Variable Voltage Board - Lincoln LT-7 Troubleshooting Manual

A-3
TRAVEL
SPEED
CONTROL
115VAC
CIRCUIT
FROM
BREAKER
WELDING
115VAC
POWER
SOURCE
115VAC
115VAC

VARIABLE VOLTAGE BOARD

Arc voltage is monitored by the voltmeter and variable
voltage board. When the LT7 tractor is being operated
in the constant current mode
board is essential in the control of the wire feed speed.
As the arc length changes the arc voltage will also
change. The variable voltage board recognizes this
change and signals the logic board to either increase or
decrease the wire feed speed. This function is neces-
sary to maintain a constant electrode arc length and a
stable and high quality weld.
The variable voltage board also generates a low volt-
age which is applied to the electrode during the inch
NOTE: Unshaded areas of the Block Logic Diagram are the subject of discussion
THEORY OF OPERATION
TRAVEL
DIRECTION
SWITCH
TRAVEL BOARD
115VAC
INCH UP
SWITCH
1CR
POWER SOURCE
CONTACT RELAY
#2
#4
R1
CONTROL
BOARD
115VAC
VARIABLE VOLTAGE
BOARD
115VAC
{
ELECTRODE
VOLTAGE
SENSING
LEADS WORK
FIGURE E.3 - VARIABLE VOLTAGE BOARD
the variable voltage
LT-7 TRACTOR
TRAVEL
CONTROL
SWITCH
WIRE
DRIVE
MOTOR
LOGIC CONTROL SIGNALS
24VDC
ARC VOLTAGE SENSING SIGNALS
START
SWITCH
STOP
SWITCH
INCH
DOWN
SWITCH
ARC
VOLTAGE
METER
down mode. When the electrode makes contact with
the work piece this low voltage is "loaded down" thus
signaling the control circuitry to stop the wire feed
motor. This feature allows the operator to utilize "work
touch sensing".
TRAVEL
MOTOR
2CR
TRAVEL
RELAY
115VAC
GLP WELD CURRENT
REED SENSING REED
SWITCH 3CR
SWITCH 4CR
LOGIC
BOARD
WIRE
SPEED
CONTROL
115VAC
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