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 liquid expansion sensor that detects smoke

3. An electronic sensor that measures light intensity

4. A pressure sensor that identifies gas concentrations

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 relies on the characteristics of a bimetallic thermal switch. This type of sensor is designed to respond to high temperatures, making it effective in identifying potential fire conditions. When exposed to temperatures that exceed its predetermined threshold, the bimetallic strip within the sensor bends and closes an electrical circuit, signaling the presence of excessive heat associated with a fire event. This mechanism is particularly useful for direct fire detection in localized areas of an aircraft or facility, allowing for timely alerts to prevent further escalation of a fire situation. Bimetallic thermal switches are favored in many applications because they are reliable, do not require external power to operate, and provide a straightforward temperature-based activation method. Other options represent different methods of detection that do not utilize the specific principles governing a spot detector sensor. The focus on heat detection over other environmental factors is what sets the bimetallic thermal switch apart and defines its role in fire detection systems.