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Procedure for Jointing and Testing Optical Fiber Cable

Jointing of Optical Cable

General

Jointing of the cable span should be carried out as soon as possible after placing the cable. The splicing technique chosen depends mainly on transmission requirements. Short cable distances with no special attenuation requirements can be spliced by use of mechanical splicing devices. Examples include indoor installation and/or temporary splices due to cable damage, etc.

Long distance cables require more accurate and more precise methods to be used.

Splicing can be carried out either above ground or in manholes or tunnel systems. If splicing is performed in manholes or in tents, the climatic conditions must be controlled by using ventilators or air-cooling units. The air inlet on the ventilator or cooling unit must be fitted with a filter in order to keep the air free from dust and other impurities.

By using a splicing van specially designed and furnished with equipment for splicing, many advantages will be achieved. The set up time will be reduced. The closeness of tools and equipment required will reduce the splicing time and the splicing operation will be performed in a controlled environment, which will have a positive effect on the splice quality.

The required excess length of cable can be coiled and protected inside the manhole or in the joint pit.

 

Physical and Delivery Test of Opto Cable

Drums and cables should be visually inspected to reveal any transportation damage during shipping and before the drum is further transported to the work site. All damage must be noted. Check that the drum’s identification numbers agree with the number on the delivery document.

The following optical parameters must be measured with an OTDR on the cable drum, before the cable is installed.
  • Optical length: meters
  • Attenuation per unit length at 1550nm: dB/km
  • The measurements should correspond to the value given by the cable manufacturer. Deviations of more than 0.03 dB/km must be reported to the logistics department for further evaluation.

    The actual measured length for the respective fibers must be noted and make sure that all fibers in the cable, on the same drum, are of the same length. A deviation of more than 0.5% from the stated “shipped” cable length is not acceptable. Contact the logistics manager if there are any major deviations in fiber length.

    The purpose of this testing is to check that the optical fiber cable has been handled during transportation from the factory to the store, in such a way that its quality and transmission characteristics have not been altered.

     


     

    Joint Closures

    A joint closure used for optical fiber cables must allow easy handling and easy installation. The closure must be easy to re-enter and require a minimum of additional material when re-sealing. The closure must maintain good mechanical protection of the spliced fibers and allow installation in very tough environments.

    The joint closure must be watertight and no re-entry compound should be required to achieve a moisture and pressure tight seal.

    The box must be equipped with fiber organizers, which protect the spliced fibers and allow easy installation, identification and future maintenance work.

     

    Check Before Jointing

  • Materials are in accordance with Plant Unit.
  • Correct tools, generators and instruments are available and in good condition.
  • The electrical power or generator has the correct voltage and frequency.
  • The correct jointing schemes, drawings and instructions are used.
  • The jointing place is correctly arranged, clean and free from dust.
  • The correct supporting materials are mounted, e.g. brackets, clamps, etc.
  • The surplus cable is of sufficient length.
  • Information is given to staff regarding the handling of instruments.
  • The specific values, e.g. refractive index, pre-fusion time, fusion time, etc. for the fiber are given to the jointing and measuring staff.
  • Necessary safety measures have been taken concerning traffic, gases in manholes, water in manholes, etc.
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    Check During Jointing

  • Tools and materials are kept in a proper way at the jointing place.
  • Dismantling measurements are correct.
  • Secondary protection of the fibers is unharmed after dismantling.
  • Cable bushings are tightened hard.
  • Cables are pulled back to reduce the slack on the messenger wires before crimping the shrink-on hoses.
  • The numbering of the fibers is correct.
  • The voltage is steady during splicing.
  • The arc is protected against wind during the fusion.
  • Splice losses are within specified limits.
  • Application of the splice protection does not harm the fiber.
  • Restored primary protection of the fiber is sufficiently cured.
  • The extra length of fiber is correctly placed on the storage shelf (bending radius, etc.).
  • The joint sleeve has been correctly located and secured.
  •  

    Check After Jointing

  • Cables are positioned correctly in the manhole.
  • Silica gel bags are placed in the joint box.
  • The bolts on the joint box cover are tightened with the recommended
  • The joint box is fixed to the joint box support or to the wall.
  • Unnecessary bending of cable is avoided when placing the joint box on the
  • The cable is fixed on the brackets and to the joint box support.
  • Warning labels are placed on the cable.
  • A filled-in identification label is placed on the joint box.
  • The manhole is neat and clean.
  • Jointing schemes, reports, drawings, etc. are revised after completion of the work.
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    Schematic Cable Diagram

    A record containing drum numbers, type of cable (duct aerial, buried) physical cable length on each drum, measured optical fiber length on each drum, geographical distances between exchange and splice points, from splice point to splice point and splice point to repeater station.

    Extra joints, if any, must also be recorded.

     

    Sample

    Local exchange to splice point 01:

  • Drum No. 1432
  • Physical length: 4085m
  • Type of cable: Buried, 16 Fiber (lose tube)
  • Optical length: 4105m
  • Geographical length: 4004m between exchange and splice point 01.
  •  

    Splice point 01 to splice point 02:

  • Drum No. 1219
  • Physical length: 3980m
  • Type of cable: Buried 16 Fiber (lose tube).
  • Optical length: 4000m
  • Geographical length: 3900m between splice points 01 and 02.
  •  

    Splice point 23 to repeater R1:

  • Drum No. 1254
  • Physical length: 4045m
  • Type of cable: Buried 16 Fiber (lose tube).
  • Optical length: 4065m
  • Geographical length: 3965m between splice point 23 and repeater R1.
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    TESTING OPTICAL FIBER CABLE

    Testing Optical Fiber Cable

    General

    The prime objective of the tests is to check that the fiber optic cables are being handled and installed in a way, which ensures that the quality of the cable and its transmission properties will not be altered during the course of the work. Thus, “Laser tlc Quality” standards shall always be complied with.

    The instruction is based on general principles and does not focus on any specific instruments.

    Measurement principles and routines might be changed in the future. We, therefore, recommend that you always contact the project manager in charge before you start measuring.

    The following types of measurements are described:

  • Measurements of cable on reel after delivery.
  • Measurements of cable after placement.
  • Measurements of splice
  • Measurements of end-to-end loss
  • Trouble shooting
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    Safety

  • Never view an unterminated optical fiber or unterminated connector unless the optical power source has been turned off.
  • Care should be taken to avoid directly viewing the end of the fiber during preparation and cleaving operations.
  • Before commencing work on a fiber end, check with an Optical Power Meter to confirm that the power source has been switched off.
  • Handle optical fiber carefully as broken fiber may be very sharp. Pieces of waste fiber should be disposed of in a manner, which prevents particles from blowing into people’s eyes.
  • Keep exposed fiber ends away from the eye.
  • Pieces of glass fiber, off-cuts etc. must be collected or swept up and properly disposed of in a suitable container.
  • Be careful with the fiber, it is important that the minimum bending radius be observed.
  • Never use a knife when you remove the cable sheath, you could damage the fiber and hurt yourself.
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    Measuring Instruments

    There are three types of test instruments.

  • Optical Time Domain Reflection Meter (OTDR).
  • Stabilized Light Source.
  • Optical Power Meter with Optical Sensors.

     

    Optical Time Domain Reflectometer (OTDR)

    The OTDR is used in most measurements and may therefore be called a type of universal instrument.

    OTDR is used for quality control of cables, measurements on cable drums, cable spans, splice losses as well as fault tracing.

    Fiber parameters are to be verified at the same wavelength as the one used in the systems to be connected to the cable system. Today 1310nm and 1550nm is the most common wavelength for single mode and for multimode 850nm and 1300nm.

    The test results can be printed out on a hard copy or saved as software files (diskettes), as preferred.

     

    Stabilized Light Source

    The light source is used for measurement of total attenuation over an installed cable span line.

    The light source has to be selected for the current type of fiber (SM), and wavelength.

     

    Power Meter with Optical Sensors

    Power meters and sensors are used to measure the resulting light power from the light source and the installed fibers.

    Different types of sensors are available and have to be selected in accordance with the sensibility and wavelength required.

    Accessories such as adapters for different types of connectors will also be needed. All the connectors shall be cleaned before use.

    Handheld switchable power meters may be used if a lower accuracy of the measurement performed can be accepted. They have varying wavelength ranges (850, 1300 and 1550Nm).

     


     

    Tests when FOC is delivered

    General

    The purpose of this testing is to check that, during transportation from factory, the optical fiber cable has been handled in such a way that its quality and transmission characteristics have not been altered.

     

    FOC Reel

    Reel and cables should be visually inspected to reveal any transportation damage during shipping, and before the reel is transported to the work site. Damage, if any, shall be noted in the remark column. Check that the reel’s identification number agrees with the number of the delivery specification “Record Optical Cable”. This inspection shall be done at the project store.

    Note: A reel, which has not been tested, cannot be delivered to the installation site.

     

    Delivery Testing

    The following optical parameters have to be measured with an OTDR.

  • Optical Length (m)
  • Attenuation per length unit at 1550nm (dB/km).
  • The measurements have to be made with great accuracy so that all values correspond with the values provided by the manufacturer. It is important to detect defective lengths to avoid problems during and after installation.

     

    Optical Length

    The actual measured lengths of the respective fibers have to be noted. Make sure that all fibers on the drum have the same length. A deviation of more than 0.6% from the stated “shipped” cable length is not acceptable.

    Contact the logistics manager if there are any major deviations in fiber length.

     

    Loss Measurement

    The loss values obtained by measurement are to be checked against the delivery documents and noted on the test form. Every fiber has to be measured at 1550nm and if any deviations occur which are greater than 0.03dB/km also measure the fiber at 1300nm.

    Contact the logistics manager if there are any major deviations in fiber length.

     

    Deviations

    If any value for a fiber is too high, a poorly connected instrument may cause it. Check the fiber and cut again. If you still obtain a major deviation, measure from the other cable end.

  • Deviation in cable length of more than 0.5% is not acceptable.
  • Deviations greater than 0.03dB/km are not acceptable.
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    Test Forms

    Enter the measurement values on the form entitled “Control of Fiber Optic Cable on Reel and After Placement”.

     

    Test Equipment

  • Fiber adapter.
  • Stripping tool.
  • Cleaving tool.
  • OTDR
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    Measurement after Placement

    General

    All fibers are to be tested in laid cable lengths. The tests should not be made until at least one week after placement, to allow soil, etc. to settle.

    The test is best made at the same time as splice measurements are carried out.

    An OTDR is used for the test and the measurement is made at both 1300 and 1550nm 1550nm is used to determine more easily if the cable has been subjected to stress and to ensure that the smallest permissible bend radius has not been exceeded.

     

    Placement Test

    The optical length of all fibers is measured with the index of refraction used for the “test on reel”. Deviations greater than 0.2% are not permissible between fibers. In the case of greater deviations, the continuity of the fiber has to be checked from both ends of the cable.

     

    Length Measurement

    The optical length of all fibers is measured with the index of refraction used for the “test on reel”. Deviations greater than 0.2% are not permissible between fibers. In the case of greater deviations, the continuity of the fiber has to be checked from both ends of the cable.

     

    Loss Measurement

    The values obtained during measuring after placement are compared with the values obtained during the “test on cable reel”. Deviations greater than 0.05 dB/km are not acceptable.

     

    Test Forms

    Enter the measurement values on the form entitled “Control of Fiber Optic Cable on Reel and After Placement”.

     

    Test Equipment

  • Fiber Adapter
  • Stripping Tool
  • Cleaving Tool
  • OTDR
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    Measurement of Splice Loss

    General

    All splices need to be measured to confirm their performance.

    All fibers are to be tested with an OTDR. The optical length before and after splicing has to be noted in the test report. The measurements are to be made at 1550nm.

     

    Splice loss testing

    If possible, make the measurement from the cable’s termination point (exchange). Anyhow, measurements can be performed from the end of a cable span or from a splice point without any major difficulties.

    Owing to the dead zone of the measurement instruments, it may be difficult to measure splice loss values at the point of transition splice between indoor and outdoor cable, if the indoor cable has short length. One way to overcome this problem is to measure the transition splice using a F.O.C spool of 1000 mt.

    In general, the following rules apply to splicing to keep the number of splice attempts at a reasonable level.

    If the splice loss exceeds 0.2dB, the fiber is to be broken and spliced again. If you cannot obtain an acceptable value after three splices, leave the fiber and proceed to the next one.

    If you still cannot obtain an acceptable value for a fiber, after trying with another fiber, check the splicer’s settings and clean the electrodes carefully, following the instructions in the user’s manual.

    In some cases, splice losses exceeding 0.2dB have to be accepted. If the fibers do not match, contact the person in charge of the installation.

    When the fiber loop is placed in position in the splice closure, check the splice loss again to ensure that it has not changed.

    When testing at 1550nm, the obtained values may not exceed the value at 1300nm by more than 0.05dB.

    If the value of any one fiber deviates by more than 0.05dB, the probable cause is that the fiber is being stressed, or there might be a micro-bend in the vicinity of the fiber splice. If all fibers show deviating values, the cable might be bent too much. Fix this immediately.

     

    Test Forms

    The values are to be entered in the “Splice Loss” form.

     

    Test Equipment

  • OTDR
  • Fiber Adapter
  • Stripping Tool
  • Cleaving Tool
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    End-to-End Measurement

    OTDR Test

    The installed fiber optic plant is verified by using an OTDR to measure in both directions and at 1300nm and 1550nm, unless otherwise noted in the contract.

    The final splice loss value is measured for each fiber and splice at 1300 and 1550nm. The obtained values are entered on the form “Test of installed Fiber Optic Plant, Splice Loss”.

    The total length of each fiber is to be measured and entered into the test report. The loss value for each cable length, between splices, is to be measured in dB/km and entered on the form “Test of installed Fiber Optic Plant, Loss per Length Unit”. This measurement is made in one direction only, starting from the main location.

    An overview is then produced for all fibers, printed out and attached to form “Test of Installed Fiber Optic Plant, OTDR Test”. Or saved as software file on diskettes. The loss per length unit is measured when this test is made. This value is to be used for checking splice loss. The cursors are placed as follows: Cursor 1 is placed about 500m on the length and cursor 2 just before the cable’s end. The location of the first cursor will depend on the length to be measured and the pulse width to be used. The resolution of the above-mentioned overview will not be adequate for maintenance purposes. Make an enlargement of it.

    In some cases, it might be necessary to divide the measurement length to obtain a resolution of the curve, which will be food enough to enable you to pinpoint the location of each splice. A suitable scale division is 1 km/div and 0.5-1 dB/div. If the curve has been divided up, the pictures are glued together to provide an overall picture of the length. The location of the splices and splice numbers are to be entered on the copies. The overview is to be used for future maintenance purposes. The lengths on the respective overviews should not exceed 10 km.

    The printouts are glued onto the form “Overview of OTDR Test”.

     

    Loss measurement

    Measurements of total loss are made on the installed cable length with a stabilized light source and power meter.

    The measurement is made in both directions at 1300 and 1550nm, unless otherwise noted in the contract.

    It is important that the connectors are cleaned thoroughly before the test is made, since dirt on the connector may affect the measurement results considerable.

    To avoid “wearing out” the light source’s connector, always use a double-connected measurement cord that is connected to the light source’s port and the other end of the measurement cord is equipped with an adapter. The cord is to be connected to the light source during the entire test and must not be disconnected, since the value of the connection losses may change.

    Before the test is conducted, the light source and laser module have to be turned on for at least 10 minutes so they will provide a stable luminous flow. The test has to be made with unmodulated light (cw).

    The measurement is made by placing the light source at the one end of the cable, depending on the direction in which the test is being made.

    Then a reference value is obtained. This is measured five times. The measurement cord is disconnected and connected at the adapter. The obtained values are entered on the form, “Test of Installed Fiber Optic Plant, Attenuation Measurement”.

    Select the lowest value but one from the test and use it for your reference value.

    Then move the power meter to the other end of the cable system and connect the respective fibers to the transmitter and receiver. Measure five times here as well. Note that you disconnect and connect the measurement cord in the transmission direction and at the adapter. Do not break the connection at the light source.

    The values obtained are entered on the same form as the reference value was entered on.

    When the measurement is finished, calculate the final loss for each fiber.

    The total loss for the fiver is determined by subtracting the previously obtained reference value from the measurement value.

     


     

    Trouble Shooting

    All faults can be located with an OTDR.

    Before making the test, you have to check that the transmitter and receiver are disconnected from the fiber to be measured. This has to be done, or else the measuring instruments and transmitter/receiver might be damaged.

    To locate faults, you need network maps, splicing plans and any overviews that are available.

    The tests are made mainly on the fiber that has caused the faults.

    The measurement is usually made in two steps: first the approximate location of the fault is determined and then a more careful analysis of the fault’s position is made.

    To determine the approximate location, the instrument is set up in such a way that you can see the entire length of the cable on the display. A pulse width of 2 or 4 microseconds is normally used.

    When the measurement is made, you can see either a strong reflection if the fiber is broken, or a large break in the curve, if the fiber has a sharp loss at some point.

    The test picture is enlarged so you can read it more accurately. Determine the approximate location of the fault.

    Note: If the break in the fiber is on the cable length between two splices, the jelly filling in the cable might reduce any end reflection from the place of the break.

    When pinpointing the exact location of the fault and making a final analysis, the narrowest possible pulse width is selected. The picture is enlarged as much as possible around the area where you suspect the fault is located. After averaging the waveform, the distance to the fault is determined.

    To determine the location more precisely, you can select a known point on the cable, such as a splice, and use it as a reference point. The distance up to the fault area is then measured with an instrument set according to the reference mode. The distance is then obtained from the know point up to the fault’s location.

    The measurement is made from both ends to check if the measured lengths from the A and B sides agree with the total length of the faulty cable.

    If you have to determine the length more precisely, you can establish the actual index of refraction for the fiber as follows: A fictional value for the index is selected so the fiber length agrees with the sheath length.

    The distance from the known points is determined with the network maps and splicing plans. The index of refraction on the instrument is adjusted so the length indicated on the instrument agrees with the physical sheath length. The location of the fault is then measured according to the adjusted index value.

    After inspecting and locating the fault, the cable is repaired. Follow the rules and regulations pertaining to the type of cable in question.

     


     

    Forms

    Forms to use

    Control of Fiber Optic Cable on reel and after placement.
    Used for delivery test on cable reel and control of the fiber parameters after placement.

    Splice Loss
    Used for recording the splice loss obtained.

    Test of Installed Cable Plant OTDR Test
    Used for attachment of hard copies from OTDR test.

    Overview OTDR test
    Used for enlarged hard copies from OTDR test.
    Note: Location of splices shall be marked.

    Test of Installed Fiber Optic Plant Splice Loss
    The form is used when final acceptance test is to be performed. Values from the respective wavelengths are recorded.

    Test of Installed Fiber Optic Plant Attenuation per Length Unit
    Used for recording of attenuation per length unit.

    Test of Installed Fiber Optic Cable Plant Attenuation Measurement
    Used for recording of total attenuation