Networking
5-22 AutomationSystem S7-400 Hardwareand Installation
A5E00850741-01
5.8 PROFIBUS-DP Network with Fiber-Optic Cables

Electrical/Optical Conversion

If you want to use the field bus for larger distances irrespective of the transmission
rate, or if the data trafficon the bus is not to be impaired by external interference
fields, use fiber-optic cables rather than copper cables.
There are two ways to convert electrical cables to fiber-optic cables:
•PROFIBUS nodes with a PROFIBUS-DP interface (RS 485) are connected to
the optical network via an Optical Bus Terminal(OBT) or via the Optical Link
Module (OLM).
•PROFIBUS nodes with an integrated fiber-optic cable interface (e.g. ET 200M
(IM 153-2 FO), S7-400 (IM 467 FO)) can be directly integrated in the optical
network.
How to set up optical networks with the Optical Link Module (OLM) is described in
detail in the SIMATICNET PROFIBUS Networks manual. You will find below the
most important information on setting up an optical PROFIBUS-DP network with
PROFIBUS nodes that have an integrated fiber-optic cable interface.

Benefits and Areas of Application

Fiber-optic cables have the following advantages over electrical cables:
•Electrical isolation of the PROFIBUS-DP components
•Insensitivity to electromagnetic interference (EMC)
•No electromagnetic emission into the environment
•Thus no need for additional grounding and shielding measures
•No adherence to minimum clearances from other cables necessary for EMC
•No need for equipotential bonding conductors
•No need for lightning conductors
•Maximum permissible cable lengths independent of the transmission rate
•Easy installation of the fiber-optic cable connections of the PROFIBUS-DP
components by means of standard fiber-optic cable connectors (Simplex
connectors)