The main factor of fiber cable OTDR test error in fiber maintenance

OTDR test instrument is a vital instrument for the fiber cable test when do the cabling or maintanence work. There would be errors if details haven’t been selected properly. what would be reasons for those errors?

1. Error caused by the refractive index deviation of the instrument.
Different types and manufacturers of optical fiber cables have different refractive index. When using OTDR to test the fiber length, the instrument parameter must be set first, and the refractive index setting is one of them. When optical cable with different reflective index, the method of section setting can be adopted to reduce the test error caused by the setting error of the refractive index.
2. Improper selection of measuring range
When the test distance resolution of the OTDR test instrument is 1 meter, it means that the graph can be realized only when the horizontal scale is enlarged to 25 meters / div. The design of the instrument is that every 25 steps of the cursor moves to 1 full grid. In this case, each move of the cursor means moving a distance of 1 meter, so the readout resolution is 1 meter. If the horizontal scale is selected to be 2 km / div, the distance will shift by 80 meters for each step of the cursor. This shows that the larger the range selected during the test, the greater the deviation of the test results.
3. Improper selection of pulse width
Under the condition of the same pulse amplitude, the larger the pulse width, the greater the pulse energy. At this time, the dynamic range of the OTDR is also larger, and the corresponding blind zone is also larger.
4. Improper selection of averaging processing time
The OTDR test curve is to sample the reflected signal after each output pulse and average the multiple samples to eliminate some random events. The longer the averaging time, the closer the noise level is to the minimum, The greater the dynamic range. The longer the averaging time, the higher the test accuracy, but the accuracy will no longer improve when it reaches a certain level. In order to improve the test speed and shorten the overall test time, the general test time can be selected within 0.5 ~ 3 minutes.
5. Improper placement of the cursor position
Fiber optic connectors, mechanical splices, and breaks in the fiber can cause loss and reflection. The broken end face of the fiber end will produce various Fresnel reflection peaks or no Fresnel due to the irregularity of the end reflection. If the cursor setting is not accurate enough, a certain error will also occur.