Siemens SIMATIC NET PROFIBUS User Manual

3-18

PROFIBUS Networks SIMATIC NET

6GK1970-5CA20-0AA1 Release 2 05/2000

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).

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.

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

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