FAA Powerplant Written Practice Test

Which of the following fire detection systems measures temperature rise compared to a reference temperature?

1. Thermocouple

2. Photoelectric sensor

3. Flame detector

4. Ionization detector

The correct answer is: Thermocouple

The thermocouple is a device that consists of two dissimilar metal wires joined at one end, creating a junction that generates a voltage proportional to temperature differences between that junction and the reference point. In fire detection systems, thermocouples can be utilized to monitor the rise in temperature relative to a predetermined reference temperature. When the temperature increases beyond a certain threshold, indicative of a potential fire, the thermocouple produces a measurable signal that can alert the system. In contrast, photoelectric sensors operate by detecting changes in light levels, often seeing the smoke from a fire but not directly measuring temperature. Flame detectors are designed to sense the presence of flames using infrared or ultraviolet light wavelengths, while ionization detectors utilize radioactive materials to detect ionization changes in the air caused by smoke particles. None of these systems directly measure temperature rise compared to a reference temperature, which highlights the specific function of a thermocouple in fire detection applications.