For synchronization purposes, we need to get a exact pulse/Hz signal from an A-B Powerflex 70 VDF. (This VFD drives a couple synchronous motors, and the pulse train is used to synchronize these motors with other servodrives.) Our older Yaskawa drives have a pulse monitor option card which does just this, but apparently there is no such option for Powerflex drives. Does anybody know how to get an exact pulse-per-cycle signal from the Powerflex? Thanks for your comments...

 

Have you considered a motor driven encoder?

 

The simplest solution would be to add rotary pulse generators to the motors.

Bill

 

A zero crossing detector comes to mind.

Regards
cww

 

But that discounts slip.

Regards
cww

 

Thanks for your replies. Generating the pulses from the motors themselves via encoder or similar is not an option, since the VFD drives the two synch motors in parallel and either (or even both) can be stopped via individual starters downstream from th drive, without actually stopping the VFD. In fact, we try to never stop the VFD because we need the pulse train as a master for other servo-driven equipment, since it can´t be done the other way around.

Right now, the way we are generating the master pulse train is just as you suggested, we have an extra free running small synch motor driven by the same VFD, and a combination of gears/shaft cams/prox switches generate the master pulse train. You can imagine upper management and visitor comments about this archaic small synchronous motor being the master for our whole "hi-tech" almost-fully-servo-driven production line!

That's basically why we want to get rid of this motor, besides the additional possible failure point added by this arrangement.

Thanks again for your comments, I´d appreciate any other possible solutions you could think of.