Using a Flex I/O 1794-ID2 to monitor speed of a motor to mantain RPM

[Baker in Virginia]

Good Morning ,

I am going to be re-working 2 portable machines. I am going to have one main panel with a CompactLogix and 3 PowerFlex 527's. I am going to have a plug to supply voltage , and the motor wires from the drives. I am going to have Flex I/O in the portable machines. I would like to attach Incremental Encoders to the motors . From these encoders I was thinking of terminating to a 1794-ID2 module. The reason I would like to attach encoders to these motors is to maintain the RPM . I know the best solution would be to terminate the encoder wires directly to the PowerFlex 527. If I use the 1794-ID2 , will it be fast enough to sense any change in RPM , so I can adjust my freqency command to the drive ? It sounds like it is unorthodox to take the encoder into the PLC instead of the Drive , correct ? I am just keeping from needing to use another plug , and deal with broken wires , etc.

Thanks so much in advance,

 

[dmargineau]

It will work, however, you will introduce some lag when compared to directly connecting the encoders to the VFDs.

If EtherNet/IP FLEX and EtheNet/IP connected PF527 then sum the 1794-AENT module RPI, the PF527 RPI and the implemented logic Task duration and you will find out the introduced lag; for a 5 ms Continuous Task and 20 ms RPIs for the FLEX and the VFD the lag will be 45 ms; you could reduce the RPIs and use a High Priority Periodic Task if you need more responsiveness.

Or you could connect the encoders directly to the VFDs; this approach will consume only a fraction of the expenses and time required by implementing of the other option.......

 

[GaryS]

the best way to have the drive maintain the speed is to have the encoder connected directly to the drive
you still have the same number of connections but far better regulation and control
you set the speed command and let the drive do what is built to do control the motor speed
check out open loop vector control on the drive It may do what you need without the need for an encoder ( cost of encoder, feedback board, wiring, programming)