Lincoln Electric IM467 SQUARE WAVE TIG 355 - Manual (Page 27)

HAND AND FOOT AMPTROL OPERATION
Both the Hand and Foot Amptrol (optional kits K870 or
K963) 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”
position, as it would be with no foot pressure, or a
Hand Amptrol in the relaxed position, with no thumb
pressure. “Maximum” refers to a fully depressed Foot
Amptrol, or a fully extended Hand Amptrol.
The Amptrol is capable of controlling the output cur-
rent 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.
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 rec-
ommended 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
minimum position will not start the arc.
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
current is too high.
If the Current Control switch is set to the Local posi-
tion, 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.
OPERATION
B-12 B-12
SQUARE WAVE TIG 355
CAUTION