Measurement of fiber optic cable loss is an established practice that has been performed for many years. However, over time, the performance of fiber optic equipment has been improved, so occasionally it is useful to perform a practical re-assessment of the accuracy of these measurements.
Multi-mode patch cord optical loss power measurement is performed using the steps described in ANSI/TIA-526-14, method A. The fiber optic patch cord is substituted for the cable plant. Because patch cords are typically no longer than 5 m, the loss for the optical fiber is negligible and testing can be performed at 850 nm or 1300 nm. The loss measured in this test is the loss for the patch cords connector pair. ANSI/TIA-568-C.3 states that the maximum loss for a connector pair is 0.75 dB.
After setting up the test equipment as described in ANSI/TIA-526-14, method A, clean and inspect the connectors at the ends of the patch cords to be tested. Verity that your test jumpers have the same optical fiber type and connectors as the patch cords you are going to test. The transmit jumper should have a mandrel wrap or modal conditioner depending on the revision ANSI/TIA-526-14 being used for testing. Ensure that there are no sharp bends in the test jumpers or patch cord during testing.
Because both patch cord connectors are easily accessible, optical power loss should be measured in both directions. The loss for the patch cord is the average of the two measurements. If the loww for the patch cord exceeds 0.75dB in either direction, the patch cord needs to be repaired or replaced.
For testing the loss of a patchcord, you only need an 850 nm LED light source for multimode cable or 1310 laser for singlemode, a fiber optic power meter and some reference patchcords. Just remember that the patchcords used for references in testing must be good for tests to be valid, so you test them as you would other patchcords, just more often.
Testing patch cords is similar to testing any fiber optic cable. Use one reference patch cord to set a 0 dB reference. Connect a patch cord to test to the reference patch cord with a mating adapter. Connect the power meter to the other end of the patch cord and measure the loss. Since the length of the fiber is short, the loss contribution of the fiber is ignoble. And since one end of the cable is attached to the power meter, not another cable, you only measure the loss of the one connection between the reference cable and the cable under test, so you can test each connector individually.
To complete the testing of the patch cord, reverse the cable you are testing to check the connector on the other end. Sometimes you will find one bad connector and can replace it to make the patch cord useful again. But often the cost of replacing the connector may be higher than replacing the patch cord itself.
If your test equipment has different connectors than the patchcords you are testing, you will need hybrid reference cables with connectors compatible with the equipment on one end and the patchcord connectors on the other end. You will also need the correct connector adapters for your power meter.
Obviously, all reference cables used for testing must have high quality connectors to get reliable test results. Use this same method to test your reference cables against each other and discard any with high losses, usually those with losses over 0.5 dB.
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