A relay function in a pyrometer is used to trigger a switching contact when a set alarm or threshold value is exceeded or not reached.

In practice, for example, a heating element is activated when the temperature falls below a certain limit in order to bring the measured object back into a certain temperature range. Similarly, a cooling process can be triggered when a defined temperature limit is exceeded, for example by using a nitrogen cooling system to cool the coal on a conveyor belt back below the critical value.

Either contact relays or optocouplers are used in the pyrometers for the relay function.

Relays are used where temperature values need to be reliably monitored. A correctly set relay can detect, report or switch faults and thus minimize, and ideally avoid, production errors.