Meas THCAD-10 noisy signal

04 Sep 2017 21:29 #98513 by rodw
rodw replied the topic: 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.
04 Oct 2017 05:22 #99895 by rodw
rodw replied the topic: Meas THCAD-10 noisy signal
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.
15 Oct 2017 07:38 #100366 by rodw
rodw replied the topic: Meas THCAD-10 noisy signal
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?
15 Oct 2017 09:29 #100378 by Mike_Eitel
Mike_Eitel replied the topic: Meas THCAD-10 noisy signal
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.
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