Infrared thermometers are temperature measuring devices which are operated contact free. They can be used to take surface temperatures remotely using handheld or fixed devices. Infrared thermometers are applied effectively to situations where it is dangerous or difficult to reach the object, or for patients that may be contagious and need their temperature taken without contact. An infrared thermometer will measure the amount of infrared radiation coming off an object, as well as how reflective the surface is or its ‘emissivity’.
The science behind infrared thermometers
An infrared thermometer detects the infrared energy emitted from surfaces which are at temperatures above absolute zero (0°Kelvin). To understand how an infrared thermometer works, we first need to understand what infrared radiation is and how it can help to provide a temperature reading of a surface.
Infrared is a type of radiation that is felt as heat radiating from an object but is not able to be seen by the naked eye. The principle of infrared thermometers is based on Planck’s law which describes the electromagnetic radiation emitted from a blackbody at a certain temperature. A blackbody is a theoretical object that absorbs all radiation.
The other significant laws of physics used in infrared technology are:
Kirchoff’s Law of thermal radiation: If a given temperature and wavelength of a surface are equal, the absorptivity and emissivity are equal.
Stephan Boltzmann Law of infrared radiation: A surface or body that does not absorb all incident radiation emits less total energy than one that absorbs all radiation and has emissivity 0 < ε < 1 where ε = emittance.
The mechanics of infrared thermometers
To measure the temperature of a surface, a lens in the infrared thermometer focuses the radiation onto a detector which then converts it into an electronic signal. Calculations compensate for emissivity and ambient temperature. Infrared thermometers need to be calibrated to mitigate interference from other nearby objects emitting their own thermal radiation (including the user) which can interfere with the reading.
To ensure the temperature is coming from the correct distant surface, handheld infrared thermometers come fitted with a laser pointer that the user can use as a visual indicator.
Common uses
Infrared thermometers are used to monitor mechanical and electrical equipment for changes in temperature that can indicate failure.
When a quick response is desired, for example temperature checking for Covid 19 when people enter a location, an infrared thermometer will both measure temperature without contact and provide an immediate result.
IR thermometers are varied and specific to purpose – users will choose the spot ratio and temperature measurement range that suits the particular application. A thermometer with a distance to spot ratio of 1:1 and a temperature range of around -33°c up to 110°c will be suited to industrial applications and general laboratory work. For environments that need surfaces to remain within strict temperature ranges such as the food industry, a thermometer with higher ratios, adjustable emissivity of 0.1 to 1.0 and a wider temperature range will be required.
Your thermometer or componentry specialist will be able to provide more information about infrared thermometers and provide advice about which specific thermometer is suitable for your purpose.