Murphy Series A900 - Manual (Page 11)

8
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 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.
3-4.1.4 Seven (7) First-out Shutdown Circuits; provide first-out
indication of cause of shutdown. These circuits deactivate the
fuel relay and lockout the A902 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.
3-4.1.5 Two (2) Alarm Indicating Circuits; provide indication
of cause of alarm. These circuits activate the alarm relay. Alarm
circuits are active as long as power is applied to the A902. All
are active when the engine is running, shutdown or on standby.
Two (2) Amber Alarm Indicating Lights are provided.
(a) Low Water Temperature; operated by low water
temperature SWICHGAGE ® .
(b) Spare Alarm; operated by an external switch. This circuit
is provided for an additional alarm that may be required
by the user.
3-4.2 Relay Module. The Relay Module, figure 3-4.2, includes
all of the control, alarm and shutdown relays that are required to
make up the generator engine control. Relays are available for
operation on either 12 or 24 volt battery systems. Three (3)
relays are included for:
3-4.2.1 Fuel Relay; this relay provides two outputs, one to
energize the engine fuel solenoid and a separate circuit to
energize the battery charging alternator field.
3-4.2.2 Shutdown Relay; this relay is operated by the shutdown
circuits of the Control / Display Module and provides an output
that can be used to trip the generator circuit breaker on an
emergency shutdown.
3-4.2.3 Local Audible Alarm Relay; provides a contact closure
to operate a local audible alarm as required by NFPA- 110, Level
1 and Level 2.
3-4.3 Status Signals. The relay module also includes three
outputs that can be used with external circuits for signaling or
control functions.
3-4.3.1 The Control On function at terminal 12 is on (closed to
negative) as long as the Mode Selector Switch is in either Auto
or Test. When the Mode Selector is turned Off, the Control On
signal is open. This can be used to signal switch position or to
reset an external circuit when the Mode Selector is turned Off.
3-4.3.2 The System Ready signal at terminal 13 is on (closed
to negative) as long as the Mode Selector Switch is in either
Auto or Test and no shutdown TATTLETALE
® circuit is
latched on. This can be used to signal that the generator engine
is ready to automatically start or is running in Test.
3-4.3.3 The Control On function at terminal 14 is on (closed to
positive) as long as the Mode Selector Switch is in either Auto
or Test. When the Mode Selector is turned Off, the Control On
signal is open. This can be used to signal switch position or to
reset an external circuit when the Mode Selector is turned Off.
3-5 A902-2.
3-5.1 Control / Display Module. The Control / Display Module,
figure 3-5.1, includes the control and test switches, the solid state
logic elements, shutdown and alarm TATTLETALE
® lights that
make up the generator engine control for a two-cycle engine.
3-5.1.1 Mode Selector Switch, OFF-AUTO-TEST:
(a) OFF; turns off the control system and resets any shutdown
circuits.
(b) AUTO; turns on the engine controls and shutdown circuits.
System is on standby waiting for a contact closure to start
engine.
DC12V
3A Fuse
1A
4
5
6
7
8
9
16
17
18
19
20
21
22
23
24
25
DC12V
DC12V
6-1/4 in.
(159 mm)
4-1/2 in.
(114 mm)
Figure 3-4.2
DISCONTINUED