Siemens SIMATIC NET PROFIBUS - Manual (Page 22)

PROFIBUS NETWORKS
1-12
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
1.2.5 Transmission Techniques for Optical Components
PROFIBUS User Organization Guideline
The optical transmission technique complies with the PROFIBUS User
Organization guideline:
“Fiber Optic Data Transfer for PROFIBUS” /3/.
Integrated Optical Interfaces, OBT, OLM
The optical version of SIMATIC NET PROFIBUS is implemented with integrated,
optical ports, optical bus terminals (OBT) and optical link modules (OLM).
Duplex fiber-optic cables are used as the medium made of glass, PCF or plastic
fibers. Duplex fiber-optic cables consist of two conducting fibers surrounded by a
common jacket to form a cable.
Modules with integrated optical ports and optical bus terminals (OBTs) can be
interconnected to form optical networks only with a bus structure.
Using OLMs, optical networks can be installed using a bus, star and ring structure.
The ring structure provides a redundant signal transmission path and represents
the basis for networks with high availability.
Advantages:
S
Regardless of the transmission rate, large distances can be covered between
two DTEs
(connections between OLM and OLM up to 15,000 m)
S
Electrical isolation between nodes and transmission medium
S
When plant components at different ground potential are connected, there are
no shield currents
S No electromagnetic interference
S No additional lightning protection elements are required
S Simple laying of fiber-optic cables
S
High availability of the LAN due to the use of a ring topology
S Extremely simple attachment technique using plastic fiber-optic cables over
shorter distances.