Inexpensive Ohmic sensor

[acourtjester]

Attached is the information about an electronics package I have used for a Ohmic sensor on my table, I works on both Plasma and Router functions.
It is very inexpensive and easy to connect to the controller. Attached are the images, a write up description, and connection drawing. I am using a Hypertherm 65 and have used it while cutting with 65 amps, I cannot state how well it may work with other Plasma units. I 3-D printed a small box to cover it up in my controller, connects with 6 small size wires.
https://www.ebay.com/itm/6Pcs-Lot-1-Cha ... 4408638154

Ohmic sensor 12 volt.JPG

Ohmic sensor Module.pdf

[adbuch]

Thanks! This could come in handy for some of the Plasmacam owners with older machines running 3.11.
David

[Rodw]

Tom, thanks for demystifying ohmic sensing. Its not rocket science.

I would be a bit concerned about using just one relay because the circuit is exposed to the full torch voltage. It would definitely be a good idea to use a properly isolated power supply like an inexpensive Meanwell HDR 15-12 which can handle 500 volts of back voltage without any issues. They are only $20 or so. See https://www.meanwell-web.com/en-gb/ac-d ... dr--15--12

When we have done this, we like to add another dual pole relay that disconnects both side of the power supply when cutting.
See:

ref: http://linuxcnc.org/docs/2.8/html/plasm ... ic-sensing

This does imply that your controller needs to be able to turn on an ohmic enable signal before probing commences. Linuxcnc's Plasmac supports this. In other systems, I've been able to set a signal from gcode as part of my probing routine.

[acourtjester]

Thanks Rod, if in the future I build table # 10 it will have LinuxCNC electronics, but at this point this work just fine for my operations.

[SeanP]

Nice one Tom
I fitted candcnc ohmic to mine a couple of years ago but for the last 12 months or so I've gone back to standard touch off, got that naffed off with small spatter bringing jobs to a halt I just didn't think it was worth it really, do you get trouble that way?

[acourtjester]

It seems to work fine but I have not used it long term, at the start of a G-code I do a simple touch of as I have a indicator on the program page. So it is easy to just drive Z down/up to touch the metal about 2 time, see the indicator and do cycle start.