I just got a Burny DNC 2.8 and...

DC servo motors, so most probably use +-10V analog control, not step/dir.
So a Mesa 7i77 with one of 7i92(eth) or 5i25(PCI) or 6i25(PCI-E).
Also there is Mesa 7i97.
First try to start and jog the machine to make sure the drives/motors work properly.

2 of Mesa THCAD10 should work just fine, but it would be better to get one and make the machine work with a floating switch first, then you can better evaluate if you need ohmic sensing or not.

tovarna wrote:

Any ideas on the thcad options I asked?
Thanks

Save yourself the hassle and skip THCAD ohmic sensing.

Phill did a nice write up on THCAD vs Relay ohmic sensing (and you can find a schematic to use the relay method there, which you can use pncconf to set up very easily): here

The setup is way less complicated, there is way less fiddling to get it to work, no components to track down in this forum and install, it's cheaper, and it's not bothered by noise/interference, and those of us who have ditched THCAD ohmic have found relay ohmic to be way more reliable, etc. It just works, right out of the box.

Also forgot to mention, ohmic sensing requires a shield on the torch, it can not be used with torches that have only the nozzle on the outside.
Unfortunately i never got the chance to test ohmic sensing as i can easily do a relay one and a THCAD one (for once in my life i have 2 of THCAD10 and a THCAD300 at once ), but due to all my torches having no shield, i can not. That nozzle is used to fire the torch so it can go up to multi thousand volts on every torch start.

PCW wrote:

I suspect the reason THCAD ohmic sensing was unreliable for you is that your
setup has higher leakage currents than others. A relay circuit would have a
_much_ higher current threshold than the THCAD circuit people are using here.

If you have higher leakage currents, a THCAD based ohmic sensing circuit
would need a lower value sense resistor (with appropriate power ratings)

That could be true about the leakage current, although from the THCAD-Ohmic standpoint, I ran the same setup/components as everyone else here, save for a Hypertherm power source, and my setup wasn't the only one to exhibit the same issues.

The relay circuit ran fine with the same resistor recommendation from the THCAD-Ohmic circuit. We moved to a lower resistance values only to make it be more water tolerant. This is something THCAD-Ohmic requires as well, it can't be fixed via a moving average algorithm in the component.

All that aside, in the end, after a TON of testing with both circuits, and now months of experience with both circuits, we found that there is no benefit to THCAD-Ohmic (yes, I know it is "less parts"). Sure, it "works", and it's an alternative, etc. But I can't see a good reason to spend the extra money, to add the extra complication (I am not talking part count), and frustration necessary to make it work. A quick search will reveal the many who struggle to make it work.

I suspect that the reason it's made it this far is due to the ultra-sexy marketing buzz word name it was given... "hypersensing".