THCAD selection including ohmic sensing

There was plasma specific firmware for the 7I76E and 7I96 but not the 5I25
So i just cobbled some up:



Contains a bitfile for a 7I76x2 config with three 'A' encoder pins on the first 7I76
encoder connector to support up to three THCAD or alternate Voltage to Frequency
type A-Ds

Yes the 5i25 --> 7I76 config is wired the same as the 7I96 and 7I76E configs:
The encoder connector has 3 encoders with only 'A' channels so instead of
the standard 1 encoder with A,B,IDX you have 3 encoders with only 'A' pins

Phill

I think you have just about got it. You need to connect the torch electrode to the plasma power supply as a separate terminal to the THCad connection which is normally to the divided arc voltage.

You have saved at least 1 optoisolator and set of relay contacts with this. The isolated power supply I use is only 12V and the opto isolator which is about 3V drop on the industrial module I use so only about 9V potential. I have never had a problem with a lack of sensitivity with my setup (actually I have thought about reducing it many times). I am sure I have published the schematics for my setup at least several times here as well as in private communication with Rod.

I know there has been a lot of discussion at times about "false" triggering of ohmic sensing. I can say with certainty that I have never had a problem with this that was a true false trigger. Yes, I have probing errors all the time but they are always caused by a flooded torch end or dross stuck in the torch end. So the probing errors are always cause by a true shorted torch which is why you check for that condition before the start of probing..

John

Phill

Sorry, my mind is always fixed on the HT or TD CNC enabled machines for production use.

John

tommylight wrote:

There is one important thing that is being left out from all this chat about ohmic/hyper sensing:
Most of the "normal" plasma sources use the shield in the torch to strike the arc between it and the electrode, that means having, in some cases, over 20000V AC on that pin/shield.
That poses a risk for everything attached to it, even relays will not stop that from arcing over.
It would be nice to mention from time to time that this type of sensing is for double shielded torches, that usually have no connection to the outside shield and a wire needs to be added and attached to that shield.
I still did not get the 5 THCAD i ordered through a "friend of a friend", for sure i will sacrifice one to see if i can find a way to use them on such devices as almost all plasma sources i use here are of this type, namely the Trafimet A141 or A161 torches with the shield wired to the high voltage arc start.

So I'm getting ready to install a THCAD-5 for ohmic sensing in my build and I was reviewing the wiring schematic in the primer doc. I have a Hypertherm Powermax 45XP with the ohmic sensing retaining cap so I'll be wiring up to that. My question is with the THCAD-5 IN- connected to the torch shield, is there a possibility of raw arc voltage going back to the electronics cabinet where the THCAD-5 will be installed due to slag shorting out the shield or some other fault? I realize it isn't an issue for the THCAD itself and the circuit is isolated, but I'm running a 3 conductor wire (small, maybe 22ga?) to the torch from the cabinet. Two wires are used for the float switch and the third is for the ohmic wire. Just wondering if there's potential for any issues or if I should run it's own separate wire just for the ohmic cap, separate from the other two.

Uthayne wrote:

So I'm getting ready to install a THCAD-5 for ohmic sensing in my build and I was reviewing the wiring schematic in the primer doc. I have a Hypertherm Powermax 45XP with the ohmic sensing retaining cap so I'll be wiring up to that. My question is with the THCAD-5 IN- connected to the torch shield, is there a possibility of raw arc voltage going back to the electronics cabinet where the THCAD-5 will be installed due to slag shorting out the shield or some other fault? I realize it isn't an issue for the THCAD itself and the circuit is isolated, but I'm running a 3 conductor wire (small, maybe 22ga?) to the torch from the cabinet. Two wires are used for the float switch and the third is for the ohmic wire. Just wondering if there's potential for any issues or if I should run it's own separate wire just for the ohmic cap, separate from the other two.

No its perfectly safe if you use an isolated power supply. There is no physical connection between the high voltage side of the THCAD and the encoder side. CNCFred proved this recently blowing capacitors on the high voltage side of the board with a 25,000 volt high frequency start. Once repaired, everything still worked and he is cutting happily!

I might add when I was testing this setup with the guidance of PCW, it took a lot of convincing from him before I was prepared to leave the ohmic circuit powered all the time, even while cutting. I don't use the optional relay shown in the primer circuit.

The ohmic comp component has an output pin that goes true when the THCAD-5 goes full scale. The only way this can happen is if the arc is on. So you can watch this pin in halshow as proof of this yourself. Thats why I added the pin to the component!