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Tip written by: Infraspection Institute

Equipment calibration can have a significant impact on the accuracy of infrared temperature measurement. In this Tip we discuss a simple technique for checking the accuracy of imaging and non-imaging radiometers.

Infrared radiometers must be within calibration in order to accurately measure temperatures. Traditionally, thermographers periodically send their equipment to the manufacturer for calibration. For some, this process can take several weeks and can be rather expensive. As an alternative, savvy thermographers can check the calibration of their instrument quickly and easily using some commonly available items.

In order to check infrared radiometer calibration, you will need at least two targets each with a known temperature and emittance. A simple solution is to use a container of ice water and a container of boiling water with a coupon of Scotch PVC electrical tape affixed to the container’s exterior surface. The size of both targets must exceed the spot measurement size of the instrument being calibrated. Container temperatures may be ascertained with a thermometer, thermocouple or contact radiometer.

Once targets have been prepared, use the following procedure:

• Turn radiometer on and allow it to stabilize to room temperature
• Set radiometer perpendicular to target surface
• If possible, set radiometer inputs for distance, humidity & air temperature
• Aim, focus and calculate Reflected Temperature
• Set radiometer emittance control. Scotch 191 tape = 0.97 LW or SW. Ice = 0.98 LW; 0.93 SW
• Using subject radiometer, measure temperature of target. For ice water, measure temperature of ice cubes. For hot water container, measure tape coupon.
• Compare radiometer’s value with contact temperature reading for each target to ensure that radiometer is within spec

A heated blackbody simulator can be used to check instrument calibration at higher temperatures. Because radiometer calibration is not user-adjustable, it will be necessary to return it to the manufacturer should you find your instrument is out of spec.

Verifying infrared equipment calibration is specifically covered within Infraspection Institute’s online short course, How to Check Infrared Equipment Calibration. Available 24 hours per day, this 27 minute course focuses on the simple, yet effective techniques for calibrating infrared equipment. The techniques demonstrated are compliant with accepted industry practice and ISO standards. For more information or to register, please visit: https://www.infraspection.com/product/successiries-108/.

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