They measure the infrared energy emitted by the target, and convert the value to a temperature. Different models offer different temperature ranges and different optics.
In general, lower cost thermometers measure lower temperatures and have bigger fields of view, so you need to be closer to the target. The advantage of infrared is that you can measure virtually instantaneously and without touching the target, so rotating shafts, moving belts and very hot surfaces can be safely measured.
Applications include bearings in housings, pumps, motors and fans, as well as electrical switchboards, busbars and transformers. Products such as plastic, glass, paper and steel can also be measured using infrared thermometers.
CBC can supply a full range of hand held thermometers, from low cost simple models from -20 to 320°C to advanced models with optics to 180:1 and temperatures to 3,000°C