Information AboutTime-domain Reflectometry |
| CATEGORIES ABOUT TIME-DOMAIN REFLECTOMETRY | |
| electronics | |
| measurement | |
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Time-domain reflectometry or '''TDR''' is a Measurement Technique used to determine the characteristics of Electrical Lines by observing Reflected Waveform s. '''Time-domain transmissometry''' ('''TDT''') is an analagous technique that measures the transmitted (rather than reflected) impulse. Together, they provide a powerful means of analysing electrical or optical transmission media such as Coaxial Cable s and Optical Fiber s. The Amplitude of the reflected signal can be determined from the Impedance of the Discontinuity . The Distance to the reflecting impedance can also be determined from the Time that a Pulse takes to return. The limitation of this method is the minimum system Rise Time . The total rise time consists of the combined rise time of the driving pulse and that of the Oscilloscope that monitors the reflections. METHOD The TDR analysis begins with the propagation of a Step or impulse of Energy into a System and the subsequent observation of the energy reflected by the system. By analyzing the magnitude, duration and shape of the reflected waveform, the nature of the impedance variation in the transmission system can be determined. Resistive load If a pure Resistive Load is placed on the output of the Reflectometer and a Step Signal is applied, a step signal is observed on the CRT , and its height is a function of the resistance. The magnitude of the step caused by the resistive load may be expressed as a fraction of the input signal as given by: : where is the Characteristic Impedance of the Transmission Line . Reactive load For Reactive Load s, the observed waveform depends upon the time constant formed by the load and the characteristic impedance of the line. SEE ALSO |
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