Thermometers are either contact or non–contact instruments. The handheld contact thermometers uses various contact probes, depending on the application to measure temperatures. The handheld instrument indicates the actual temperature reading and can perform certain tasks such as store values, monitor max/min readings and change resolutions.

The handheld infrared thermometer uses an infrared beam which sends two signals to the source of the required measuring point, one of which will be used as a reference the other will absorb a certain amount of infrared (heat)from the object. The difference between the two signals will indicate the actual temperature.

These instruments are typically used where accessibility to measure temperatures is problematic.

A fixed unit is available with the output signal being either a thermocouple (mV) or resistance signal