Infrared (IR) thermometers can be categorized by the temperature measuring technologies that they use or by certain other design elements. There are three main sensing methods that IR thermometers can use, each of which depends on different wavelengths of light. Brightness sensors use a single wavelength, ratio sensors make use of two, and multi-variant versions are capable of using two or more. These technologies can be used in different kinds of IR thermometers, such as handheld gun types, highly portable stick versions, and infrared thermocouples. Similar temperature monitoring technologies can also be found in certain infrared scanning systems and thermal imaging cameras.
There are a number of different ways that infrared radiation is measured to determine the temperature of an object. IR thermometers function by measuring blackbody radiation that is given off as infrared light. The simplest type of IR thermometer is known as a brightness sensor because these devices use only a single wavelength to determine temperature. An IR thermometer equipped with a brightness sensor functions by measuring the amplitude of the infrared energy radiated by a particular object within that single wavelength. Since only one wavelength is used, these devices can have trouble returning accurate readings if there is any type of interference.
Ratio sensors are used by IR thermometers that are capable of measuring two different wavelengths. These IR thermometers are sometimes called two color sensors because two wavelengths within the infrared range are measured. Using two wavelengths can allow these thermometers to obtain accurate readings through obstructions, such as dust or smoke, that would adversely affect a single color brightness sensor. The temperature reading of a two color sensor can be skewed towards the high side though if there is significant background interference from a hot source.
Multi-variant sensors can observe several wavelengths and are typically adjusted for use in a specific application. In this case, an object's emissivity is typically known before measurement takes place and the sensor is adjusted accordingly. This can allow a multi-variant IR thermometer to provide highly accurate readings.
Each of the different IR sensing technologies can be used in a number of devices. One common variety of IR thermometer is the handheld type. These IR thermometers often bear a superficial resemblance to guns, including a handle, trigger, and often a laser sight. Some handheld types also include built-in tripods so that they can be set in place.
Smaller stick type IR thermometers also exist. These devices are similar in design to other handheld types, though they are often small or compact enough to be easily carried in a pocket. Another type of IR thermometer is the infrared thermocouple, which is a small device capable of producing the same type of output as a normal thermocouple sensor.