THCAD selection including ohmic sensing

Pull down the zip file for the 7i76 and see if he's made it while you are waiting.

rodw wrote: Pull down the zip file for the 7i76 and see if he's made it while you are waiting.

I did

I do see it for the Ethernet based cards, _plasma

But I don’t see it for the 7i76, unless I missed it.

well, I ordered a 300 and a 10
should I try to get a hold of mesa and have them just switch to 2 10's ?

I am going to end up making a few machines with the controller combo I am working out so I would rather take the time and do this first one right

Thank You
C

I'm jumping on this thread as i'm wondering if i add a Ohmic sensing or nat.
I have the THCAD-10 for the height control, and i'm thinking of using it for the Ohmic sensing as well.

I got the idea of using a relay connected to the same output as the torch on/off that will switch between a voltage supply and the torch on the THCAD-10 arc voltage input, but behind the voltage divider to get a highe r sensitivity

jay1st wrote: I'm jumping on this thread as i'm wondering if i add a Ohmic sensing or nat.
I have the THCAD-10 for the height control, and i'm thinking of using it for the Ohmic sensing as well.

I got the idea of using a relay connected to the same output as the torch on/off that will switch between a voltage supply and the torch on the THCAD-10 arc voltage input, but behind the voltage divider to get a highe r sensitivity

You might be able to do this without too much drama, With the hypersensing circuit, there is absolutely no need to keep the ohmic sensing circuit isolated from the arc voltage because the THCAD in conjunction with the Isolated power supply is impervious to the torch voltage. (both can handle over voltage of 500 volts)

Therefore, there is no reason to use a relay at all.

Because of this, there is no need to use Plasmac's Ohmic enable signal to switch the ohmic sensing circuit off. But in this scenario, it would be useful to know when its probing and when its not because if the probe was disabled we would know any voltage its seeing is the arc voltage.

I would have to think through this a bit and it might need a few mods to the component but it there was an out pin for voltage, it could be introduced to plasmac with scaling of 1.0. (Which is what I do now anyway from another component I had in place when I adopted plasmac which had a bug at the time).

But just say you calibrated a THCAD-10 to see 200 volts as full scale, 24 volts would be be at 1.2 volts on the 10 volt scale and that is probably enough to do the ohmic sensing. In fact, a lot of you you could probably calibrate the THCAD for somewhere around 150 volts depending on your plasma cutter. (my 120 amp machine has a maximum cutting voltage off 165 volts in the book speeds)

Its just that I never thought through this becasue I already had torch voltage sorted with a THCAD-10 when PCW donated a THCAD-5 to the cause so we could work this all out.

Well it may not be quite that simple depending on ones actual hardware. In most case the arc voltage sensing (THC) is sensed between the torch electrode and the work piece. For ohmic sensing usually you want to measure the potential between the torch shield and the work piece.

John