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.
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