Lincoln Electric SVM127-A service manual ARC VOLTAGE, Wire Speed Control and Metering

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E-4 E-4

THEORY OF OPERATION

FIGURE E.4 – ARC VOLTAGE, WIRE SPEED CONTROL AND METERING

VOLTAGE CONTROL

							WORK VOLTAGE SENSING
					GEAR		ELECTRODE VOLTAGE SENSING		POLARITY
					BOX				SWITCH
									WIRE
					WIRE				SPEED
									CONTROL
					FEED
					MOTOR	TACH
						BOARD
	POWER SOURCE OUTPUT TRIGGER			(#2 )
							WIRE SPEED CONTROL
			TRIGGER		T2		+ 15VDC
	CIRCUIT	TRIGGER	BOARD
		CONNECTOR						C
	BREAKER			24VAC
								O	B
							TRIGGER SIGNAL
INPUT								N	O
					F
					U			T	A
CONNECTOR					S				R
					E			R
	R1						+ 15VDC		D
					P	B		O
					O
						O		L
					W	A
							S
					E	R
							H
					R	D	U
							T
TO							D
							O
CONTROL							W
BOARD							N
	T1						R	V
							E	O
							F
TO								L
							E
								T
VOLTAGE							R
							E	A
BOARD							N	G
							C	E
METER							E
	10VAC	28VAC
BOARD
					WIRE FEED				VOLTAGE
									CONTROL
					MOTOR
VOLTS					THERMOSTAT
SPEED
SWITCH								VOLTAGE
								BOARD

TRIGGER SIGNAL

GROUND

LEAD

PROTECTOR

ARC VOLTAGE, WIRE SPEED

CONTROL AND METERING

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The arc voltage, which is sensed at the work piece and motor gear box, is connected through a polarity switch to the voltage board. This actual arc voltage is com- pared to the reference preset voltage that is set by the voltage control. The voltage board determines what correction signal needs to be sent to the Lincoln weld- ing power supply. This voltage control signal is cou- pled to the power supply through the input connector. The Lincoln power supply then adjusts the welding arc voltage to meet the demands of the preset reference voltage.

The tach board sends motor speed information to the control board. This feedback voltage is compared to the reference command preset by the wire speed con- trol. The control board determines what correction is needed and sends the appropriate signal to the power board. The power board then adjusts the motor arma- ture voltage to comply with the command from the con- trol board.

A three-digit meter is provided to read both arc voltage and wire feed speed. Either the preset or the actual welding parameters can be displayed.

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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

LN-9 Wire Feeder