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Author Topic: DRO number for brain to control RPM?  (Read 4423 times)

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DRO number for brain to control RPM?
« on: August 24, 2014, 05:36:01 AM »
I have a Hitachi X200 VFD controlled via modbus.  I can start/stop, change direction, and set RPM just fine.  S2000 = 2000 RPM on my laser tachometer.

I noticed the RPM DRO was reading oddly... something like "364" when stopped, "1736" when running at 2K.  I don't know where it was getting that number, it's junk.  Might be noise off a tach input with nothing hooked up to it.

So I went to make a Brain to read the RPM back off the Modbus.  But I'm not clear what the RPM DRO is.  I tried "True Spindle RPM" and it didn't change anything.  I took the Brain and change the Function to "f(out)=1234" so it should read a flixed 1234 regardless of whether the spindle's on at all or what its rpm target was set to.  I tried everything which sounded remotely like the name of an RPM DRO but no luck.
Is "True Spindle RPM" the correct DRO?  Do I need to go under General Config or Ports And Pins to change the input for the RPM readout?
« Last Edit: August 24, 2014, 05:46:45 AM by MechanoMan »
Re: DRO number for brain to control RPM?
« Reply #1 on: August 26, 2014, 03:42:42 AM »
Hmm was Googling further:


MSM uses DRO 39 as does the 1024 screen set - that is the DRO mach updates with the true spindle RPM.
DRO 39 is updated by Mach - neither MSM nor 1024 have a hand in determining the DRO value. it's just on a page and mach updates it's value as mach does all the other DROs.

With the plug-in my impression is that the RPM data comes from the VFD and the plug-in then displays it in a user DRO (at least that's what the plug-in manual seems to imply to me).

Hmm, so I guess they're saying "DRO 39: True Spindle RPM" is in fact what's supposed to control that display, but due to a limitation in Mach3, a Brain can't currently control it, it's hardwired to the encoder/pulley setting?

Is there any plugin that would make DRO 39 actually work?
« Last Edit: August 26, 2014, 03:58:49 AM by MechanoMan »

Offline ger21

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Re: DRO number for brain to control RPM?
« Reply #2 on: August 26, 2014, 11:43:06 AM »
Something must be configured incorrectly if the rpm is reading wrong. Rather than creating a Brain, why not just try to find out what's causing the display to be incorrect?. Should be an easier solution.

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Re: DRO number for brain to control RPM?
« Reply #3 on: August 26, 2014, 03:40:08 PM »
It can't read correctly because it's using a default method which doesn't exist.

Mach3 is meant to take tachometer pulses off a sensor and calculate the measured RPM number from that.  That's different from the commanded target RPM of course, and part of the control loop that increases PWM pulse duty when measured RPM is below the commanded RPM. 

My Hitachi X200 VFD is being controlled via Modbus.  I don't have a need for Mach3's software control loop, the VFD already has a hardware control loop I've written the command to.  I don't have a physical tach sensor and will not be installing one. I have a Modbus data reg with the actual RPM value already right there.

So the RPM display won't ever work as-is, the tach input doesn't exist in my system.  Mach3 needs to be configured with a Brain to forward a register from the Modbus onto that RPM DRO.  That's the only way it's gonna display, and it's actually much simpler... but it looks like this is just weird uncoded territory inside Mach3.  There's a number for that DRO to be a node's terminator but that functionality seems unimplemented in Mach3, looks like it'll remain hooked up to the tachometer pulse integrator.