Siemens SIMATIC NET PROFIBUS - Manual (Page 198)

Passive Components for Electrical Networks
7-2
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
7.1 Fiber-Optic Cables
Fiber-Optic Cable (FO)
On fiber-optic cables (FO) data is transmitted by modulating electromagnetic
waves in the range of visible and invisible light. The materials used are high-quality
plastic and glass fibers.
This chapter describes only the fiber-optic cables from the SIMATIC NET range
intended for PROFIBUS. The various types of fiber-optic cable allow components
to be connected together in a way suitable for the operating and environmental
conditions.
Compared with electrical cables, fiber-optic cables have the following advantages:
Advantages
S
Electrical isolation of nodes and segments
S
No potential equalization currents
S
Transmission path immune to external noise
S
No lightning protection required
S
No noise emission along the transmission path
S
Light weight
S
Depending on the fiber type, cables several kilometers long can be used even
at higher transmission rates.
S The transmission rate does not affect the maximum permitted cable length
Point-to-Point Link
For technological reasons, only point-to-point connections are possible with
fiber-optic cables; in other words, one transmitter is connected to one receiver. For
duplex transmission between two nodes, two fibers are therefore necessary (one
for each transmission direction).
With the optical components for PROFIBUS, bus, star and ring structures can be
implemented.