compactlogix and power flex vfd

Been having some on and off problems with a powerflex connected by ethernet to a compactlogix. I can connect to the drive just fine and read all the parameters. The only errors I have got so far on the drive is a comm fault and a DC bus undervoltage.

The problem is the drive will not respond to the instructions in the program. IE. Forward,Reverse.

The output is turning on to tell the drive to move forward and also the reverse turns on, but the drive does nothing.
The status lights on the drive will change from forward to reverse but the Run light doesnt come on. As I said this is off and on, sometimes it works fine and sometimes not.

What could be causing this?

where does the drive get the enable command is it hard wired and have you checked its connection?

What do you have "Comm Fault Action" set to?
What do you have "Idle Fault Action" set to?
Is your DC Buss Undervoltage fault happening only on power down?
What do you have P36 set to?
What do you have P38 set to?

Are you using a 22-Comm-e module?

I'll bet you a box of donuts that your logic turns on the STOP bit anytime the START bit is false.

This is a classic way to inadvertently send a START and a STOP bit both true to the drive, which causes the STOP bit to trump the START bit.

The way I program the drives is to assert the START bit until the drive status indicates that it has started.

Likewise I assert the STOP bit until the drive status indicates it is no longer active.

Help earn me a box of donuts: post your PLC program or a screenshot of the PowerFlex drive logic.

Also If its a pf40 I think you have to give it a momantary fwd and a rev to go rev but that may only be in the hardwired requirement ken should know?

Im going to try to answer everyones questions the best I can.

The faults I have not witnessed, its just what is stored in the paramenters. Fault 1,2,3.

PowerFlex 40
Using a 22 Comm E module
Comm Fault Action: Fault
Idle Fault action: Fault
P36:Comm Port
P38:Comm Port

It is using an internal start and stop bits. The stop bit is on until given a start command, and then its given a forward/reverse command.

Im sorry Ken but I cannot post the program or a screenshot at this time.

bce123, this particular set up sets the forward and reverse as long as the conditions are true. There are 6 other setups just like this one, except this is the only one giving us problems and was working fine till recently.

I suspect you should have your direction chosen prior to or simultaneously with the start command. If it sees the start prior to the direction it may be guarding against you making a sudden direction reversal while running.

I have mine set up like a 2 wire control. One user bit. I use the normally open of that bit for the start OTE and the normally closed in a network below for the stop OTE. So it always ever sees only one or the other. I haven't experienced the anomoly that Ken mentions by doing it this way, possibly because I change the two bits within the same scan consecutively and they both update simultaneously (because I buffer my IO). Ken's method is definitely much more foolproof.

I don't use the forward/rev bits. Looking at the documentation it seems to indicate that I should HAVE to.

The manual say:
00 no command
01 forward
10 reverse
11 toggle direction

I have been running with the two direction bits at 00 so that is ambiguous to me. Perhaps what it is saying is if you set it to 11 and then reset both to 00 that a start signal thereafter will simply send it in the last direction chosen?

Check on P207 SAVE vs. RAM. Apparently multiple writes to EPROM (such as speed changes) can ruin the Drive.

Damian, that is in a nutshell what I have. When the forward or reverse bits become true, it makes the stop go false and the start true.
We are still trying to troubleshoot this problem and there is nothing just standing out at us. As I said, it does not follow any pattern and the drive is not faulted. Although, the PLC is sending a Start and Forward/Reverse command to the drive, but the drive does nothing.

Question: Would there be any sort of "lockout" on the drive in case direction is swapped too soon/too many times?

Orn, Speed is only changed via a limit switch, then it goes to half speed. Otherwise it is set for 60Hz. When this problem occurs, it is operating at full speed.

Remember that the Output tags from the ControlLogix tag database get sent via the Ethernet port to the 22-COMM-E asynchronously to the program scan.

Consider what would happen if the Output tag values got updated in between the rung that turns on the Start bit, but before the rung that turns on the Stop bit.

You would end up sending .START = 1 and .STOP = 1 at the same time. The drive needs to see .START go from 0 to 1 while .STOP is = 0.

If .START =1 and .STOP goes from 1 to 0, that's not the same thing. Removing the Stop isn't the same as asserting the Start.

I'm not insisting that this is definitely your problem; I don't need the donuts that badly. But I've seen it often enough that I always eliminate it as a possibility.

I don't need the donuts that badly

Click to expand...

seems like a fair price to me LOL

This switch in state caused me a bit of grief the other day when I moved a 10HP VFD from hard wire control to Devicenet, I forgot to invert the result of one reference to that Stop bit in the existing spaghetti logic (which is a whole 'nuther thread).

Like Ken, it works best if you program the NOT stopped condition to send the Stop bit when your program calls for a stop condition.

This way, it drops out as soon as it is true, putting the drive in a ready state to receive the next command cleanly as well as providing the PLC with a measurable response time (How long the STOP command stays high combined with At Speed, Stopped, or other conditions) of the load.

Same thing with start, and switch directions intelligently (first) so they can't be preceded by the start commands at the drive end.