Siemens SIMATIC NET PROFIBUS - Manual (Page 448)

Network Topology
4-2
PROFIBUS Optical Bus Terminal (OBT)
C79000-G8976-C122-02
4.2 Using Long Fiber Optic Sections
The maximum permitted length of PCF FO cables with the OBT is 300 m. If longer
distances are required with fiber-optic cables, then other fiber-optic types such as
graded glass fibers or monomode fibers are necessary and these can be used in a
combination of OBT with OLM (Optical Link Module). The OBT is then connected
electrically to the OLM (for example OBT/CH 1 to OLM/CH 1) and the OLM is
attached to the long fiber-optic section. At the other end of the fiber-optic section,
the arrangement is reversed by another OLM/OBT pair.
PC
PG
OP
SIMATIC S7-400
with IM 467 FO
ET 200M with
FO interface
1) PROFIBUS cable (terminated at both ends)
2) Plastic FO cable or PCF FO cable with two fibers
3) FO cable for long distances
À
Terminating resistor activted
2)
3)
1)
2) 2)
1)
OBT
OBT
OLM/G11 OLM/G11
OBT
1)
А
А
А
А
А
А
Figure 4-1 Example of Including Long Fiber-optic Segments with OBT and OLM
The maximum permitted transmission rate and the type and maximum length of
the fiber-optic segment are determined by the OLM type.