Anyone know how to calibrate the spindle RPMs? Past breakout boards that I have used had a potentiometer to adjust the 0-10 volt output to the VFD. I don’t see any way to do that on the Acorn board. My tachometer readings read fairly high for the full range but get worse for the lower RPMs. At 18000 commanded 19800 was read on the tachometer while at 6000 commanded it read 10500. I am using the standard Avid 4hp spindle with the Delta VFD.
Right now there’s no way to tune it, but we’re working on a software update that will allow for some adjustment. Should be available in the next few weeks.
Until then I guess I can use the spindle RPM over ride on the VCP. I typically only use a few RPM values for my tools so it won’t be too bad. Surprised that Centroid doesn’t have something but I haven’t been able to find anything so far.
Have you checked the VFD manual? I think they let you calibrate the speed vs the voltage input.
I think it does to a limited degree. With breakout boards that have a potentiometer for adjustment, the guidance has been to make coarse adjustments with it and then finer adjustments in the VFD. I was always happy with the potentiometer adjustments so never tried VFD adjustments. In this case the lowest RPM I can set is about 10500 as read on the tachometer when the Acorn commands a 6000 RPM. I will check to see if I can get that kind of correction in the VFD but I am not optimistic. The good news is that I seldom need RPMs below 10000 and the errors above it are in the 1000-1500 range. Do you know the exact manual to use for this Delta VFD? I don’t think I ever got one from Avid.
Ya, yours is way off, and isn’t linear across the range… When I was running Mach4/ESS mine was running about10% fast (across the whole range too), so I just left it because that was good enough. I have not measured it under Centroid control, but it sounds about the same to me.
The manual is too big to attach here, but if you search for Delta-VFD-EL-Manual.pdf you should find it (if you have the same old VFD I have).
Thanks. I worked on it today but the best interim workaround I have found to is to set the RPM with the VFD keyboard potentiometer and disconnect the 0-10v from the Acorn board. That gives you the exact RPM I set and the spindle is still turned off and on by the controller. I tried changing the minimum frequency and lower frequency limit but the VFD continued to run the spindle at 6000 when 0 volts are applied (disconnected from the Acorn board) regardless of what I did. Makes me think the problem is in the VFD but it worked fine before under Mach4.
Sit tight everyone. There’s a software update (a PLC update actually) coming shortly for this.
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I finally got the VFD working properly today. I went into the VFD 4.12 which is Minimum AVI Frequency and change it from 25% to 0%. I then changed 4.11 which is Minimum AVI Voltage from 0 to 0.3 volts to take out some of the error I was still getting. That did it. My RPM error now is about +/- 100 Hz over the full range. Avid had the minimum AVI frequency set to 25% to limit the spindle from going slower than 6000 Hz. That worked fine for my Mach4 setup but with the Acorn board the 6000 Hz became additive so when zero volts was applied the spindle turned at 6000 Hz and as more voltage was applied the RPM remained very high. Maybe I was able to compensate for it with the potentiometer on my Mach4 breakout board. If you set the minimum RPM at 6000 Hz in CNC12 you still can’t command anything lower than that. That is enough of a protection factor for me.
Ah, thats why I didn’t notice the error, I had set my min to 2% before converting to the EX so I could run a lot lower rpm.
2% is certainly better than 25% but it still will put an upward bias on the 0-10v scaling. Running at 0% eliminates that and actually is the Delta default setting. I also measured the minimum output coming from the Acorn board to be a few tenths of a volt causing a slight upward bias. Slightly increasing the Minimum AVI Voltage setting in the VFD can offset that making any RPM error quite low. I know most people don’t check the spindle RPM with a tachometer but it does reveal the true RPM profile.