Rockwell Automation 1747-L40 SLC 500 Fixed Hardware Style - Manual (Page 112)

Appendix A
Setting Up the DH-485 Network
A–7
Running the communication cable through conduit provides extra
protection from physical damage and electrical interference. If you route
the cable through conduit, follow these additional recommendations:
– Use ferromagnetic conduit near critical sources of electrical
interference. You can use aluminum conduit in non–critical areas.
– Use plastic connectors to couple between aluminum and ferromagnetic
conduit. Make an electrical connection around the plastic connector
(use pipe clamps and the heavy gauge wire or wire braid) to hold both
sections at the same potential.
– Ground the entire length of conduit by attaching it to the building
earth ground.
– Do not let the conduit touch the plug on the cable.
– Arrange the cables loosely within the conduit. The conduit should
contain only serial communication cables.
– Install the conduit so that it meets all applicable codes and
environmental specifications.
For more information on planning cable routes, see Industrial Automation
Wiring and Grounding Guidelines, publication number 1770–4.1.
Software Considerations
Software considerations include the configuration of the network and the
parameters that can be set to the specific requirements of the network. The
following are major configuration factors that have a significant effect on
network performance:
•
number of nodes on the network
•
addresses of those nodes
•
baud rate
•
maximum node address selection
•
5/03 only: token hold factor
The following sections explain network considerations and describe ways to
select parameters for optimum network performance (speed).
Number of Nodes
The number of nodes on the network directly affects the data transfer time
between nodes. Unnecessary nodes (such as a second programming terminal
that is not being used) slow the data transfer rate. The maximum number of
nodes on the network is 32.