Standard for sealing in and stopping a forward/reverse motor on a VFD.

I have a Powerflex 700 and a 1.5 hp motor I've hooked up to my Micrologix 1500 and test box. I was trying different start/stop setups today, and noticed something that made me wonder.

When set up with Run Forward/Run Reverse on the Powerflex, I tried using the Digital Out/Run relay in the drive to "seal-in" the circuit when I place it into forward or reverse with momentary switches. The problem is that there is a delay between when I hit the momentary N.C. stop button and the drive turning the relay to "release" the sealed-in circuit. That means I have to hold the stop button for a second to get it to stay stopped. Also, there's only two relays so to keep the fault output function I have to use the motor running relay for both forward and reverse seal-in.

Is there an industry standard for sealing in a circuit. I've been taught that it's not "correct" to seal it in with the PLC output, and it can be unsafe to use a latch due to the PLC going to the last state during power off and back on.

So what's the right way to do it?

Here's a copy of the basic program I was using to run the motor in forward/reverse.

I'm thinking about it and wondering if the guy that told me it's not "correct" to just use the PLC output to seal it in is probably full of **it.

I'm gonna keep doing it that way until someone with more experience tells me a better way.

Wait a second? Seal in?
First, what configuration for the run/stop commands are you using on the drive? For the 700's, I've always used the separate start/stop commands, and they only need to be pulsed momentarily, not sealed in.

For the 75x drives, I use the level "Close to run, Open to stop" commands.

It does sound like your 'expert' is full of it in any event.

From your program, it seems that you are using the level run commands, and not the pulsed ones. There is no reason to have to hold the stop button in, as the rung will drop out the instant it is seen by the PLC, so unless you have a scan time in seconds, the stop will kill any run command right away.

The configuration on the drive is level start forward, level start reverse, and pulse stop. The input has to be maintained to keep the drive running.

The Powerflex 700 has a relay with one n.o. contact and one n.c. contact that signals whether the motor is running. I tried to use that to seal-in the motor running.

Let me look at the manual on the 700 and see if I can find the pulse start parameter. That will make things easier.

You are using your own output to seal in the run circuit.
As soon as you hit stop, that output goes off, dropping the seal in. You shouldn't have to change anything if you are using the level based commands.

Are you just waiting for the ramp to finish before the drive actually hits zero speed maybe?

REVERSEOUT and FORWARDOUT should drop immediately on hitting the stop button.

I told you wrong, sorry. There's no stop input set up on the drive. If there is no Run Forward/Run Reverse Signal, the drive does not run. When I tried sealing it in with the "Running" output from the drive, the delay of the relay activating after the drive stop was causing it not to break the seal in unless you held the stop button.

The thing I want to be sure of is that it's ok to use my own output to seal in the circuit. I don't want to start a bad habit. If that is the proper way to do it, I'll continue to do that.

Yes, use your own output. You are commanding the drive to run and stop, waiting for the drive to tell you that it has stopped is just information.

And of course, have a hard-wired method of causing an emergency stop should all else fail.

Did you actually wire the running output to the start input of the VFD?
Or are you using a PLC output continuously to the start input of the drive?
I would have examined your PLC program but can't get RS500 to run right now