Let’s assume you are trained on the operation of the instrument you are using and have some basic understanding of OTDR traces. Connect the OTDR to the cable or cable plant you want to test with a reference launch cable at least 100 meters long for multimode cable and 1 km long for single-mode. The connectors on the launch cable should be tested occasionally to ensure they are in good condition, just like reference cables for insertion-loss testing with a light source and power meter.
The first OTDR parameter to set is the range, which is the distance over which the OTDR will measure. The range should be at least twice the length of the cable you are testing, usually 2 km for premises cabling. Longer ranges will make the resolution of the trace poorer, and shorter ranges may create distortions in the trace. OTDR manufacturer also provides fusion splicer.
Then set the OTDR test pulse width to the shortest pulse width available, which will provide the highest resolution, giving the best “picture” of the fiber being tested. This is usually listed in nanoseconds (ns), with typical choices of 10 to 30 ns.
Next choose the wavelength. Normally, you start with 850 nm on multimode fiber and 1,310 nm on single-mode; the shorter wavelength has more backscatter, so the trace will be less noisy. After initial tests, you can make measurements at the longer wavelengths (1,300 nm on multimode and 1,550 nm on single-mode) and compare traces at the two wavelengths.
The final parameter is the number of averages for each trace. To improve the signal-to-noise ratio of the trace, the OTDR can average multiple measurements, but more averaging takes more time. Usually, 16 to 64 averages are adequate.