Plasma Current Control on the Fly (synchronous with motion)

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17 Apr 2021 07:22 #206158 by robertspark
thanks Rod, but we are going off topic, as I just want to know WHO is controlling their current on the fly and HOW they are doing it or have done it.

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17 Apr 2021 07:28 #206159 by rodw
I don't think anyone has controlled current except with the Hypertherm RS485
And Grotius as I mentioned but it was a different brand of machine.

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17 Apr 2021 07:49 #206160 by robertspark
thanks, no problem I'll see if anyone else puts their head above the sandbags.

I've got a little while before the 2x SPINx1 arrive. I'm also dabbling with a PCB to integrate a max325, I think I may just plonk one on a tiny PCB interface board.

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17 Apr 2021 08:15 #206161 by phillc54
A little bit OT as well but I used a ACPL-M484-000E as a replacement for a pot to control the spindle speed of my mill using PWM via a parallel port.

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17 Apr 2021 08:47 #206163 by rodw
Here is what Grotius did. You may like to read back a few posts..
forum.linuxcnc.org/27-driver-boards/3559...tall?start=20#124610
He never did share further info on this.

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17 Apr 2021 09:00 #206165 by robertspark
thanks very much Rod, I'm going to get a bit more info off my pmx45 today as I know what the pot is, have high Res photos of my pmx45 internals.... but forgot (how!) to measure the differential voltage across the pot. (to be fair it was not important with my earlier solution... but with the Mesa SPINx1 it has a range listed in the manual of 5-15v)

I also wanted to have a closer look at the torch fire circuit (from the 2x CPC pins) too
The following user(s) said Thank You: rodw

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17 Apr 2021 10:19 - 17 Apr 2021 10:21 #206169 by rodw
You can see Grotius wrote a custom component to manage the current.

I think if I was doing this, this component would have 3 inputs:
requested-current (from your M67, 0-45 amps for you)
motion.current-vel
motion.feed-upm (2.9 only)
Ref: linuxcnc.org/docs/devel/html/man/man9/motion.9.html

Two parameters.
Max-current (setp to 45 amps for you)
Max-PWM (setp to your PWM max voltage)

And one output
PWM-output

So the component would scale the M67 requested-current value in amps to output an appropriately scaled PWM

Then over time, you could start looking at some calculations to automatically set the PWM output.
eg.
if( feed-upm/60.0 < current-vel)
{
    // do some algorithm to set pwm output.
}
Last edit: 17 Apr 2021 10:21 by rodw.

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17 Apr 2021 10:35 #206170 by robertspark
remember the manual pot does not go from zero to 45 A,

at the extreme LHS it goes into an air test mode, and the lowest amperage is 20A



the 45xp goes from 10A to 45A (annoyed the hell out of me about 2months after I bought the 45 the 45xp came out as I would have gone with the 45xp with CPC and rs485... c'est la vie!)
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17 Apr 2021 11:01 - 17 Apr 2021 11:01 #206174 by rodw
Thats exactly the reason why a custom component was suggested. Those peculiarities can be incorporated into it.
You could have another pin for air test mode that if true would send the correct PWM and it could also make sure the minimum value is set to 20 amps or higher. The minimum value (20amp/10amp) might be another parameter.
Last edit: 17 Apr 2021 11:01 by rodw.

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17 Apr 2021 11:11 #206175 by robertspark
I'll see where it goes, just happy to have it gcode controlled at the moment on some static M67 parameters

the default (initial startup) pwm setting will also be 100% duty cycle (45A), as I don't want it blowing compressed air for no reason other than the board was just enabled. it will also make the transition from manual pot to digital pot appear seamless.

I have a 200A current sensor to hand that I'd like to check the effect on adding this arrangement does not detrimentally affect the 45a cutting current

uk.farnell.com/allegro-microsystems/acs7...726&gross_price=true


that is the plan...

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