Ohmic probe wiring diagram

Hi,

I'm preparing hardware for the ohmic probe for my plasma machine and I have found that this wiring diagram:
linuxcnc.org/docs/devel/html/plasma/plas...r.html#ohmic-sensing
linuxcnc.org/docs/devel/html/plasma/imag...er_ohmic-sensing.png

I think markings on this diagram are slightly misleading. I'm attaching a diagram that I have prepared. The marking A1 / A2 are usually for the coil side of the relay. Pins 11 / 14 are usually for NO (Normally Open) and COM (COMmon).

Also, coils for probe enabled were connected in series, I think if two relays are used they should be in parallel.

In my system, I have used a single dual-channel relay to enable/disable the probe.

Modifed diagram:


My scrible notes and photos of my unit:

I do agree with the relays should be in parallel.

Note that the original circuit was contributed by theislander261 (John) and specified the use of opto isolated relays for additional protection (he used an opto22 module) Note point 4 in the primer. Using Opto isolated relays is to provide an additional level of protection as if something goes wrong the torch voltage could jump mechanical relay contacts...
Whilst the temptation is to use a single dual channel relay, this does not provide a significant level of protection in our view. ( I can say our view as the primer includes input from a number of users).

So if Opto isolated relays are used, there is no need for flyback diodes.

For your own safety, I would recommend that you replace you relay with opto isolated ones. (I am assuming you are using a mechanical relay as you have suggested the use of flyback diodes)

Of course an updated diagram via a pull request would be welcome!

Thank you for the advice.

If you take a look closer at my application I have trans-optor on the dual-channel relay (white 4N35 module with 1.5k resistor on the diode side). The single-channel relay will connect to my MESA 7i96 board input - already opto-isolated.

You sound like you know a bit about electronics. Thanks for posting schematics

Ohmic probe installed:

Good work!

Hey! Sorry to revive the topic, but im trying to built this aswell.
I have got one from a vietnamese store but it just doesn't work after a while!

I want to build my own.
Could you please state the relays and diodes, condensers used please?

thank you

Its covered here
linuxcnc.org/docs/2.9/html/plasma/plasma...itial_height_sensing

Thanks for the response.