I will explain better my aproatch to the issue. The plasma machine is a metal cutting unit, that makes an high frequency arc (starting arc) until the cutting arc is estabilish. This final arc (cutting) can be up to 350VDC. During normal operation of the machine (during cutting) the circuit explained below is working fine, during the initial arc no.
For this reason I have made a simply voltage divider to target the range of my measure equipment, I have made more or less 100:1 voltage divider using 150K and 1.5K with a ceramic 10uF capacitor; more or less was this.
The amazing thing, was that during the initial arc, the output voltage (after the voltage divider) could be up to 200VDC (my inexpensive multimeter registed it), and this could be 3 things:
1) multimeter damaged - unlikelly;
2) That the input voltage was 100 times greather; so about 200*100 ?! unlikelly
3) Noise - probably
And probally noise is/was the reason. I made the voltage divider inside the machine, and maybe the wires after the voltage divider were piking up the frequency noise of the plasma unit. Maybe the voltage divider should be far away from the machine.
I have damaged one expensive piece and I did not tryed again, but I want to.
Any opinions are apreciated, before I make anything.
Thanks