Murphy MURPHYMATIC A900 Series Installation And Operating Manual Download Page 8

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energize the battery charging alternator field.
3-2.2.2 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.
3-2.2.3 Local Audible Alarm Relay; provides a contact closure
to operate a local audible alarm as required by NFPA-110, Level
1 and Level 2.
3-2.2.4 Remote Audible Alarm Relay; provides a contact
closure to operate a remote audible alarm as required by NFPA-
110, Level 1.
3-2.2.5 Remote Visual Alarm Relay; provides a contact closure
to operate a remote visual alarm as required by NFPA- 110,
Level 1.
3-2.3 Status Signals. The relay module also includes three
outputs that can be used with external circuits for signaling or
control functions.
3-2.3.1 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.
3-2.3.2 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.
3-2.3.3 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.

3-3 A901-2.
3-3.1 Control / Display Module. The Control / Display Module,
figure 3-3.1, 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.
3-3.1.1 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.

A start signal is applied to the automatic control and the
engine start sequence begins.

3-3.1.2 Lamp Test Pushbutton: Tests the lights on the A- 901-2
module.
3-3.1.3 Alarm Silence Pushbutton: Turns off any audible alarm
that is connected to the Local or Remote Audible Alarm Relays.
The indicating light will remain on as long as the condition
exists. If the Alarm Silence pushbutton is not operated, the
audible alarm will turn off when the alarm contact clears.
3-3.1.4 The A901-2 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
rises 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.

NFPA-110, is provided as a back up for the Crank Discon-
nect 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.
This same delay also locks out the Low Oil Pressure Pre-
alarm and High Water Temperature Pre-alarm circuits
when the engine is not running.

Low Water

Temperature

AUTO

OFF

TEST

Loss of Speed

Signal

Lamp Test

Water

Temperature

Air Damper

Closed