Ohmic sensing with IPTM-60

A break-out box.
A car relay.
Break the arc start ground cable when sensing.
And ohmic sensing works with the IPTM-60.
No modifications to the plasma cutter.
Standard arc voltage reader used, I use my own THTIC2.
 
 

You may be interested in LCSC electronics/JLCPCB.

They offer tons of components, custom cables, PCB fabrication, and PCB assembly.

You could produce these on a largish scale.

Not really interested to produce and sell.
Would take so much time, time I want to spend to make new things.
And it's not so unique, it's a remix of existing ideas.
Quite convenient though.
I don't mind at all if you sell units, will only help people.

Schema here 
 

Unique inventions went extinct long, long ago.

All new inventions/creations are a remix or a knockoff.

New "Music" is all remixes and knockoffs too.

Unfortunately this goes back to work-in-progress state.
The normal arc voltage reader didn't give a reliable output during ohmic sensing.
I'll put in another voltage sensor, right over the 24V-ish supply to the torch and ground.

Now it works. Again
The arc voltage connector is not connected directly to the arc and the work piece. There is some electronics in-between I don't even want to know about. The arc voltage is fine when cutting, but not reliable at all when not cutting. And ohmic probing is not cutting.

Instead I had to resort to a second voltage reader and read the voltage where the probing voltage is applied.
And now it works reliably. At least on the tests I have done so far.
Test patterns. I might have used wrong material setting on some but that doesn't matter for the probing test.
 

A new voltage reader was put in the box, next to the relay that applies probing voltage.
 

Cover on and pushed in next to the plasma cutter.
 
 

Schematics and code is available at github.com/MetalMusings/MyOwnEtherCATDev...th-the-iptm-60-torch
It uses my own Ethercat device. But nothing hinders this principle to be used with other arc voltage measurement devices such as those from Mesa. 
 

Here is the code used to detect contact
plasmac.ohmic-enable is connected to the "enable" signal in the code below, as well as to the output that activates the relay.
"limitVoltage" = 12V, halfway to 24V
"inVoltage" is the read voltage from the voltage reader.
"ohmicState", internal variable, is used to make sure the voltage first go above the limit and then start watching for contact. The relay has some reaction time, some 10 msecs, enough to need to be handled.
"voltageState", internal, indicates successful voltage reading.
"sensed" is the outsignal for contact yes/no.

Update of this project.
Regarding water on the table and difficulty to properly detect contact.
Yes, been there, done that. 
It seems to be caused by too low R1 resistance. Which means too low current at short-circuit.
Stray currents through water are in the same order of magnitude as the short-circuit current
and influences the voltage measurements. 
Too high R1 (low short-circuit current) and water on the table causes two things:
1. The measured voltage will only go to single-digit voltages, like 8V instead of 24V
2. The measured short-circuit voltage drop is only a few Volts. The voltage stays at some 8-3 = 5 V, where it should be 0V.
When looking at the voltage, well working means sharply up to some 23V, then sharp drop to 0V.
Not well working: Damped rise to some 10-ish V, damped drop of a few Volts at short-circuit.

Using R1 = 100 kOhm, short-circuit current = 0.24 mA. This is too low.
Using R1 = 2k7 kOhm, I = 8.9 mA works much better.
 

Updated schematics