Rockwell Automation 1395 Multi-Comm Hardware/Software - Manual (Page 86)

Chapter 4
Installation
4–11
Twinaxial Cable Guidelines
Twinaxial cable used for Remote I/O (RIO) and Data Highway + (DH+)
communications represents a communications transmission line in which
certain characteristics exist. The following are some general guidelines
which apply to this particular transmission line and should be adhered to in
order to obtain the best possible results.
Note that these are general rules and certain deviations may be warrented
since diverse installation and environmenal concerns could change the
requirements.
Cable Type – Only 1770–CD Belden #9463 is approved for RIO and
DH+ installations. All other cable types or manufacturers, no matter how
similar, are untested. Usage of other cable types is strictly at the installer’s
risk.
Cable Length – A minimum of 10 feet of cable should be used for all
connections. Shorter lengths may cause signal reflections and have been
known to cause signal retry problems.
Connections – All three conductors, blue, clear, and shield, should be
connected at each wiring point. No additional ground connections should
be made to the shield.
IMPORTANT: DO NOT use star type connections. Only two cables may
be connected at any wiring point on a series connection application.
Terminators – Two 1770–XT or 150 ohm (82 ohm for 230 Kbaud)
resistors should be placed (or switched in), one at each end or farthest point
of the cable.