Ohmic probe aborts immediately

Hello all. I've got an odd problem with ohmic probing that recently cropped up.

When I tap the Ohmic Probe button in QtPlasmaC, probing immediately aborts without moving the Z axis. Normally I would assume that the ohmic sensing circuit is always closed for some reason, but it's definitely not that.

halscope shows that the ohmic sense feedback pin is never activated. The ohmic enable pin is however correctly activated.

I've verified that the relay on my breakout board closes when ohmic probing is activated. If I connect the ohmic sense wire directly to the table, probing again immediately aborts and the ohmic sense pin is correctly activated. I've also verified that the relay that closes when the sense circuit is closed is not activated. 

Z axis is homed. It correctly probes when using only the float switch.

So my question is: what can cause a situation where ohmic probing aborts no matter if the sense pin is active or not?

Sometimes LinuxCNC acts up.

It only happened to me maybe twice, but restarting the PC fixed it.

Is it intermittent?

Unfortunately it happens 100% of every time.

It really feels like a bad setting somewhere, but AFAIK I haven't changed anything relevant since the last time I used it a few months ago. I've been cutting thick material for a while so I just was just using float switch probing.

What I can't get my head around is that there is no indication that the ohmic sense pin is ever on. This makes me think there is an unrelated setting keeping it from probing. I tried adjusting the probe height, but that didn't change anything.

Float switch probing continues to work fine.

I see.

Sometimes stuff shifts mechanically, electrical stuff wears out too (Caps degrade and/or change capacitance, etc.), sometimes leading to random, unexplained changes in operation.

Switches and other mechanical actualtors get flabby over time, requiring less force to actuate.

Is the PC you use to control the machine "frozen in time" (not connected to the internet or outside world)?

I do have the same problem, I see the ohmic probe is activated then when probe start it "find the plate" and try to go back however torch is in the up limit, then you have a error, I set the threshold to 18V and worked in probing but fail again during real cuts, mine is a water table.
please let us know if find the solution.

> I do have the same problem
If your torch moves at all you have a different problem than me. I'd recommend opening a new thread and ask for help there.

> Sometimes stuff shifts mechanically

I verified that the PCB is working as expected. No welded contacts, etc.

> Is the PC you use to control the machine "frozen in time" (not connected to the internet or outside world)

It is connected to the internet, but there are no automatic updates happening. The software hasn't changed in at least 6 months. I also haven't touched the relevant HAL sections in as long.

> 2. Where are the videos ?

Coming soon. Our 4G cell service and broadband internet went down for nearly a day :|