What does MISSING PULSE mean?

[johnnyelectro]

What does MISSING PULSE mean? I've got an alarm on an obsolete Parker motor drive. I was thinking it was an encoder pulse but I'm not positive. any thoughts on troubleshooting a missing pulse alarm?

Thank you!

[Cheller]

A Missing Pulse alarm sounds like a fault with an encoder or some type of feedback problem but I don't think that is the case with this one. View the post with the  complete list of Parker drive Alarms for DC drives, not sure if that alarm list pertains to your problem. Anyway, here is what it says for the Missing Pulse alarm. As you can see, there are quite a few causes for this alarm:

MISSING PULSE (This alarm is caused by a missing pulse from the 6-pulse armature current waveform. It trips when the motor loading exceeds 1.5 times the DISCONTINUOUS parameter value. Ripple from the speed loop from either the setpoint or feedback can cause unstable current.)

Possible Reason: Drive not Autotuned (unstable current loop)  Corrective Actions: Perform the AUTOTUNE procedure

Possible Reason: SCR gate connection loose Corrective Actions: Check SCR gate connections from the trigger board to the SCR gate leads

Possible Reason: SCR defective Corrective Actions: Check SCRs with an ohmmeter.

Possible Reason: SCR firing pcb defective Corrective Actions: Replace the pcb

Possible Reason: Motor has opened or shorted coil Corrective Actions: Check the motor with an ohmmeter and megger for insulation and continuity

Possible Reason: Coupling between motor and feedback device slipping Corrective Actions: Stop drive and isolate power - check coupling tightness

Possible Reason: Feedback device noisy or defective Corrective Actions: Replace tachometer generator if noise is present while observing feedback with an oscilloscope

Possible Reason: Bottom two LEDs on the 5701 Microtech receiver board are out Corrective Actions: Weak feedback signal intensity; check connections, fiber optic wire integrity, and transmission distances

Possible Reason: Speed loop gain too high Corrective Actions: Retune drive speed loop

[johnnyelectro]

I think the problem may have been a loose set screw in the coupling for the encoder after all. I thought I would check the coupling just to be on the safe safe and it was a little loose. I restarted the motor and haven't had the missing pulse alarm yet. So I am going ot keep my fingers crossed that it was that simple.