PF700 to PLC-5 DeviceNet Question

Greetings all,

Troubleshooting here. I have 9 legacy AB drives (1336+) daisy-chained on device net controlled with PLC-5. One drive failed, and is replaced with a PF700. Still daisy-chained, but the new drive is relocated 80' away and connected into the daisy chain with a 5 conductor shielded cable landing on new terminals where the old legacy drive once was....thus "preserving the DeviceNet chain". It doesnt want to communicate, could there be an impedence issue with the extra wire? This is node 2 of the 9.

Wondering if it could be a baudrate issue, or something else...

All thoughts appreciated.

It sounds like you've created a "drop cable" between the location of the old drive (drop length off the trunk = 0) and the location of the new drive (drop length off the trunk = 80 ft).

Drop cables on DeviceNet networks are limited to 20 feet. You can stretch it to 25, maybe sometimes 30, but definitely not 80 feet.

If the cable isn't DeviceNet cable with a 120 ohm characteristic impedance, then you have two strikes against that network.

You could break the trunk cable then run "down and back", you would be extended the trunk by 160 feet (probably allowed) instead of creating an 80 foot drop (definitely not allowed).

Thanks! You have confirmed my suspicion, and then some....so now I can go about fixing it properly. very much appreciated!!

RefGino,

I can't stress enought that you should use real DeviceNet cable for the media and not some other "twisted-pair" cable. I have been on job sites where customers have used Blue-Hose cable as DeviceNet media and things did not go so well (Act II microwave popcorn install).

Weight the costs of running that DeviceNet cable down and back to eliminate the Drop distance. TURCK does offer a DeviceNet Repeater that costs about $380 and could be used in place of that added cable. Just an idea that I throw out there.

Thanks,
Joe_WaZoo

If your remaining drives are all connected in less than 30 feet, you could simply move your terminating resistor to the end of the 80 foot trunk, and make that you main trunk line and the other drives on the drop leg.

However using the designated devicenet cable is a must. I have found some really interference issues on devicenet even with the proper cable. I can't imagine how it would be with standard shielded cable, especially for 80 feet.