Rockwell Automation 1786-series ControlNet Fiber Media Planning and Installation Guide User Manual
Page 40
40
Rockwell Automation Publication CNET-IN001C-EN-P - October 2011
Chapter 2 Topology and Signal Considerations
Delay Path 5: 3000 m of 62.5 micron fiber cable
Delay 5: 3000 m fiber cable x 5.01 ns/m = 15030 ns
Delay Path 6: Fiber modules; 1786-RPFM, 1786-RPA/B, 1786-RPFS modules
Delay 6: 153 ns (1786-RPFM module) + 901ns (1786-RPA/B module)
+ 94 ns (1786-RPFS module) = 1148 ns
Delay Path 7: 100 m of 200 micron fiber cable
Delay 7: 100 m fiber cable x 5.01 ns/m = 501 ns
Delay Path 8: Fiber modules; 1786-RPFS and 1786-RPA/B modules
Delay 8: 94 ns (1786-RPFS module) + 901 ns (1786-RPA/B module)
= 995 ns
Delay Path 9: 20 m of coax cable
Delay 9: 20 m coax cable x 4.17 ns/m = 83 ns
Total delay =
27109 ns (27.1
μ
s)
This is a valid network because the calculated propagation delay of 27.1
μ
s is
less than the maximum allowable propagation delay of 121
μ
s.
Maximum Propagation Delay and Skew Through a Redundant
Network
For redundant networks, not only do you have to calculate the worst-case path
delay between two nodes, but you also must calculate the worst-case delay skew
between channel A and channel B of the network.
The following example (that uses the cable lengths in
) depicts a
redundant network with these conditions:
• Node 1 and Node 2 are separated by four fiber repeaters in series on
both A and B channels
• Channel A uses 3600 m fiber segments total versus 3300 m fiber segments
total on channel B. Channel A uses 1520 m of coax cable total versus
1770 m of coax cable total on channel B.
IMPORTANT
The worst-case skew between redundant paths shall be less than
or equal to 1.6 µs.