Siemens SIMATIC NET PROFIBUS Owner's Manual page 251

OTDR Evaluation
The OTDR provides the measurement results graphically
Backscatter
Power ]dB[
Figure A-5
Figure A-5 clearly illustrates that the power of the launched light reduces
constantly along the fiber-optic link. There are significant jumps at the coupling
points of the fiber.
The following conclusions can be drawn from these results:
S Whether the coupling points should be replaced due to excessive attenuation
S Whether the fiber has been damaged when installing the cable
S The distance between the impairments and the start of the fiber
Based on this information,
S defects resulting from installation can be eliminated,
S fiber-optic links can be documented in detail and, if problems are occurring, can
be compared with the link at the time it was installed (warranty or not).
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
Start of fiber
Coupling
Distance
Representation of the OTDR Measurement Results
Testing PROFIBUS
Fusion splice
Bonding splice
End of fiber
A-11