Access or read amperage going to the motors

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24 Mar 2021 14:03 #203510 by bierluiz
Hello,

I'm working on a CNC mill which was retrofitted with LinuxCNC (someone else did it).

It uses a Motenc Lite board, connected to the original VFDs and motors ("Red cap" Fanuc 5,5 Kw, I think it is a 3S model).

There is basically no documentation from who did it, plus I am a rookie on LinuxCNC.

What I need is to access/read the electrical current going to the motors.

I checked the outputs from the motenc and could not find a connection from the board to the VFD. In fact, the VFD does not appear at all in HAL or Classicladder.

Couldn't find any topic related.

Thank you.

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25 Mar 2021 01:29 #203562 by andypugh
The VFD might be connected via a +/- 10V output. Or it could be on Modbus.

Look through all the HAL files to find where (depending on LinuxCNC version) either motion.spindle-speed* or spindle.0.speed* is linked.

There is a choice of spindle speed outputs, rpm or rps, absolute or signed. But one of them will be connected, Follow it through.
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25 Mar 2021 10:08 #203599 by bierluiz
Thank you,

But what about the X, Y and Z motors?

For X, for example, Xoutput fluctuates between -1 and 1, depending on the feed. What is confusing me is that Xoutput is connected to a DAC pin, but it is already analog.

And what unit is Xoutput?

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27 Mar 2021 01:51 #203766 by andypugh
Xoutput is a signal, it could be anything as signal names are created at the integrators (ie your) discretion.

You could use "Xoutput" to refer to spindle speed in, though that would be wilfully eccentric.

But, guessing at likely options, it sounds like the signal from the PID to the drive. It could easily be volts, rpm, or -1 to 1 or -100% to 100% duty cycle.

From what you say, it goes to a DAC. you say that it is analogue, but it isn't, it is probably a flaoting point number, bit in HAL it's a binary, digital, number.
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29 Mar 2021 07:37 #203985 by bierluiz
Ok, thank you,

But I am still confused in HAL. There should be an output in the Motenc card which sends the signal to the VFD right?

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29 Mar 2021 17:43 #204079 by andypugh

bierluiz wrote: But I am still confused in HAL. There should be an output in the Motenc card which sends the signal to the VFD right?


Yes, there will be a HAL input pin (that accepts a value set by another HAL pin, such as spindle.0.velocity-cmd, and converts that to an analogue voltage (or a PWM) on the Motenc output pin.
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06 Apr 2021 17:22 #205151 by bierluiz
When you say motion.spindle-speed, do you mean only the actual spindle of the machine, or the ones for the axes motors are also called "spindle"?

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06 Apr 2021 22:40 #205202 by andypugh

bierluiz wrote: When you say motion.spindle-speed, do you mean only the actual spindle of the machine, or the ones for the axes motors are also called "spindle"?


You mentioned a VFD, so I assumed that you were talking about a spindle.

The pins created by the motion component are here:
linuxcnc.org/docs/2.8/html/man/man9/motion.9.html

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07 Apr 2021 17:22 #205270 by bierluiz
Sorry now I see that I was no very clear.

I mean the axis motors, not the spindle.

VFDs are not common to drive the axes?

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07 Apr 2021 23:13 #205293 by andypugh

bierluiz wrote: VFDs are not common to drive the axes?


Very uncommon, actually. Are you driving the axes with induction motors?

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