Installation guide

Testing and Maintaining an RIO Network
890 USE 101 00 October 2006 135
Problem Sources on an RIO Network
Overview Noise on the RIO network is a frequently identified problem source in the
troubleshooting process. The symptom is usually excessive retries at the RIO drop
adapters. Most noise problems are caused either by inadequate spacing of RIO
cable or components from power cables or by an inadequate earth ground. The
other common problem source is poor installation.
Solving Spacing
Problems
Spacing problems can frequently be identified in a visual check on the network.
Make sure that a spacing of 12 ... 14 in per kV of power is maintained between the
cables and components in your RIO system and any type of low to medium power
cable.
We recommend that you avoid all power cable including DC power cables. DC
power cables pick up spikes from AC power cables and then induce the spikes onto
the RIO cable. Even the low power AC cables can induce spikes onto the RIO cable
system.
Potential
Grounding
Problems
A low impedance earth ground is typically hard to measure properly; even after the
measurement is performed, it can be misleading. A properly installed Modicon RIO
system is grounded at or near (within 20 ft) the RIO processor at the head-end of the
network. The only other condition under which you should ground the network is
when the cable enters or exits a building (per NEC code).
If the system is not properly grounded, it will produce excessive retries. We
recommend that you connect a separate ground wire from the programmable
controller directly to plant ground. The wire should minimally be 14 gauge green or
bare wire; solid conductor is preferred. If the controller is grounded only to the panel,
make sure the panel wire is sufficient (typically 2 gauge) to handle the load of the
panel and that a separate wire is used to ground the panel. Do not use conduit to
ground a controller or panel.
Another prevalent grounding problem is with the equipment connected to the
controller. When large motors, drives, or spindles are not properly grounded, they
cause an excessive amount of EMI/RFI and conduct this noise onto the power
system. EMI/RFI interferences are sometimes misinterpreted as programmable
controller problems. You should consult with the manufacturer of these products to
ensure that they are properly grounded.
This document provided by Barr-Thorp Electric Co., Inc. 800-473-9123 www.barr-thorp.com