GB1508351A - Apparatus for the location of faults in cables - Google Patents

Abstract

1508351 Cable fault location ELECTRICITY COUNCIL 16 Jan 1976 [17 Jan 1975] 2235/75 Heading H4D Apparatus for location of a fault in a cable comprises a generator which supplies a signal to one end of the cable, and a digital transient recorder which records the waveform of the resultant reflected signal from the cable, and includes means for repetitively sampling the waveform to be recorded, A to D conversion means arranged to convert the sample signal amplitudes into digital form, and a digital signal store for recording the digitized sampled information. As described, an impulse generator producing current waveforms in a linear coupler as described in Specification 1,508,352 is used, although it is stated that a voltage waveform may alternatively be utilized. The output signal from the linear coupler 20 is sampled at an accurately controlled rate typically 29 MHz in a sampler 40 controlled by a clock frequency signal generator 41 and the amplitudes of the output samples are converted from analogue to digital form in an analogue-todigital converter 42, typically providing a 6-bit output thereby enabling 64 different amplitude levels to be recorded. The digital output from converter 42 is applied, via a switch 43, to a memory 44 which is typically a semi-conductor memory. When it is required to examine the waveform, the switch 43 is put in the re-play condition and the stored signal in memory 44 is fed both to a digital-to-analogue converter 45 and is also fed back via the switch 43 to be re-stored in the memory 44. The output of the digital-to-analogue converter 45 may be applied to a cathode ray oscilloscope 46 and/or to an automatic plotter 47. The stored signal in the memory may be fed to a paper tape perforator 48 to produce a permanent record. It may be fed to numerical indicators 49 if numerical information is required, for example for communication to a remote station. The output of the memory additionally or alternatively may be applied to data transmission equipment 50 for feeding over a data link 51 to a central station. The central station has a digital data processor 52 including a memory 53 for receiving the transmitted data. The incoming data can be compared in the processor with pre-recorded information representative of the waveform to be expected or pre-computed information representative of possible fault conditions from a data store 54. Additionally or alternatively a display device 55 fed from a digital-to-analogue converter may be provided to enable the incoming data to be displayed visually in analogue form. In operation, the complete waveform from an applied impulse would be stored in the memory and, when the recording cycle is complete, the stored data would be replayed through the digitalto-analogue converter 45. The re-play may be at a faster or slower rate than the original sampling and is usually made repetitive by recirculating the stored data through the switch 43 so that a steady trace is obtained on the display oscilloscope 46.