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TABLE OF CONTENTS
-THEORY OF OPERATION SECTION-
Theory of Operation .............................................................................................................Section E
General Description ....................................................................................................................E-2
Input Power Circuit:
Input Voltage, Contactor, Reconnect Panel, Pilot Transformer, Control Transformer,
Power Factor Capacitors, and Main Transformer.......................................................................E-2
Output Rectification and Feedback Control...............................................................................E-3
High Voltage/High Frequency Circuit..........................................................................................E-4
DC Welding Output.....................................................................................................................E-5
AC Welding Output .....................................................................................................................E-6
SCR Operation............................................................................................................................E-7
Protective Circuits.......................................................................................................................E-8
Thermal Protection ...............................................................................................................E-8
Overload Protection..............................................................................................................E-8
Section E-1 Section E-1
SQUARE WAVE TIG 355
FIGURE E.1 – SQUARE WAVE TIG BLOCK LOGIC DIAGRAM
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
REMOTE
RECEPTACLE
GAS/WATER
SOLENOIDS
FANS
115VAC
RECEPTACLE
INPUT
CONTACTOR
R
E
C
O
N
N
E
C
T
POWER
FACTOR
CAPACITORS
FEED - THRU
BOARD
CONTROL
BOARD
POWER
BOARD
SNUBBER
BOARD
MAIN
TRANSFORMER
AC
AC
DC-
DC+
POLARITY
SWITCH
SHUNT
C
H
O
K
E
BY-PASS
BOARDS
WORK
ELECTRODE
HI-FREQ
TRANSFORMER
PILOT
TRANSFORMER
START/
STOP
PANEL
SWITCHES
UPPER
CONTROL
PANEL
LOWER
CONTROL
PANEL
DISPLAY
BOARD
STATUS
BOARD
ELECTRODE SENSE
HIGH FREQUENCY SPARK
115VAC
INTERLOCK
HI-FREQ AND GAS/WATER
115VAC -
115VAC
CONTROL TRANSFORMER
INTERLOCK
ELECTRODE
SENSE
REMOTE
COMMANDS
GATE COMMANDS
HI-FREQ/
WATER/GAS
COMMANDS
INTERLOCK
115VAC
SCR
TRIGGER
15VDC
115VAC