FAA Powerplant Written Practice Test

Which fire detection system measures temperature rise compared to a reference temperature?

1. Thermocouple

2. Ionization detector

3. Spot detector

4. Photoelectric sensor

The correct answer is: Thermocouple

The thermocouple is a device specifically designed to measure temperature differences by generating a voltage that corresponds to the difference in temperature between its junctions. When it comes to fire detection systems, thermocouples can be used to monitor any significant rise in temperature, indicating potential fire conditions. By comparing the measured temperature against a predetermined reference temperature, a thermocouple can effectively detect abnormal increases that could suggest the presence of a fire. This capability makes thermocouples suitable for applications where early detection of temperature changes is critical, such as in aircraft engines or other environments where fires can pose serious risks. In contrast, the other devices—ionization detectors, spot detectors, and photoelectric sensors—operationally rely on different principles, such as ionization of air particles or changes in light patterns caused by smoke, rather than directly measuring temperature changes. Hence, the thermocouple stands out as the correct choice for a system that explicitly measures temperature rise in relation to a reference temperature.