Rockwell-automation 1786-RPFRXL ControlNet Fiber Ring Modules Installa User Manual download pdf (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.

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Rockwell-automation 1786-RPFRXL ControlNet Fiber Ring Modules Installa User Manual Page 21