm, portable, battery-powered, extensive diagnostic software.

Land

Cyclops PPM

Radiometric version of the Raytheon PalmIR 250 (same as Raytheon PalmIR 500D) modified by Electrophysics and sold by Land); 320(H)x 240(V) uncooled BST FPA, 0°C–300°C, PC memory card.

FTI-6

FPA imager with on-board diagnostic software.

MikroScan 5102

Stirling-cycle cooled 255x223 element HgCdTe FPA, 8–12 µm, line- or batterypowered portable viewer, on-board display, and flip-up LCD option.

MikroScan 5104

TE-cooled 255x223 element HgCdTe FPA, 3–5.2 µm, line- or battery-powered portable viewer, on-board display, and flip-up LCD option, spectrally selective models available for working with glass or flame.

MikroScan 5104i

TE-cooled 255x223 element HgCdTe FPA, 3–5.2 µm, line-powered fixedmount camera for on-line process monitoring and control.

MikroScan 7102i

Un-cooled micro-bolometer 320x240 element FPA 8–14 µm, fixed-mount camera for on-line process monitoring and control.

MikroScan 7200

Lightweight, un-cooled micro-bolometer 320x240 element FPA 8–14 µm, battery-powered portable viewer, on-board display, and flip-up LCD option.

MikroScan 7515

Lightweight, un-cooled micro-bolometer 320x240 element FPA 8–14 µm, battery-powered portable viewer, on-board display, and flip-up LCD option, upgrade version of the 7200 with remote control option and analysis and report-writing software.

M9000 series

Imaging Pyrometer, un-cooled 776x484 near infrared FPA detector for hightemperature targets, multi-range with selected filters from 600°C to 2400°C, extensive diagnostic software integrates PC with color monitor.

Mikron

2-27

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-1 (cont.) Instrument Characteristics Manufacturers

Models

Characteristics

FPA Imaging Radiometers (Measuring) (cont.) Nikon (see HGH)

Laird S270 and 3A series

537x505 and 768x494 element Stirling-cycle cooled PtSi FPAs, (3–5 µm) battery- and line-powered, ac adapter, interchangeable color display available. Multiple temperature measurement on multiple selected pixels, emissivity compensation.

Quantum Focus Instruments

InfraScope, InfraScope II

Lab-operated imager for microelectronics applications, features liquid nitrogen-cooled InSb FPA, automatic emissivity compensation, full field temperature measurement, spatial resolution down to 2.5 µm, 60 Hz frame rate.

Raytheon

Radiance HSX

Stirling-cycle cooled 256x256 element InSb FPA, 3–5 µm, 60 Hz frame rate (Radiance HS has selectable frame rates up to 1400 Hz, optional displays, extensive thermal analysis software).

PalmIR 500D

Radiometric version of the Raytheon PalmIR modified by Electrophysics and sold by Land); 320(H)x240(V) un-cooled BST FPA, 0°C–300°C, PC memory card.

Thermoteknix

VisIR

Un-cooled micro-bolometer 160(H)x120(V) element FPA, portable, batterypowered, 7.5–13 µm, integral LCD display, image storage, radio link, extensive diagnostic software.

Thermal Wave Imaging

EchoTherm

EchoTherm is an NDE system, built around a selection of high-speed FPA imagers. Includes flashlamp sources, power supplies, synchronizing electronics, and analytical software for TRIR. ThermoScope is a field-portable version.

ThermoScope Wuhan

2-28

IR912 and 913

Un-cooled micro-bolometer 320(H)x240(V) element FPA, portable, batterypowered, 8–14 µm, 912 and 913 have fold-out LCD display, extensive diagnostic software.

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-2 Equipment Manufacturers Company Name

Mailing Address

Phone Number

Web Site or E-mail

AIM Infrarot-Module GmbH

Theresienstrasse 2 D-74072 Heilbron, Germany

+49-7131-6212-460

www.aim-ir.com

BAE, Information and Electronic Warfare Systems

2 Forbes Rd., LEX01-112 Lexington, MA 02421-7306

(781) 863-3684

www.iews.baesystems.com/iris

Bales Scientific Inc., div. CTI

1620 Tice Blvd. Walnut Creek, CA 94595

(510) 945-0144

www.balesscientific.com

CEDIP, SA

19 Blvd. G. Bidault F-77183 Croissy Beaubourg, France

(+33) 01 60 37 01 00

cedip@wanadoo.fr

CMC-Cincinnati Electronics Corp. Div BAE Systems

7500 Innovation Way Mason, OH 45040-9699

(513) 573-6744

www.cmccinci.com greed@cine.com

Compix

15824 SW Upper Booneâ&#x20AC;&#x2122;s Ferry Road Lake Oswego, OR 97035

(503) 639-8496

www.compix.com info@compix.com

The Dickson Company

930 S. Westwood Ave. Addison, IL 60101

(800) 323-2448

http://www.dicksonweb.com/

Electrophysics Corp.

373 Rte 46 West, Building E Fairfield, NJ 07004

(973) 882-0211 (800) 759-9577

www.electrophysicscorp.com

E2Technology Corporation (part of Mikron)

4475 Dupont Court, Unit 9 Ventura, CA 93003

(805) 644-9544

www.e2t.com sales@e2t.com

Everest Interscience Corp.

1891 N. Oracle Rd. Tucson, AZ 85705

(520) 792-4545 (800) 422-4342

http://www.everestinterscience.com/ meverest@aol.com

Exergen Corporation

51 Water St. Watertown, MA 02472

(617) 923-9900 (800) 422-3006

www.exergen.com industrial@exergen.com

2-29

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-2 (cont.) Equipment Manufacturers Company Name

Mailing Address

Phone Number

Web Site or E-mail

FLIR Systems, Inc. World Headquarters

16505 SW 72 Ave. Portland, OR 97444

(503) 684-3771 (800) 322-3731

www.flir.com

FLIR Systems, Boston Formerly Inframetrics

16 Esquire Road N. Billerica, MA 01862

(978) 670-5555

www.flir.com

FLIR Systems AB, Sweden Formerly AGEMA

Rinkebev채gen 19, PO Box 3 SE182-11 Danderyd, Sweden

+(46) 8 753 2500

www.flir.com

Guangzhou SAT Infrared Technology Co., Ltd.

10 Diongjiang Ave., Guangzhou Econ. & Tech. Dev. District, China 51073

+86-20-82229925 +86-20-82227947

www.sat.com.cn sat@sat.com.cn

HGH Systemes Infrarouges

3, rue du Saule-Trapu, F91300 Massy, France

(33-1) 60110141

http://www.hgh-infrarouge.fr/ hgh@hgh-infrarouge.fr

Horiba

17671 Armstrong Ave. Irvine, CA 92614

(800) 446-7422 (949) 250-4811

www.horiba.com labinfo@horiba.com

Indigo Systems Corp.

5385 Hollister Ave. #103 Santa Barbara, CA 93111

(805) 964-9797

www.indigosystems.com

Infrared Solutions, Inc.

3550 Annapolis Lane North, Suite 70 Plymouth, MN 55447

(763) 551-0038

sales@infraredsolutions.com

IRCON Instruments

7300 N. Natches Ave. Niles, IL 60714

(847) 967-5151 (800) 323-7660

www.ircon.com

IRISYS

Towcester Mill, TowcesterNorthants NN12 6AD, UK

+44(0)1327 357824

www.irisys.co.uk ti@irisys.co.uk

Irtronics

132 Forest Blvd. Ardsley, NY 10502

(914) 693-6291

No e-mail address

JENOPTIK, GmbH

Goschwitzer Strabe 25, D-07745 Jena, Germany

+49(3641) 65 33 11

www.jenoptik.de norbert.thiel@jenoptik.com

2-30

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-2 (cont.) Equipment Manufacturers Company Name

Mailing Address

Phone Number

Web Site or E-mail

Land Infrared

10 Friends Lane Newtown, PA 18940-1804

(215) 504-8000

www.landinst.com irsales@landinstruments.net

Linear Laboratories

42025 Osgood Rd. Fremont, CA 94538

(800) 536-0262

www.linearlabs.com

Marconi Electronic Systems

4 Westchester Plaza Elmsford, NY 10523

(914) 592-6050 (800) 342-5338

www.marconitech.com mtech.usa@marconi.com

Mikron Instrument Co., Inc.

16 Thornton Road Oakland, NJ 07436

(201) 405-0900 (800) 631-0176

www.mikroninst.com

Mine Safety Appliances

1000 Cranbury Woods Road Cranbury, PA 16066

(800) 821-3642 (724) 776-7700

www.msanet.com

Minolta (see Land)

101 Williams Dr. Ramsey, NJ 07446

(201) 529-6049 (888) 473-2656

www.minoltausa.com

NEC

(see Mikron)

Nikon (see Pyrometer Instruments and HGH) Omega Engineering, Inc.

One Omega Drive P.O. Box 2349 Stamford, CT 06906

(203) 359-1660 (800) 826-6342

Info@omega.com www.omega.com

Palmer Wahl Instrumentation Group

234 Old Weaverville Road Asheville, NC 28804

(828) 658-3121 (800) 421-2853

www.instrumentationgroup.com

Pyrometer Instrument Co.

209 Industrial Pkwy. Northvale, NJ 07647

(201) 768-2000 (800) HOT-PYRO

www.pyrometer.com pyroinfo@pyrometer.com

2-31

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-2 (cont.) Equipment Manufacturers Company Name

Mailing Address

Phone Number

Web Site or E-mail

Quantum Focus Instruments Corp.

990 Park Center Drive, Suite D Vista, CA 92083

(760) 599-1122

www.quantumfocus.com

Raytek, Inc.

1201 Shaffer Rd. Santa Cruz, CA 95060

(831) 458-1110

www.raytek.com annas@raytek.com

Raytheon Corporation

5756 Thornwood Dr. Goleta, CA 93117

(805) 683-6621 (800) 990-3275

www.raytheoninfrared.com

Raytheon Corporation, Ind. Auto. Div.

P.O. Box 655012 Dallas, TX 75265

(800) 990-3275

www.raytheoninfrared.com

Santa Barbara Focal Plane Division of Lockheed Martin

69 Santa Felicia Dr. Goleta, CA 93117

(805) 562-8777

www.sbfp.com

Teletemp Corp.

P.O. Box 5160, 351 S. Raymond Fullerton, CA 92635

(800) 321-5160 (714) 879-2901

www.telatemp.com techsales@telatemp.com

Thermal Wave Imaging, Inc.

845 Livernois Street Ferndale, MI 48220-2308

(248) 414-3730

www.thermalwave.com

US Infrared

1535 S. Memorial Dr. Suite 117 Tulsa, OK 74112

(918) 663-7833

www.bpcintl.com

Williamson Corp.

70 Domino Dr. Box 1270 Concord, MA 01742

(978) 369-9607

www.williamsonir.com wbarronsr@williamsonir.com

Wuhan Guide Electronic Industrial Co. Ltd.

Hongshan Chuangye Ctr. Bldg. Luoyu Rd. No. 424 Wuhan, China

+86-27-87659277 +86-27-87659069

www.wuhanguide.com whguide@public.wh.cb.cn

Thermoteknix Systems, Ltd.

2-32

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-3 Compilation of Typical Industrial Applications of Thermal Imaging Instruments Typical Applications by Industry Industry

Applications

Metals

Continuous casting, strip annealing, extrusion presses, rolling mills, induction heating, resistance heating, heat treating, electrolytic refining

Glass

Tank refractories, glass body temperatures, mold temperatures, bottle machines, float glass, tempering and annealing, fiberglass manufacturing

Cement

Kiln shell, refractory insulation, bridge delamination inspection

Textiles

Permanent press heat setting, dye setting, foam lamination, carpet backing

Plastics

Vacuum forming, extrusion, film process monitoring and control

Paper

Dryer drums, coating ink drying

Chemical and Petroleum

Furnace tube temperatures, pipe and vessel corrosion, mixing process monitoring and control

Food and Confectionary

Rotary cooker temperatures, continuous infrared ovens, mixers, continuous baking ovens, freeze-dry processes

Asphalt Paving

Road stone dryer, mixing temperature, rolling temperature

Rubber

Hot rubber sheetsâ&#x20AC;&#x201D;cooling and rolling, tire testing

Utilities

Electrical systems, steam valves, motors, pumps, boilers, circuit boards, switchyards, transmission and distribution lines

2-33

EPRI Licensed Material A Compendium of Commercial Infrared Sensing and Imaging Instruments Table 2-3 (cont.) Compilation of Typical Industrial Applications of Thermal Imaging Instruments Typical Applications by Discipline Discipline Design

Workmanship

Component Failure

2-34

Applications •

Exhaust stacks, flue pipes

•

Heating units (ovens, boilers, furnaces)

•

Buildings (offices, schools, hospitals, plants)

•

Process pipes, vessels, lines—steam and water lines

•

Kilns

•

Cryogenic storage vessels

•

Electrical and electronic circuits and micro-circuits

•

Operational procedures

•

Installation of refractory materials

•

Installation of foam insulation materials

•

Installation of fiberglass materials (roof insulation and so on)

•

Replacement of parts and other repairs

•

Roof inspection for moisture saturation

•

Steam traps, underground steam lines, plumbing lines and systems

•

Electrical lines and substations

•

Electrical and electronic components and modules

•

Insulation—foam, fiberglass, and refractory

•

Seals—low- and high-temperature

•

Doors, ports, windows

•

Cooling towers, heat exchangers

•

Motors, pumps, ventilators, bearings

3. The Measurement Mission The successful completion of a field measurement mission requires planning, caution, and the ability to interpret the thermographic results. The thermographer also needs a clear understanding of the thermal behavior of the targets involved in the measurement mission. The mission tasks can be subdivided as follows: â&#x2013; Understanding the thermal behavior of the target â&#x2013; Preparing the equipment for the mission â&#x2013; Using correct instrument operating procedures

Charlie Chong/ Fion Zhang

3.1 Thermal Behavior of the Target There are 10 sources of energy transfer at the target surface that can cause IR thermal imaging equipment to register apparent temperature changes. Some of these represent real temperature changes at the target surface and some do not. It is important for the thermographer to understand these phenomena and to be able to distinguish between apparent and real target temperature changes. Examples of the 10 sources of apparent & real target temperature differences will be described. They are tabulated as follows: Apparent

Real

• Emissivity difference ε

• Mass transport difference

• Reflectance difference ρ

• Phase change difference

• Transmittance difference τ

• Thermal capacitance difference Cp

• Geometric difference G

• Induced heating difference • Energy conversion difference • Direct heat transfer difference

Charlie Chong/ Fion Zhang

3.1.1 Emissivity Difference As discussed in Appendix A, Section A.3.3, the radiant energy emitted by a target surface is proportional to emissivity as well as to a power of the target temperature. If the emissivity of the target surface changes, or if the wrong effective emissivity value is assumed for the target, the apparent temperature reading will be in error. The resultant inaccuracy will not be the result of a real temperature change at the target surface. 3.1.2 Reflectance Difference An apparent temperature change will occur when thermal radiant energy from an external heat source is reflected off the target surface. The apparent change will be proportional to a power of the temperature difference between the actual target and that of the external heat source. It will also be proportional to the reflectance (1.0 minus the emissivity value) of the target and to the emissivity of the external heat source. This apparent change will not be the result of a real temperature change at the target surface.

Charlie Chong/ Fion Zhang

3.1.3 Transmittance Difference An apparent temperature change will occur when thermal radiant energy from an external heat source behind the target surface is transmitted through the target surface. The apparent change will be proportional to a power of the temperature difference between the actual target and that of the external heat source. It will also be proportional to the transmittance of the target and to the emissivity of the external heat source. This apparent change will not be the result of a real temperature change at the target surface. 3.1.4 Geometric Difference An apparent temperature change might occur as a result of the geometric shape of the target. If the target surface is shaped so as to form a cavity, for example, multiple reflections of radiant energy between the cavity walls will result in an apparent increase in emissivity. The corner of an enclosure with three mutually perpendicular surfaces in close proximity is a good example of this. The apparent change will be similar to that caused by an emissivity variation and will not be the result of a real temperature change at the target surface. (the geometric difference will affect both the reflectance and the emissivity differences) Charlie Chong/ Fion Zhang

3.1.5 Mass Transport Difference An example of a mass transport difference is air leakage from the inside of a building through the building surface that happens to be the target. The air in transit might heat or cool the target surface. This results in a real temperature change at the target surface. 3.1.6 Phase Change Difference An example of a phase change difference is water that condenses (changes from gas to liquid) on or behind a target surface and temporarily cools the surface. This results in a real temperature change at the target surface. 3.1.7 Thermal Capacitance Difference An example of a thermal capacitance difference is when solar heat stored in water-saturated sections of a roof warms the surface of the roof at night, in contrast to the non-saturated sections. This is because the water-saturated sections have higher thermal capacitance than the dry sections and it results in a real temperature change at the target surface.

Charlie Chong/ Fion Zhang

3.1.8 Induced Heating Difference An example of an induced heating difference is the inductive heating of ferrous bolts that are improperly installed in an aluminum buss bar. The magnetic field will cause inductive heating in ferrous materials, which results in a real temperature change at the target surface. 3.1.9 Energy Conversion Difference Most temperature rises observed in a plant environment are the result of energy conversion (friction to heat, chemical reaction to heat, and so on). A common example of an energy conversion difference is when the resistance of a poor connection converts electric current to heat. This results in a real temperature change at the target surface. 3.1.10 Direct Heat Transfer Difference A direct heat transfer difference occurs by conduction, convection, or radiation as described in Appendix A, Section A.2. Examples of direct heat transfer are found in the nondestructive testing of materials where a uniform heat flow is generated and observed thermal anomalies indicate flaws. These are real temperature changes at the target surface.

Charlie Chong/ Fion Zhang

Thermogram - Mass Transport Difference

Charlie Chong/ Fion Zhang

Thermogram - Mass Transport Difference

Charlie Chong/ Fion Zhang

Thermogram - Thermal Capacitance Difference

Charlie Chong/ Fion Zhang

Thermogram - Thermal Capacitance Difference

Charlie Chong/ Fion Zhang

Thermogram - Energy Conversion Difference

Charlie Chong/ Fion Zhang

Thermogram - Energy Conversion Difference

Charlie Chong/ Fion Zhang

3.2 Equipment Preparation 3.2.1 The Mission Checklist In preparation for the measurement mission, the thermographer should use checklists to ensure that there are no surprises on site. A standard checklist should be prepared to include all items in the thermographic equipment inventory. The list should include: instruments, spare lenses, tripods, harnesses, transport cases, carts, batteries, chargers, liquid or gaseous cryogenic coolant, if applicable, safety gear, special accessories, film, diskettes, spare fuses, tool kits, data sheets, operator manuals, calibration data, radiation reference sources, inter-connecting cables, accessory cables, and special fixtures. Well in advance of the mission, the thermographer can highlight all of the items that will be required for a particular job. The highlighted standard list will then become the checklist for the job.

Charlie Chong/ Fion Zhang

3.2.2 Equipment Checkout and Calibration All quantitative thermography equipment (what about qualitative equipment?) should be calibrated periodically in accordance with the manufacturer’s recommendations found in the operator’s handbook. In addition, a quick operation and calibration check should be performed by the thermographer to make certain that the equipment is in working order and in calibration. This can be performed by using an infrared radiation reference blackbody source or by a more quick and simple means such as a two-point check. This approximate test can be performed by using two known targets such as ice water (0°C) and the palm of the thermographer’s hand (approximately 35°C).

Charlie Chong/ Fion Zhang

3.2.3 Batteries Too many thermographic measurement missions have had to be postponed or prematurely terminated because the thermographer ran out of charged batteries. This can be very costly in terms of lost inspection time and customer confidence. The batteries item on the mission checklist should be understood to mean fully-charged batteries and it is the thermographerâ&#x20AC;&#x2122;s responsibility to ensure that there is a comfortable surplus of battery power available for each mission. The fact that batteries become discharged more rapidly in cold weather also needs to be considered in preparing for the mission.

Charlie Chong/ Fion Zhang

3.2.4 Facility Personnel Participation A knowledgeable facility representative should accompany the thermographer on the measurement mission or be available during measurements. By providing expert information concerning the processes taking place and the likely sources of temperature differences, this assistance will enable the thermographer to anticipate thermal behavior and to better understand and interpret the thermographic results.

Charlie Chong/ Fion Zhang

3.3 Some Cautions for Correct Instrument Operation Assuming that the instrument selected is appropriate to the measurement application, there are a few things that the thermographer should remember to avoid common mistakes in use. These include the following: • • • •

Learn and memorize the start-up procedure. Learn and memorize the default values. Set or use the correct effective emissivity. Make sure that the target to be measured is larger than the instantaneous field of view for measurement (IFOVmeas) of the instrument. • Aim the instrument as close to normal (perpendicular) with the target surface as possible. • Check for reflections off the target surface. • Keep portable inspection instruments as far away as possible from very hot targets.

Charlie Chong/ Fion Zhang

3.3.1 Start-Up Procedure Thermographers that operate several different models of thermographic and thermal-sensing equipment need to be certain that they re-familiarize themselves with the start-up procedure of the equipment selected for each measurement mission. This allows the data-gathering process to begin with no unnecessary delays. It saves valuable on-site time and inspires confidence on the part of facility personnel. A quick review of the operatorâ&#x20AC;&#x2122;s manual and a short dry run prior to leaving home base is usually all that is required.

Charlie Chong/ Fion Zhang

3.3.2 Memorizing the Default Values The operator’s manual also provides default values for several important variables in the measurement such as emissivity, ambient (background) temperature, distance from sensor to target, temperature scale (°F or °C), lens selection, and relative humidity. These are the values that the instrument processor automatically uses to compute target temperature unless the thermographer changes these values to match the actual measurement conditions. Typical default values are: 1.0 meter distance to target, emissivity of 1.0, and ambient temperature of 25°C. Failure to correct for these (for example, if the target is known to be 10 meters away, is known to have an effective emissivity of approximately 0.7, and is in an ambient of 10°C) can result in substantially erroneous results. By memorizing the default values, the thermographer will know when it is necessary to change them, and when time can be saved by using them unchanged, without having to refer to a look-up menu.

Charlie Chong/ Fion Zhang

3.3.3 Setting the Correct Emissivity Table 3-1 and Table 3-2 list various targets and their approximate generic emissivities. There are emissivities shown for various temperatures and in several spectral bands. Where it is not otherwise indicated, temperatures should be assumed to be 30째C. If possible, it is always better to directly determine the actual effective emissivity of the surface to be measured by using the actual instrument to be used in the measurement. Effective emissivity (e*) is defined as: ..the measured emissivity value of a particular target surface under existing measurement conditions, that can be used to correct a specific measuring instrument to provide a correct temperature measurement..

Charlie Chong/ Fion Zhang

EPRI Licensed Material The Measurement Mission Table 3-1 Table of Normal Spectral Emissivities Short Wave (SW) = 2–5.6 µm Long Wave (LW) = 6.5–20 µm Material

3-6

Wavelength (micrometers)

Temperature (°C)

Emissivity

Alumina brick

0.68

Aluminum, heavily weathered

0.83–0.94

Aluminum foil

0.09

Aluminum foil (bright)

0.04

Aluminum disk, roughened

0.28

Asbestos slate (wallboard)

0.96

Brick, common

Brick, facing, red

0.92

Brick, facing, yellow

0.92

Brick, masonry

0.72

Brick, red

0.94

Brick, waterproof

0.9

Chipboard, untreated

Concrete, dry

0.95

Concrete, rough

0.92–0.97

Copper, polished, annealed

0.01

Fibre board (hard), untreated

0.85

Fibre board (porous), untreated

0.85

Filler, white

0.88

Firebrick

0.68

Formica

0.937

Frozen soil

Glass, chemical ware (partly transparent)

0.97

Granite, natural surface

0.96

Gravel

Hardwood, across grain

0.82

Hardwood, along grain

0.68–0.73

Hessian Fabric, green

0.88

Hessian Fabric, uncolored

0.87

0.81–0.86

0.9

0.93

0.28

EPRI Licensed Material The Measurement Mission Table 3-1 (cont.) Table of Normal Spectral Emissivities Material

Wavelength (micrometers)

Temperature (°C)

Emissivity

Iron, heavily rusted

0.91–0.96

Limestone, natural surface

0.96

Mortar

0.87

Mortar, dry

0.94

P.V.C.

0.91–0.93

Broma Alkyd enamel 102 gold leaf

0.98

Broma Alkyd enamel 113 light blue

Chromatone® stabilized silver finish— Alumatone Corp.

3 10

0.26 0.31

Krylon® flat black 1502

0.95

Krylon flat white

0.99

Krylon ultra-flat black

0.97

3M® black velvet coating 9560 series optical black

>0.99

Oil

0.87

Paint (by manufacturer)

0.95

black flat

0.94

black gloss

0.92

gray flat

0.97

gray gloss

0.96

Plastic, black

0.95

Plastic, white

0.84

Paper, cardboard box

0.81

Paper, white

0.68

Perspex , plexiglass

0.86

Plaster Pipes, glazed

0.83

Plaster

0.86–0.9

3-7

EPRI Licensed Material The Measurement Mission Table 3-1 (cont.) Table of Normal Spectral Emissivities Material

Wavelength (micrometers)

Temperature (°C)

Emissivity

Plasterboard, untreated

0.9

Plastic, acrylic, clear

Plastic paper, red

Plywood

0.83–0.98

Plywood, commercial, smooth finish, dry

0.82

Plywood, untreated

Polypropylene

0.94 0.94

0.83 17

0.97

Redwood (wrought), untreated

0.83

Redwood (unwrought), untreated

0.84

Rendering, gray

0.92

Roofing Metal Azure blue, smooth

0.54

Azure blue, textured

0.51

Burnished copper, smooth

0.54

Burnished copper, textured

0.56

Dark bronze, textured

0.7

Mansard brown, smooth

0.58

Matte black, smooth

0.73

Roman bronze, smooth

0.69

Slate gray, smooth

0.64

Stone white, smooth

0.57

Terra Cotta, smooth

0.61

Adobe

0.77

Black

0.83

Bright red

0.96

Chestnut brown

0.67

Colonial green

0.83

Dawn mist

0.76

Desert tan

0.74

Frost blende

0.76

Meadow green

0.78

Noire black

0.90

Shingles—asphalt (sm. Ceramic-coated rock granules)

3-8

EPRI Licensed Material The Measurement Mission Table 3-1 (cont.) Table of Normal Spectral Emissivities Material

Wavelength (micrometers)

Temperature (°C)

Emissivity

Shingles—asphalt (sm. Ceramic-coated rock granules) cont. Sea green

0.83

Shadow gray

0.81

Slate blende

0.65

Snow white

0.81

Wedgewood blue

0.75

Wood blende

0.75

Average

0.89

Frost blende

0.83

Mahogany

0.84

Meadow mist

0.98

Noire black

0.93

Snow white

0.74

Wood blende

0.81

Average

0.86

0.79

Fiberglass—asphalt (sm. Ceramic-coated rock granules)

Solid vinyl Autumn gold, textured Butternut beige, textured

0.80

Lexington green, textured

0.86

Oyster white, textured

0.88

Quaker gray, textured

0.89

Sunshine yellow, textured

0.75

White, smooth

0.93

Average

0.94

Styrofoam, insulation

0.60

Tape, electrical, insulating, black

0.97

Tape, masking

0.92

Tile, floor, asbestos

0.94

Tile, glazed

0.94

3-9

EPRI Licensed Material The Measurement Mission Table 3-1 (cont.) Table of Normal Spectral Emissivities Material

Wavelength (micrometers)

Temperature (°C)

Emissivity

Varnish, flat

0.93

Wallpaper (slight pattern) lt. gray

0.85

Wallpaper (slight pattern) red

0.90

Wood, paneling, light finish

0.87

Wood, polished spruce, gray

0.86

Table 3-2 Emissivity for Wavelengths of 8–14 µm at 0°C Material

3-10

Emissivity (%)

Material

Emissivity (%)

Asbestos Board Paper Slate

96 94 96

Aluminum, polished Rough surface Strongly oxidized

5 7 25

Brick Glazed, rough Fireclay Red, rough Carbon, purified Cement Charcoal, powder Clay, fired Enamel Fabric, asbestos

85 85 94 90 80 54 96 91 90 78

Brass, dull, tarnished Polished

22 3

Bronze, polished Porous, rough

10 55

Cast iron, casting Polished

81 21

Glass Frosted

92 96

Chromium, polished

Ice

Copper, commercial burnished Electrolytic, polished Oxidized Oxidized to black

7 2 65 88

Lacquer, bakelite Black, dull Black, shiny (on metal) White

93 87 87 87

Gold, polished

Lampblack

Iron, hot-rolled Oxidized Sheet, galvanized, burnished Sheet, galvanized, oxidized Shiny, etched Wrought, polished

77 74 23 28 16 28

Pure and Oxidized Metals

EPRI Licensed Material The Measurement Mission Table 3-2 (cont.) Emissivity for Wavelengths of 8â&#x20AC;&#x201C;14 Âľm at 0Â°C Material

Emissivity (%)

Material

Emissivity (%)

Oil paint, various colors

Paper, black, shiny Black, dull White

90 94 90

Lead, gray Oxidized Red, powder Shiny

28 63 93 8

Porcelain, glazed

Mercury, pure

Nickel on cast iron Pure, polished

5 5

Pure and Oxidized Metals

Quartz

Platinum, pure

Rubber

Steel, galvanized Oxidized strongly Rolled freshly Rough surface Rusty, red Sheet, nickel-plated Sheet, rolled

28 88 24 96 69 11 56

Shellac, black, dull Black, shiny on tin plate

91 82

Tin, burnished

Snow

Tungsten

Tar paper

Zinc, sheet

Water

There are several methods described in Section 4 that can be used to estimate target effective emissivity quickly. Using the instrument chosen for measurement, one method of determining the setting needed for a particular target material is to: 1. Prepare a sample of the material large enough to contain several spot sizes or IFOVs of the instrument. A 10 cm x 10 cm (4" x 4") sample is a good choice. 2. Spray one half of the target sample with flat black (light absorbing) paint; cover it with black masking tape or use some other substance of known high emissivity. 3. Heat the sample to a uniform temperature as close as possible to the temperature at which you estimate your actual measurement will be made. 4. Set your instrument emissivity control to the known emissivity of the coating and measure the temperature of the coated area with your instrument. Note the reading. 5. Immediately point to the uncoated area and adjust the emissivity set until you repeat the reading you obtained in 4. above. This is the effective emissivity, the value you should use in measuring the temperature of this material with this instrument. For quick reference, this procedure is illustrated and summarized in Appendix C, Plate 5. 3-11

3.3.4 Filling the IFOVmeas for Accurate Temperature Measurements If you need to measure the temperature of a spot on a target, be certain that this spot completely fills the Instantaneous Measurement Field of View (IFOVmeas) of the instrument. If it doesnâ&#x20AC;&#x2122;t, you can still learn some useful things about the target with the instrument, but you can't get an accurate reading of target temperature. Use the quick calculation that is provided in Appendix C, Plate 2 to determine spot size based on IFOVmeas and actual working distance. If your target spot size is 5 cm or larger, for example, and the calculated spot size is 5 cm, move the instrument closer to the target or use a higher magnification lens, if either is possible. If not, expect to see some background effect in your reading. Also, be sure to allow for aiming errors and instrument imperfections; to be sure, allow an extra 30%. (Does the IFOVmeas has the necessary allowance, for IFOVmeas = 3 x IFOVgeom?)

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3.3.5 Aiming Normal to the Target Surface The effective emissivity of a target surface is due partially to the surface texture. It stands to reason, then, that if you look at a surface at a skimming angle, you won’t see the texture; the effective emissivity will change greatly and you will see misleading reflections. These can result in cold errors as well as hot errors. A safe rule is to view the target at an angle within 30° of normal (perpendicular). If the target effective emissivity is very high, you can go as high as a 60° angle if necessary.

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3.3.6 Recognizing and Avoiding Reflections From External Sources If there is a source of radiant energy in a position to reflect off your target surface and into your instrument, you should take steps to avoid the misleading results of this effect. The greatest likelihood of errors due to reflections from external sources occurs when: • The target emissivity is low. (1= ε + ρ, for τ = 0 ) • The target is cooler than its surroundings. • The target surface is curved or irregularly shaped. You can find out if a thermal anomaly is due to a point source by moving the instrument and pointing it at the target from several different directions. If the anomaly moves on the thermogram, it is a reflection. You can eliminate the effect of an interfering source, once you identify it, by changing your viewing angle, by blocking the line of sight to the source, or by doing both (refer to Appendix A, Figure A-9). For reflections from hot backgrounds, refer to Appendix A, Section A.3.3.

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3.3.7 Avoiding Radiant Heat Damage to the Instrument Unless specifically selected for continuous operation in close proximity to a very hot target, your instrument might be damaged by extensive thermal radiation from a target. Donâ&#x20AC;&#x2122;t leave the instrument in areas that are too warm to place your hand comfortably.

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4. Inspection Techniques This section is divided into two sub-sections that deal with the common problems and solutions that are encountered when using infrared thermography in a plant or industrial environment. The first section deals with the inherent or indigenous problems, such as emissivity or reflectance. The second section explains the tricks of the trade that are used to get the best possible information out of the imaging systems. The references (Appendix D) and the bibliography (Appendix E) provide many sources of additional information on a wide variety of problems, both theoretical and practical.

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4.1 Mitigating Inherent Effects There are several factors that affect the production and subsequent proper interpretation of a thermal image. These factors include the (1) targetâ&#x20AC;&#x2122;s emissivity, (2) reflectance, (3) distance from the imager, (4) temperature, (5) background temperature, (6) ambient temperature, (7) orientation, (8) target size, (9) and the transmittance of the intervening atmosphere. In addition, the image, as presented on the imager, is not temperature but radiosity. Imagers measure the radiant energy emitted by the target plus the radiant energy reflected from and transmitted through the target. The sum of these radiant energies is the commonly accepted definition of radiosity. There are practical considerations that will simplify the following discussions of the inherent effects. In general, the transmittance (energy transmitted through the targets) can be ignored in most, if not all, cases for targets in a power plant. Transmittance is an important factor in industries where the temperature of a thin film of plastic or other infrared opaque targets are being observed. Also, with the exception of absolute temperature measurements being required, the transmittance through the atmosphere can be ignored as well. The major exception would be in cases where long distances were involved in a humid atmosphere (that is, hydrogen igniters or spray nozzles in containment). Charlie Chong/ Fion Zhang

4.1.1 Emissivity and Reflectivity A review of the references in the bibliography (Appendix E) will show that no one subject is discussed more than emissivity. The effective emissivity of a target clearly must be known in order to measure its absolute temperature. This is discussed in detail in Appendix A. Table 4-1 provides some values of emissivity for common objects. Aluminum, the most commonly used electrical conductor, can range from 0.55 for a rough highly oxidized plate, to 0.039 for a highly polished plate. In practical terms, this means that 45% of the anodized plate and 96% of the polished plateâ&#x20AC;&#x2122;s incident energy are reflected and that any hot or cold objects in the optical background will reflect their energy off these surfaces. These mirrors do have surface thermal patterns. It is difficult to measure them, however, because of the low emitted energy and the natural ability to reflect thermal energy as well as light. In general, if a target is acting as a visible mirror, it is acting as an infrared mirror as well. An exception to this rule is the germanium lenses used on the thermal imager. These lenses transmit more than 90% of the energy in the infrared spectrum but have light-reflecting coatings that reflect more than 90% of the energy in the visible spectrum.

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Germanium Lenses - used on the thermal imager. These lenses transmit more than 90% of the energy in the infrared spectrum but have light-reflecting coatings that reflect more than 90% of the energy in the visible spectrum.

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Germanium Lenses (Night Vision) - used on the thermal imager. These lenses transmit more than 90% of the energy in the infrared spectrum but have light-reflecting coatings that reflect more than 90% of the energy in the visible spectrum.

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Table 4-1 Normal Emissivity Values of Common Materials

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Given that shiny objects have surface thermal patterns that are hard to image, there are several techniques that improve the ability to establish a satisfactory image. The most common way to obtain a useful thermal image from a shiny or low-emissivity surface is to add a coating to it that has a higher emissivity. (This is not practical and is not recommended for an energized electrical surface.) There are three common non-permanent materials that have been used to improve emissivity. These are: • Foot powder • Dye check developer • Electricians’ tape

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4.1.2 Foot Powder Foot powder is sprayed on a target to create a uniform layer that reduces the reflections. After the powder has reached thermal equilibrium with the surface, the temperature measurements can be made. The emissivity of foot powder has been estimated to be 0.96. Before any coating is applied, however, the chemical composition of the coating should be determined to avoid any negative effects from its application.

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4.1.3 Dye Check Developer An alternative to foot powder is liquid dye penetrant developer. It has an estimated emissivity of 0.97 and might already have been formulated to conform to QA requirements for sulfur and halogen purity. Application of it is identical to the foot powder. Given the temperature of the target, it might take several minutes for the developer to reach thermal equilibrium as its propellant cools the targetâ&#x20AC;&#x2122;s surface. The best way to use this in an actual survey would be to apply it to all targets to be surveyed before commencing the actual survey. This will ensure that all target surfaces will have reached thermal equilibrium. (Caution: Ensure that all manufacturer precautions are followed prior to use of any developer. For example, Magnaflux ZygloÂŽ developers, such as ZP-9E and ZP-9F, might produce chlorine gas or become flammable when they come in contact with moderately heated surfaces.)

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Dye Check Developer An alternative to foot powder is liquid dye penetrant developer. It has an estimated emissivity of 0.97 and might already have been formulated to conform to QA requirements for sulfur and halogen purity.

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The target in Figures 4-1 and 4-2 is a shiny metal can of dye check developer with the label removed. There are no hot objects in or near the can. With the imager’s emissivity set at 1.0, an analysis of the temperature distribution over the can yielded a temperature range of 74.6°F to 67.9°F (6.7°F ΔT). The reason for the variation is reflection of the cold window plus geometric considerations in measuring a curved surface. Setting the emissivity at 0.10, a more realistic figure for a shiny surface, yielded a maximum temperature of 66.2°F and a minimum temperature of 23.9°F (42.3°F ΔT). The room ambient temperature was 68°F. Without changing anything, the can surface was coated with developer and allowed to achieve thermal equilibrium. The first effect noted was the observation of the level of the developer in the can (Figure 4-3). This was due to the difference in the heat capacity of the liquid and vapor present inside the can.

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The cooling action of the propellant developed a thermal transient that resulted in the liquid level visible on the thermogram. The emissivity was reset to 0.97 and the can was allowed to achieve thermal equilibrium with the room. After 10 minutes, the maximum temperature observed was 70.4°F and the minimum temperature was 69.5°F (0.9°F ΔT), close to room ambient of 68°F. (The 0.9°F temperature spread is normal because the dye check developer might not have uniformly coated the surface.) Clearly, the developer served its intended function of improving the surface emissivity and, therefore, the results. 4.1.4 Electricians' Tape Another alternative that improves the surface emissivity is the use of electricians’ tape (it has an estimated emissivity of 0.95). This method is easy to use and apply but can present problems if the glue on the tape contains chlorine or other chemicals that can attack the target surface.

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Electricians' Tape Another alternative that improves the surface emissivity is the use of electriciansâ&#x20AC;&#x2122; tape (it has an estimated emissivity of 0.95).

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Figure 4-1 Emissivity Improvement by Coating.Setup

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Figure 4-2 Thermogram of an Uncoated Shiny Metal Container

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Figure 4-3 Container Has Been Coated to Improve Emissivity. Thermogram Now Reveals Fluid Level

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4.2 Proven Inspection Techniques 4.2.1 Mirrored Surfaces A commonly encountered situation is one where there is little or no room to place the imager and the area of interest is behind another object. This is commonly found in electrical switchgear. One method that works well is to use a material with a high reflectivity (low emissivity) as an infrared mirror. The mirror is placed in such a manner that the reflected image is viewed from a more convenient position. This is a common technique for visual inspection. The determination of temperature, though, requires that the emissivity of the reflecting surface be taken into account. Also, as in the visual technique, the mirrored image will appear reversed, thus requiring care in interpreting the data. There are excellent front surface mirrors available for this technique. These mirrors have the reflecting material on the front surface so that the incoming energy is not refracted by the glass. Sources for these mirrors include most optics manufacturers.

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4.2.2 Thermal Transfer Imaging As reported in “Subsurface Flaw Detection in Reflective Materials by Thermal-Transfer Imaging”, there are a number of inspection techniques that can easily be applied in the field to handle targets with low emissivity. One of these techniques is called Thermal Transfer Imaging (TTI). This technique was developed primarily for the steel industry where low emissivity and high temperatures exist as major problems in infrared imaging. In a case included in “Subsurface Flaw Detection in Reflective Materials by Thermal-Transfer Imaging”, the surface thermal patterns of a piece of hot steel needed to be determined. The resultant thermal image provided too much reflection and too little emission to observe meaningful surface thermal patterns. The patterns were observed after they had been transferred to a material that had a higher emissivity. In other words, the surface patterns of the target were observed on the surface of another object after the two had been in contact with each other. If the emissivities of both materials are known and accounted for, temperature measurements can be made this way.

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4.2.3 Thermal Transients Another useful inspection technique for handling targets with low emissivity is to add or subtract heat from a target. Most uses of IR are in the steady state condition. When there are two materials with different heat capacities involved, however, a thermal transient is most useful. A graphic example of this is shown in Figure 4-3, dealing with the can of dye check developer. A thermal transient was induced on the can just by spraying it. The endothermic reaction of the propellant as it evaporated caused heat to transfer from the inside of the can (warmer) to the outside. In the case of the propellant inside, the liquid had a higher heat capacity (Cp) than the vapor space above it. During the transient, the liquid, therefore, caused a larger transfer and resultant temperature difference due to conduction on the can surface. The higher emissivity of the developer on the canâ&#x20AC;&#x2122;s surface allowed it to be seen more readily.

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This is an extremely useful technique. Where large masses are concerned, however, a large amount of heat transfer might be needed for observation. This technique can be used to determine relative thicknesses of material and locations of voids, delaminations, and internal structures. The heat transfer can be induced by several methods. In the case of locating reinforcing bars (rebar) in concrete, a large induction coil placed on the concrete causes the bars to heat. The locations of the bars and their relative depth can, subsequently, be observed on the surface. When looking for voids in composite materials, a flash lamp can be used for a short pulse of energy. Hot air from a compressor can be used for containment spray ring header nozzle inspections and for locating materials near the surface of concrete. It should be noted, however, that heating is not always the most effective approach. Cooling is sometimes more effective, especially in hot areas.

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4.2.4 Differential Thermography Another state of the art inspection technique is differential thermography. This method was originally developed for the U.S. Army for the identification of defective components on the surface of a printed circuit board. The reports, “Infrared Automatic Mass Screening (IRAMS) System for Printed CircuitBoard Fault Detection” and “Infrared Automatic Screening (IRAMS) Progress Report”, provide details on this successful technique and results. As applied in a power plant, a good example would be to observe the resultant surface thermal patterns of reflective insulation to learn about its efficiency. Given that the reflective insulation on a pipe or heat exchanger is not only reflective but large in size, coating with dye check developer or tape is impractical; an infrared imager shows the surface and all reflections from it.

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The technique here involves a computer, image enhancement, and commercial software. A baseline image is taken at one temperature, for example, during start-up. This image is digitized and stored on a computer. A second image, or subsequent images, are taken from the same location but at a different temperature, at full power for example. This image is also digitized and stored on the computer. The two images are then subtracted. The high reflectance due to the low emissivity exactly cancels out, leaving an image of true surface thermal patterns. One important assumption here is that the background remains the same. These patterns can then be correlated with a visual image for location of internal insulation damage. Also, knowing the emissivity of the insulation and the resultant temperature patterns provides an opportunity to measure the R-value of the insulation. This should help in determining the cost-effectiveness of insulation repair or replacement.

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The differential thermography technique requires that the images be taken from the same place. There are several ways to do this. The first is called pin registration and involves drilling small pilot holes into the floor so that the pins of a tripodâ&#x20AC;&#x2122;s feet would fit in to them. The only variable then becomes the orientation of the thermal imager head on the tripod. A better application of this differential thermography technique is to have the computer at the imager. The original is placed on the screen as a mask. When the mask and the live image cancel each other out, there is exact registration (within the accuracy of the optics). In some cases, such as measuring the R-value for the entire heat exchanger, the temperatures above and below certain targets are canceled out (chopped). The analysis is then done on the resultant images. The criteria for chopping can be due to background sources and/or hot reflective sources.

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4.2.5 Using Infrared Transmitting Windows For the purpose of safety, it might be inadvisable or in violation of safety regulations, to remove bolts from operating high voltage equipment or to open panels. However, it might be possible to install viewing windows of infrared transmitting materials for infrared inspection. There are numerous materials available for this purpose. In Appendix A, Figure A-12 shows the spectral transmission characteristics of several of these materials, many of which transmit energy past 10 Âľm. These materials are often used as lenses and optical elements in low-temperature infrared sensors. Installing IR transmitting windows in critical locations is a growing trend, enabling periodic inspection of these locations without the hazard or inconvenience of opening panels or removing bolts.

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Thermogram of Tower

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5. EXAMPLES OF INFRARED APPLICATIONS 5.1 Current Applications The applications described below are broken down into three categories: electrical, mechanical, and miscellaneous. The primary use of infrared thermography has been in the electrical area. The mechanical area involves rotating equipment, heat exchangers, valves, and buildings. The miscellaneous section describes research in progress and unique applications. The Bibliography section of this Guide (Appendix E) provides references to many other publications where examples of other applications are presented.

5.2 Electrical Applications The primary use for infrared thermography, and usually the most straightforward application for it, is in the area of electrical predictive maintenance. Within this area, there are three main categories of problems: (1) high electrical resistance, (2) inductive currents, and (3) open circuits.

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5.2.1 High Electrical Resistance High electrical resistance is the most common problem that can be identified by using an infrared imager. Based on Ohmâ&#x20AC;&#x2122;s law, power (watts) is calculated as the square of the current multiplied by the resistance (P = I2R). When the resistance is high, the power that is dissipated will be high. A higher power translates into a higher temperature at the same location. This creates the hot spots that are detected by the infrared thermal imager. Typical problems in this category include loose and/or corroded connections (see Figure 5-9), under-sized electrical conductors, and open individual strands of a multipletranded conductor. A special case in this category is phase imbalance. The situations that cause a phase imbalance are numerous, but all involve the situation where the current in one phase of a three-phase circuit is significantly different than in the other phase(s). The difference in the higher current phase will be seen as a heating difference. The individual phase currents should be measured to verify this.

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Another special case within the category is high resistance within a battery cell. Normally, batteries under trickle charge will be near ambient temperatures. High resistance, internal to the battery, can be observed on the battery exterior as areas of higher temperature when compared to similar batteries. These observed temperature differences on an unloaded battery cell will be very small (that is, 0.25째F to 1.0째F). Any temperature differences along the inner cell connections with the battery on float indicate a potentially serious connection problem. There have been several cases where high internal battery resistance has gone unnoticed and has subsequently led to battery failure.

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5.2.2 Induced Currents In situations involving high currents, hot spots might appear, not from the primary current but from currents induced in nearby ferrous elements or structures. This is often the case near the main electrical generator. These hot spots can appear in unlikely places such as the supporting steel structure of the generator. Other inductive hot spots have been observed on the generator stator casing and on the frames of motors. Not all of the hot spots are problems, however. In the case of the steel structure, the hot spots might be at the location where the electrical fields from the generator coincide. Hot spots are also common on motors. In both cases, this type of problem should be well documented and, where necessary, trended for future evaluation.

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Induced Currents

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Induced Currents

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5.2.3 Open Circuits One frequently overlooked application of infrared thermography is in identifying open circuits. For example, a common problem with inverters happens when one or more capacitors fail open. In this case, the failed capacitors will appear to be cooler than other similar capacitors within the inverter.

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5.3 Mechanical Applications IR applications that do not fall into the electrical category are usually described as mechanical. Within this category, there are four major subsets: (1) heating due to friction, (2) valve leakage/blockage, (3) insulation, and (4) building applications. 5.3.1 Friction In the case of rotating or moving equipment, the result of friction is readily observable as an increase in temperature. Typical situations evolve in the area of bearings on pumps (see Figure 5-26) and motors. If a bearing or coupling is inadequately lubricated, internal friction can cause heating, which can usually be observed during operation. A misaligned shaft can result in unequal loading, which causes heat generation at the point of highest mechanical resistance. This situation can be detected from the resultant elevated temperatures seen at the shaft bearing or coupling.

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5.3.2 Valve Leakage/Blockage The leakage of fluid past a normally closed valve might be easy to observe with an infrared imager, provided that the insulation on the pipe is accounted for or removed, and that there is a sufficient temperature difference between the pipe surface and ambient. Typical situations are leaking safety valves (see Figures 5-21, 5-22, 5-23, and 5-25), drain valves, and steam traps. Blockage in a pipe or a valve is a special case. In this situation, it might be necessary to add or remove heat from the area in question in order to locate the blockage. As an example, if a blockage were suspected in a boric acid transfer line, adding or removing heat in the area of the blockage would result in a thermal discontinuity at the location of the blockage. The discontinuity exists because boric acid, in the solid form, has a different heat capacity (Cp) than boric acid in the liquid form. Therefore, if a uniform amount of heat is added or removed from both areas, the areas will cool or heat at different rates. The rate difference will, for some period of time, show up as a temperature difference. The interface will be at the location of the blockage. This same mechanism, transient heating or cooling, is the mechanism that allows the remote detection of fluid levels in a tank by means of thermal imaging. Charlie Chong/ Fion Zhang

5.3.3 Insulation Insulation on piping and equipment can be tested for integrity using an infrared imager. IR applications include the assurance of complete coverage of the area, thinning/degradation of the insulation, and wet insulation. A most challenging application is when the insulation is a reflective type of insulation or has a reflective covering. The very low emissivity of the surface can result in reflected hot spots from the background, thus, making temperature measurements difficult. One process that can be used is to observe the insulation over a period of time when the system is heating up or cooling down. Using differential thermography, and subtracting two images, cancels out the effects of emissivity and might result in an interpretable thermal difference image. Keywords: Differential thermography (subtracting algorithm)

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5.3.4 Building Envelopes Buildings can be inspected for energy conservation with an infrared imager. Typical problems that can be found include air infiltration or exfiltration, poor insulation, and wet roofs. These are traditional applications for infrared thermography. The bibliography (Appendix E) provides sources of further information on these types of applications.

5.4 Miscellaneous Applications There are numerous applications for infrared thermography that are unique to the nuclear industry or that require special mention. These applications include, inspecting the containment spray ring header, the hydrogen igniters, and the condensers for air in-leakage, and observing thermal plumes.

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5.4.1 Containment Spray Ring Header Due to the inaccessibility of the containment spray ring header for physical inspection, infrared imagers have proven to be quite useful in detecting nozzle blockage. In the past, verification of unblocked nozzles on the header has involved several methods including smoke tests and balloons. The infrared method involves pumping heated air into the header and observing the thermal patterns at the nozzles. A blocked nozzle will not pass any hot air and an unblocked nozzle will. Due to the small size of the nozzle and the distance involved, a telescopic lens must be used with the imager for this inspection. 5.4.2 Hydrogen Igniters Infrared thermography has been used for inspecting the containment hydrogen igniters. Through the use of telescopic attachments, the temperature of the igniters can be measured from a remote distance. This technique eliminates the need for staging for close-up inspection.

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5.4.3 Condensers Infrared thermal imagers have been used for inspecting condensers for both tube leaks and vacuum leaks (air in-leakage). As the air is drawn into the condenser, the leaks are observable as cooler areas. This inspection technique, however, is very labor-intensive and requires close and careful inspection of valve stems, bonnets, flanges, penetrations, and tubes. 5.4.4 Thermal Plume Detection The use of an infrared imager in a helicopter or airplane can assist the plant in verifying thermal discharge patterns in cooling ponds or other bodies of water. The thermal plume, or outfall, is easily observed from the air. The hottest spots on the surface of the water are easily located. This facilitates routine environmental monitoring for thermal discharge.

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IR Thermogram â&#x20AC;&#x201C; F1 Charlie Chong/ Fion Zhang

IR Thermogram

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IR Thermogram

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IR Thermogram

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IR Thermogram

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IR Thermogram

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Hydrogen/ Flame Igniters at Flare Boom Infrared thermography has been used for inspecting the containment hydrogen igniters. Through the use of telescopic attachments, the temperature of the igniters can be measured from a remote distance. This technique eliminates the need for staging for close-up inspection.

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5.5 Applications Summary Table 5-1 is a composite list of potential applications for infrared thermal imaging in the areas discussed. Electrical • Electrical connections (loose/corroded) • Switchyard disconnects • Transformers (connections, arrestors, cooling) • Transformers (internals) • Misaligned contacts, brushes, fuses, fuse clips, holders • Splices, crimps • Motor Control Center (MCC) heaters • Conductors (stranded, undersized, damaged) • Inductive heating (structure, bus ducts) • Batteries (connections, cells) • Open circuits (capacitors) • Load imbalance • Printed circuit boards • Motors (frames, bearings, connections) • Motors (failed coil in stator) Charlie Chong/ Fion Zhang

Mechanical • Valves (leakage, blockage) • Bearings • Couplings • Insulation (wet, damaged, coverage) • Pipes (thin areas, blockage, missing lining) • Refractory buildings (insulation, air leakage, roofs) • Reinforcing bar location • Underground leaks • Steam traps • Boiler tubes Miscellaneous • Containment spray ring header nozzles • Containment hydrogen igniter temperatures • Condensers (air in-leakage, tube leaks) • Thermal plumes • Heat transfer evaluation of heat exchangers

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To assist utility personnel in thermal image interpretation and recognition, this section also contains a number of examples of applications. These are thermal and visual images of components that appear to be in a degraded condition, along with a number of thermal and visual images of other components that appear to be in good working order. Table 5-2 is a listing of the example images that follow.

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Table 5-2 List of IR Application Examples 5-1 Step-Up Transformer High-Resistance Connection 5-2 250 kV Transformer 5-3 Steam Line Leaks 5-4 Isophase Bus Bellows 5-5 Electric Generator 5-6 Regulating Transformer Cooling Oil Migration 5-7 Generator Casing 5-8 Energized Ground Cable 5-9 480 V Breaker Connection 5-10 Current Transformer 5-11 Fuse Holder 5-12 Connection to Fuse Holder 5-13 Knife Switch 5-14 Motor Control Center Breaker 5-15 Motor Control Center Terminal Block

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5-16 5-17 5-18 5-19 5-20 5-21 5-22 5-23 5-24 5-25 5-26 5-27 5-28 5-29 5-30 5-31

Motor Control Center Control Wire Padmount Transformers Vacuum Leak on Turbine Condenser Small Transformer Motor Shell Relief Valve Shell Relief Valve (Weeping) Shell Relief Valve (Leaking) Vacuum Leak on Turbine Steam Trap Pump Bearing Office Building Building Roof with Water Saturation Induction Motor Air Intake Plenum Generator Step-Up Transformer Printed Circuit Module

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