How do you test operation of a thermocouple fire detection system?

How do you test operation of a thermocouple fire detection system?

• A. Press the test switch to heat the thermocouple and close the sensitive relay.
• B. Route a signal to the control panel and observe a gauge.
• C. Replace the thermocouple with a known good unit.
• D. Disconnect the aircraft's electrical system and measure continuity.

Answer: (A)

The test is based on how a thermocouple fire detector proves its own operation: heating the thermocouple element so it generates a signal that drives the sensitive relay. When you press the test switch, a built-in heater or dedicated heat source near the thermocouple is activated, producing the temperature rise needed for the thermocouple to generate the millivolts that the detection circuit relies on. That signal causes the sensitive relay to close, which in turn triggers the fire warning indicators or alarms. This directly validates the sensing element, the relay, and the alarm circuitry all together. Routinely routing a signal to the control panel and watching a gauge would test the display or signal path, not the detector’s ability to sense heat. Replacing the thermocouple checks only the component itself, not the integrated system response. Disconnecting the aircraft’s electrical system and measuring continuity doesn’t simulate heat input or verify the fire detector’s response, and it’s not how the system is tested in service.

The test is based on how a thermocouple fire detector proves its own operation: heating the thermocouple element so it generates a signal that drives the sensitive relay. When you press the test switch, a built-in heater or dedicated heat source near the thermocouple is activated, producing the temperature rise needed for the thermocouple to generate the millivolts that the detection circuit relies on. That signal causes the sensitive relay to close, which in turn triggers the fire warning indicators or alarms. This directly validates the sensing element, the relay, and the alarm circuitry all together.

Routinely routing a signal to the control panel and watching a gauge would test the display or signal path, not the detector’s ability to sense heat. Replacing the thermocouple checks only the component itself, not the integrated system response. Disconnecting the aircraft’s electrical system and measuring continuity doesn’t simulate heat input or verify the fire detector’s response, and it’s not how the system is tested in service.