Serial Comms to VFD

[freecrowder]

Just a general question on basic serial comms. In most plcs that are controlling basic functions to a VFD. Start, Stop,jog etc. When i start the drive does that start bit stay latched in the PLC? So that even though the drive is running at commanded speed the start bit is still communicated to the drive? If I am monitoring feedback from the drive in the PLC and it knows that the drive is running can the start bit be turned off and the drive stays running untill I set the stop bit on another bit?

 

[mk42]

It depends on the serial protocol and the drive system. Some drives, especially for positioning, can start moving based on an edge/signal transition from 0->1. Many require the signal to be true for as long as you want it to move. Some of a special stop signal, some just have you remove the enable to stop it. Sometimes enable and start are the same signal, sometimes they are seperate. It all depends.

Short answer, it can work just about any different way you can think of, depending on which products you are using.

 

[GeoffC]

And how you configure the various vsd systems