Lincoln Electric PRECISION TIG 375 ROHS Operator's Manual page 22

B-7
• In 4-Step position allows welding without continu-
ously holding the start switch trigger. The arc start
switch functions in the following manner:
1. Closing switch starts preflow, then arc starts
at Minimum (Start) setting level (See Item
7). If the trigger is maintained closed after
preflow time the output remains at the Start
level until it is released.
2. Opening switch initiates fixed (0.5 sec.)
ramp time from Start setting level to Weld
setting.
3. Reclosing switch initiates Downslope ramp
time setting (See item 17) from Weld setting
down to the Crater-fill level (See Item 7) of
the machine.
4. Reopening switch after Downslope time
holds Crater-fill level until switch opens,
then stops the arc and initiates the Postflow
Time (See Item 9). Or, reopening switch
during Downslope time immediately stops
the arc and initiates the Postflow.
Note: See Section B-7 for 4-Step operation during
Downslope with Restart feature selected to be
enabled, instead of disabled (as shipped).
13. PULSE / SPOT MODE SWITCH – Turns on the
Pulse Mode as indicated by the Green panel light
turning on.
• PULSE ON provides a Peak current level set by
REMOTE and/or LOCAL control of the output cur-
rent (See Item 5), for a time determined by the
Pulse Frequency Control setting (See Item 14) and
the % ON Time (See Item 15). The balance of the
cycle time is at the Background Current level (See
Item 16). The Green panel light blinks at the pulse
frequency and time setting rate.
• Pulsing begins after upslope when the output cur-
rent rises above the Background Current level and
ends when the output current drops below this level.
• SPOT ON mode provides the peak current level set
by the Maximum Output Control for a time deter-
mined by the SPOT TIME control (see below). The
red panel light is on for Spot mode.
14. PULSE FREQUENCY CONTROL – This knob is
used to set the Pulse Frequency over the peak
pulse range of about 0.1 pps to 20 pps. (One pulse
cycle time = 1/pps = 10 to .05 sec. range.)
OPERATION
15. PULSE % ON / SPOT TIME CONTROL –This
knob sets the time for Pulse or Spot modes:
• % ON TIME sets duration of the peak current as a
percentage (5% to 95% on white scale) of one pulse
cycle. The balance of the cycle time will be at the
Background Current setting.(See Item 16)
• SPOT TIME sets the duration of the Spot pulse (0.5
to 5.0 seconds on red scale).
16. PULSE BACKGROUND CURRENT CONTROL –
This knob controls the level of the Background
Current as a percentage (MIN.-100%) of the Peak
(REMOTE and/or LOCAL) output level (See Item
6) down to the Minimum Output setting (See Item
7).
17. DOWNSLOPE TIME– This knob is used to set the
time, over the range of zero to about 10 seconds,
to ramp down from weld setting to Crater-fill level
(See Item 7).
• If the arc goes out after the Downslope time is initi-
ated, the Downslope time is interrupted and the
Postflow time is initiated. This prevents Hi-Freq re-
initiation during ramp down crater fill
• When using an Amptrol remote control, where the
downslope is controlled by the operator down to the
crater-fill level, the Downslope time should be set to
zero so as not to have the Downslope time delay
when the arc start switch is opened.
18. HIGH FREQUENCY INTENSITY CONTROL (NOT
SHOWN)– Allows setting the lowest intensity which
still gives good TIG arc starting with minimized
Radio Frequency Interference (RFI). Control knob
is located on a recessed panel near the easy
accessible spark gap side panel. As shipped, the
control is set to minimum.
PRECISION TIG ® 375
B-7