Arc Voltage, Wire Speed Control And Metering - Lincoln Electric SVM138-A Service Manual

E-4
FIGURE E.4 – ARC VOLTAGE, WIRE SPEED CONTROL AND METERING
CIRCUIT
BREAKER
INPUT
CONNECTOR
TO
CONTROL
BOARD
T1
TO
VOLTAGE
BOARD
METER
10VAC
BOARD
VOLTS
SPEED
SWITCH
ARC VOLTAGE, WIRE SPEED
CONTROL AND METERING
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.
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
THEORY OF OPERATION
GEAR
BOX
WIRE
FEED
MOTOR
POWER SOURCE OUTPUT TRIGGER (#2 &#4)
TRIGGER
T2
BOARD
TRIGGER
CONNECTOR
24VAC
R1
28VAC
LN-9 GMA Wire Feeder
WORK VOLTAGE SENSING
ELECTRODE VOLTAGE SENSING
HALL EFFECT
DEVICE
WIRE SPEED CONTROL
+ 15VDC
GAS
SOLENOID
TRIGGER SIGNAL
F
U
S
E
+ 15VDC
P
B
O
O
W
A
S
R
E
H
U
D
R
T
D
O
W
N
TRIGGER SIGNAL
The hall effect device sends motor speed information
to the control board. This feedback voltage is com-
pared to the reference command preset by the wire
speed control. The control board determines what cor-
rection is needed and sends the appropriate signal to
the power board. The power board then adjusts the
motor armature voltage to comply with the command
from the control 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.
VOLTAGE CONTROL
POLARITY
SWITCH
WIRE
SPEED
CONTROL
C
O
B
O
N
A
T
R
R
D
O
L
R
V
E
O
F
L
E
T
R
E A
N G
C E
E
VOLTAGE
CONTROL
VOLTAGE
BOARD
GROUND
LEAD
PROTECTOR
E-4