Simoreg DC drive 6RA70

Hi All, I have the analog output (0-10vdc) of a Siemens 6RA70 DC drive connected to the analog input on an ABB ACS550 ac drive for speed reference. This worked fine for several days . Now the output has changed polarity and is steady at 14vdc weather the drive is running or in stand-by. No fault indications.
The connection between the drives is 18awg sheilded cable with the screen connected at the ABB drive side. Cable lenght about 50ft.
I have this same set-up on another production line and have had no problems.
Siemens suggested maybe using some type of isolation but they did not elaborate on how to do this...they told me to use google!
Any suggestions would be greatly appreciated. I have a new drive ordered and don't want to have the same problem.
Sorry not a plc questions but you guys have so much field experience I thought I would run this by you.
Thanks again
Dean

Have you disconneted the cable and confirmed the voltage Is OK at each end when not connected? If it is then you may have a reference common issue. An isolator would help with that.


If you do need an isolator, Action Instruments, Phoenix and ABB are just e few choices.

Keith

I disconnected the cables -- no change
Thanks for the tipp on where to get the isolator
dean

So it sounds like the analog output on the Siemens drive is blown or otherwise upset.

If it is blown due to ground plane differences then an isolator would help. If it is blown due to other reasons an isolator may not help. If it is not blown at all then an isolator won't help at all.

You might want to dig into this a little closer. I don't know anything about Siemens drives. With any luck there is a parameter you can look at that shows you what the D/A command is for that output. You may want to start there.

Keith

Sounds like the Siemens drive output has gone bad. The ABB analog input is optically isolated so I doubt that reference conflicts have anything to do with it, particularly when another pair is working fine.