Theory of operation, Output rectification and feedback control, Output rectification and feedback – Lincoln Electric WIRE-MATIC 255 SVM 119-A Manuel d'utilisation
Page 45: E-2 wire-matic 255
E-2
THEORY OF OPERATION
E-2
WIRE-MATIC 255
OUTPUT RECTIFICATION AND
FEEDBACK CONTROL
The AC output from the main transformer secondary
weld winding is rectified and controlled through the
SCR rectifier assembly. Output voltage and current
are sensed at the shunt and output terminals and are
fed back to the control board. The control board com-
pares the commands of the ARC Voltage Control
potentiometer with the feedback signals. The appro-
priate gate firing pulses are generated by the control
board and applied to the SCR rectifier assembly. The
control board controls the firing of the SCRs, thus con-
trolling the output of the machine. See
Operation. The control board also powers and com-
mands the gas solenoid and the wire drive motor.
Figure E.3 - Output Rectification and Feedback.
OUTPUT RECTIFICATION AND FEEDBACK
LINE
SWITCH
MAIN
TRANSFORMER
RECONNECT
FAN
MOTORS
SCR
RECTIFIER
C
A
P
A
C
I
T
O
R
S
SHUNT
CHOKE
WIRE
DRIVE
MOTOR
TACH
POSITIVE
TERMINAL
NEGATIVE
TERMINAL
GAS
SOLENOID
WIRE
SPEED
ARC
VOLTAGE
CONTROL BOARD
FEEDBACK
GUN TRIGGER AND THUMB SWITCH
F
E
E
D
B
A
C
K
G
A
T
E
I
G
N
S
A
L
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion