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Technical Notes
S908 Bus Lengths
By Geoff Nash
Product: PLC IO Interface

This application note describes S908 Remote IO bus length limitations when using the PLC IO Interface for Modicon S908 Remote IO.

The following information is from the S908 remote IO planning documentation; refer to this for a more detailed discussion. The S908 bus length is dependent on the type of coaxial cable that is used. There are three types of cable, each has a maximum length. The length specified below includes the trunk and drop cables, drop cables may be up to 100 feet from the trunk.

Cable type
Maximum Cable Length
dB loss/1000 ft
RG-6/U
5000
7.0
RG-11/U
8000
2.0
CATV
15000
0.8

The maximum dB loss between PIO and any drop is 35 db. Taps and splitters have an effect:

Cable type
dB loss on trunk
dB loss on drop
Tap
1
14
Splitter
6
 

The RIO cable must be terminated with a 75 Ohm terminator.

Actual maximum cable length may be extended using a fiber optic repeaters.