Hardware reference guide

Modbus Plus NOM
35013379 11/2011 289
Calculating Number of Modules in a Fiber Network
Calculate the number of NOM25200 modules in a fiber network using the following
method:
Step Action
1 The total allowable pulse width distortions and jitter are limited to 20% of the bit
period and is 200 nsec for the full fiber optic network.
2 The jitter contributed by the NOM252 is 5 nsec max.
3 Jitter contributed by fiber optic repeaters (if used) is 40 nsec.
4 The formula to determine the number (N) of chained repeaters is:
where "L" is the total cable length (km), and "X" is the jitter (added by the fiber
optic cable) in nsec/km:
X = 3 ns/km for 50/125 μm
5 ns/km for 62.5/125 μm
7.5 ns/km for 100/140 μm