Spindle PWM / PDM glitch

Hi all,

I am at the beginning of a LinuxCNC setup phase. I am using a parallel port to control the motors.

I am having an issue with the Spindle speed - every few seconds (randomly) it momentarily increases speed, then comes back down. It's only very brief.

I have placed an oscilloscope onto the PWM signal, I can that the PC is generating a single extra wide pulse, which is making this happen.

It does the same if I use PDM, or vary the frequency for PWM (100, 500, 1000Hz).

Can anyone help with this issue?

Kind regards
Pedro

 

Do you get latency warnings when starting LinuxCNC?
Might also be interference, use a shielded cable for PWM.

Thank you for your reply @tommylight.

My bad - for some unknown reason, the BIOS had the PCI bus frequency at 333MHz. I've put it back to the standard 100MHz - all good now.

Where do I find the latency warnings?

Kind regards
Pedro

Depends on GUI being used, Axis shows warnings on lower right side, GmoccaPy shows them on upper right, QtPlasmaC shows them on a separate tab.