Protective Circuits - Lincoln Electric SQUARE WAVE TIG 175 Service Manual

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PROTECTIVE CIRCUITS

Protective circuits are designed into the Square Wave
TIG 175 to sense trouble and shut down the machine
before the trouble damages the internal machine com-
ponents. Both thermal protection and current overload
are included.
THERMAL PROTECTION
Thermostats protect the machine from excessive
operating temperatures. Excessive operating temper-
atures may be caused by a lack of cooling air or by
operating the machine beyond the duty cycle and out-
put rating. If excessive operating temperature should
occur, causing either thermostat to open, the machine
output will be disabled. If the primary thermostat
opens, the machine will stay on (pilot light, meters and
fans running), but output current will be limited to no
more than 5 amps.
Once the machine cools sufficiently the thermostats
are self-resetting. If the thermostat shutdown is
caused by excessive output or duty cycle and the fan
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.
THEORY OF OPERATION
is operating normally, the power may be left on, and
the reset should occur within a 15 minute period. If the
fan is not functioning properly or the air intake louvers
are obstructed, then the input power must be removed
and the fan problem or air obstruction corrected.
OVERLOAD PROTECTION
The machine is electronically protected from produc-
ing excessively high output currents. The output is lim-
ited to 190 amps.
SQUARE WAVE TIG 175
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