Murphy Series A900 - Manual (Page 12)

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(c) TEST; turns on the engine controls and shutdown circuits.
A start signal is applied to the automatic control and the
engine start sequence begins.
3-5.1.2 Lamp Test Pushbutton: Tests the lights on the A- 902-2
module.
3-5.1.3 The A902-2 SELECTRONIC
® Control Module includes
the following engine control features:
(a) Cycle crank circuit; will crank the engine for 15 seconds
then rest for 15 seconds until the engine starts. The
crank/rest time is selectable for either 10, 15, 20, 25 or 30
seconds. If the engine false starts, goes above crank
disconnect speed then drops below that speed, the control
will rest for a fixed 10 second period before cranking
again.
(b) Crank Disconnect Speed Switch; this circuit detects
engine speed and terminates cranking when engine speed
rise above the speed switch setting. The speed switch is
adjustable, 25 Hz to 2000 Hz, and is factory set at 1180
Hz. This would be 600 RPM on an engine with 118 teeth
on the flywheel ring gear.
(c) Auxiliary Crank Disconnect Circuit; this circuit, required
by NFPA-110, is provided as a back up for the Crank
Disconnect Speed Switch. It is operated by an external
switch sensing either speed, generator voltage or some
other variable that could be used to terminate cranking.
Either circuit will disconnect the starter when the engine
starts.
(d) Overcrank circuit; will stop automatic cranking and
indicate overcrank if engine fails to start after 3 attempts.
The number of cranks are selectable for 1, 2, 3, 4 or 5
cycles before shutdown. The overcrank circuit may also
be turned off so no overcrank shutdown occurs.
(e) Shutdown Time Delay Bypass; this delay prevents the oil
pressure, water temperature and loss of speed signal
shutdown circuits from operating for 15 seconds after the
engine starts as detected by the crank disconnect circuit.
(f) Overspeed Speed Switch;
1. Provides a signal to the overspeed shutdown circuit if
the engine exceeds the preset speed. The factory
setting is approximately 3894 Hz, or 1980 RPM on an
engine with 118 teeth on the flywheel ring gear. The
adjustment range is 300 Hz to 10,000 Hz.
2. A push to test switch is provided to allow testing of the
overspeed circuit without overspeeding the engine.
When switch is depressed, the set point of the speed
switch is lowered approximately 10%.
3. The push to test switch can also be used to set the
overspeed switch at approximately 110% of running
speed. Hold the switch depressed while adjusting the
setting until the overspeed trips. When switch is
released, the set point will be 10% above normal
running speed. This is the method used to make the
factory setting. With engine speed at 1800 RPM or
3540 Hz.
(g) Cooldown circuit; this circuit keeps the engine running
for five minutes after the transfer switch has removed
the load from the generator and signaled the A902-2 to
stop the engine. This feature may be selected (turned
On, standard setting is Off) with a switch on the back of
the Control / Display Module.
3-5.1.4 Seven (7) First-out Shutdown Circuits; provide first-out
indication of cause of shutdown. These circuits deactivate the
fuel relay and lockout the A902-2 until reset. Shutdown circuits
are activated by the crank disconnect circuit and are not active
when the engine is stopped. Six (6) Red Shutdown Indicating
Lights are provided. The Remote Shutdown circuit does not
have an indicator light.
(a) Overcrank; tripped by the overcrank sensing circuit which
counts the number of cranking attempts.
(b) Overspeed; tripped by overspeed switch when engine
exceeds a preset speed.
(c) Oil Pressure; tripped by the oil pressure SWICHGAGE ®
if pressure drops below preset point while the engine is
running.
(d) Water Temperature; tripped by the water temperature
SWICHGAGE ® if engine coolant temperature exceeds the
switch setting.
(e) Spare Shutdown; tripped by an external switch. This
circuit is provided for an additional shutdown that may be
recommended by the engine supplier.
(f) Loss of Speed Signal; tripped by an internal sensing
circuit that detects the loss of the Magnetic Pickup
frequency signal for the speed switches while the engine
is still running. Since the Overspeed shutdown circuit is
activated by the frequency input, it prevents the engine
from running without overspeed protection.
(g) Remote Shutdown; this circuit is provided to shutdown
the engine generator from a remote location. No
indicating light is provided.
3-5.1.5 Two (2) Alarm Indicating Circuits; provide indication
Low Water
Temperature
AUTO
OFF
TEST
Loss of Speed
Signal
Lamp Test
Water
Temperature
Air Damper
Closed
Oil Pressure
Overspeed
Overcrank
6-1/2 in.
(165 mm)
9-3/4 in.
(248 mm)
Figure 3-5.1
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