Range
Before measuring with the Optical Time Domain Reflectometer (OTDR), the length of the fiber cable to be tested should be estimated, and an appropriate range should be selected to test the length of the fiber cable.
Wavelength
Currently, if the 1310nm wavelength is used for transmission, the dispersion is the smallest, and if the 1550nm wavelength is used for transmission, the loss is the smallest. Therefore, it is usually considered ideal to use a wavelength of 1550nm to test the length of the fiber cable.
Measurement time
The OTDR measures the fiber cable multiple times within a unit of time and calculates the average value of the measurements. Therefore, the longer the measurement time, the more times the fiber cable length is measured, and the closer it gets to the actual length.
Pulse width
Pulse width refers to the width of the pulse. If the pulse width is larger, the energy contained will be higher, the transmission distance will be further, and the testing distance will be longer, but the accuracy will be lower. Conversely, if the pulse width is smaller, the energy will be lower, the transmission distance will be shorter, the testing distance will be smaller, but the accuracy will be higher. Therefore, when changing the measurement range, the pulse width changes accordingly. When the range increases, the pulse width increases, and the accuracy decreases, and the opposite occurs when the range decreases. That's why if the range is not set properly, it will be impossible to measure the fiber cable length accurately.
Other parameters of the OTDR do not need to be changed and can be used with the default settings for routine testing.
Real-time measurement
When the OTDR measures with the method of multiple measurements in a unit of time and calculates the average value, if real-time measurement is used, each measurement result will be displayed on the screen without averaging, and we will observe a curve that continuously jumps slightly. Usually, real-time measurements can be used to calibrate fibers, splice fiber cables, and detect fault points.
Average measurement
The measuring method of the OTDR is to measure multiple times within a unit of time and calculate the average value. Therefore, the longer the measuring time, the more times it is measured, and the closer it gets to the actual length. Generally, for engineering fiber optic cable testing, the measuring time should not exceed 30 seconds, which is sufficient for achieving the required accuracy for fiber cables of about 100 km in length. Further extending the measuring time becomes meaningless.
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