Hand And Foot Amptrol Operation - Lincoln Electric SQUARE WAVE TIG 355 Service Manual

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HAND AND FOOT AMPTROL OPERATION

Both the Hand and Foot Amptrol (optional kits K870 or
K812) work in a similar manner. They are meant to be
used for remote current control when Remote Current
control is selected. The TIG 2-Step mode must be
selected when using an Amptrol for remote current
control. As explained below, Amptrols can also be
used as arc start switches if Local Current control is
selected.
For simplicity, the following explanation will refer only to
"Amptrols," meaning both Foot and Hand models. The
term "minimum" refers to a Foot pedal in the "up" posi-
tion, as it would be with no foot pressure, or a Hand
Amptrol in the relaxed position, with no thumb pres-
sure. "Maximum" refers to a fully depressed Foot
Amptrol, or a fully extended Hand Amptrol.
The Amptrol is capable of controlling the output current
from 2 amps to whatever current is preset on the
ammeter. For example, if the ammeter is preset for
200 amps and the Current Control switch is in the
Remote position, the Amptrol, when depressed just
past its minimum position, will cause the Square Wave
TIG 355 to weld at 2 amps. At the Amptrol's maximum
position, the output would be near 200 amps. See
Figure B.4.
CAUTION
Since the full output of the current setting is available
when the Amptrol is fully depressed, care must be
taken not to set a current which will exceed the current
carrying capacity of the tungsten. When in doubt, use
a lower current setting first, then increase.
It is important to note that, for many applications, the
tungsten will not start an arc at only 2 amps. To start
an arc reliably, it is important to depress the Amptrol far
enough so that the machine output current is near the
tungsten operating range. (See Table B.2 for recom-
mended tungsten currents.) In the example above, a
3/32" (2.4 mm) tungsten may be used on DC- to weld
near 200 amps. To start the weld, the operator may
have to depress the Amptrol approximately 1/4 of the
way down, or to nearly 70 amps, in order to start the
arc. Merely depressing the Amptrol to its 2 amp mini-
mum position will not start the arc.
OPERATION
A similar situation occurs when the Start controls are
used. For example, a 3/32" (2.4 mm) tungsten is again
used for welding DC- up to 200 amps (preset on the
ammeter). A Start current of 50 amps is set on the
Start Level control. When you depress the Amptrol,
the start circuitry sets the output current to 50 amps. If
the Amptrol is kept near the minimum position, at the
end of the start period the output current will drop to 2
amps, causing the arc to go out in most cases.
Depress the Amptrol at least 1/4 of the way down, or to
around 70 amps, so that the tungsten remains lit when
the start period ends.
The same holds true for a "hot" start, or one in which
the Start current is set to a current higher than the cur-
rent preset on the ammeter. Again, at the end of the
start period, the Amptrol must be depressed far enough
so that the machine output will be high enough to keep
the arc lit.
The best technique when using the start controls and
an Amptrol is to press the Amptrol to maximum at the
beginning of the weld, wait until the end of the start
period, and then back off on the amptrol only if the cur-
rent is too high.
If the Current Control switch is set to the Local position,
an Amptrol can be used as an arc start switch.
Depressing the amptrol just past minimum will cause
the Amptrol's built-in arc start switch to close, and
backing off completely causes the built-in start switch
to open. The Amptrol will have no effect on the weld-
ing current when used as an arc start switch. See
Figure B.5.
SQUARE WAVE TIG 355
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