If the loss measurement FAILs:
- There could be one or more dirty, damaged, misaligned, or unseated connections in the cabling. Check all connections and clean all fiber end faces; then retest.
- There could be a kink or sharp bend/break in a patch cord or the fiber under test. A visual fault locator could help to reveal these faults. An OTDR, such as the Fluke Networks OF-500 OptiFiber Certifying OTDR, can help you locate faults not revealed with a visual fault locator.
- The number of adapters or splices on the Setup menu was too low (for standards that use a calculated loss value).
- For multimode fiber, the wrong mandrel size was used for testing. Smaller mandrels create tighter bends in the fiber, resulting in more loss.
- A patch cord or fiber segment had the wrong core size.
- The cabling had a bad fusion or mechanical splice or a sharp bend.
If your loss reading is negative:
- The fiber ends may have been dirty during referencing.
- The connections to the tester may have been disturbed after referencing.
- There may have been a kink in a reference patch cord during referencing.
- The testers may have been colder during referencing than during testing.
A known length of cable measures too long or too short:
- The wrong fiber type may have been selected on the Setup menu.
- The index of refraction might need adjustment. Change n on the Setup menu.
Power meter measurement is too low:
- Fiber end face was dirty or damaged.
- Wavelength selected on tester may not match source wavelength.
- Source may have been set to modulated output.
- Patch cord or adapter is the wrong type (SM or MM) or patch cord has the wrong core size.
- Cabling was cracked or broken.
Power meter measurement is too high
- Tester is connected to an active CATV fiber.
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