Lincoln Electric LN-25 Service Manual page 37

E-4
ELECTRODE
INPUT CABLE
P
O S
L W
A
I
R
T
TO WORK
I
C
SENSING LEAD T H
Y
OPTIONAL CIRCUITS
CONTACTOR
The contactor , contactor PC board, and cold
inch switch are commonly incorporated in the
LN-25. This feature enables the user to have an
electrically ÒCOLDÓ gun even though the power
sources output terminals are electrically ÒHOTÓ.
Upon receiving a command from the control
board, the contactor PC board sends a current
signal to activate the contactor
closes the welding current path from the cable
to the conductor block, making the gun
electrically ÒHOTÓ. The cold inch switch allows
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.
THEORY OF OPERATION
FIGURE E.3 Ð OPTIONAL CIRCUITS.
COLD
OPTIONAL
INCH
CONTACTOR
SWITCH
BOARD
VOLT
METER
CONTROL
BOARD
WIRE FEED
MODE SWITCH
SOLENOID
PC BOARD
. The signal
OPTIONAL
CONTACTOR
CONDUCTOR
ARMATURE VOLTAGE
RPM FEEDBACK
RANGE
SWITCH
WIRE SPEED
CONTROL
GAS
SOLENOID
the user to feed wire without closing the
contactor . In this manner , the electrode wire can
be fed through the gun with the gun tip
electrically ÒCOLDÓ. See Figure E.3.
GAS SOLENOID
The gas solenoid feature permits the LN-25 to
be used for gas metal arc welding (GMA
processes. When the gun trigger circuit is
activated, the control board signals the solenoid
PC board to activate the gas solenoid, which
allows shielding gas to flow through the gun to
the arc.
LN-25
GUN CABLE
BLOCK
GUN
M
O TRIGGER
HALL
T
CONNECTOR
O EFFECT
R
MODULE
E-4
W)