FAA Powerplant Written Practice Test

What is the operating principle of the spot detector sensor in a fire detection system?

1. A bimetallic thermal switch that closes when heated to a high temperature

2. A semiconductor device that measures electrical resistance

3. A pressure-sensitive switch that reacts to smoke

4. A mechanical lever that activates at high temperatures

The correct answer is: A bimetallic thermal switch that closes when heated to a high temperature

The operating principle of a spot detector sensor in a fire detection system involves a bimetallic thermal switch. This type of sensor operates by utilizing two different metals that expand at different rates when subjected to heat. As the temperature increases, the differential expansion causes the bimetallic element to bend or deform in such a way that it closes an electrical circuit. This closing action indicates the presence of high temperatures, which may indicate a fire hazard. Bimetallic thermal switches are commonly used in various applications because they are straightforward, reliable, and do not require external power to operate. Their sensitivity can be calibrated to respond to specific temperature thresholds relevant to fire detection, making them effective for indicating potential fire situations.