280B-PL Series heat detectors offer fixed temperature or combination rate-of-rise and fixed temperature detection. A temperature increase at the sensor of 15degF (9degC) or more per minute activates the rate-of-rise feature, closing the contacts in the sensor to transmit the alarm condition to the fire alarm control panel. When the rate-of-rise element alone has been activated, the sensor is self-restoring. If the temperature of the center disk rises to the sensor’s rated temperature, the fixed temperature element activates, closing contacts in the sensor and transmits an alarm condition to the fire alarm control panel. The fixed temperature element is non-restorable and, when activated, the detector must be replaced. The need for replacement is indicated when the center disk has fallen free from the detector. Edwards 280B series heat sensors come standard with a white plastic reversible mounting plate. The plate is designed for surface or flush mounting and installs directly to a standard North American 3-1/2 or 4 in octagon box. Once the mounting plate is fixed, a simple twist will lock the sensor in place. It can be removed using a screwdriver to release the tamper-resistant locking finger.