Westermo ODW-710-F1 - Manual (Page 20)

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Calculating system processing delay
Data exchange between a PROFIBUS DP master and slave via ODW-710-F1 fibre optic
link, will be delayed due to the length of the optical fibre and the signal processing within
the ODW-710-F1. The signal processing delay is dependent on the data rate, and the fibre
delay is dependent on the total length of the optical fibre. The additional time resulting
from the optical fibre and ODW-710-F1 is the Overall system delay.
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 tbit + 1 µs 9 tbit + 1 µs
Signal processing, fibre to electrical (max) 0.3 µs 0.3 µs
Signal processing, fibre to fibre (max) 1.3 µs 1.3 µs
Note! tbit = 1 / Baud rate (Baud rate in bit/s)
Example
One PROFIBUS DP master and slave using a data rate of 12 Mbit/s. and a total fibre length of 40 km.
A data frame sent from the master to a slave.
1. Fibre: The total optical fibre length delay.
40 x 5 µs = 200 µs
2. Converter electrical to fibre: Signal processing delay
(ODW-710-F1 connected to PROFIBUS DP master).
9 tbit + 1 µs = 9 x 0.083 µs + 1 µs ≈ 1.1 µs
3. Converter fibre to electrical: Signal processing delay
(ODW-710-F1 connected to addressed slave).
0.3 µs
4. The system delay is calculated by summing the delays in item 1 to 3 above:
200 µs + 1.1 µs + 0.3 µs = 201.4 µs