By the Number: Testing of Fiber Optic Cable

Part 3

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.

How the instruments are to be configured for the test: Part 3

Configuring your instruments to perform the actual fiber test varies with the type of test equipment used.

For example, Optical Loss Test sets (OLTS) require that you first perform a reference zero function test which may appear as REF or ZERO on your test meter.

First select the proper reference method (A, B, C or 1 jumper, 2 jumper, 3 jumper method) as stated in EIA/TIA-568C. Next, clean all reference jumpers and the connection ports to the OLTs units. Use only approved cleaning devices and compounds for final fiber finishing. Do not use straight isopropyl or anhydrous alcohol for cleaning instrument ports or fiber end faces. An example of an approved finishing cleaning solution is FNTs part number MCC-POCO3M. This solution leaves no impurity contaminants on the tip of the fiber and is completely "air travel” safe.

Once the reference is complete, do not turn off the instruments as this will drop the reference data, more often than not. Should your instrument go into auto shut down during the test, it is always considered "best practices” to re-reference the instruments.

Some OLTs units have test save features, but never rely entirely on "push to save” features as your sole source of test sequence. The reason for this is because test shots are often saved in and "A,B,C or 1,2,3” sequence with no direct correlation to what you were testing. Always hand document 1) where you were for any given test sequence and 2) failures that required retests.

Most OLTs units have auto sense on the meter so the only important thing that you need to remember is to set the test wavelength(s) at the exact wavelength(s) that the systems transceivers will be operating at.

When it comes to the OTDR, most manufacturers have equipped their instruments with an "AUTO TEST” feature, which uses generic values of the fiber under test and does not necessarily produce an accurate test, especially in regard to distance to or between events.

In order to achieve the most accurate trace document possible, use the real time or PRO setting on the instrument and log the appropriate information about the fiber in the machine before starting. One of the most important factors that must be entered into the instrument is the Index of Refraction of the fiber to be tested. This information comes from the reel card data or can be retrieved from the manufacturers tech support by giving them the cable part number and the date the cable was manufactured (as printed on the cable jacket).

Note that many of the set up files cannot be accessed if you have chosen to perform an AUTO TEST because the instrument will use only default settings to perform the test.

Other settings that are important are: Range, Pulse Width, Wavelength and Averaging.

Range is set at the appropriate value to include the required front end launch cable and test subject, so that both appear entirely on the OTDR screen. Remember when adding the numbers together that most outside plant cable is spiral wound which means that the glass length can be significantly longer than the footage numbers that are printed on the cable jacket. How much longer is determined by the cables overall length and the number of fiber tubes within the cable jacket. The additional (glass) length is often referred to as the helix factor, and can be derived from the manufacturer’s specification on the cable in question. The longer the cable run and higher fiber count, the greater the helix factor.

Pulse Width is used to enhance hard to interpret events on the trace and can often be changed or manipulated when the laser is on. The technician should increase or decrease the Pulse Width value to clearly define the most obscure event on the screen. Pulse Width can also be varied in order to shrink or increase the dead zone distance of an event, which is quite useful when shooting very short test subjects.

Wavelength(s) are selected or chosen based on the customer’s request. Even though they may only be intending to run their system at 1310 nm for example, they may want a dual wavelength test to be performed at 1310 and 1550 nm for future upgrade reference. Most OTDRs today have a dual wavelength test function, but if you have an older unit that you still keep calibrated, a dual wavelength test means twice the test time for you and this is where setting your Averaging function to the minimum value possible.

Averaging is the number of timed pulse series that the OTDR performs in order to produce the trace line. If you ever shot your OTDR in real time, you will know that it will only take a second or two for the OTDR to produce an accurate trace on the screen. If your Averaging value is set to 10 or 15 seconds, this is how long you will wait to get a single test done. I recommend that you stay away from AUTO TEST and high Averaging values if you want to make money in the testing business.

Pull out your machine and try a few of the tips given above. I would like to hear from you if you don’t believe that I have passed on some money making tips to you here.

FNT Instructors Recommend

Select the proper reference method. Then clean all reference jumpers and connection ports. Once the reference is complete, do not turn off the instrument. For the most accurate trace setting, use the real time or "PRO" setting and log the appropriate cable information in the machine before starting.

Be sure to enter the Index of Refraction received from the reel card or manufacturer.

Note that many of the setup files cannot be accessed if you have chosen to perform an AUTO TEST.

Other settings to pay close attention to include Range, Pulse Width, Wavelength and Averaging.

Part 4 will cover identification of test reference method(s) and reference jumpers or launch cords needed to perform the referencing step.

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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