Siemens SIMATIC NET PROFIBUS - Manual (Page 250)

Testing PROFIBUS
A-10
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
How an OTDR Functions
An OTDR can be compared to a radar unit The OTDR sends laser light pulses on
the FO cable to be tested (the end of the cable is open). These light pulses are
reflected more or less strongly by all problem points along the cable. A meter
evaluates the intensity and propagation time of the reflected pulses.
Transmitter
(Laser light)
Analysis
and
display
Measuring
receiver
1. Send light pulses
2. Evaluate reflections for
– intensity
– propagation time
Test FO
cable
Figure A-4 How an OTDR Functions