Modified a machine in our facility during the Christmas Break.

The Old RIO network was 57.6 with the following devices:
2 - 1771 ASB for 16 slot racks
4 - PF700 VFD full rack
4 - DL40 DIsplay for full rack each
1 - PV500 for full rack
4 - Scale Modules at 1/4 rack each.

The New RIO network is 57.6 with the following devices:
2 - 1771 ASB for 16 slot racks
4 - PF700 VFD full rack
4 - DL40 DIsplay for full rack each
1 - PV500 for full rack
13 - Scale Modules at 1/4 rack each.

We have had 3 catastrophic failues of Scale Modules since the conversion. We did find that the End of Line resistor was missing today on the PLC end of the wire.
Opinions is the missing resistor to cause a failure of a comm module on this large a network or should I be suspecting teh scale module vendor for defective material.

Bob,

I gotta diagree with their reply about the resistor...I had forgot to install it several times and never, ever experienced that problem....agian weirder stuff has happened though...I would have a tendancy to think the later is suspect...

How is the system wired? is it daisy chained or trunkline/dropline? Sometimes daisy chained systems can be a problem. Check overall length of run and connections at each junction.

I am not positive about RIO, but on other communication networks (DeviceNet, ControlNet, Ethernet), I have not been sucessful with putting more than 18 nodes on a network and get reliable communications. Infact, I will usually drop nodes at random.

Two things...
-A missing resistor will not cause a physical hardware failure of a device. It will cause comm problems & losses. Remember two total resistors, one at each end. The PLC does not have to be on the end. Follow the AB guidelines for trunk & drops. I follow the DH+ guidelines. Check the value of the resistors (57.6KBaud & 115KBaud require two 150 ohm, 230KB requires two 86 ohm)
-There is a limit to the number of physical nodes allowed on RIO. The limit depends on which PLC model, but it is typical 15 adapters max, some PLCs will support 31)

Hardware failures would be a Manufactory’s issue.
End of line resistors are installed to stop signal echo, that wouldn't cause hardware failure.

Why is the network running at a low speed?
Since adding to the network you might have to run the network faster to stop congestion.
This would only help if you are experiencing communication failure not hardware failure.

I agree that the number of nodes on the RIO link would affect communication performance and reliability, but certainly should not damage the scale modules.

When you have more than 16 physical adapters on the network, you should go to 82 ohm termination resistors.

The rules on number of adapters vs. termination resistor value are in the PLC-5 User Manual, 1785-UM012, pages 6-5 and 6-6.

The network speed is slow because of two things.
1. Age of the original installation. Most is pre Y2K stuff or older.
2. Distance covered by the network. 1/2 the width of the plant and up 3 floors and down 3 floors as well.

Some of that older stuff only support 56K.

Also the max length decrease as the speed goes up