Another plasma component...

I don’t have an extensive tool table built for plasma cutting at this time but I can send what I have to you for testing if you want.

If you can send a tool table that was exported directly from Fusion360 that would be good.

phillc54 wrote: Does it have a "sensitivity" adjustment?
Would it be possible to wire it into your current config?

No it does not have a adjustment pot or anything like that,

Reading through the manual for it and this stands out,

"It’s sensor input is surge and voltage protected so normal plasma start and run voltages do not effect it. It offers a fairly low
sense impedance and filtering to prevent false triggering."

So would it be possible to add a variable sense impedance and filtering circuit to our open source ohmic circuit?

So would it be possible to add a variable sense impedance and filtering circuit to our open source ohmic circuit?

That sounds feasible but beyond my capabilities.
I also wonder if the water becomes less resistive over time as suspended metal particles increase and what effect that has.

rodw wrote: Yes
www.candcnc.net/store-home/feather-touch-ohmic-sensor/

I think other systems have a sensitivity setting (eg a pot.) I wonder if we could use a Mesa analog input somehow as part of this?

I am working on a new SSerial connected THC interface
( Have proto PCBs but it will definitely take quite a while to do the firmware )

One thing the new interface has is a real time analog Ohmic sensor.
This will allow setting the threshold dynamically and perhaps doing
things like monitoring the leakage current (when the torch is up and off)
and perhaps warning or changing the threshold based on
background leakage.

In the mean time, it might be worth testing a bit with a Ohmic sensor
based on a THCAD and a floating 24 to 100V or so power supply.
(maybe some 9V batteries to guarantee floating and high isolation)

I can donate a THCAD If someone wants to try this. if nothing else
it would be interesting to see if leakage can be distinguished from
contact by getting real time resistance information.

Beware that everything on the torch side including Ohmic sensing connections
can be at lethal potentials so this is not something to be undertaken lightly

PCW wrote:
In the mean time, it might be worth testing a bit with a Ohmic sensor
based on a THCAD and a floating 24 to 100V or so power supply.
(maybe some 9V batteries to guarantee floating and high isolation)

I can donate a THCAD If someone wants to try this. if nothing else
it would be interesting to see if leakage can be distinguished from
contact by getting real time resistance information.

Peter, I'd be interested in trying this is shipping down under is not too much of an impediment. I am acquiring a couple of test PC's this week and was thinking of getting a 7i96 or another 7i76e because you can't easily set up a SIM for a Mesa card. I think my current setup qualifies as a floating (Isolated) power supply as there is no common ground with anything else. I've got another Mesa 7176e user locally who works with the Atmel Mega CPU's who is happy to help with any plasma stuff. I still want to play with the Mesa UART for plasma too. I think I've got your email so I will touch base that way.

PCW wrote: In the mean time, it might be worth testing a bit with a Ohmic sensor
based on a THCAD and a floating 24 to 100V or so power supply.
(maybe some 9V batteries to guarantee floating and high isolation)

I can donate a THCAD If someone wants to try this. if nothing else
it would be interesting to see if leakage can be distinguished from
contact by getting real time resistance information.

Beware that everything on the torch side including Ohmic sensing connections
can be at lethal potentials so this is not something to be undertaken lightly

I am happy to volunteer to give it a try, I have attached our ohmic sensing circuit diagram to this post,

Could you have a look and let me know how the THCAD will wire up to our existing circuit.


Edit: Rod beat me to it, Hes the better man for the job!