RS-485 connection problem with FP-1001

[rhardy]

At irregular and unpredicable intervals, the FP-1001 fails to communicate over the RS-485 cable. The failure always repairs itself (it can take minutes to hours, and is unpredictable). The problem can also be immediately fixed by wiggling the FP-1001 on the DIN connector. The RS-485 cable has been checked out and is fine.

Has anyone else experienced this kind of problem, and if so, is there a fix available?

Thank you!

[Greg Caesar]

You mention that the cable has been checked and is fine, but I've been burned by that statement many times before. I've learned to never underestimate the mischief that subtle cabling problems can cause. I would definately triple-check that the cable is properly terminated, that the length and type is within specs, and that the 485-bus has the correct topology. An excellent resource for rs-485 guidelines is B&B Electronics. They have a section of an app note on rs-485 cable selection that is worth reading. The link is below.

http://www.bb-elec.com/technical_library.asp

Regards,
Greg Caesar
National Instruments,
Applications Engineer