Radiodetection Limited

Stephen Maslen

The present invention provides a time domain reflectometer for testing an electrical cable. The time domain reflectometer includes a test signal generator, at least one line feed resistor, connected between the test signal generator and a pair of terminals, for connection to the ends of the electrical cable under test, and a signal processor, connected to the terminals, to receive a line signal including a reflection of a test signal transmitted into the cable under test. The signal processor is programmed to filter the line signal to enhance a portion of the signal indicative of any fault on the cable by balancing the signal according to the electrical characteristics of a normal cable of the same type as the cable under test by applying a filter function, and acquiring at least one estimate of the input admittance of the transmission line from known or estimated electrical characteristics of the cable under test.

Time-domain reflectometer

The present invention provides a method of time domain reflectometry including transmitting a test signal along a cable under test from one end and sensing and recording a reflected signal from the cable at that end, using the recorded, reflected signal to estimate the distance, Ldist, from the one end to a discontinuity on the cable, separating a test signal component from the remainder, Vr, of the reflected signal; estimating the impedance, Zfault, of the discontinuity from known, predetermined values of the characteristic impedance, Zline, and of the characteristic gain, T, of a reference cable, and from the said separated test signal and reflected signal components, calculating the estimation error as a difference between the model reflection signal, Vrmod, expected of the cable under test based on the characteristic impedance and characteristic gain and the estimated impedance, Zfault and distance, Ldist, and the actual reflection signal Vr, choosing new estimated values of Ldist and Zfault in accordance with a predetermined algorithm such as to approach optimal values, repeating the aforesaid step of calculating the estimation error until a predetermined condition has been satisfied, and outputting the values of Ldist and Zfault that gave the least error.

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Somerset, United Kingdom

Stephen Maslen