The main factor in the test error

1) OTDR test instrument bias inherent in
      Seen by the OTDR test theory, it is based on a certain cycle light pulses sent to the fiber under test, then at a certain rate of backscatter from the fiber optic signal sampling, quantization, encoded, stored and displayed. OTDR instrument itself, due to sampling error interval exists, this reflects the inherent bias in the distance on the resolution. OTDR resolution is proportional to the distance sampling frequency.
   

2) Test instrument error caused by improper operation
      In the cable fault location test, OTDR instrument accuracy and the use of barriers is directly related to the accuracy of the test, set the instrument parameters and accuracy of the inappropriate choice of instrument range or set the cursor are not allowed and so the test results will lead to errors.

      (1) Set the instrument error caused by the refractive index deviation
      Different types and manufacturers of optical fiber refractive index is different. When using the OTDR test fiber length, the instrument parameters must be set, the setting is one of the refractive index. When the refractive index of fiber optic cable is not the same paragraphs of sub-set of methods can be used to reduce errors caused by the refractive index of the test set error.

      (2) the inappropriate choice of range
      OTDR test instrument resolution of 1 meter distance, it is amplified to the level of graphical scale of 25 meters / div can be achieved. Instrument design is based on every move the cursor to a full 25-step format. In this case, the cursor moves one step each, that means moving 1 meter distance, so read the resolution of 1 meter. If you choose the level of scale 2 km / per cell, the cursor moves one step each, will be offset 80 meters away. Thus, the selection of the test the greater the range, the greater the deviation of test results.

      (3) the inappropriate choice of pulse width
      In the pulse amplitude under the same conditions, the greater the pulse width, pulse energy, the greater, then the greater the dynamic range of OTDR, and the corresponding big blind also.

      (4) inappropriate choice of the average processing time
      OTDR test curve is the reflection of each output pulse signal sampling, and the average processing times to eliminate sampling to do some random events, the average of the longer, the closer the minimum noise level, the greater dynamic range. Average of the longer, the higher the testing accuracy, but accuracy is no longer up to a certain extent improve. In order to improve test speed and shorten the overall test time, test time can generally 0.5 to 3 minutes in the selection.

      (5) improper placement of the cursor position
      Fiber Optic connectors, mechanical connectors and fiber fracture will lead to loss and reflection, the end of the broken fiber end face as the face will produce a variety of irregular Fresnel reflection peak, or does not produce Fresnel reflections. If the cursor set is not accurate enough, will have some error.