The Complete Handbook of Infrared Thermometers

Chapter 1: Understanding Infrared Thermometers

An infrared thermometer does not measure temperature directly. It measures the infrared radiation emitted by an object's surface and converts that reading into a temperature display using the physics of thermal radiation. That is a critical distinction for every professional who uses these instruments, because it means the accuracy of your reading depends as much on the surface you are measuring and the surrounding environment as it does on the quality of the instrument itself. A unit that reads accurately in a controlled lab can give you readings that are off by 10, 20, or even 50 degrees in the field if you do not account for the factors described in this chapter.

These instruments appear in nearly every maintenance shop and service truck, from the electrician checking the load side of a breaker for hot spots to the HVAC technician comparing supply and return duct temperatures to the food safety inspector verifying the temperature of a hotel pan held under a heat lamp. They are preferred over contact thermometers in many situations for practical reasons. You can measure a rotating shaft, a conveyor-belted product, a live electrical connection, or a surface that is too hot, too cold, or too dirty to touch. The measurement happens in under a second, which makes them ideal for scanning multiple points quickly. But that speed and convenience come with a cost: the reading you get is an interpretation of radiation arriving at the instrument, and that interpretation can