Wednesday, August 4, 2010

Cable construction should focus on good single-disc test

Single-disc test fiber cable line construction is a very important aspect. It is mainly after the use of optical time domain reflectometer (OTDR), optical disc on a single length of optical fiber attenuation coefficient and scattering curves were measured after inspection, to determine whether the cable's key performance indicators to project design and procurement requirements, and provide the basis for the cable distribution site.

Single-disc test fiber cable quality is also defined responsibilities and an important part of project construction. Cable in the production, storage and long-distance transportation, the fiber may be damaged. According to "Military fiber optic cable construction and acceptance of digital transmission systems engineering technical specifications" requirement, in the optical disk shipped to the construction site, you must on each fiber of each cable tray test (detection rate 100%), consistent with technical indicators before they can be with plate and laying. However, some construction units do not pay attention to this link, that manufacturers have already provided relevant information, the test is carried out sampling (detection rate of 50% or less), or just check for a fiber length, other indicators be neglected in more even are, simply do not do a single disk test, this is very wrong. Once the cable laying fiber optic cable was found after completion of performance failure, it is difficult to distinguish between fiber quality or construction quality.

Based on years of construction experience, we believe that the construction should be strictly in accordance with the procedure, do a good job single-disk test, to ensure quality. The main procedures are as follows:

The first step: check the information: to reach test at the scene, should first check the cable factory quality certificate, and check the factory single-disc test data provided are complete, its content, including cable type, core number, length, end other, structural sections map and sequence of fiber-fiber, attenuation coefficient, refractive index and so on, to see whether the order contract required.

Step Two: Appearance check: mainly the optical disc packaging for damage during transport, and then check the cable opening with or without skin damage, cable skin print writing is clear, wear resistant, cable terminations packaging is intact. The existing problems, should make a detailed record, in the optical index test, key test should be done.

Third step: check the other side: from the outside to open stripped cable ends about 30cm, according to optical beam (or optical fiber ribbon) cable outside the chromatographic reason and do not judge, and contrast with the information provided by the factory to see if there are errors . Then in the cable tray cable side marked A, B-side to facilitate cable laying.

Step Four: Fiber Inspection: Stripper fiber loose tube about 20cm, clean optical fiber, optical fiber core number and check whether there are errors chromatography, and determine the optical fiber sequence.

Step Five: Testing technical indicators: measured with the activities of the connector to connect fiber optic pigtails and testing, OTDR testing and then the fiber length, the average loss, and the factory test target with the optical contrast, look for errors. View fiber after taking the curve to the scattering and reflection of whether the peak attenuation level. The entire fiber optic cable in there as long as there is a broken fiber, attenuation exceeded its apparent attenuation level or reflection peaks (not including the fiber end reflection peaks) should be regarded as substandard products.

Step Six: Check the electrical characteristics: If there are to much for cable or monitoring of the metal wire pairs should be tested on the electrical characteristics of wire indicators to see whether the national standards.

Step Seven: Waterproof performance check: test metal sheathed cable, metal parts such as strengthening the insulation resistance to ground to see whether the factory standards.

Step eight: Recovery Package: testing is completed, the first cut of light apparent reason Qi, with the heat shrink tube ends can be sealed, and then pull the cable shrouded in a fixed cable tray and cable tray in the same time, restoration of optical disc packaging.

In the process of optical single-disk test, should also pay attention to the following questions:

1, optical fiber cable in the surplus in the calculation: when tested with the OTDR, the fiber is longer than the length of cable that is fiber-optic cable in the surplus in the degree. And this margin of manufacturers do not usually provide, but it is also indispensable to maintain fiber optic cable line a parameter. We can be calculated by the following formula: degree = slim 梅 surplus cable length - 1. Thus, we maintain the course of optical cable, you can OTDR measured margin of fiber length and to determine the exact location of cable fault location: cable length = slim 梅 (1 + surplus degrees).

2, optical fiber attenuation coefficient test: OTDR testing with certain optical attenuation coefficient of error, the same fibers of different OTDR testing, the test results may not be the same, that is the same OTDR set different parameters, test results may not be the same. So, as long as the test results in the standard range, but with little difference between the data provided by the manufacturer, should be regarded as qualified. The test results exceeded the standard, not blindly to a conclusion, should a change of OTDR parameters or work environment, or for an OTDR to repeatedly test, compare, see if it really excessive.

3, "Magic peak" phenomenon: "Magic peak" phenomenon known as "ghost" phenomenon, which is in the use of OTDR test optical fiber, optical pulses in optical fibers due to multiple reflections, the fiber optic backscatter curve formed a reflective peak. Because of this reflection peak is formed with the fiber fracture is very similar to the reflection peak, the tester is easy to "magic peak" is formed as a fiber breakage caused by the reflection peak of misjudgment. Therefore, the optical scattering curve after the peak reflection occurs, it is necessary for further analysis, may come and go test pulse, measuring the length or the wavelength of measurement several times to compare the identification. If you can not judge, can be measured from the other side, or replacement of test instruments, re-measurement.

Has been identified as unqualified for the optical disc products, to register a clear, timely reporting and contact with manufacturers.


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