Ohmic Still Struggling

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02 Feb 2021 14:54 #197433 by CBEAR
Ohmic Still Struggling was created by CBEAR
I have had intermittant ohmic issues with my "hypersensing" set up. Halwatch with show Ohmic volts at almost 0v to start, and then after 2 or so pierces, it will show 22+v and hold a charge. The charge will slowly blead away over a long period of time, but it makes it unusable to cut with so I usually have to turn it off or else it won't probe correctly. Any ideas?

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02 Feb 2021 15:20 #197435 by snowgoer540
Replied by snowgoer540 on topic Ohmic Still Struggling
I'm not sure why your hypersensing "holds a charge".

But one thing you could try is to change the "ohmicsense.ohmic-low" value in your _connections.hal file to something that is above the voltage it gets stuck at. So right now say it's 21.5 (that's what mine is), and your voltage gets stuck at 22, change the ohmic-low to 22.5 or if that isn't high enough, 23.

I haven't plotted my ohmic signal to see what the voltage does after each cut is complete, but I think it goes back to around 0. The above might not fix the "root" cause of your problem, but it should get you cutting reliably with ohmic again.

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02 Feb 2021 20:58 #197474 by rodw
Replied by rodw on topic Ohmic Still Struggling
Did you see this post?
forum.linuxcnc.org/plasmac/38848-hyperse...ons?start=210#175839

Be sure to read the whole thread...

At a guess, you have an enable relay connected to the mains input to the ohmic power supply. The slow bleeding away is the power supply capacitors discharging over time once the relay turns the mains power off. I have not looked at it for a while but I always struggled to find a pin that would turn off the relay once cutting is done.

So I think that leaves you struggling with the water table problem that the revised ohmic3.comp and the circuit revisions in the link attempt to resolve.

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02 Feb 2021 22:37 #197487 by snowgoer540
Replied by snowgoer540 on topic Ohmic Still Struggling

rodw wrote: Did you see this post?
forum.linuxcnc.org/plasmac/38848-hyperse...ons?start=210#175839

Be sure to read the whole thread...

At a guess, you have an enable relay connected to the mains input to the ohmic power supply. The slow bleeding away is the power supply capacitors discharging over time once the relay turns the mains power off. I have not looked at it for a while but I always struggled to find a pin that would turn off the relay once cutting is done.

So I think that leaves you struggling with the water table problem that the revised ohmic3.comp and the circuit revisions in the link attempt to resolve.


Having attempted to help Cody with this offline I can tell you that He doesn’t run a relay on his power supply for the hyper sense (I didn’t at first either). But in this case I don’t think it would help to have a relay since the relay is in the entire time the program is running. He starts to see his issue after the second pierce.

Also he is running ohmic3 with the circuit reversions.

And where my table goes to near zero between each ohmic sense during a running program, his gets to like 22v and won’t go lower.

I suspected a wiring issue but everything I’ve ever asked him to check turned out to be how I would have expected it to be (per the latest diagram).

Changing the low threshold will help, but I don’t believe it’s the root of the problem.

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02 Feb 2021 22:56 #197490 by rodw
Replied by rodw on topic Ohmic Still Struggling
Thanks for the background. The reason why I wrote Ohmic3 in the first place was others were experiencing what Cody describes.

Fortunately for Snowgoer he is not getting water inside the torch nozzle. But I think Cody is.
Cody, you could try pulsing the torch before starting a job to get the post flow started before cutting.

I've got my ohmic.low set to 21.5 volts.
I think the Hypertherms needed to be higher so try 22.5 volts

But rather than guessing, I would use halscope to monitor the ohmicsense.ohmic-volts pin while sensing before setting the threshold.

Its pretty easy. Just open it from your GUI, click through to get to the scope page, click on 1, search for the pin, make sure its running and probe normally (do it with the torch disabled first to get the hang of it). Just alt tab to the scope after you get the job running. Hit stop when you see anything interesting

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