Transactions in measurement and control -- 1.7

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ecause of normal variations in The properties of materials used to construct radiation
temperature sensors, new instruments must be individually calibrated in order to achieve even moderate levels of accuracy. Initial calibration is likely to be performed by the sensor manufacturer, but periodic recalibration—in-house or by a third-party laboratory or the original manufacturer—is necessary if any but the most qualitative measurements are expected.

The ongoing accuracy of a non-contact temperature sensor will depend on the means by which the calibration is performed, how frequently it is recalibrated, as well as the drift rate of the overall system. Ensuring the absolute accuracy of non-contact temperature measurement
devices is more difficult than with most direct contacting devices, such as thermocouples and
resistance temperature detectors (RTDs). Limiting the absolute accuracy to 1% is difficult; even in the most sophisticated set-ups, better than 0.1% accuracy is seldom achieved. This arises, in part, from the difficulty in accurately determining the emissivity of real bodies.
Repeatability or reproducibility is, however, more readily achievable than absolute accuracy, so don't pay more if consistency will do.

If absolute accuracy is a concern, then traceability to standards such as those maintained by the National Institute of Standards & Technology (NIST) will also be important. Traceability, through working to secondary to primary standards is central to the quality standards compliance such as those defined by the ISO 9000 quality standard.

Topics covered in this chapter include:
1.  Why Calibrate?
2.  Blackbody Cavaties
3.  Tungsten Filament Lamps

Other chapters of Transactions will systematically cover other aspects of temperature, humidity, pressure, strain, flow, level, pH, and conductivity instrumentation as well as other measurement, data acquisition and control topics. Click here to view the other chapters of Volume I, or to download Non-Contact Temperature Measurement in its entirety.

 

We hope the Transactions in Measurement and Control series will find a permanent home on your reference shelf, and that it proves itself of great value now and in the future.

Click the Download Now button below to view and save Chapter Seven: IR Thermometer Calibration.