【2017年整理】OTDR培训.ppt

3 7 1 8 2 5 3 4 6 3 7 1 8 2 5 3 4 6 3 7 1 8 2 5 3 4 6 3 7 1 8 2 5 3 4 6 3 7 1 8 2 5 3 4 6 5 6 1. The “A” cursor is set at the end of the initial launch dead zone -- after the first reflection levels out to a relatively straight line. The level where the backscatter starts indicates how good the connection to the OTDR is, how much loss there is in the first few hundred feet of fiber, and the amount of power injected into the fiber. 2. A “Reflective Event” is normally a mechanical splice or in-line connector. It is characterized by a sharp spike up from the line of backscatter. There may also be a shift in the backscatter levels before and after the event indicating the amount of loss at the splice/connector. 3. A “Non-Reflective Event” is a fusion splice, a bend in the fiber, or a defect. It could also be a mechanical splice that does not reflect any light. The loss in the splice/defect/bend is the amount of shift in the backscatter levels from before to after the event. 4. All fiber has some loss due to scattering and other mechanisms. Normally this loss is linear -- it is a steady loss -- and falls within a certain range for a specific testing wavelength. The normal way to describe this standard loss is in dB/Km. This loss/distance value is also its slope. Steeper slopes mean more loss per unit of distance. 5. The “B” cursor is set at the end of the fiber. It is on the last point of backscatter before the end reflection spikes up. If there is no fiber, then there is no backscatter. Therefore, the last point of backscatter is the definition of the end of the fiber. Normally there is a reflection at the fiber end, especially if it is connectorized. 6. The horizontal and vertical scales show the distance (horiz) and dB levels (vert) of the data points. 7. The data section shows the distance to the A and B cursors, the distance between them, the loss between them, and the value of any reflections just past the A cursor. This display also shows an overview of the fiber.