Rockwell Automation 1747-L40 SLC 500 Fixed Hardware Style - Manual (Page 111)

Appendix A
Setting Up the DH-485 Network
A–6
Carefully plan your network configuration before installing any hardware.
Listed below are some of the factors that can affect system performance:
•
amount of electrical noise, temperature, and humidity in the network
environment
•
number of devices on the network
•
connection and grounding quality in installation
•
amount of communication traffic on the network
•
type of process being controlled
•
network configuration
The major hardware and software issues you need to resolve before installing
a network are discussed in the following sections.
Hardware Considerations
You need to decide the length of the communication cable, where you route
it, and how to protect it from the environment where it will be installed.
When the communication cable is installed, you need to know how many
devices are to be connected during installation and how many devices will be
added in the future. The following sections will help you understand and
plan the network.
Number of Devices and Length of Communication Cable
You must install a link coupler (1747–AIC) for each node on the network. If
you plan to add nodes later, provide additional link couplers during the initial
installation to avoid recabling after the network is in operation.
The maximum length of the communication cable is 1219 m (4000 ft). This
is the total cable distance from the first node to the last node on the network.
Planning Cable Routes
Follow these guidelines to help protect the communication cable from
electrical interference:
•
Keep the communication cable at least five feet from any electric motors,
transformers, rectifiers, generators, arc welders, induction furnaces, or
sources of microwave radiation.
•
If you must run the cable across power feed lines, run the cable at right
angles to the lines.
•
If you do not run the cable through a contiguous metallic wireway or
conduit, keep the communication cable at least 0.15 m (6 in) from ac
power lines of less than 20 A, 0.30 m (1 ft) from lines greater than 20 A,
but only up to 100 kVA, and 0.60 m (2 ft) from lines of 100 kVA or more.
•
If you run the cable through a contiguous metallic wireway or conduit,
keep the communication cable at least 0.08 m (3 in) from ac power lines
of less than 20 A, 0.15 m (6 in) from lines greater than 20 A, but only up
to 100 kVA, and 0.30 m (1 ft) from lines of 100 kVA or more.
Important Planning
Considerations