Lincoln Electric SVM138-A service manual ARC VOLTAGE, Wire Speed Control and Metering

E-4 E-4

THEORY OF OPERATION

TOC	TOC		FIGURE E.4 – ARC VOLTAGE, WIRE SPEED CONTROL AND METERING
Section	Master										VOLTAGE CONTROL
									WORK VOLTAGE SENSING
to	to						GEAR		ELECTRODE VOLTAGE SENSING		POLARITY
							BOX				SWITCH
Return	Return										WIRE
							WIRE				SPEED
											CONTROL
							FEED
							MOTOR		HALL EFFECT
									DEVICE
			POWER SOURCE OUTPUT TRIGGER			(#2 )
									WIRE SPEED CONTROL
									+ 15VDC
					TRIGGER		T2
				TRIGGER	BOARD				GAS
			CIRCUIT
				CONNECTOR					SOLENOID	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
TOC							O
	TOC							O		L
							W	A
									S
							E	R
									H
							R	D	U
Section	Master								T
		TO							D
									O
		CONTROL							W
		BOARD							N
			T1						R	V
									E	O
to	to	TO							F	L
									E
										T
		VOLTAGE							R
									E	A
Return	Return
		BOARD							N	G
									C	E
		METER							E
			10VAC	28VAC
		BOARD
											VOLTAGE
											CONTROL
		VOLTS
		SPEED
		SWITCH								VOLTAGE
										BOARD

TRIGGER SIGNAL

TOC	TOC
		PROTECTOR
		GROUND
		LEAD

Section	Master	ARC VOLTAGE, WIRE SPEED
to	to	CONTROL AND METERING
Return	Return		to the control board.	This feedback voltage is com-
		motor gear box, is connected through a polarity switch
		The arc voltage, which is sensed at the work piece and	The hall effect device sends motor speed information
		to the voltage board. This actual arc voltage is com-	pared to the reference command preset by the wire
			speed control. The control board determines what cor-
		pared to the reference preset voltage that is set by the
			rection is needed and sends the appropriate signal to
		voltage control. The voltage board determines what
			the power board. The power board then adjusts the
		correction signal needs to be sent to the Lincoln weld-
			motor armature voltage to comply with the command
		ing power supply. This voltage control signal is cou-
			from the control board.
		pled to the power supply through the input connector.
		The Lincoln power supply then adjusts the welding arc	A three-digit meter is provided to read both arc voltage
TOCSectionto	TOCMasterto	voltage to meet the demands of the preset reference	and wire feed speed.	Either the preset or the actual
		voltage.	welding parameters can be displayed.
Return	Return	NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
		LN-9 GMA Wire Feeder