Drives

[Recoh]

I am using controlnet to run two PF70 drives, but one drive keeps dropping out.

The system goes from PLC to drive 1 to drive 2 using 2 T adapters and 4 BNC to TNC adapters.  The total run of the system is less than 100ft.

If we put a 4 ft cable instead of a 13 ft cable the system works fine, but as soon as the 13 ft cable is added the last drive flickers in and out of the network.  We also tried swapping out the 13 ft cable with another and no success.

Any ideas what I can try to keep both drives active?

[Ken_Roach]

Are these "T Adapters" actually ControlNet taps, like 1786-TPS, or are they literally BNC fittings ?    Do you have ControlNet terminating resistors are both ends of the network segment ?

Omitting the proper taps or the terminators will cause intermittent network communication failures like the ones you are describing.

ControlNet has some very specific wiring and termination requirements that are well documented in the ControlNet Media Planning and Installation Guide and in other publications like the ControlNet Modules in Logix 5000 Control Systems (CNET-UM001).

[Recoh]

We are used the 1786-TPS taps and 75 ohm terminating resitors on either end of the network, everthing on this network has been purchased from Allen Bradley fas per the instructions in the CNET-001 manual.  All the connections have been re-inspected.  This one has us both confused and frustrated.

[fordtt]

Since you mentioned the system was less than 100FT, I guess I can assume that they are more than 50?  Where are you using the 4' and 13' cables?

[Recoh]

I've attached a simplified drawing of our network, please let me know if there are any questions.

[Recoh]

Sorry forgot to answer the question, the 4 and 13 foot cable is being used between VFD 1 and VFD 2.

[Ken_Roach]

It looks to me like you have as many as 7 segments of cable, so you have as many as 14 connectors that could possibly be bad.

How exactly did you inspect the connections ?  A short between shield and conductor inside the connector won't be detectable except by a meter.

What precisely counts as "dropping off" with respect to the drives ?  Is this visibility in RSLinx, or a fault in the drive ?  

The only possibility for this to not be a cable problem is if the 20-COMM-C itself or the DPI ribbon cable to the PowerFlex is failing.

[Recoh]

I've had the technician meter and scope all the cables, so that should not be an issue.

By dropping off, when looking at RS Links during scanning it will find node 4 for a scan or two than lose it for 4-5 scan and find it again. 

I can try another 20-comm-C if you think that may be an issue we do have a couple for the second build around.

[fordtt]

Not sure why you're using BNC to TNC adapters.  You should be using BNC all the way.  What type of cable are you using to justify using TNC connectors?

[Recoh]

Unfotunetly the original designer is no longer with us, but I can tell you we are using 1786-RG6 quad shield coax for all cable and for the TNC part we are using 1786-TNCCL10 connectors.