280B-PL Series heat detectors offer fixed temperature or combination
rate-of-rise and fixed temperature detection.FIXED TEMPERATURE: If the
temperature of the center disk rises to the sensor's rated temperature, the
fixed temperature element activates. This closes 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 .