Siemens SIMATIC NET PROFIBUS manual Figure A-4 How an Otdr Functions

Testing PROFIBUS

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	Measuring
and
	receiver
display

Test FO cable

1.Send light pulses

2.Evaluate reflections for

–intensity

–propagation time

Figure A-4 How an OTDR Functions

A-10	PROFIBUS Networks SIMATIC NET
	6GK1970-5CA20-0AA1 Release 2 05/2000