OTDR (Optical Time Domain Reflectometer) is the main tool to maintain the test cable barriers,used to test the cable breakpoint location, in order to repair a timely manner to arrive at the scene to repair. It works according to the Rayleigh scattering, by collecting the backscattered signal curve analysis points. Here, the author detailed analysis of the barriers of the fiber optic lines to find and deal.
Part of the system blocking obstacles
If the obstacle is an obstacle to a system, under the premise of rule out equipment failure, precise adjustment of refractive index, pulse width and wavelength of the OTDR instrument, so that the measured core parameters to minimize the test error. Subsequently measured distance information and data matching, to confirm the obstacles point in the joints.
OTDR curve observed with the barriers Fresnel reflection peak (Fresnel reflection is a special case of Rayleigh scattering, which is a special phenomenon that occurs when mutations in the fiber refractive index), and data matching, and a connector distance close, the initial judgment for the box fiber obstacles specular fracture (fiber boxes fracture are large Fresnel reflection peak). Repair personnel to the scene, and engine room personnel to further judgment, and then processed.
If the obstacle point and the connector distance is quite different obstacles compared to cable. Hidden nature of such obstacles, if the positioning is not allowed to blindly find may be an unnecessary waste of manpower and material resources, such as direct burial fiber optic cable a lot of earthwork excavation, overhead cable detaching and attaching a large number of linked, will extend obstacles lasted. These barriers can be used as follows accurately determine the barrier point.
OTDR instrument accurate test with the barriers relative to the adjacent joints point distance (slim), Lengthening of the test are translated into the fiber optic cable length (skin), and then the fiber skin long converted into the size of the growth of the obstacle point to the precise positioning with the barriers location. The specific algorithm is as follows:
(1) slim translated into the skin length of La = (S1-S2) / (1 + P). Where La for the fiber optic cable of long; S1 is the relative distance of the test length; S2 to stay the length of the cable connector box of unilateral disk, generally take 0.6 to 1.0; P of the cable twist shrinkage, due to different cable structure spare fiber optic cable can be used the same model tested provided by the manufacturer of the indicators. P = (Sa-Sb) / Sb, Sa for the single-disk fiber optic cable testing slim; Sb single disk cable marked leather long size length.
(2) the calculation of the cable barrier point leather long size Ly, = Lb ± La. Where Ly is the leather long size of the obstacle point value; Lb box the root of the adjacent joint points of fiber optic cable length leather Size + - the choice of symbols according to the cloth of the fiber optic cable put side do not determine. Determine the value of the Ly, the specific location of the obstacle point can be determined according to the information. The method can reduce measurement errors caused due to the engineering data are not allowed to, instrumentation, and optical fiber refractive index deviation, to avoid long distance accounted for fiber optic cable length, more accurate test results. Practice has proved that this method is simple and effective.
Fiber optic cable the whole resistance obstacles
Optical cable line blocking obstacles, easy to find , usually external impact caused by OTDR measurement of the distance between the obstacle point and the bureau (station), combined with maintenance data, determine the location of the obstacle point command line patrol officers along cable route to see if building construction, aerial optical fiber cable is obvious strain, etc.,.Generally you can find the barrier point. If you can not find the method described above, you have to use the accurate calculation to determine the barrier point.
Optical fiber attenuation caused by obstacles
OTDR test system disorders core, if the obstacle is the attenuation of spatially variable, and can determine the basic obstacle point is located in a junction due to the bending loss. Box remaining fiber plate remain inappropriate or heat-shrinkable tube off to form a small circle, so I fiber radius of curvature is too small. In addition, the connector box water may cause an obstacle to the joints. Open the connector box, you can further determine the normal core around on the finger, its curvature radius is too small, then the OTDR test (1550nm) there will be a large attenuation point, the point of the attenuation and obstacles fiber attenuation is consistent with the barrier point is the point. And then carefully review the barriers to fiber without injury or disk small circle, if there is a small circle ,ampplify it , otherwise reconnection treatment.
Engine room line terminal obstacles
If the disorder in the terminal room, in the obstacle-side test, OT-DR instrument purification no regular curve in the terminal test can be found in the normal curve of obstacles core test. For precise positioning, plus the period of the pigtail to avoid the instrument blind to the general length of less than 500m, the first accurate measurement of the pigtail length, and barriers to access fiber-optic test.
The above analysis shows that the fiber optic cable and fiber optic jumpers obstacles causes a lot, except the force of outside joints are more barriers. Therefore, we must strictly control construction quality, so in line with operating procedures, to strengthen the maintenance, set up a full, complete, accurate maintenance of information and constantly sum up experience in practice, in order to quickly find and deal with various obstacles.
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