Lincoln Electric SVM114-C service manual Feedback and Control Circuits, Trigger Circuit

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E-3	THEORY OF OPERATION	E-3
	FIGURE E.3 – CONTROL CIRCUITS.

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ELECTRODE INPUT CABLE

TO WORK

SENSING LEAD

			OPTIONAL
			CONTACTOR
			CONDUCTOR	GUN CABLE
			BLOCK
COLD			M		GUN
		OPTIONAL	O	HALL	TRIGGER
INCH			T		CONNECTOR
SWITCH		CONTACTOR	O	EFFECT
		BOARD	R	MODULE
P
O S
L W			ARMATURE VOLTAGE
A I	VOLT
R T
I C	METER	CONTROL	RPM FEEDBACK
T H
Y		BOARD
WIRE FEED			RANGE
			SWITCH
MODE SWITCH
			WIRE SPEED
			CONTROL
		SOLENOID	GAS
		PC BOARD	SOLENOID
		EARLY MODELS ONLY - LATER MODELS HAVE CIRCUITRY
			INCLUDED ON CONTROL BOARD

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FEEDBACK AND CONTROL CIRCUITS

The combination of the range switch and wire speed control provides a command voltage for the control board. The hall effect module transforms the motor RPM to a digital voltage frequency that is “fed back” to the control board. When operating in the constant voltage (CV) mode, the control board monitors the “feedback signal”, compares it to the command voltage and delivers the appropriate armature voltage to the wire feed motor. In this manner, a constant wire feed speed is maintained. See Figure E.3. When the LN-25™ is connected to a constant current (CC) power source, a variable wire feed speed

is desirable to compensate for the varying arc voltages associated with the constant current process. To accomplish this, the control board monitors the command voltage, the feedback signal from the hall effect module and the arc voltage. These three factors are monitored and compared, and then the appropriate armature voltage is applied to the wire feed motor.

TRIGGER CIRCUIT

When the gun trigger is closed, the control board is “signaled” to apply armature voltage to the drive motor and to activate any auxiliary circuits that may be incorporated within the LN-25™. See Figure E.3.

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NOTE: Unshaded areas of block logic diagrams are the subject of discussion.

LN-25™