By the Number: Testing of Fiber Optic Cable

Part 2

By: Jeff Dominique, Chief Instructor

FNT Consulting & Training


Fiber Optic Test Plan Outline to be discussed:

  • Part 1: The subject(s) to be tested.
  • Part 2: The instruments involved in performing the test.
  • Part 3: How the instruments are to be configured for the test.
  • Part 4: Identification of test reference method(s) and reference jumpers or launch cords needed to perform the referencing step.
  • Part 5: Validation and gathering proof of instrument(s) calibration.
  • Part 6: Identification and documentation of "to end(s)” and "from end(s)”.
  • Part 7: Identification of wavelength(s) used to perform the test.
  • Part 8: Identification of job specification test requirement i.e. single direction test or bi-directional test.
  • Part 9: Gathering of information regarding test location, client information.

The instruments involved in performing the test: Part 2

Now that you have established a clear test plan (see previous issue), it is important to verify your test instruments are within the required manufacturer’s calibration dates. If there is no calibration sticker on the equipment, check your office files for current calibration documents. Some customers require that copies of these documents are in the possession of the user at the time of test in order to support Quality Control inspections.

Using the appropriate Standards document such as ANSI EIA/TIA 526-7 or ANSI EIA/TIA 526-14, choose the appropriate reference cables for the type of test to be performed. If this is an Optical Loss Test Set configuration, there are three reference Methods to choose from. Any of the three methods are approved for use, but are often selected for how they best satisfy the application such as Channel testing, Permanent Link testing or Proprietary Connection testing.

Channel testing means that you are intending to test both the entire circuit end to end, through the interfacing patch cables. Permanent Link testing means that you will be excluding the patch cables and testing only that portion of the circuit that is permanent. Proprietary connection testing means that either the two end connections are not common connectors or that each end connection is different from the opposite end.

No matter which reference configuration is used there is always some confusion about what you are allowed to include or exclude from the reference number. Adding in a coupler after the reference has been taken, extracting a couple after the reference has been taken and even excluding an entire patch cable after the reference has been taken, as is the case with Proprietary connection testing, are all negligible offsets from the true number.

The nice thing about the three methods is that they enable you to create many configurations for plug end, socket end or specialized connector end.

Test Reference Method A (the 2 cord method) allows you to either throw out the referenced center couple resulting in two separate plugs to insert into the Permanent Link network couplers or to add a second coupler which results in two sockets, enabling channel testing through the connected patch cables.

I perceive this as the most useful and common of all reference methods, because of its versatility and convenience for bi-directional testing.

Test Reference Method B is a one jumper method. This method can be used when the "user end” patch cable is being eliminated from the test requirement however, the convenience factor drops off drastically when bi-directional testing is specified.

If using the Reference Method B, once the reference is set, do not unplug the reference jumper from the transmitter end, only from the meter end. This is because of the variables that will occur due to numerical aperture (or) coupling alignment of the transmitter to the connected reference cord.

Test Method C is a 3 jumper method which comes in quite handy when testing proprietary connectors such as MTRJ, MU or E2000. It is also a handy method to use when each end connector is dissimilar to the other. In the case of the 3 jumper reference method, the center cord can be removed after referencing allowing direct connection to the varying connector styles.

When performing Optical Loss Testing, I recommend avoiding loop back testing. Even though the original thought may be that you are cutting your testing time in half, this only is true if you have no failures. That is, on loop back testing, the total loss of both circuits under test, cannot exceed the sum of the both links combined. If it does, you now have two failed circuits instead of one. Also, if you do experience circuit failures, it becomes more difficult and time consuming to determine exactly where the failure has occurred.

Finally, in accordance with Standards, always test, clean frequently and have documented expectations of what losses are to be excluded or added in from a reference standpoint, so that acceptance criteria can be adjusted accordingly.

In the case of OTDR testing, job site specifications often call for bi-directional tests. Choose your launch cable according to the length of the link under test. Shorter test subjects in the range of 100 meters to 1000 meters typically use 150 meter launch cables. On the trace view, this will ensure that the end of the launch cable can be clearly seen. On longer link subjects, extend the length of the launch cable accordingly, noting that a 5 kilometer link subject will use a shorter launch cable than a 50 kilometer link subject. A good rule of thumb is, after adding in your desire length launch cable and setting your range to include the launch plus the link subject, if you cannot clearly see the end of the launch cable and the end of the link subject, launch length adjustments will be necessary.

FNT Instructors Recommend

It is very important to verify your test instruments are within the required manufacturer's calibration dates.

Using the appropriate Standards document such as ANSI EIA/TIA 526-7 or ANSI EIA/TIA 526-14, choose the appropriate reference cables for the type of test to be performed. If it is an Optical loss test set configuration, reference the three methods to choose from:

Channel testing, Permanent Link testing or Proprietary Connection testing. Any of these three methods are approved for use.

In accordance with Standards, always test, clean frequently and have documented expectations of what losses are to be excluded or added in from a reference standpoint

Part 3 will cover how the instruments are to be configured for the test.

Sources: FNT Fiber Network Training and Consulting Services, Certified Test Technician Course June 2013, ANSI EIA/TIA 568 C, ANSI EIA/TIA 526-7, ANSI EIA/TIA 526-14, ANSI EIA/TIA 606A, ANSI EIA/TIA TSB140 IEEE 1682-2011, IEEE 1428-2004

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