Rockwell Automation 1786-RPFRXL ControlNet Fiber Ring Modules Installation Instructions - Manual (Page 21)

ControlNet Fiber-optic Ring Repeater Modules 21
Rockwell Automation Publication 1786-IN003D-EN-P - April 2011
Determine Maximum Network Length
The quality of the fiber cable determines the maximum distance between
modules in a networked system. The delay in the system (described in the
following table) determines the maximum length you can achieve with your
network.
The worst-case delay (between any nodes) must be less than 121 μs. This table
lists worst-case delays for physical layer components.
See Figure 4 on page 22 and the example on page 23 to understand how to
determine the worst-case delay for your system.
Table 1 -Worst-case Delay
Component Delay
Coaxial cable 4.17 ns/m
Fiber 5.01 ns/m
1786-RPA/B module 901 ns
1786-RPFM module 153 ns
1786-RPFS module 94 ns
1786-RPCD module 100 ns
1786-RPFRL/B
1786-RPFRXL/B modules 100 ns
TIP When determining the worst-case delay for your system,
consider how many components you want to use. You can use as
many as twenty fiber repeater modules in a ring or series as long
as you do not exceed the maximum network length, as
determined by the worst-case delay.
The maximum cable distance (that is, the longest route between
any two adjacent or non-adjacent nodes) is limited by the
ControlNet protocol to 20 km or less. Refer to Determine
Maximum Network Length on
page 21 for more information.