Calibration of “Low” Temperature IR Thermometers

Calibration of Low-Temperature Infrared Thermometers (PDF 327KB).. Plus two.
main From the website of the Measurement Standards Laboratory – MSL – of New Zealand comes this very useful and interesting, downloadable, free “Technical Guide” plus more. Of course, the term “Low Temperature” needs to be placed in context.

Here it assumes the use of popular devices designed for use in the –50 °C to 500 °C range (about -10°F to 1000 °F, but in practical terms, despite their calibration over a wider range, such devices are most widely used in the region of about -40 °C to about 150 °C (-40 °F to about 300 °F).

Also, most of the available devices are handheld, relatively low cost (less than a few hundred US Dollars and a lot less on websites like ebay.com) measure in the spectral range of about 8 to 10 microns (micrometers or ?m).

It is described as follows:

TECHNICAL GUIDE 22 – Calibration of Low-Temperature Infrared Thermometers

The advent of low-cost handheld infrared thermometers, which make non-contact measurements in the range –50 °C to 500 °C, has led to a proliferation of the thermometers in the food, building, and low-temperature processing industries.

However, these instruments are not as simple to use as they first appear due to systematic effects related to emissivity, reflections, and the temperature of the thermometer itself.

This guide explains how to calibrate low-temperature infrared thermometers and gives methods for correcting for the systematic effects.

One of the main conclusions of this Guide is:
” Because low-temperature IR thermometers are designed to automatically overcome the problem of reflected radiation when used to carry out temperature measurements, calibration of such devices is not a straightforward task. Procedures for calibrating IR thermometers need to be carefully designed to take into account the instrumental emissivity setting on the device, its detector temperature, and ambient temperature, as well as the properties of the blackbody calibration source and the reference thermometer.”
Two related Technical Guides, also free and downloadable, supplement this one.

Technical Guide 1 – The Ice Point (PDF 811KB)

How to make a simple temperature reference at 0 °C accurate to 0.01 °C. Suitable for anyone using liquid-in-glass thermometers, thermocouples, thermistors or platinum resistance thermometers.

Technical Guide 2 – Infrared Thermometry Ice Point (PDF 190KB)