Every fiber optic installer should have familiarity with basic fiber optic testers and their proper use. Here are some basic test situations. Can you pick the right tester from the fiber optic toolbox for the job? Correct answers and explanations are in red.

1. Check the continuity of a fiber in a cable.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

For testing continuity, a simple visual tracer or fault locator can tell if a fiber can transmit light from one end to the other.

2. Check the polarity of two fibers in a link.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

Polarity means the transmitter is connected to the receiver, a simple continuity test using a visual tracer or fault locator.

3. Measure the loss of a connector on one end of a short patchcord.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

A LSPM or OLTS can measure the loss of the connectors on each end of a patchcord no matter how short it is. An OTDR can do it too but only if the patchcord is long enough for the OTDR to see both ends.

4. Measure the loss of an installed cable plant ~10 meters (~33 feet) long.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

A LSPM or OLTS is the proper tool for insertion loss testing. This link is too short for an OTDR.

5. Measure the loss of an installed cable plant ~10 kilometers (~6 miles) long.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

A LSPM or OLTS is the proper tool for insertion loss testing. This link is long enough for an OTDR to test it, but unless a reference cable is attached at the far end, the last connector will not get tested.

6. Measure the loss of a spliced joint between two cables ~5 kilometers (~3 miles) long.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

OTDRs are the only tool for checking splices in cables, but you may need to test in both directions to get a valid loss measurement if the fibers are different.

7. Use from both ends of the cable to determine real loss of a gainer.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

OTDRs show gainers at a splice or connection when the two mated fibers are different, so you may need to test in both directions to get a valid loss measurement if the fibers are different.

8. Diagnose high loss connectors.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

Inspection microscopes are used to diagnose connectors, looking for dirty ends, scratches or cracks.

9. Find stress losses in poorly installed cables.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

OTDRs can show stress losses in fibers caused by poor installation practices. The event will look like a non-reflective loss in the wrong place.

10. Find stress losses or breaks too close for other instruments to find.
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

OTDRs cannot find problems too close for their resolution, so a visual fault locator is used to find it.

Bonus question:
Which tester gets confused and shows what is either a cable with ~20-decibel loss in the middle or a ghost?
A. Visual tracer/fault locator
B. LSPM or OLTS
C. OTDR
D. Inspection microscope

OTDRs and OTDR operators can be confused by highly reflective events that reflect multiple times in the cable, looking like a second cable that isn’t there.


HAYES is a VDV writer and educator and the president of The Fiber Optic Association. Find him at www.jimhayes.com.