For optical cables, there will also be various faults, so what are the methods for locating faults in optical cable lines? While understanding these methods, we also need to improve the accuracy of optical cable fault location. Let's learn together.
Correct and proficient in the use of the instrument
Accurately set the parameters of the OTDR, select the appropriate test range file, apply the amplification function of the instrument, and accurately place the cursor on the corresponding inflection point, such as the inflection point of the fault point, the start point of the fiber, and the inflection point of the fiber end, so that a more accurate measurement can be obtained. Test Results.
Create accurate and complete source data
Accurate and complete optical cable line data is the basic basis for obstacle measurement and judgment. Therefore, attention must be paid to the collection, arrangement and verification of line data, and a true, credible and complete line data must be established.
Establish accurate line routing data, including marker (pole number) - length (cable length) comparison table (refer to appendix), records of "fiber length accumulation" and "fiber attenuation", when establishing "fiber length accumulation" data, The distance from the end station to each connector should be measured from both ends. For accurate test results, transition fibers can be used according to the situation. On-the-job acceptance personnel collect and record various reserved lengths. The more carefully registered, the smaller the error in obstacle determination.
Build complete and accurate route profiles
The building line information not only includes many data in the line construction, as-built technical documents, drawings, test records and pictures of the backscattered signal curve of the optical fiber in the relay section, etc., but also retains some original data of the optical cable and optical fiber provided by the manufacturer when the optical cable leaves the factory. (such as the shrinkage rate of the optical cable, the refractive index of the optical fiber, etc.), these data are the basis and comparison basis for future obstacle testing.
make the correct conversion
To accurately determine the location of the fault point, it is also necessary to convert the length of the fiber tested to the ground length from the test end (or a joint point) to the fault point.
The ground length from the test end to the fault point can be calculated by the following formula (the unit of length is m):
L = [(L1-L2)/(1+P)-L3]/( 1+a )
In the formula, L is the ground length from the test end to the fault point (in meters), L1 is the optical fiber length (in meters) from the test end to the fault point measured by the OTDR, and L2 is the length of the optical fiber reserved in each splice box (unit is meter), L3 is the length of the optical cable and all coils at each joint (unit is meter), P is the shrinkage rate (ie twist coefficient) of the optical fiber in the optical cable, it is best to use the value provided by the manufacturer, generally is 7‰, a is the natural bending rate of the optical cable (0.5% for pipeline laying or overhead laying, and 0.7%-1% for direct burial laying). With accurate and complete original data, the faulty fiber length measured by the OTDR can be compared with the original data, and the location of the fault point can be accurately identified.
Keep the obstacle test consistent with the test conditions on the data
During the fault test, try to maintain the consistency of the test instrument's signal, operation method and instrument parameter setting. Because the optical instrument is very precise, if there is a difference, it will directly affect the accuracy of the test, resulting in the difference between the two tests themselves, making the test results incomparable.
Flexible testing, comprehensive analysis
Under normal circumstances, two-way fault testing can be performed at both ends of the optical cable line, and the location of the fault point can be calculated based on the original data. Then comprehensively analyze and compare the test and calculation results in the two directions to make the judgment of the specific location of the fault point more accurate. When there are no obvious features on the route near the obstacle point, and the specific obstacle point cannot be determined on site, methods such as measuring at the nearest joint can also be used, or excavation at the obstacle point of the preliminary test, and the test instrument of the terminal station is in a real-time measurement state. Find the change of the curve at any time, so as to find the exact fiber fault point.
The above content is a detailed introduction to the method of fault location of optical cable lines. If you have a demand for optical fiber cabling product solutions, please contact ZR Cable, ZR Cable optical fiber cabling manufacturers, optical fiber products are complete, direct delivery from stock, and provide you with comprehensive solutions. .
