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An infrared thermometer is a device that measures the infrared radiation – a type of electromagnetic radiation below the visible spectrum of light – emitted by an object. The most basic design of infrared thermometers consists of a lens to focus the infrared thermal radiation onto a detector, which converts the radiant energy into an electric signal. This configuration facilitates temperature measurement from a distance, without the need for contact with the object to be measured. The device is useful for measuring temperature under circumstances where thermocouples or other probe type sensors cannot be used.

There are many types of infrared temperature sensing devices available today, including configurations designed for flexible and portable handheld use as well as for mounting in a fixed position to serve a specific purpose.

Types of Infrared Thermometers
The most common types of infrared thermometers include:

Spot infrared thermometers – These devices measure the temperature at a spot on a surface.
Infrared scanning systems – These devices scan a larger area as the spot thermometer points at a rotating mirror. They are widely used in manufacturing processes involving conveyors or web processes, such as continuous piles of material along a conveyor belt or large sheets of metal or glass exiting an oven.
Infrared thermal imaging cameras – These cameras are essentially infrared radiation thermometers used for measuring temperature at many points over a relatively large area to create a two-dimensional image called a thermogram. This technology is more software- and hardware-intensive compared to other types of infrared thermometers.
Working Principle of Infrared Thermometers

Infrared thermometers work based on black body radiation, According to which any material with a temperature above absolute zero has molecules moving within it. The higher the temperature, the faster the molecules move. The molecules emit infrared radiation as they move, and emit more radiation, including visible light, as they get hotter. This is why a heated metal emits a red or white glow. Infrared thermometers detect and measure this radiation.

Infrared light can be focused, reflected or absorbed like visible light. Infrared thermometers employ a lens to focus infrared light from an object onto a detector known as a thermopile. The function of the thermopile is to absorb infrared radiation and convert it to heat. The thermopile gets hotter as it absorbs more and more infrared energy. The excess heat is converted into electricity, which is transmitted to a detector which determines the temperature of the object.

Read more: The Working Principle and Applications of Infrared Thermometers