What would likely cause a false fire alarm in a thermistor-type continuous-loop system?

What would likely cause a false fire alarm in a thermistor-type continuous-loop system?

• A. A loose connector at the controller.
• B. A kinked or pinched continuous-loop element.
• C. Ambient light shining on the loop.
• D. A faulty warning bell.

Answer: (B)

In a thermistor-type continuous-loop system, the detectors along the loop change resistance with temperature, and the controller watches that loop resistance as an indicator of heat along the path. If the loop is kinked or pinched, the physical deformation can alter the local electrical characteristics or even cause slight heat buildup at the bend. That abnormal reading can be interpreted by the controller as a hot spot, triggering a false fire alarm even though the surrounding environment isn’t actually hot. A loose connector would tend to cause intermittent signaling or loss of alarm capability rather than a spurious heat reading. Ambient light has no effect on thermistors, unlike certain other sensor types. A faulty warning bell is an output device issue and doesn’t produce a false alarm by changing the sensing loop readings.

In a thermistor-type continuous-loop system, the detectors along the loop change resistance with temperature, and the controller watches that loop resistance as an indicator of heat along the path. If the loop is kinked or pinched, the physical deformation can alter the local electrical characteristics or even cause slight heat buildup at the bend. That abnormal reading can be interpreted by the controller as a hot spot, triggering a false fire alarm even though the surrounding environment isn’t actually hot.

A loose connector would tend to cause intermittent signaling or loss of alarm capability rather than a spurious heat reading. Ambient light has no effect on thermistors, unlike certain other sensor types. A faulty warning bell is an output device issue and doesn’t produce a false alarm by changing the sensing loop readings.