Heat Detector for fire alarm systems

Heat detectors are used in conventional heat detectors to detect heat. While one of these thermistors is sealed inside the detector housing, the other is exposed to the surrounding temperature. Both thermistors read similarly when things are normal. As a fire grows, the exposed thermistor’s temperature will rise quickly, creating an imbalance that will set off the alarm on the detector.

If the rate of temperature increase was too slow to set off the detector earlier, rate of rise heat detectors also have an upper temperature limit at which the detector will sound an alarm. One thermistor makes up the Frye Class CS (Static response or fixed temperature) heat detector, which goes into alarm mode at a predetermined temperature.