MK Products MK 2000A - Manual (Page 18)

MK 2000A - Owner's Manual - Page 18
The effect that Rise Time has on the pulse is shown in (Figure 8). At 100%
the pulse is rectangular, but by turning the rise time toward 0%, the leading
and trailing edges become increasingly tapered. Slow rise times and narrow
pulses will result in the output voltage never reaching the maximum voltage.
In this operating mode, the welding engineer has almost complete control of
the welding conditions throughout the entire heat and metal transfer portions
of the weld
Control Characteristics
All controls are calibrated to provide -0- to 100% of the controlled parameter
maximum value. Thus the Background Slope control provides a slope of -0-
volts per ampere when set to CV (0%) and -0- amperes per volt when set
to CC (100%).
With 0% slope (CV) the Background Level control provides 0-50 V output.
For example 18 volts is 36% of 50 volts, or 36.0 on the dial.
With 100% slope (CC) the Background Level control provides 0-300 amperes
output. For example 180 amperes is 60% of 300 amperes or 60.0 on the
dial.
A control line may be drawn on a graph of voltage vs. current which connects
the origin (-0- volts, -0- amperes) with the maximum (50 V., 300 A.). The
operating volt-ampere line will always cross this control line at the value
corresponding to the dial setting. For example, an output dial setting of 60%
will provide a volt-ampere line passing through 30 volts (.60 X 50V) and
180 amperes (.60 X 300A). As shown in Figure 1 and Figure 2, changing
the background slope rotates this volt-ampere line around the set point and
controls the no load and short circuit values of voltage and current.
The Pulse Level and Pulse Slope controls operate in an identical manner
(except that the pulse operation adds to the Background Level control setting
only). Both Background and Pulse controls may be used simultaneously to
create an operating volt-ampere line such as shown in Figure 4.
The Inductance Control shapes the output current to approximately match
that of an inductor of -0- to 3 millihenries. This is most useful in welding steel
or similar metals to control the rate of use of arc current.
The Pulse Controls include Repetition Rate (frequency), Height, Width, and
Rise Time. The Repetition Rate may be varied from 20 to 2000 pulses per
second (pps), thus 60 pps is 3% of 2000 and 120 pps is 6% of 2000 (or 6
on the dial). The pulse Height adds to the Background level control so that,
in the CV mode, the pulse height may be -0- to 50 volts. For example, if the
Background Level is at 30% (15V) and the Pulse Height is set to 40% (20V)
the “background” will be 15 volts and the pulses will be 35 volts (15 + 20).
The discussion of current limit on the output applies equally to the output
plus pulse levels.
With the Background Slope set to CC conditions (nearer 100% slope) the
pulse height still adds to the background level and represents a current
controlled pulse rather than a voltage controlled pulse. As indicated
previously, the Pulse Level and Slope may be used to provide a constant
current condition during the pulse with a constant voltage background.
The Pulse Width control provides pulse widths from nearly 0% to 100% of
the pulse interval. Of course at -0- width there is no pulse and at 100%
there is no background level. Within rather wide limits, the heat in the weld
may be controlled by adjusting the pulse width with minimum effect on other
parameters.
The Pulse Rise Time may be used to limit the rate of voltage or current
rise during the pulse. The leading and trailing edges of the pulse are