SP-100
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E-3
THEORY OF OPERATION
NOTE: Unshaded areas of block logic diagram are the subject of discussion.
TRIGGER, GAS SOLENOID AND
WIRE DRIVE
Closure of the trigger circuit (pulling the gun
trigger) signals the control board to start
several functions. 115 vac is applied to the
gas solenoid to allow shielding gas to flow.
The SCRs are activated and voltage is
applied to the main transformer. Output volt-
age is developed at the output terminals and
fed back to the control board. This welding
output voltage is also used to power the wire
drive motor.
FIGURE E.3 – Trigger, Gas Solenoid and Wire Drive
The welding output voltage that powers the
wire drive motor is varied and controlled on
the control board. The control board moni-
tors the drive motor armature current and
voltage and compares the feedback infor-
mation with the commands sent from the
wire speed control. The control board varies
and controls power to the drive motor,
which, in turn, controls the speed of the wire
drive. The SP-100 also has an automatic
protection circuit which protects the wire
drive motor from excessive motor over-
loads.
