Voltage Scale and Auto Volts

Hi all,

I had a look with Halscope and the voltage is fluctuating about 3 volts at idle. About the same when cutting. The fluctuations seem pretty consistent in time, I don't see spikes larger than 3 volt when at idle or cutting. Can a 3 volt fluctuation trigger this behavior ? The THC treshhold is set at 1 Volt.

Do we consider setting the voltage divider on the Hypertherm at 20:1 and make the relevant adjustments ? Will there be an advantage in doing that ?

I checked the cable and shielding for the arc voltage and that looks like it is grounded as per info I have been able to find here on the forum. The THCAD has it's own power supply, separate from the motor drivers and breakout boards. I am reasonably confident that is okay, but I will try to route a different cable from the plasma cutter to the controller to see if that makes a difference. On that note, we have the THCAD in the controller box, would it be better to have the THCAD mounted in an enclosure on the back of the Hypertherm, to minimize noise on the cable feeding the arc voltage in the breakout board ?

Cheers, Peter

If you look in halscope you will probably find there is an AC ripple at 50 /60Hz depending on your  supply.
As Snowgoer mentioned, try with  the GND wire from the THCAD removed. In most countries the Neutral wire is bonded to earth at the meter box so the AC ripple comes back up the earth wire. I found it added quite a lot of noise at the THCAD with this connected to frame ground.

Just let halscope run without cutting and remove the GND and see what happens at 0 volts. It may quieten down.

There is no need to move the THCAD. I've always had mine in the cabinet with a 120 amp machine.

If you can change the divider to 30:1 on your larger machine its 300 v full scale. Otherwise 20:1 is OK with full scale of 200V which is higher than cut volts except when piercing and the THC is not looking then!

Also,  the THCAD should be powered from the mesa card. From memory there are 5v signals on the encoder for this purpose.
Its coming back to me now, thefabricator03 had similar issues to you and I think the separate power supply is the culprit! Should be an easy fix.

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?