Control Units, Signaling, and Supervisory Functions
The fire alarm control unit (FACU) processes initiating signals and drives notification and transmission. Know conventional vs. addressable control units, and the functions a control unit must perform: receive alarm, supervisory, and trouble signals; activate notification; transmit off-premises; and supervise itself.
Supervisory functions include monitoring suppression systems (valve position, waterflow, low air pressure) and other off-normal conditions that are not fires. Trouble signals indicate the system cannot perform its function (open circuit, ground fault, battery failure, loss of primary power).
Know signal priority: alarm overrides supervisory and trouble; supervisory overrides trouble. Know annunciation and remote annunciators. Know drill and silence functions and that silencing an alarm does not reset it.
Traps: assuming silencing resets the system (it does not); assuming a supervisory signal is a trouble; forgetting that loss of primary power is a trouble condition even when batteries carry the load.
Rule of thumb: alarm > supervisory > trouble in priority. Silence ≠ reset. Loss of AC power = trouble, even on battery.
Worked example: A system loses 120 VAC but batteries keep it running. The correct condition is a trouble signal for loss of primary power, while the system continues to operate on standby.