Power Flex 70 & 20-COMM-E

Equipment:
VFD: PF70 20AD014C0AYNANC0
Comm: 20-COMM-E
1756-L71
RSLogix 5000 v20

This will be my first time using the PF70 and Ethernet so I have a few questions.
As of now all control will be over ethernet.
Got this from the 20-COMM-E manual that I will need to pulse to start/run forward and then pulse to stop? So my question is what happens if I loose communication with the drive and its been started? Will it continue to run? At what speed? The last speed reference?
Or
Will it be better to do a hardwire discrete start/run forward then handle all other comms over ethernet, this way I could remove the run signal upon comms loss.

Thanks

Don't think of it as a "pulse" output, but rather a "rising edge" output. You need to hold that START bit true until the drive reads it over the I/O connection and starts. I usually confirm that the drive is Running using its Status bits before setting the START bit false.

Similarly, set the STOP bit true to stop the drive, and keep it true only until the drive tells you it has Stopped by setting the "Running" bit false. Don't let your logic set STOP and START at the same time or STOP will win.

The default behavior of the drive when it loses communications with a ControlLogix over Ethernet is to stop and fault. That's also the default behavior if the controller goes to PROGRAM mode.

You can set up the 20-COMM-E to behave differently, though. My usual configuration is to set it up to Stop but not fault. In some very rare occasions I have set it up to keep running at the last speed reference.

With ControlLogix, you have full control over the drive over the network.

You might have read some recommendations about hard-wiring the Start and Stop functions when using drives with MicroLogix or SLC-500 controllers over the network, but those controllers don't have the automatic connection establishment, handling, and timeout features that ControlLogix implements over Ethernet.

Great info. Thanks Ken
I will go with the stop on comms loss.
Im sure at some point they will want to incorporate a safety relay.

Thanks again

As Ken mention above those COMM-E can be configured differently. We are using it with PowerFlex 40 and CompactLogix. We are using maintained N.O. bit to Start/Run and the same bit but N.C. to Stop VFD. Alex

When using a 20-Comm-E, I always do as almk above and have a N.O. bit hold Start in and the same N.C. bit hold stop in.

Just a note for future projects that the Powerflex 525 includes built in ethernet and will do everything a PF40 will do plus some for a lower cost. I'm not 100% sure on how its feature set compares with the PF70, but I'd be willing to bet it will replace a PF70 for most applications.

Thanks for the info almk and Helliana.

Helliana, we went with the PF70 because they offer it in indoor NEMA4X and space was to limited to enclose the VFDs

Switching the Start and Stop bits opposite one another makes logical sense but it can cause timing problems, especially if the drive stops and start frequently. This is due to the asynchronous way that the ControlLogix updates the output data tags. Sometimes the data will update at exactly the wrong instant between rungs, and a packet will go out that has both the START and STOP command bits true.

Someday I'll write a reference post about this that I can just link to.

In short:

To start the drive over the network, set the START Command bit true until the RUNNING Status bit becomes true.

To stop the drive over the network, set the STOP Command bit true only until the RUNNING Status bit becomes false.