Centroid Community CNC Support Forum

Hello, got a strange issue. I have my Acorn controlling my generic VFD (LS M100) and I have everything working except my spindle speed is surging. The VFD is fluctuating its output frequency by as much as 15-20hz. I tried reading the output voltage to see if it was fluctuating, however, while running, as soon as I touched just one probe on my multimeter to the positive 10v output on the acorn, the surging instantly stopped and it was steady. I took the probe off and it started again. For some reason, I can touch just one probe on the multimeter and it stops the surging every time. Any suggestions?

Would love any suggestions. Thanks!

Test the analog output from Acorn with the VFD disconnected using spindlebenchtest.cnc located in the ncfiles folder. Open the file in an editor and read the header first.

Include some information on how you have the VFD hooked up for rpm control via 0-10v. Looking at a LS M100 quick start guide, page 8 may be what you want to reference for parameter settings and wiring the analog signal from Acorn.

Try placing a 0.1uF ceramic (non-polarized) capacitor across the analog input to the VFD.

Sword,

I did the bench-test with the VFD and the voltages were dead on with no issues. I am unable to watch voltage fluctuations while the VFD is connected because as soon as I touch the multi meter probe to the +12v, it instantly stabilizes.

I have the Acorn analog output 10v and common connected to V1 on the M100 which is the voltage input. I then have the other connection connected to the M100 common. When I have the multi meter connected, everything works perfectly and I am able to go thorugh the range of voltages and speeds perfectly. It is only once I take the multi meter off that the surging starts. I am still able to change the spindle speed using the anolog output on the Acorn but it still surges.

Tblough, I will give that a shot. Thanks for the suggestion! I'll let you know if that solves it. Do you think that capacitance in the multi meter is what is solving the issue when I am touching it to the 10v output?

There is some small resistance and capacitance added by your meter. If you have a manual for the meter, the actual values should be in there. Adding the equivalent resistor or capacitor or both will calm down the fluctuations like the meter does.

This is an example input specification on a high quality bench meter for DC voltage ranges (may not be similar to what you're using):
Input Impedance:
10 Mohm in parallel with <100 pF

tblough wrote: ↑Sun Sep 19, 2021 3:56 pm Try placing a 0.1uF ceramic (non-polarized) capacitor across the analog input to the VFD.

This typically always solves the problem.

Here is some more information about suppressing analog output oscillations:
viewtopic.php?f=60&t=5364&p=46032#p46032

Thank you all so much! This helps a ton! I had not heard of this issue before and I'm glad to see it is an easy solution. I will get that cap on there ASAP and that should fix the issue.