Calibration and data acquisition finally meet
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 4/1/2005
PC-based and modular data-acquisition systems—cards and boxes—have been around almost as long as the PC itself (Ref. 1). But because these components were usually just part of a larger system, users rarely gave much thought to calibrating them. That's changing. Users of modular instruments now want manufacturers to provide calibration certificates and measurement traceability to national standards.
Scott Ludwick, software engineering manager at IOtech, has seen a recent jump in calibration inquiries. "Customers are now inquiring about calibration before buying a data-acquisition product," he noted. Ludwick is still investigating the reasons for the surge, but he believes that ISO 9000, which requires documentation of measurement quality, is the catalyst.
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| More and more, users of PC-based data-acquisition systems inquire about calibration. Courtesy of IOtech. |
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Read other articles from this issue: Table of contents, April 2005 FEATURES Combining talents Cellular or WiFi? X-ray inspection—Not all black or white Keep it safe Biological pulses |
Paul Packebush, senior group manager for engineering services at National Instruments, also points out that card-based instruments are closing in on traditional instruments in accuracy and resolution. Thus, users need to maintain card-based instruments the same way they maintain traditional instruments.
Packebush, along with consultant Dave Braudaway, are members of IEC Working Group 13, which has developed a draft standard for specifying and calibrating multifunction data-acquisition devices. Braudaway presented a paper called "Uncertainty Specification for Data Acquisition Devices" at the 2005 Measurement Science Conference (www.msc-conf.com). The draft standard addresses how manufacturers should specify accuracy in PC-based data-acquisition systems. Manufacturers use different ways to express uncertainty, which makes comparing systems difficult. The standard also defines a calibration procedure by which you can verify that a data-acquisition system meets its published specifications.
Although the draft standard isn't ratified, equipment makers have responded to requests for calibration certificates, procedures, and software. Some users, particularly those in large aerospace companies, want to perform their own calibrations. Thus, Data Translation, Measurement Computing, and National Instruments now provide stand-alone software for calibrating their products. Others will surely follow suit. National Instruments also provides a calibration application programming interface and a published calibration procedure for customers who want to write their own automated calibration procedures.
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Agilent Technologies has published eight application notes that cover its model 34980A switch/measurement unit, which combines a DMM with a switch card. The titles include "Test System Signal Switching," "Benefits of a Switch/Measure Unit for Data Acquisition and Electronic Functional Test," and "Using the 34980A in a System." 
