Murphy A900 Series manual 3-6A903

of cause of alarm. These circuits activate the alarm relay. Alarm circuits are active as long as power is applied to the A902-2. 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)Air Damper Closed; operated by an external switch or by the Overspeed Relay circuit. This circuit is provided with a selector switch to allow the user to determine the source of the signal.

3-5.2Relay Module. The Relay Module, figure 3-5.2, 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. Four (4) relays are included for:

reset an external circuit when the Mode Selector is turned Off. 3-5.3.2The 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.

3-5.3.3The 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.

3-6 A903.

3-6.1Control / Display Module. The Control / Display Module, figure 3-6.1, 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 four cycle engine. This module is the same as Model A- 901 except 7 of the alarm circuits are un-labeled. This allows the customer to specify labels other than those recommended in NFPA-110. This model has shutdown and alarm circuits labeled to meet the

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3A Fuse

DC12V DC12V

DC12V

DC12V

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6-1/4 in.

(159 mm)

requirements of NFPA-110, Level 2.

4-1/2 in.

(114 mm)

Figure 3-5.2

3-5.2.1Fuel Relay; this relay provides two outputs, one to energize the engine fuel solenoid and a separate circuit to energize the battery charging alternator field.

3-5.2.2Shutdown 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.

3-5.2.3Overspeed Relay; operates only on an Overspeed shutdown. This relay provides an output to trip an air shut off solenoid to close the air damper on a two-cycle engine.

3-5.2.4Local Audible Alarm Relay; provides a contact closure to operate a local audible alarm as required by NFPA- 110, Level 1 and Level 2.

3-5.3Status Signals. The relay module also includes three outputs that can be used with external circuits for signaling or control functions.

3-5.3.1The 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

Figure 3-6.1

3-6.1.1Mode 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.

(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.

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