Lincoln Electric LN-15 WIRE FEEDER SVM166-A Service Manual page 36

E-4
FIGURE E.4 – WIRE FEED SPEED CONTROL & FEEDBACK
ELECTRODE
INPUT VOLTAGE
TOROID
ASSEMBLY
FULL
WAVE
BRIDGE
ON/OFF
SWITCH
WORK
SENSING
LEAD
"WORK" VOLTAGE FEEDBACK #21
WIRE FEED SPEED CONTROL AND
FEEDBACK
The combination of the Procedure Switch and the Wire
Feed Speed control provide a command voltage for
the Feed Head Control Board. The Hall Effect module
(Tach) monitors the motor RPM and outputs a digital
voltage frequency "feed back" that is delivered to the
Feed Head Board.
When operating in the constant voltage (CV) mode the
Feed Head Board monitors the feedback signal and
compares it to the command voltage and delivers the
appropriate armature voltage to the wire feed motor.
In this manner a constant wire feed speed is main-
tained.
When the LN-15 is connected to a constant current
(CC) power source a variable wire feed speed is desir-
able to compensate for the varying arc voltages asso-
ciated with the constant current process. To accom-
plish this the Feed Head Board monitors the command
voltage, the feed back signal from the Hall Effect mod-
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
.THEORY OF OPERATION
CONTACTOR
FEED HEAD
BOARD SUPPLY
BOOST
POWER
SUPPLY
MOV
BOARD
DRIVE MOTOR
SUPPLY
LN-15
GAS
SOLENOID
"ELECTRODE"
FEEDBACK
VOLTAGE #67
ARMATURE
FEED HEAD
CONTROL BOARD
TRIGGER
TRIGGER
COLD
WIRE
INPUT &
INTERLOCK
INCH
FEED
PROCEDURE
SWITCH
SWITCH
SPEED
CONTROL
ule and the arc voltage. These three factors are com-
pared and the appropriate armature voltage is applied
to the wire feed motor to compensate for the varying
arc lengths and associated arc voltages.
E-4
WELDING
FEED
PLATE
M
O
HALL
T
EFFECT
O
R
MODULE
RPM FEEDBACK
SPI COMMUNICATIONS
SHIELDED CABLE
DISPLAY
BOARD