12
6650-2212
Note
t
bit
= 1 / Baud rate (Baud rate in bit/s)
System delay in an optical network
Data exchange between a PROFIBUS DP master and slave via ODW-612 fibre optic link,
will be delayed due to the length of the optical fibre and the signal processing within the
ODW-612. The signal processing delay is dependent on the data rate, and the fibre delay
is dependent on the total length of the optical fibre.
There is no limitation of the total length of optical fibre for Multi-drop applications. In
Redundant ring applications the data transfer time in a ring is limited to 10 milliseconds.
This means the total length of the optical fibre ring is about 2 000 km, excluding the 1
microsecond delay at each optical repeater unit.
The additional time resulting from the optical fibre and ODW-612 is the Overall system
delay. The Redundant ring and Multidrop application Overall system delays differ, see
below.
… Redundant ring, one data exchange.
•
The data exchange between PROFIBUS DP master and slave via ODW-612 fibre
optic link will run one direction through all units of the ring. The system delay is
calculated by summing the following:
1.
Fibre:
The total optical fibre ring length delay.
2.
Optical repeaters:
The optical repeater delay x Number of optical repeat-
ers (excluding the ODW-612 units connected to PROFIBUS DP master and
addressed slave).
3.
Converter electrical to fibre:
Signal processing delay x 2
(ODW-612 units connected to PROFIBUS DP master and addressed slave).
4.
Converter fibre to electrical:
Signal processing delay x 2 (ODW-612 units
connected to PROFIBUS DP master and addressed slave).
Delay @ < 1.5 Mbit/s
Delay @ 3 to 12 Mbit/s
Optical fibre length delay (typical)
5 μs/km
5 μs/km
Signal processing, electrical to fibre (max)
1 t
bit
+ 1.0 μs
9 t
bit
+ 1.0 μs
Signal processing, fibre to electrical (max)
0.3 μs
0.3 μs
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