THC config that works.

It is mentioned that it does not use limit switches, that should include the Z axis.
In the xml file you set the initial values for your machine and all of them can be adjusted during use.
The Z axis home and offset should be set in the ini file. This also should be set after testing on an actual machine, as in general they do not need to be edited, i use the same settings on several different machines.

Hi Tom and company.

My proma THC turned out to be faulty and I want to say: Lukasz replaced it quickly, though I have had it for years and way out of any guarantee I expected: it's unusual to get customer service that good! Thanks Proma...

I started again with a fresh installation of the THC config you provided and a new THC. I'm going through your calibration procedure: Pressing F9 makes the Z drop til the float switch triggers. Axis retracts to 3mm, TorchOn lights up, plasma fires, ArcOK light goes on...all good. Then, the THC sends 'MoveUP' and Z axis starts rising and rising til it's maybe 50mm above the work. I lowered the voltage setting on THC unit gradually down to around 85, so Z axis stays roughly around the same height for a bit longer but then starts to rise again. So I try setting voltage to 80, and now the Z axis moves down into the work...and keeps moving down, triggers the float switch, keeps moving down til the torch is pushed out of the holder and the shroud is smashed, tip is melted etc (I should have been quicker on the Estop button!).

I thought that the purpose of THC control is to keep the arc voltage close to the set point, but i seem to have something wrong - set point too high and Z just rises and rises, too low and Z drops and drops - as if MoveUP and MoveDOWN are working the wrong way? The THC lights and the LEDs in Axis GUI agree with each other, though, I believe the wiring and pins are correct (ie I haven't wired UP to DOWN).

Any suggestions?
a

Try the voltage in between 80 and 85, Proma THC can be set to be sensitive to -+1V.
Also set the TEST time longer on the THC so you can clearly identify if the UP/Down signals are correct. You can do that by holding both buttons on the THC till you get TST then release and click on the UP till you get to 10, that will give you 10 seconds to check the signals on Linuxcnc screen.

is there any difference

FERROR = 1
MIN_FERROR = 500

vs

FERROR = 500

Yes there is, ferror should be for high speed or rapid moves, min_ferror should be for slow moves.
I am a bit fuzzy on that, so you should confirm that.

Based on this:

limiting ferror = maxFerror/limitVel * vel


If ferror < minFerror :
then OK
else:
if ferror < limiting ferror :
then OK
else:
ERROR
( this is from the source )

I think that there is no difference.