Installation guide

Planning and Designing RIO Cable System
52
890 USE 101 00 October 2006
Designing a Coaxial Cable System to an Attenuation Limit
Overview Attenuation happens naturally as a communication signal passes through taps,
splitters, splices, cable, connections, and feed-through terminators. Your goal as
designer is to provide successful RIO services while holding the attenuation to a
maximum of 35 dB (32 dB in the case of the 984 host-based PLCs) from the head
processor to any drop adapter on the network.
Cable
Attenuation
The most important decision the system designer must make with regard to signal
loss is the type of cable used in the system. Many designers use semirigid cable for
the trunk cable in high noise environments or when maximum distance is necessary.
But the majority of RIO networks use the more flexible RG-6 and RG-11 cables.
RG-6 can be used as a trunk cable, but its best use is as a drop cable. It can be used
as the trunk on small networks. RG-6 has more attenuation than RG-11. See RG-6
Cable, p. 68 for cable attenuation values for RG-6 at 1.544 MHz, the RIO network
transmit frequency. See RG-11 Cable, p. 69 for cable attenuation values for RG-11
at 1.544 MHz.
Tap Attenuation All drop adapters must be connected via a tap—never directly to a trunk cable. A
direct trunk connection causes a severe impedance mismatch. All RIO taps have a
tap drop loss of 14 dB and an insertion loss of 0.8 dB:
Note: If your cable design exceeds the maximum attenuation limit for your PLC,
transmission errors can occur on the network.
Trunk
Cable
0.8 dB
Trunk
Cable
MA-0185-100
Tap
Drop Cable
Trunk
Cable
Trunk
Cable
MA-0185-100
Tap
Drop Cable
14 dB
Tap Insertion Loss Tap Drop Loss
This document provided by Barr-Thorp Electric Co., Inc. 800-473-9123 www.barr-thorp.com