Spindle speed not matching command speed Emco 120P

[dmon86]

I am having issues with the setup of my spindle on my Emco 120P.
The command RPM does not match the actual, and it isn't proportionate and im stuck on what to look for now.

Machine: Emco 120P with Acorn, 4000L Quad encoder, Marathon 1760 RPM 3HP motor, Hitachi WJ 200 VFD.
Spindle max RPM is 3480RPM ~
Things I have done:
Initial Analog out spindle testing
I have checked through the maintenance pages that 1 revolution of the spindle = 4000 encoder counts.
In Wizard the encoder counts is set to 4000 and the max RPM is set to 3480.

Here are some of the the readings i get Commanded - Actual:
S200 - 780rpm
S500 - 1040rpm
S1000 - 1500rpm
S1500 - 1970rpm
S2000 - 2440rpm
S2500 - 2910rpm
S3000 - 3350rpm
S3480 - 3480rpm

thanks for help with any next steps I need to look at.

[cncsnw]

Things I have done:
Initial Analog out spindle testing

By that, do you mean that you ran the "spindlebenchtest.cnc" program (with the analog wires NOT connected to your VFD), and your measured voltages were all within specification?

Your next step would be to try some more similar tests, with and without the analog wires connected to the VFD.

For example, if you leave your "Max spindle speed (high range)" set to 3480 RPM, and then you run "M3 S348" at the F3/MDI prompt, you should measure 1.0 volts on the analog output. If you run "M3 S3132", you should measure 9.0 volts on the analog output.

If you do both those things (M3S348 and M3 S3132) with your VFD connected, what voltages do you measure on the analog output?

If you then disconnect the analog wires between the Acorn and your VFD and repeat the same test, what voltages do you measure on the analog output?

If you get distorted readings with the VFD connected, and good readings with the VFD disconnected, then it is likely that you will need to add a snubber circuit to your analog output.

See viewtopic.php?f=63&t=5398&p=46127

It is a fairly common issue.

[dmon86]

Thank you I am going to work through your suggestions.