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E-2
THEORY OF OPERATION
E-2
GENERAL DESCRIPTION
The LN-8 is a semiautomatic wire feeder
designed for Innershield (FCAW) and
gas metal arc processes with the appro-
priate accessories. It is also suitable for
constant voltage (CV) submerged arc
welding processes. With the optional
variable voltage board installed the LN-8
can be used with constant current (CC)
procedures. The wire feed speed and
welding power source output can be
controlled from the LN-8.
POWER INPUT CIRCUITS
The 115VAC is applied (usually from the
welding power source) via the input
receptacle, through the circuit breaker
and 2 ohm resistor to the control board,
the relay board, and the trigger trans-
former.
The 24VAC developed at the trigger
transformer is rectified on the relay
board and applied to the gun trigger cir-
cuit which controls the 1CR relay.
The 115VAC that is applied to the con-
trol board is rectified and controlled by
SCRs (See SCR Operation) and
applied to the armature of the wire feed
motor.
The relay board rectifies the 115VAC
and applies it to the field winding of the
wire feed motor.
FIGURE E.1 – POWER INPUT CIRCUITS
LN-8
REMOTE
OUTPUT
CONTROL
ELECTRODE
METER
SHUNT
WIRE
FEED
MOTOR
CIRCUIT
BREAKER
INPUT
RECEPTACLE
VARIABLE VOLTAGE
BOARD
CONTROL
BOARD
WIRE FEED
SPEED CONTROL
THERMAL
CIRCUIT
BREAKER
RELAY
BOARD
GLP
REED
SWITCH
TRIGGER
TRANS.
WIRE
FEED
SWITCH
INTERLOCK
SWITCH
FUSE
GUN
CABLE
RECEPTACLE
FIELD
ARMATURE
#3
2
A
OPTIONAL
BURNBACK
BOARD
CONTROL
#2
&
#4
C
O
N
T
A
C
T
O
R
#531
#31
2 OHMS
#32 #32A
#75
#76
#77
#21
#567
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.
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