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Precautions when testing an optical fiber link

2022-09-15
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1. Preheat the boot

Generally, the higher the temperature of the light module, the greater the power generated by the light module. In the test process, the light source module needs a period of time to warm up, so that the transmitted light source power value can reach stability. If the reference value is set before the light source module is preheated, the test results will gain as the temperature of the light source module rises, thus affecting the accuracy of the test results.

 

For example, when the reference value is initially set, the optical power meter accepts and stores a power value of -6.00dB. At this time, if the reference value setting model is maintained and the link under test is not added, the test result of 0.00dB should be obtained. However, after the optical power module is preheated, the power emitted by the optical power module will increase, and the power received by the power meter may rise to -6.20dB. When tested again, a gain of -0.2dB will be obtained.

ftth cable

The preheating time of the light module depends on the temperature of the test environment. The lower the test environment temperature, the longer it will take to warm up. Normally, the warm-up time is 5 minutes. If the instrument is stored or used at a lower temperature, the warm-up time can be as long as 30 minutes. The method to check whether the light source module is stable is very simple. As long as the reference value is set and the reference value model is tested, the test value between -0.04dB and 0.04dB is acceptable. If you exceed this value, you need to wait a little longer and reset the reference value.

 

2. Check the performance of reference jumper

At present, there are some test instruments on the market, with a reference jumper performance verification function. Using this function, the performance of the reference jumper can be verified to determine whether it meets the standard requirements. During testing, reference jumpers may wear out or suffer from degradation of coupling performance due to repeated use and insertion. Therefore, the performance of the reference jumper should be checked periodically. If the test result exceeds the standard requirement, replace the test jumper. In normal use, the reference jumper should be replaced every 500-1000 tests.

 

3. Connect the reference jumper to the light source

Fiber optic connectors have slightly different loss values each time they are coupled. Especially for the light source end, because of its smaller end diameter, the loss results generated by each coupling are more different. Therefore, when the reference value is established, the reference jumper should not be unplugged from the light source port, otherwise the accuracy of the test results will be affected. If this happens, you need to reset the reference value after the connection. In addition, to ensure the most accurate test result, do not remove the reference jumper at the optical power meter.

 

Occurrence and handling of negative values

 

When testing a single-mode fiber link, if the length of the link under test is less than 100 m and the entire link is connected by pigtail fusion, the loss of the entire link may be only 0.15dB. In this case, insufficient preheating time of the light source module, large changes in the temperature of the test environment, coupling effect between the reference jumper and the test instrument, and inaccurate setting of the reference value may lead to negative values of the test results, such as -0.03dB. At this point, it is best to reset the reference value.

 

The faulty link is rectified

If the loss value obtained by the test exceeds the limit value, the following aspects can be used to troubleshoot the fault.

 

First, re-clean the connector faces of all links under test and reference jumpers. Reconnect and ensure that all connectors are fully inserted into the fiber adapter.

 

Secondly, check whether the bending radius of cable and jumper meets the standard requirements. In particular, whether the bending radius of the cable in the optical fiber box is too small.

 

Test again. If it fails to pass the test, refuse the tail fiber in the fusion mode, and replace the connector in the end mode. Run a new test.

 

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