Meas THCAD-10 noisy signal

Bevins, thanks, Funny I also thought of running an external earth from the plasma cutter case back to the main building electrical ground.stake.

Anyway thanks everybody for the brainstorming. I have a couple of ideas to try now.

Well I finally followed this up with Everlast again and got a response. They have suggested I add a 100 nF 630 V capacitor to where the raw voltage comes onto the voltage divider board. RS Components have stock so I ordered 5 of them for $3.50 with free shipping! With some luck, I'll have them tomorrow.

Well, the capacitor made no difference so I bought a Hantek 6022BL USB oscilloscope. I measured the divided voltage with the plasma cutter on but not cutting at the entrance to the control box. I could see a 50 Hz ripple.



And then I turned the power on to the control box and it overlaid massive noise over this ripple.


I disconnected both the enclosure ground and the cable shield from the THCAD and it made no difference.

Any Ideas on where to go from here?

You should place an inductivity before your capacitor an make a low pas filter. Measure the frequency of the noice an than you can decide for the coil you need, or what I would do without calculating is taking a ring coil that is used in 50 herz ac devices. You can f.x. find them in electronic board of cheap fluorescent lamps.. Good luck.