20kW Plasma Power!

Today, the long-awaited generator arrived (actually last night); 3-phase 480 volts, 25 kVA:Brian+Generator

So Brian (pictured) & I wired it up to the diminutive 5.22 inch tall rack-mountable MKS Optima OPT-200 plasma power supply:mks-DCG-200Z

Its size belies its power..   The OPT-200 has the great ability to create a plasma arc, and hold one of voltage, current, or power (Watts/Joules) constant, and vary one or both of the other values to “make it happen”.      We ran the voltage as low as 3.5 volts and as high as 2000, and while the specs say it will output up to 42 amps, we never pushed it past 20.    The unit can be programmed to change its output over time.   From the front panel, the time resolution is 0.025 seconds, but over the RS-232 (or RS-422) interface, the time resolution is a millisecond.    Sooo.. to stress it a bit, I programmed the output to stay on for 1ms, then off for 1ms, then loop back to the start (on for 1 ms).    I was expecting a 500Hz, high-voltage, square-wave output.   While the display was very busy:

The output voltage & current (as monitored with a Pearson current probe & Tek scope) showed the voltage varying to maintain the specified output current, but no apparent (on/off) oscillation.   I’ll try lower frequencies later..

The only niggly we had getting it going was jumpering an (obscure) interlock on the back panel (there are three) – between pins 11 and 12 of the 16-pin “Analogue Interface Connector” (user port).  It’s amazing what an inch of 18-gage wire can do:


When programming the OPT-200, each programming step actually takes 2;  the first to specify the ramp volts/amps/watts & how long to ramp for, and the second for the target volts/amps/watts, and duration.    Issuing the SQD command via the serial interface, a “two step” program looks like:

—————    ——–
0:        20.00A      0.000
1:        20.00A      0.001
2:        0.000A      0.000
3:        0.000A      0.001

To generate a 500Hz pulsed-DC output.

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