Installation guide

Planning and Designing RIO Cable System
890 USE 101 00 October 2006 51
Terminating a Coaxial Cable System
Overview Ideally, all connections on the RIO network are terminated in 75 Ω at all times.
Depending on the criticality of your application, you may choose to disconnect a
drop cable from a drop adapter for short-term maintenance. The trunk cable and any
unused tap ports must remain terminated at all times.
Terminating the
Trunk Cable
To prevent the build-up of a standing wave that can destroy communications
integrity on the network, the trunk cable must be terminated at all times with a
Modicon 52-0422-000 Trunk Terminator (see Network Terminators, p. 83). The
trunk terminator is inserted in the trunk-out port of the last tap on the trunk cable. Do
not terminate a trunk cable by connecting it directly to the drop adapter.
Terminating
Unused Tap
Ports
Unused taps may be installed along the trunk for future system expansion. These
taps will not have drop cables connected to them, and they must be terminated at
all times with Modicon 52-0402-000 Tap Port Terminators (see Network
Terminators, p. 83).
Terminating the
Drops
Open connections on a drop cable can subject the network to impedance
mismatches and retries. Your application may be able to tolerate these errors for
short-term maintenance—e.g., swapping a device in the drop—but if you intend to
leave the drop cable disconnected from the drop adapter for a long time or if you are
running a critical application elsewhere on the network, you should put a 75 Ω
terminator on the drop cable. You can install a female F connector on the drop cable
at the time you disconnect it, then install a Modicon 52-0402-000 Tap Port
Terminator. The drop will always remain terminated as long as the cable is
connected to the RIO drop adapter, even when the device is turned OFF or removed
from the I/O rack (exception: the adapter devices and Motion modules in RIO
Network Cable System, p. 16).
Optionally, you may design a mechanical terminator into all the drop cables—such
as a Modicon 52-0411-000 Self-terminating F Adapter; this adds up-front cost to
your system design but assures you of a completely balanced system at all times.
This document provided by Barr-Thorp Electric Co., Inc. 800-473-9123 www.barr-thorp.com