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Understanding New Developments in Data Acquisition, Measurement, and Control Understanding New Developments in Data Acquisition, Measurement and Control
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Edition
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A Practical Guide to High Performance Test and Measurement
Understanding New Developments in Data Acquisition, Measurement, and Control A Practical Guide to High Performance Test and Measurement 1st Edition
A
G R E A T E R
M E A S U R E
O F
C O N F I D E N C E
SECTION 1
Data Acquisition and Measurement Overview 1.1 1.2
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-2 Data Acquisition and Control Hardware . . . . . . . . . . . . . . . . . . . . . . .1-3
SECTION 2
Computer Buses, Protocols, and Hardware 2.1 2.2 2.3 2.4 2.5 2.6
Computer Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-2 Processors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-2 Bus Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4 Industrial Computer Expansion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-8 Connectivity/Data Communications . . . . . . . . . . . . . . . . . . . . . . . .2-16 Networked Instrument Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-26
SECTION 3
Software Overview 3.1 3.2 3.3 3.4 3.5 3.6 3.7
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2 Development Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2 Source Code and Source Code Management. . . . . . . . . . . . . . . . . .3-7 Reusable Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-7 System Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-11 General Program Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-13 Making Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-15
SECTION 4
Basic Component Theory 4.1 4.2 4.3 4.4 4.5
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 Passive Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 Op Amp Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-11 Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-19 Digital I/O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-20
SECTION 5
Basic Analog and Digital I/O 5.1 5.2 5.3 5.4 5.5
A/D Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 D/A Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-11 Interfacing Digital I/O to Applications. . . . . . . . . . . . . . . . . . . . . . . .5-12 Isolation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-17 Ground Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-19
SECTION 6
Temperature Measurement 6.1 6.2
Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 Thermocouples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 iii
6.3 6.4 6.5 6.6
Resistive Temperature Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . .6-12 Thermistors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-19 Semiconductor Linear Temperature Sensors. . . . . . . . . . . . . . . . . 6-21 Thermal Shunting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-22
SECTION 7
Strain Measurement 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10
Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-2 Poisson’s Strain. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-2 Strain Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-2 Gauge Factor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6 Sources of Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-7 Strain Gauge Signal Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . .7-10 Shunt Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11 Load Cells, Pressure Sensors, and Flow Sensors . . . . . . . . . . . . . . 7-11 Acceleration, Shock, and Vibration . . . . . . . . . . . . . . . . . . . . . . . . . .7-12
SECTION 8
Related Topics of Interest 8.1 8.2
Current Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2 Connection Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4
SECTION 9
Application Examples 9.1 9.2 9.3 9.4 9.5 9.6 9.7
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2 OEM/Factory Automation and Data Acquisition . . . . . . . . . . . . . . . 9-2 Magnetic Field Monitoring in a Synchrotron Facility . . . . . . . . . . . . 9-5 Tensile Test Stand Application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9 Burn-In and Stress Testing of Electronic Devices . . . . . . . . . . . . . 9-10 Performance Characterization of Shock Absorbers. . . . . . . . . . . . 9-12 Instrument-Grade, Low Cost Analog Output Control . . . . . . . . . . .9-13
APPENDIX A
Selector Guides for Plug-In Boards, USB Modules, PXI Systems, and External Data Acquisition Instruments APPENDIX B
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1 APPENDIX C
Safety Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1
iv
U N D E R S TA N D I N G N E W D E V E L O P M E N T S I N D ATA A C Q U I S I T I O N , M E A S U R E M E N T, A N D C O N T R O L
SECTION 1
Data Acquisition and Measurement Overview
1
1.1
Data Acquisition and Measurement Overview
Definition Although concepts like data acquisition, test, and measurement can be surprisingly difficult to define completely, most computer users, engineers, and scientists agree there are several common elements in systems used today for these functions: UÊ Ê«iÀà > ÊV «ÕÌiÀÊ* ®Ê ÃÊÕÃi`ÊÌ Ê«À }À> Ê> `ÊV ÌÀ ÊÌ iÊÌiÃÌÊ> `Ê measurement equipment, and to store or manipulate data subsequently. / iÊÌiÀ ʺ* »Ê ÃÊÕÃi`Ê Ê>Ê}i iÀ> ÊÃi ÃiÊÌ Ê V Õ`iÊ> ÞÊV «ÕÌiÀÊÀÕ ning any operating system and software that supports the desired result. / iÊ * Ê >ÞÊ > Ã Ê LiÊ ÕÃi`Ê v ÀÊ ÃÕ«« ÀÌ }Ê vÕ VÌ Ã]Ê ÃÕV Ê >ÃÊ Ài> Ì iÊ }À>« }Ê ÀÊÀi« ÀÌÊ}i iÀ>Ì °Ê/ iÊ* Ê >ÞÊ ÌÊ iViÃÃ>À ÞÊLiÊ ÊV stant control of the data acquisition and measurement equipment, or even remain connected to some pieces of equipment at all times. UÊ Ê ÌiÃÌÊ ÀÊ i>ÃÕÀi i ÌÊ ÃÞÃÌi Ê V> Ê V à ÃÌÊ vÊ `>Ì>Ê >VµÕ Ã Ì Ê « Õ} Ê L >À`ÃÊv ÀÊ* Ã]ÊiÝÌiÀ > ÊL >À`ÊV >Ãà Ã]Ê` ÃVÀiÌiÊ ÃÌÀÕ i ÌÃ]Ê ÀÊ>ÊV L >Ì Ê vÊ> ÊÌ iÃi°Ê ÝÌiÀ > ÊV >Ãà ÃÊ> `Ê` ÃVÀiÌiÊ ÃÌÀÕ i ÌÃÊÌÞ« V> ÞÊ V> ÊLiÊV iVÌi`ÊÌ Ê>Ê* ÊÕà }Êi Ì iÀÊÃÌ> `>À`ÊV Õ V>Ì Ê« ÀÌÃÊ ÀÊ >Ê«À «À iÌ>ÀÞÊ ÌiÀv>ViÊL >À`Ê ÊÌ iÊ* ° UÊ/ iÊ ÃÞÃÌi Ê V> Ê «iÀv À Ê iÊ ÀÊ ÀiÊ i>ÃÕÀi i ÌÊ > `Ê V ÌÀ Ê «À cesses using various combinations of analog input, analog output, digiÌ> Ê É"]Ê ÀÊ Ì iÀÊëiV > âi`ÊvÕ VÌ Ã°Ê7 i ÊiÝÌiÀ > Ê ÃÌÀÕ i ÌÃÊ>ÀiÊ used, most or all of these functions could reside within the instruments. / iÀiv Ài]Ê i>ÃÕÀi i ÌÊ> `ÊV ÌÀ ÊV> ÊLiÊ` ÃÌÀ LÕÌi`ÊLiÌÜii Ê* Ã]Ê ÃÌ> ` > iÊ ÃÌÀÕ i ÌÃ]Ê> `Ê Ì iÀÊiÝÌiÀ > Ê`>Ì>Ê>VµÕ Ã Ì ÊÃÞÃÌi ð The difficulty involved in differentiating between terms such as “data acquisition]»Êºtest and measurement]»Ê> `ʺmeasurement and control»ÊÃÌi ÃÊvÀ Ê the blurred boundaries that separate the different types of instrumentation in ÌiÀ ÃÊ vÊ «iÀ>Ì ]Êvi>ÌÕÀiÃ]Ê> `Ê«iÀv À > Vi°Ê ÀÊiÝ> « i]Êà iÊÃÌ> ` > iÊ instruments now contain card slots and embedded microprocessors, use operating system software, and operate more like computers than like traditional instruments. Such instruments now make it possible to construct test systems with high channel counts that gather data and log it to a controlling computer at high throughput rates, with high measurement accuracy. Accuracy aside, plug-in boards can transform computers into multi-range digital multimeters, oscilloscopes, or other instruments, complete with user-friendly, on-screen virtual front panels. For the sake of simplicity, this handbook uses the term “data acquisition and V ÌÀ »ÊLÀ >` ÞÊÌ ÊÀiviÀÊÌ Ê>ÊÛ>À iÌÞÊ vÊ >À`Ü>ÀiÊ> `Êà vÌÜ>ÀiÊà ÕÌ ÃÊV>«>L iÊ
1-2
1
vÊ > }Ê i>ÃÕÀi i ÌÃÊ> `ÊV ÌÀ }ÊiÝÌiÀ > Ê«À ViÃÃiðÊ/ iÊÌiÀ ʺV «ÕÌiÀ»Ê ÃÊ> à Ê`iw i`ÊÀ>Ì iÀÊLÀ >` Þ°Ê i iÀ> ÞÊ ÊÌ ÃÊ > `L ]Ê>Ê* ÊÀiviÀÃÊÌ Ê any personal computer running Microsoft® Windows 98®, or a later Windows ÛiÀà °Ê ÜiÛiÀ]ÊÜ i ÊiÝÌiÀ > Ê ÃÌÀÕ i ÌÃÊ>ÀiÊV L i`ÊÜ Ì Ê`>Ì>Ê>VµÕ à tion boards, the result is often referred to as a hybrid system. Hybrid systems are becoming more common as engineers seek the optimum combination of throughput and accuracy for their test and measurement applications.
1.2
Data Acquisition and Control Hardware Data acquisition and control hardware is available in a number of forms, which offer varying levels of functionality, channel count, speed, resolution, accuracy, and cost. This section summarizes the features and benefits generally associated with the various categories, based on a broad cross-section of products, V Õ` }ÊiÝÌiÀ > Ê ÃÌÀÕ i ÌðÊ,iviÀÊÌ Ê ««i ` ÝÊ Êv ÀÊ>Ê ÀiÊ`iÌ> i`ÊV «>À Ã Ê vÊ« Õ} ÊL >À`ÃÊ> `ÊiÝÌiÀ > Ê ÃÌÀÕ i Ìð
1.2.1
Plug-in Data Acquisition Boards
iÊ` ë >ÞÊ>`>«ÌiÀÃ]Ê `i Ã]Ê> `Ê Ì iÀÊÌÞ«iÃÊ vÊiÝ«> à ÊL >À`Ã]Ê« Õ} Ê data acquisition boards are designed for mounting in board slots on a computer motherboard. Today, most data acquisition boards are designed for the current * Ê *iÀ « iÀ> Ê « i ÌÊ ÌiÀV iVÌ®Ê ÀÊ i>À iÀÊ - Ê `ÕÃÌÀÞÊ -Ì> `>À`Ê ÀV ÌiVÌÕÀi®ÊLÕÃiÃ°Ê - Ê> `Ê>Ãà V >Ìi`Ê`>Ì>Ê>VµÕ Ã Ì ÊL >À`ÃÊ>ÀiÊÀ>« ` ÞÊLiV }ʺ i}>V޻ʫÀ `ÕVÌÃ]Ê> `Ê >À}i ÞÊÀi« >Vi`ÊLÞÊ* °Ê >Ì>Ê>VµÕ Ã Ì Ê« Õ} Ê L >À`ÃÊ> `Ê ÌiÀv>ViÃÊ >ÛiÊLii Ê`iÛi «i`Êv ÀÊ Ì iÀÊLÕÃiÃÊ - ]Ê Ê VÀ Ê
> i ]Ê> `ÊÛ>À ÕÃÊ «« iÊLÕÃiî]ÊLÕÌÊÌ iÃiÊ>ÀiÊ Ê }iÀÊV à `iÀi`Ê > ÃÌÀi> Ê«À `ÕVÌÃ°Ê Ê>`` Ì ]Ê>ÊÜ `iÊÀ> }iÊ vÊ1- Ê`>Ì>Ê>VµÕ Ã Ì Ê `Õ iÃÊ>ÀiÊ ÜÊ>Û> >L iÊv ÀÊ« Õ}} }Ê Ì Ê>Ê* ½ÃÊ1- Ê« ÀÌÃ]Ê ÀÊ1- Ê ÕLÃÊ>ÌÌ>V i`ÊÌ ÊÌ ÃiÊ « ÀÌÃ°Ê ÃÊ` ÃVÕÃÃi`Ê Ê-iVÌ ÊÓ]Ê iÜiÀÊ* ÃÊ >ÞÊ> Ã Ê >ÛiÊ* Ê Ý«ÀiÃÃÊà ÌÃ]Ê Table 1-1. Features of plug-in data acquisition boards Inexpensive method of computerized measurement and control. High speed available (100kHz to 1GHz and higher). Available in multi-function versions that combine A/D, D/A, digital I/O, counting, timing, and specialized functions. Good for tasks involving low-to-moderate channel counts. Performance adequate to excellent for most tasks, but electrical noise inside the PC can limit ability to perform sensitive measurements. Input voltage range is limited to approximately ±10V. Use of PC expansion slots and internal resources can limit expansion potential and consume PC resources. Making or changing connections to board’s I/O terminals can be inconvenient.
1-3
1
Data Acquisition and Measurement Overview
vÌi Ê ÊV L >Ì ÊÜ Ì Ê* Êà ÌÃ]Ê«>ÀÌ VÕ >À ÞÊ ÊV «ÕÌiÀÃÊLÕ ÌÊiÝ«ÀiÃà ÞÊ for industrial applications. As a category, plug-in boards offer a variety of test functions, high channel counts, high speed, and adequate sensitivity to measure moderately low signal levels, at relatively low cost. Table 1-1 lists additional attributes of typical boards. 1.2.2
External Data Acquisition Systems
/ iÊ À } > Ê « i i Ì>Ì Ê vÊ> ÊiÝÌiÀ > Ê`>Ì>Ê>VµÕ Ã Ì ÊÃÞÃÌi ÊÜ>ÃÊ>ÊÃi v powered system that communicated with a computer through a standard or «À «À iÌ>ÀÞÊ ÌiÀv>Vi°Ê ÃÊ>ÊL Ýi`Ê> ÌiÀ >Ì ÛiÊÌ Ê« Õ} ÊL >À`Ã]ÊÌ ÃÊÌÞ«iÊ vÊÃÞÃtem usually offered more I/O channels, a quieter electrical environment, and greater versatility and speed in adapting to different applications. Another alter >Ì ÛiÊÌ `>ÞÊ ÃÊ>ÊÃÞÃÌi ÊL>Ãi`Ê ÊiÝÌiÀ > Ê1- Ê`>Ì>Ê>VµÕ Ã Ì Ê `Õ ið 1.2.2.1 USB Data Acquisition Modules
1- Ê`>Ì>Ê>VµÕ Ã Ì Ê `Õ iÃÊ vviÀÊ > ÞÊ>`Û> Ì>}iÃÊ ÛiÀÊ« Õ} ÊL >À`Ã]Ê V Õ` }Ê« Õ} > ` « >ÞÊV>«>L ÌÞ]ÊLiÌÌiÀÊ ÃiÊ Õ ÌÞ]Ê> `Ê« ÀÌ>L ÌÞ°Ê1- Ê `Õ iÃÊ` Ê ÌÊÀiµÕ ÀiÊ «i }ÊÌ iÊ* ]ÊLiV>ÕÃiÊÌ iÞÊV iVÌÊ` ÀiVÌ ÞÊÌ ÊÌ iÊ 1- Ê« ÀÌÃÊÛ >ÊÃÌ> `>À`ÊV>L iðÊ/ iÊ* Ê `i Ì wiÃÊÌ iÊ«ÀiÃi ViÊ vÊ>Ê iÜÊ`iÛ Vi]Ê then prompts the user for the location of the necessary driver software for installation. Table 1-2Ê ÃÌÃÊvi>ÌÕÀiÃÊ vÊÌÞ« V> Ê1- Ê `Õ ið Table 1-2. Features of USB data acquisition modules True plug and play means a simple connection between the PC and USB module. Because USB modules are external to the PC, they offer performance benefits for noisesensitive measurements. USB 1.1 supports data acquisition rates up to 400kHz. USB 2.0 supports data acquisition rates up to 500kHz in each direction, similar to PCI boards. Most USB modules handle of large array of I/O connections. USB modules are compact and portable. With USB hubs, additional modules can scale up measurement capacity. USB modules can be installed or removed while the PC is running (hot swapping). USB modules have simple power connections, either directly through the bus or through an external power source.
1.2.2.2 External Box/Rack Systems
/ `>Þ]ÊiÝÌiÀ > Ê`>Ì>Ê>VµÕ Ã Ì ÊÃÞÃÌi ÃÊ vÌi ÊÌ> iÊÌ iÊv À Ê vÊ>ÊÃÌ> ` > iÊ test and measurement solution oriented toward industrial applications. The applications for which they are used typically demand more than a system L>Ãi`Ê Ê >Ê * Ê Ü Ì Ê « Õ} Ê L >À`ÃÊ V> Ê «À Û `i]Ê ÀÊ Ì ÃÊ ÌÞ«iÊ vÊ >ÀV ÌiVÌÕÀiÊ ÃÊÃ « ÞÊ >««À «À >ÌiÊv ÀÊÌ iÊ>«« V>Ì °Ê `iÀ ÊiÝÌiÀ > Ê`>Ì>Ê>VµÕ Ã Ì Ê systems offer: 1-4
1
UÊ «« V>Ì ÃÊ Û Û }Ê > ÞÊÌÞ«iÃÊ vÊÃi à ÀÃ]Ê } ÊV > i ÊV Õ ÌÃ]Ê ÀÊ the need for stand-alone operation. UÊ } ÊÃi Ã Ì Û ÌÞÊÌ Ê ÜÊ iÛi ÊÛ Ì>}iÊà } > Ã]Ê °i°]Ê>««À Ý >Ìi ÞÊ£ 6Ê ÀÊ lower. UÊ «« V>Ì ÃÊÀiµÕ À }ÊÌ } Ì]ÊÀi> Ì iÊ«À ViÃÃÊV ÌÀ ° iÊÌ iÊ« Õ} ÊL >À`ÊL>Ãi`ÊÃÞÃÌi ]ÊÌ iÃiÊiÝÌiÀ > ÊÃÞÃÌi ÃÊÀiµÕ ÀiÊÌ iÊÕÃiÊ vÊ a computer for operation and data storage. However, the computer can be built up on boards, just as the instruments are, and incorporated into the board rack. / iÀiÊ>ÀiÊÃiÛiÀ> Ê>ÀV ÌiVÌÕÀiÃÊv ÀÊiÝÌiÀ > Ê `ÕÃÌÀ > Ê`>Ì>Ê>VµÕ Ã Ì ÊÃÞÃÌi Ã]Ê V Õ` }Ê6 ]Ê68 ]Ê 8 ]Ê 8 ]Ê «>VÌ* ]Ê> `Ê*8 °Ê/ iÃiÊÃÞÃÌi ÃÊÕÃiÊ iV anically robust, standardized board racks and plug-in instrument modules that vviÀÊ >Ê vÕ Ê À> }iÊ vÊ ÌiÃÌÊ > `Ê i>ÃÕÀi i ÌÊ vÕ VÌ Ã°Ê - iÊ iÝÌiÀ > Ê ÃÞÃÌi Ê `ià } ÃÊ V Õ`iÊ VÀ «À ViÃà ÀÊ `Õ iÃÊÌ >ÌÊÃÕ«« ÀÌÊ> ÊÌ iÊÃÌ> `>À`Ê* ÊÕÃiÀÊ interface elements, including keyboard, monitor, mouse, and standard communication ports. Frequently, these systems can also run Microsoft Windows and Ì iÀÊ* Ê>«« V>Ì Ã°Ê ÊÌ ÃÊV>Ãi]Ê>ÊV Ûi Ì > Ê* Ê >ÞÊ ÞÊLiÊ ii`i`ÊÌ Ê develop programs or off-load data for manipulation or analysis. Other features vÊiÝÌiÀ > ÊL >À` L>Ãi`ÊÃÞÃÌi ÃÊ>ÀiÊ ÃÌi`Ê ÊTable 1-3. Table 1-3. Features of external data acquisition chassis Multiple slots permit mixing-and-matching boards to support specialized acquisition and control tasks and higher channel counts. Chassis offers an electrically quieter environment than a PC, allowing for more sensitive measurements. Use of standard interfaces (IEEE-488, RS-232, USB, FireWire, Ethernet) can facilitate daisy chaining, networking, long distance acquisition, and use with non-PC computers. Dedicated processor and memory can support critical “real-time” control applications or stand-alone acquisition independent of a PC. Standardized modular architectures are mechanically robust, easy to configure, and provide for a variety of measurement and control functions. Required chassis, modules, and accessories are cost-effective for high channel counts.
1.2.2.2.1 Real-Time Data Acquisition and Control
À Ì V> ÊÀi> Ì iÊV ÌÀ Ê ÃÊ> Ê « ÀÌ> ÌÊ ÃÃÕiÊ Ê`>Ì>Ê>VµÕ Ã Ì Ê> `ÊV ÌÀ Ê systems. Applications that demand real-time control are typically better suited Ì ÊÌ iÊÌÞ«iÊ vÊiÝÌiÀ > ÊÃÞÃÌi Ê`iÃVÀ Li`Ê«ÀiÛ Õà Þ]ÊÌ > ÊÌ ÊÃÞÃÌi ÃÊL>Ãi`Ê Ê * Ê« Õ} ÊL >À`Ã°Ê Ì Õ} Ê VÀ à vÌÊ7 ` ÜÃÊ >ÃÊLiV iÊÌ iÊÃÌ> `>À`Ê «iÀ >Ì }ÊÃÞÃÌi Êv ÀÊ* Ê>«« V>Ì Ã]Ê ÌÊ ÃÊ>Ê `iÌiÀ ÃÌ VÊ «iÀ>Ì }ÊÃÞÃÌi ÊÌ >ÌÊ V> ½ÌÊ«À Û `iÊ«Ài` VÌ>L iÊÀië ÃiÊÌ iÃÊ ÊVÀ Ì V> Ê i>ÃÕÀi i ÌÊ> `ÊV ÌÀ Ê >«« V>Ì Ã°Ê/ iÀiv Ài]ÊÌ iÊà ÕÌ Ê ÃÊÌ Ê ÊÌ iÊ* ÊÌ Ê>ÊÃÞÃÌi ÊÌ >ÌÊV> Ê «iÀ>ÌiÊ>ÕÌ Õà ÞÊ> `Ê«À Û `iÊÀ>« `]Ê«Ài` VÌ>L iÊÀië ÃiÃÊÌ ÊiÝÌiÀ > ÊÃÌ Õ °Ê / ÃÊ ÃÊ>VV « à i`ÊÜ Ì ÊiÝÌiÀ > ÊÃÞÃÌi ÃÊÌ >ÌÊ >ÛiÊÌ i ÀÊ Ü Ê`i` V>Ìi`ÊÀi> time processor and real-time deterministic operating system. 1-5
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Data Acquisition and Measurement Overview
1.2.2.3 Discrete (Bench/Rack) Instruments
Originally, discrete electronic test instruments consisted mostly of single-channel meters, sources, and related instrumentation intended for general-purpose test applications. Over the years, the addition of more channels, communication interfaces and advances in instrument design, manufacturing, and i>ÃÕÀi i ÌÊÌiV }ÞÊ >ÛiÊiÝÌi `i`ÊÌ iÊÀ> }iÊ> `ÊvÕ VÌ > ÌÞÊ vÊÌ iÃiÊ ÃÌÀÕ i ÌÃ°Ê iÜÊ«À `ÕVÌÃÊÃÕV Ê>ÃÊÃV> iÀÃ]Ê Õ Ì « iÝiÀÃ]Ê- ÕÀVi iÌiÀ® instruments, counter/timers, nanovoltmeters, micro-ohmmeters, and other specialized instrumentation have made it possible to create computer-controlled ÌiÃÌÊ> `Ê i>ÃÕÀi i ÌÊÃÞÃÌi ÃÊÜ Ì Ê>Ê >À}iÊ Õ LiÀÊ vÊV > i ÃÊÌ >ÌÊ vviÀÊiÝceptional sensitivity, resolution, and throughput. Even low channel count inÃÌÀÕ i ÌÃÊV> ÊLiÊV L i`ÊÜ Ì ÊÃÜ ÌV Ê >ÌÀ ViÃÊ> `Ê Õ Ì « iÝiÀÃÊÌ Ê ÜiÀÊÌ iÊ cost per channel by allowing one set of instruments to service many test inputs while preserving signal integrity. These instruments can also be combined with computers that contain plug-in data acquisition boards to form a hybrid test system. Table 1-4 lists other characteristics of these systems. Table 1-4. Features of discrete instruments for data acquisition Support measurement ranges and sensitivities generally beyond the limits of standard plugin boards and eternal data acquisition systems. Use standard interfaces (e.g., IEEE-488, RS-232, FireWire, USB, and Ethernet) that support long-distance acquisition, compatibility with non-IBM-compatible computers, or use with computers without available expansion slots. Most suitable for measurement of voltage, current, resistance, capacitance, inductance, temperature, etc. May not be effective solutions for some types of specialized sensors or signal conditioning requirements. Generally slower than plug-in boards or external data acquisition systems. More expensive than standard data acquisition systems on a per-channel basis.
1.2.2.4 Hybrid Data Acquisition Systems
ÞLÀ `ÊÃÞÃÌi ÃÊ>ÀiÊ>ÊÀi >Ì Ûi ÞÊÀiVi ÌÊ`iÛi « i ÌÊ ÊiÝÌiÀ > Ê`>Ì>Ê>VµÕ Ã Ì Ê ÃÞÃÌi Ã°Ê ÊÌÞ« V> Ê ÞLÀ `ÊÃÞÃÌi ÊV L iÃÊ* Ê« Õ} ÊL >À`Ã]Ê ÀÊ> ÊiÝÌiÀ > Ê`>Ì>Ê acquisition system, with discrete instruments to perform the desired test and measurement functions. However, some bench and rackmounted instruments >ÛiÊvi>ÌÕÀiÃÊÌ >ÌÊ V Õ`iÊÃÌ> `>À`Ê`>Ì>Ê>VµÕ Ã Ì ÊvÕ VÌ ÃÊ> `ÊiÝ«> Ã Ê capabilities in a compact, instrument-like package, making them stand-alone hybrid systems. These instruments have a user interface is much like a typical
Ê«À `ÕVÌ°Ê ÞLÀ `ÊÃÞÃÌi ÃÊÌ >ÌÊV L iÊ« Õ} ÊL >À`Ã]ÊiÝÌiÀ > ÊÃÞÃÌi Ã]Ê > `Ê` ÃVÀiÌiÊ ÃÌÀÕ i ÌÃÊ >ÞÊÕÌ âiÊ>Ê}À>« V> ÊÕÃiÀÊ ÌiÀv>ViÊ 1 ®ÊÌ >ÌÊ>««i>ÀÃÊ>ÃÊ>ÊÛ ÀÌÕ> Ê ÃÌÀÕ i ÌÊ ÊÌ iÊ* ÊÃVÀii °Ê Ê> ÞÊV>Ãi]ÊÌÞ« V> Ê ÞLÀ `ÊÌiÃÌÊ ÃÞÃÌi ÊvÕ VÌ ÃÊ V Õ`iÊ Ê> `Ê
ÊÛ Ì>}iÊ> `ÊVÕÀÀi ÌÊ i>ÃÕÀi i ÌÃ]ÊÌi perature and frequency measurements, event counting, timing, triggering, and 1-6
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process control. They allow the user to get the best combination of speed and accuracy for the application.
Figure 1-1. Keithley PXI-based hybrid test system
i Ì iÞ½ÃÊ-iÀ iÃÊ *8 ÊFigure 1-1®Ê ÃÊ`ià } i`Êv ÀÊ } Êëii`Ê>ÕÌ >Ìi`Ê«À duction testing as part of a hybrid test system using precision instruments. This series consists of simultaneous data acquisition boards, multi-function analog I/O boards, high speed analog output boards, a 130MS/s digitizer module, ` } Ì> Ê É"Ê `Õ iÃ]Ê*8 ÊV >Ãà Ã]Êi Li``i`Ê* ÊV ÌÀ iÀÃ]Ê 8 ÊLÀ `}iÃÊv ÀÊ Ài ÌiÊ* ÊV ÌÀ ®]Ê> `Ê * Ê ÌiÀv>ViÊV>À`Ã°Ê *8 Ê«À `ÕVÌÃÊ>ÀiÊ`ià } i`Êv ÀÊ «Ì > Ê Ìi}À>Ì ÊÜ Ì Ê«ÀiV Ã Ê ÃÌÀÕ i Ì>Ì ]ÊÃÕV Ê>ÃÊ i Ì iÞ½ÃÊ-iÀ iÃÊ 2600 System SourceMeter®Ê Õ Ì V > i Ê 6Ê ÌiÃÌÊ Ã ÕÌ Ã]Ê Ü V Ê vi>ÌÕÀiÊ /-*ÒÊ> `Ê/-* ÒÊÌ >ÌÊ iÌÊÕÃiÀÃÊÌ> iÊ>`Û> Ì>}iÊ vÊ` ÃÌÀ LÕÌi`Ê«À }À> }Ê > `Ê V VÕÀÀi ÌÊ iÝiVÕÌ Ê Ì Ê «iÀv À Ê } Ê Ã«ii`]Ê >ÕÌ >Ìi`Ê ÌiÃÌÊ ÃiµÕi ViÃÊ >VÀ ÃÃÊ Õ Ì « iÊV > i ÃÊqÊ `i«i `i ÌÊ vÊ>Ê* Ê «iÀ>Ì }ÊÃÞÃÌi Ê> `Ê ÌÃÊ>Ãà ciated communication delays. Table 1-5 summarizes the features of hybrid test systems.
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Data Acquisition and Measurement Overview
Table 1-5. Features of a hybrid data acquisition and control system Delivers accuracy (typically 18- to 22-bit A/D), range, and sensitivity of benchtop instruments (superior to standard data acquisition equipment). Allows optimization of throughput speed by distributing measurement and control functions to the appropriate hardware. May have a DMM front end with a digital display and front panel controls, or a PC GUI (often a virtual instrument panel), or both. External intruments used in these systems often have built-in data and program storage memory for stand-alone data logging and process control. Uses standard interfaces (IEEE-488, LXI, PXI, Ethernet, etc.) that support long-distance acquisition, and compatibility with non-PC computers. Cost-effective on a per-channel basis. Easily expanded or modified as test requirements change.
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