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Infrared temperature measurement technology What is heat radiation? – Principles It is a well-known fact in daily life that all bodies emit electromagnetic waves, or radiation, depending on their temperature. During dispersion of the radiation, energy is transported, a fact which means that radiation can be used to measure body temperature without contact. The radiated energy and its characteristic wavelengths are primarily dependent on the temperature of the radiating body. If, for example, you point a parabolic mirror with a match directly towards the sun, then it will ignite after a short period of time. This is because of the heat radiation from the sun, which is concentrated by the parabolic mirror onto a point.
Example of heat radiation
Sun
Parabolic mirror
Heat radiation
Light radiation Match
Advantages of IR measuring technology • Infrared measuring technology • No influence on the object being enables simple temperature measured means that recording of fast, dynamic measurements can be performed processes. This is assisted by on sensitive surfaces and sterile the short reaction time of sensors products, just as well as and systems. measurements on hazardous points or points that are difficult to access. Infrared thermometers are particularly suitable for: …Determining the surface … Parts which cannot be touched, …Poor heat conductors, such as temperature of gears, housings e.g. freshly painted parts, sterile ceramics, rubber, plastics etc. A and bearings in large and small parts or for corrosive probe for contact measurement can motors. substances. only display the correct temperature if it can take on the temperature of … Moving parts, e.g running paper … Measuring very small and very the measured body. In the case of webs, running sheet metal large areas. poor heat conductors, this is not tracks etc. usually the case and/or the response times are very long.
…Live parts, e.g. electrical components, conductor rails, transformers etc. …Small and low-mass parts from which a contact probe would remove too much heat thus resulting in incorrect readings.
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Emissivity table of important materials Material Aluminium, bright-rolled Cotton Concrete Ice, smooth Iron, emeried Iron with cast skin Iron with rolled skin Gypsum Glass Rubber, hard Rubber, softgrey Wood Cork Heat sink, black anodised Copper, lightly tarnished Copper, oxidised Plastics (PE, PP, PVC) Brass, oxidised Paper Porcelain Black paint (matt) Steel (heat-treated surface) Steel oxidised Clay, fired Transformer paint Brick, mortar, plaster
Temperature 170 °C 20 °C 25 °C 0 °C 20 °C 100 °C 20 °C 20 °C 90 °C 23 °C 23 °C 70 °C 20 °C 50 °C 20 °C 130 °C 20 °C 200 °C 20 °C 20 °C 80 °C 200 °C 200 °C 70 °C 70 °C 20 °C
Applications and practical tips E 0.04 0.77 0.93 0.97 0.24 0,80 0.77 0.90 0.94 0.94 0.89 0.94 0.70 0.98 0.04 0.76 0.94 0.61 0.97 0.92 0.97 0.52 0.79 0.91 0.94 0.93
• Error sources during infrared measurement In the case of non-contact temperature measurement, the composition of the
transmission path between the instrument and the object being measured can also have an effect on the measured result.
Meas. object Disturbance variable e.g. dust, steam
Measuring instrument
Infrared measuring range
Disturbance variables include, e.g. – Dust and dirt particles – Moisture (rain), steam, gases
• Incorrect set emissivities can lead to significant errors.
• Temperature change of a measuring instrument not yet adjusted to the new temperature (comparison point) can lead to Set emissivity using emissivity significant measuring table or check via contact probe. errors. A coating e.g. paint, oil or emission adhesive tape with a If possible, store the instrument defined emissivity must be in the place where the applied to the object being measurement is to be measured in the case of nonperformed. This will avoid the contact measurement on objects problem of adjustment time (but with low emissivity. observe instrument operating temperature).
• IR measurement is a purely optical measurement: Clean lens is essential for accurate measurement. Do not measure with misted-up lens, e.g. due to steam
• IR measurement is surface measurement Always make sure that the surface is clean. If there is dirt, dust, rime etc. on the surface, only the top layer will be measured - the dirt, in other words. Do not measure at occlusions (e.g. in packaging)
Only measure if there are no disturbing variables
• Distance between IR measuring instrument and object being measured too large - measuring spot is bigger than object. Keep distance between instrument and object being measured as small as possible.
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Measurement spot and distance from object being measured
Ø 16
Ø Measurement spot mm
Ø 170
Ø 66 Ø 33
testo 825-T1 / -T2 / -T3 / -T4 826-T1 / -T2 / -T3 / -T4 Ratio of measuring distance to measurement spot 3:1
100
200 500
Measuring distance mm
Ø Measurement spot mm
Ø 32.4
testo 850-1
Ø 10.1 Ø 2.5 30
50
Measuring distance mm
Ø 14
Ø Measurement spot mm Ø 72 Ø 40
500
1000
100
Ø 140
testo 850-2 Ratio of measuring distance to measurement spot 12:1
2000
Measuring distance mm
Ø Measurement spot mm Ø 25 at 0 mm Ø 29 Ø 19
Ø 58
testo 860-T1 / -T2 Near field 60:1 Far field
1150
35:1
1500 2500
Measuring distance mm
Ø Measurement spot mm Ø 25 at 0 mm
Ø 70
Ø 23
testo 860-T3 Near field 50:1
Ø 15.5
Far field 150
500
Ø 6 at 300 mm Measuring distance mm
1000
12:1