THCAD 10 to Herocut 55i (1:1)

Did you check if there is any resistance between the electrodes and the raw arc outputs?
That would need to be included as part of  your scaling resistors to get the thcad scaled correctly.
If it does have say 100k on each pin, the external voltage won't be lethal so it will be safe to keep it all outside as you have now.
The Everlast and Thermal Dynamics machines I have had both had 100k resistance mentioned in  the manual and I measured that on the everlast with a multimeter.

I have now moved the resistors inside the machine. Thanks for the feedback

Did you use your multimeter to check if there was any resistance between the pins and the electrodes before you started?
YO really need to know that.

Oh didn’t know that it was important, thanks! I measured 120kohm on both ground and plus. Do I need to compensate with a smaller resistor or how do I do it?

Ekholm wrote:

Oh didn’t know that it was important, thanks! I measured 120kohm on both ground and plus. Do I need to compensate with a smaller resistor or how do I do it?

Yes, you need to adjust as its part of the scaling resistance the THCAD sees.
Recalculate the full scale reading  as per the formula in the THCAD manual including ALL resistance in the circuit (eg 240k Ohm plus the resistors you added).

If its not satisfactory, adjust your resistor values to account for this.

I tested this on my plasma cutter and the adjustment is definitely required. Be sure to scale your software scaling parameters correctly

PS: For others contemplating this plasma cutter, there is no need to locate resistors inside the plasma case with this plasma cutter as the 120k resistance on each terminal ensures the current is non-lethal. In fact, there is no reason why the THCAD can't be located inside the main control box.

sorry for all the questions! I’m not following how I calculate this values. I found that there is a online calculator where I tried to add all information. I guess that voltage divider ratio is 1? 1.12Mohm +1.12MOhm?
and I don’t understand the frequency devider jumper settings. Should I use F/32? 

You read the manual. Use 1/32

Hi!
I’m not sure if I understand this correctly. But should I do it this way?
If I measure  the voltage between the nozzle and the ground clamp. Then I know the full scale voltage input (VFS)? And the maximum current (100uA)
then I can solve the REXT equation added in attachment . 

the example then shows a 4.9M resistor if VFS=500.

If I use this example should I take 4.9 M - (1M + 120k )=3.78M
and add another 3.78Mohm to each output pin?!