Siemens SIMATIC NET PROFIBUS - Manual (Page 84)

Configuring Networks
3-18
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Mixing Plastic Fiber-Optic and PCF Fiber-Optic
To make the best use of the different cable lengths, the plastic fiber-optic cables
and PCF fiber-optic cables can be mixed.
For example, connection between distributed local DP slaves using plastic
fiber-optic (distances
t
50 m) and connection between DP master to the first DP
slave of the bus topology with PCF fiber-optic (distance
u
50 m).
3.2.4 Calculating the Power Budget of Glass Fiber Optical Links with
OLMs
Calculation Examples
The following work sheets show typical calculations of the power budget for
SIMATIC NET PROFIBUS glass optical fibers, one with OLM/G11, OLM/G12 at a
wavelength of 860 nm and one with OLM/G11-1300 and OLM/G12-1300 at a
wavelength of 1300 nm.
Note
Please note that the information on fiber attenuation in the data sheets and type
specifications of fiber-optic cables are based on measurements with narrow-band
laser light sources exactly adapted to the wavelengths.
The LED transmission elements used in practice produce a wider band spectrum
whose mid frequency deviates slightly from the measured wavelength.
You should therefore use the following attenuation values on all connections with
SIMATIC NET multimode glass fiber-optic cable between SIMATIC NET
PROFIBUS components:
3.5 dB/km at 860 nm
1.0 dB/km at 1310 nm
Note
The following distances between two OLMs must not be exceeded regardless of the
optical power budget:
OLM/P11, OLM/P12 400 m
OLM/G11, OLM/G12, OLM/G12-EEC 3 km
OLM/G11-1300, OLM/G12-1300 15 km