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 TM 55-1905-220-14-9
4-48. ALARM SWITCHBOARD - MAINTENANCE INSTRUCTIONS.
a. General.
(1) The Alarm Switchboard is an electrical system installed aboard ship for the detection and warning of
a variety of important functions or conditions that require continuous monitoring. For example: low engine oil
pressure, high engine temperature, high magazine temperature, magazine sprinkler operation, high sewage
level, gyro compass failure and other functions. Various contact making sensors are used. The magazine high
temperature alarm uses mercury-operated thermostats. It will detect an overheated condition in the magazine
long before serious fire actually occurs.
(2) The magazine sprinkling alarm system is installed aboard ship for detection and warning when water
is present in the sprinkling system, whether the presence of water is due to opening of the magazine group
control valve, or by leakage past the valve. The system depends upon the flooding of a water switch which is
connected to the piping on the dry side of the magazine group control valve.
(3) Warning is also given when trouble or failure occurs in the alarm circuit and indicates which section
of the equipment is involved.
(a) The alarm switchboard.
1 The system is designed to operate on 120 volts D.C. and is obtained by rectifying (within the
panel) an interior communication supply of 120 volts A.C.
2 The top section of the alarm switchboard is the alarm panel. On this panel are mounted the
audible alarm and trouble signal as well as miscellaneous test equipment common to all
circuits.
3 The lower section or sections of the alarm switchboard are line panels. Each line supervises
two lines mounted together on a plate. As many line panels are installed as are necessary to
care for the total number of contact maker circuits installed aboard ship.
(b) Contact makers. Supervised, normally open, contact makers installed in various shipboard
systems operate individual alarm circuits to give trouble indications associated with these systems, such as
high temperature, high and low pressure, high and low level etc. A 7000 ohm, 5 watt resistor is connected
across the terminals of the last contact maker associated with that line to complete the individual alarm
supervisory circuit.
4-1226
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