Technical data

Network configuration
3.2 Configuring optical networks
PROFIBUS Network Manual
52 System Manual, Edition 04/2009, C79000-G8976-C124-03
System reserve
When calculating the power budget, a link power margin of at least 3 dB (at a wavelength of
860 nm) or at least 2 dB (at a wavelength of 1300 nm) must be maintained.
If the calculated link power margin is lower, the transmission path will not be reliable long-
term in its currently planned form. This means that the transmission path may well function
when it is first started up since components are normally better than their rated performance
(particularly when brand new) but due to aging, replacement of components as a result of
repairs and changing environmental conditions, the bit error rate will tend to rise to an
unreliable level the longer the equipment is in use.
Note
To avoid possible errors during the installation of the transmission link, when installing glass
fibers, the installed sections must be tested prior to commissioning and the measured values
logged (see Section A2 "Testing fiber-optic cable").
Form
Section "Calculating the signal loss on glass fiber-optic links with OLMs (Page 54)" of this
manual contains a work sheet for calculating the power budget of glass fiberoptical links.
3.2.4 Cable lengths for plastic and PCF FO links
Cable lengths
The transmission distance over fiberoptic cables is not dependent on the transmission
speed.
Each node on the optical PROFIBUS network has repeater functionality so that the following
distance information relates to the distance between two adjacent, interconnected
PROFIBUS nodes.
The maximum cable length between two PROFIBUS nodes depends on the type of fiberoptic
cable used and the optical network components.
Table 3- 8 Permitted cable lengths with integrated optical interfaces or OBT
Fiber-optic cables
SIMATIC NET
PROFIBUS
Maximum cable
lengths between two nodes
(in m)
Projected for 1 network
(= 32 nodes) (in m)
Plastic fiberoptic,
duplex cord
50 1550
Plastic fiberoptic,
standard cable
50 1550
PCF fiberoptic,
standard cable
300 9300