I have 3 fuji VFD's for 3 belt conveyor motors I don't have PLC with the help of pot. i would like to synchronize their speeds how?

<b>Moderator's Note:</b> I think pot is an abbreviation for Potentiometer.

 

Are the three motors pulling on the same belt or on three physically separate belts that need to be synched, whether loosely or closely?

If all on the same belt, one method is to have one VFD be a master, and respond to a speed setpoint. Then you take an analog output from that drive that represents torque, and feed that as the control signal to the other drives running in torque mode (possibly with a speed limit set just a little bit faster than the master).

If separate belts, you could try the same approach, but with the analog signal representing frequency rather than torque, or still designate one belt the master, and have an encoder or tach on that belt generating a speed reference for the other drives. (Or even Belt 1 is master to Belt 2, which in turn is master to Belt 3, all depending on the physical configuration)