Sketch a circuit that may be incorporated in a control panel for an array of fire detectors. Describe Audible fire alarm circuits, Identification of zone of fire, and Automatic change over from normal power supply.

Sketch: The fire alarm control panel circuit consists of:

• A power supply (normal supply from the ship's main supply, with an automatic changeover to the emergency/battery supply).
• The detector circuits (zones): each zone has a loop of fire detectors (smoke/heat) connected in parallel, with an end-of-line resistor/device.
• A relay/control circuit for each zone that operates when a detector actuates.
• The audible alarm circuit: a bell/sounder (and a visual indicator) operated by the alarm relay.
• The zone indication: a lamp/LED for each zone that lights when that zone's detector operates.
• A test/reset facility and a fault indicator.

Description:

• Audible fire alarm circuits: When a detector in a zone operates, it closes the circuit, energising the zone relay, which operates the audible alarm (a bell/sounder) and the visual indicator. The audible alarm is a continuous or distinct signal (distinguished from other alarms). The alarm continues until it is acknowledged/reset. The circuit is monitored so that a fault (e.g. a broken wire) is indicated.
• Identification of zone of fire: Each zone has its own indicator lamp/LED on the panel. When a detector in a zone operates, the corresponding zone lamp lights, identifying the zone of the fire. The panel may also show the zone number and the alarm state. This enables the crew to locate the fire quickly.
• Automatic changeover from normal power supply: The panel is normally powered from the ship's main supply. On failure of the main supply, an automatic changeover circuit transfers the panel to the emergency supply (the emergency generator or the battery). The changeover is automatic and is indicated; the panel continues to operate on the emergency supply so that the fire detection and alarm system remains functional during a power failure. The battery provides a standby supply for a defined period.

The circuit is designed so that the fire detection and alarm system is reliable, identifies the zone of the fire, sounds the alarm, and continues to operate on the emergency supply, in accordance with SOLAS Ch. II-2 and the FSS Code.