Another plasma component...

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01 Jun 2019 03:07 #135528 by phillc54

What do you mean real voltages? Calibrate with the actual plasma machine running? Or apply a known voltage to the plasma machine's voltage divider? If so is that a trivial task?

From the plasma machine so all components are in play.

Yes but the 9 volt test would not have picked up the fault I experienced and it was not related to the THCAD at all. The main problem I had was that the THCAD saw the simple resistor divider network on the Everlast board as part of its divider network so that the 16:1 divider I was using was actually 24:1. This is not a problem with my Thermal Dynamics or I believe the Hypertherm units who have much more sophisticated circuitry on their divider board.

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.

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01 Jun 2019 03:12 #135529 by rodw
Replied by rodw on topic 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!

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01 Jun 2019 03:25 #135530 by phillc54
Rod, did you try the change to the glade file for the button color?

Cheers, Phill.

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01 Jun 2019 03:35 - 01 Jun 2019 03:40 #135531 by AgentWD40

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.

Last edit: 01 Jun 2019 03:40 by AgentWD40.

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01 Jun 2019 03:49 #135532 by phillc54

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?

Do a short cut with THC disabled and measure the raw arc voltage from the machine.

Cheers, Phill.
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01 Jun 2019 03:54 #135533 by rodw
Replied by rodw on topic Another plasma component...

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.
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01 Jun 2019 03:59 #135534 by phillc54

rodw wrote:

phillc54 wrote: Yes, I did comment out that line if thats what you mean. It made no difference. I did report back here at the time.

Yes, I saw that but I posted a later request.
Could you please try this:
In plasmac_buttons.glade change line 4 with a text editor from:
<requires lib="gtk+" version="2.24"/>
to:
<requires lib="gtk+" version="2.18"/>


Cheers, Phill.

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01 Jun 2019 04:13 #135536 by AgentWD40
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?

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01 Jun 2019 04:17 #135537 by phillc54
You only need the two voltages to be as close as possible to each other if you are using the voltage from a factory cut chart to set the THC height.

Cheers, Phill.

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01 Jun 2019 04:28 - 01 Jun 2019 04:42 #135538 by AgentWD40
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.
Last edit: 01 Jun 2019 04:42 by AgentWD40.

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