Which fire detection system utilizes heat for normal testing?

The thermocouple system is a type of fire detection that relies on the measurement of temperature to detect the presence of a fire. It operates on the principle that as temperature increases, the resistance in a thermocouple changes, which can signal a potential fire event. This system is particularly useful in environments where high temperatures may be expected under normal operating conditions, allowing for reliable detection of abnormal temperature increases indicative of fire.

In terms of testing, utilizing heat as part of the normal testing process helps to ensure that the system is functioning correctly by simulating the conditions under which it is designed to operate. This method helps to verify the sensitivity and response time of the thermocouples.

The other systems listed do not primarily use heat in the same manner for testing purposes. Instead, they may rely on different mechanisms such as smoke detection, ionization, or other chemical reactions, making them less reliant on direct measurements of temperature for their normal testing protocols.