Rockwell Automation 1756-DH485 ControlLogix DH-485 Communication Module User Manual - Manual (Page 28)

Publication 1756-UM532A-EN-P - May 2006
2-10 Overview of the DH-485 Network
Important Planning
Considerations 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 will
route it, and how to protect it from the environment where it will be installed.
Before you install the communication cable, 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 communications adapter (1747-AIC or
1761-NET-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.