Another plasma component...

phillc54 wrote:

No, nor would using theoretical results, but using the actual plasma voltage would have.
Not everyone has a HT or TD machine and not everyone has a CNC port...
Any way there are bigger fish to fry than worrying about the "correct" way to calibrate...

Cheers, Phill.

Absloutely. In fact using the raw arc voltage is actually far easier for people inthat situation as you have total control about what the THCAD receives as you are not dependent on anybody else's dubious quality electronics!

phillc54 wrote:

From the plasma machine so all components are in play.

Just so I'm all clear, all you're saying is to cut some metal with the torch or fire it in the air, with a multimeter on the thcad inputs, and watch the multimeter vs voltage-out to check calibration?

phillc54 wrote:

Any way there are bigger fish to fry than worrying about the "correct" way to calibrate...

I hope I'm not being a pest. I certainly care more about the more accurate way than the theoretically correct way. I want to fully understand exactly how you physically do it. I do remember you outlined an overview of the procedure to me the other day, but I'm after the specifics of what you mean. I figure If I don't ask some other newbie will.

- run LinuxCNC
- open halshow and watch plasmac.arc-voltage-in and plasmac.arc-voltage-out
- set Voltage Scale in the Plasma Config tab to 1
- set Voltage Offset in the Plasma Config tab to the value read from plasmac.arc-voltage-in
- apply a known voltage to the TCHCAD input < ---- this part here is what loses me as a complete newbie
- set Voltage Scale in the Plasma Config tab to (known-voltage / plasmac.arc-voltage-out)
you could probably keep tweaking to fine tune further.

phillc54 wrote:

Rod, did you try the change to the glade file for the button color?

Cheers, Phill.

Yes, I did comment out that line if thats what you mean. It made no difference. I did report back here at the time.

AgentWD40 - known voltage means a 9 volt battery but you have done more work than most on calibration, go with your calculated scale.

Working through this at 0 volts and no offset, plasmac.arc-voltage-in will be the 0 volt frequency which you already know from the THCAD sticker. Entering this as the offset and a scale of 1, you should get the same reading as the input volts.

Got it! I thank you guys for your patience.

What's the +- tolerance or how close does the calculated voltage need to be to the raw arc voltage for a good cut?

What I mean to ask is how far off can the actual arc voltage be from the optimal arc voltage before it noticeably effects cut quality?

[edit]
I think I found the answer I was looking for: +- 1 volt

John,

The electronics...and sometimes the mechanics of the torch height control can probably achieve 1/4 volt resolution (rule of thumb, 1 volt change in arc voltage is approx equal to .004"....although that varies with different processes)....but if you can hold arc voltage to plus or minus 1 volt....you will have a very good system.

Arc voltage THC from 10 years ago had a plus or minus 5 volt deadband....so the height could vary as much as .040"....todays plasma systems need accuracy in the plus or minus .010" range or plus or minus a little over a volt for best performance. Since minute variations in cut speed, surface condition, material content, plasma gas flow/pressure, and when a cloud passes under the moon all affect the arc voltage/torch height relationship......there really is not a good reason to try to get much better than 1 volt.

Many really nice arc voltage THC's end up getting "detuned" a bit to minimize torch z axis oscilation!

Jim

www.cnczone.com/forums/general-waterjet/...c-voltage-range.html

I'm just asking because I'm guessing my scaled up error from before is about +-0.5 volts.