Voltage Scale and Auto Volts

Hi all,
I have tried all suggestions made here (thanks for all the input !), but the gremlin is still there. As per Tommy's suggestion I have set up a configuration with lower accelerations. I have added a lowpass frequency, tried different settings for that, to no avail. I have bumped up THC treshold to 8 and 10 Volts, to no avail. Halscope shows a reasonably flat line, as least as flat as I would expect when cutting 25mm thick plate (the Hypertherm works pretty hard on that !) Disconnected the ground wires from the THCAD, that doesn't make a difference, either while cutting or on Halscope. The THCAD got power from the computer power supply, which I suggest is has a nice smooth output.

The bloody thing can just cut along nicely, and just like that the torch goes up or down very rapidly, respectively triggering the float switch or causing lost arc. I mean, if the torch lifts up, it lifts up 15, 20mm very rapidly, in the blink of an eye. I cannot imagine the THC is responsible for that. It just seems that the Z-axis gets triggered by something else than the THC, but I cannot work out what that would be.

The frustrating thing is that it just happens so randomly, I can cut 1 meter without trouble and all of a sudden the thing plays up. Just when I think I make progress the thing decides to do its own thing. Just running out of ideas.

Cheers, Peter

This is the thread I was thinking of where Stefan had similar issues.
forum.linuxcnc.org/plasma-laser/40712-th...fluctuations?start=0
Possibly ambient temp related,
Possibly noise (THCAD ground again)
Possibly becasue its not using power from the mesa card.

I really think Peter was on the money with outside environmental factors.
I'd look for the Hypertherm electrical grounding document and implement every recommendation. I did.

 

Can you cut manually with that plasma?
Might be Z axis drive interference.
Run the machine with torch off in LinuxCNC, and start the torch manualy see if that happens.
If it does, check Z axis wiring and shielding.

Do you run the default P I D values for the THC in the Parameters tab?

You could possibly try plotting axis.z.eoffset and joint.3.motor-pos-cmd (assuming joint 3 is your axis z) probably with both having a gain of 50/div.
You would need to use the Roll Run Mode and see if either or both of these have any value while your Z axis is doing it's odd thing.

Hi all,

I have redone the wiring and shielding on the THCAD, changed the frequency divider to F/64 and changed the voltage divider on the plasma cutter to 20:1, along with the voltage scale and offset adjustments. I have cut 12mm plate at 65A no problem, but again got in trouble cutting 25mm plate on 125A, 610mm/min.

I had a play with the THC Speed setting, and it improved when I set that at 1. Setting it at zero basically locks the THC. I have set PID-I at 1000 after a few trials and that made a minor improvement. But every now and then the gremlin still rears its ugly head, and the torch just dives or lifts up, albeit much slower than before, I suppose due to the Speed (PID-P) set at 1.

I wonder if it is possible to set the Speed (PID-P) somewhere at a fraction, for instance at 0.5 to see what effect that has ? The current interface only allows for multiples of 1. Is there a value in a config file which I can manually set ? Or a way to change it in the interface ?

Cheers, Peter