Memory of vfd erases

Hmm, let's see.

First off, I'd say that you should contact your supplier and ask for help. Or you could contact Siemens to ask for advice. For the meantime, this is what I can offer.

Are you saying that when you connect 0V to any digital input, the unit's memory is erased and reverts to default settings? Or is it just one particular input?

I'm not familiar with the Siemens MM440 so I don't know if you can configure a digital input to erase the program memory. 'Seems like a foolish thing to have .

Where is the source of your 0V? Is this referenced to the VFD COM? If not, you're supposed to use the VFD's own control supply (not the AC supply, the controls) for your signals. They usually have their own +24V and 0V or COM terminals for this.

If you're using a 0V signal from somewhere else, this could cause the problem you're experiencing.

Your other concern about the reversing seems unusual for a VFD. If the drive is running in forward mode, it's not supposed to immediately change to reverse mode. If I am wrong in interpreting your statement, please say so. Explain a little further.

We use many siemens vfd's in our plant and have never had this problem with ours. I would suggest that you replace the programmer unit if possible. You should contact the siemens hot line with your problem and explain the problems to them. They may have experience with that problem.

Mike Love