Study On Cable Fault Distance Measurement Based On Time-Domain Pluse Reflection

Because of imperceptibility and extensity of its service environment, therewould be a wide coverage if the cable can’t work well, and it is difficult to findout the fault location, that would bring huge economic losses. So a fault distancemeasurement system, which is of high accuracy, small dead zone, easy to operateand saving labor, is needed to detect the cable fault. Once there is somethingwrong in the cable, it would detect the type and the location of cable fault, tosave the repair time and lessen the economic loss.This thesis introduced an overall design whicn has STM32and EP3C25asthe core of the system based on TDPR, the transmission properties and thereflective characteristics at the impedance not matching point of electromagneticwaves. STM32outputed PWM wave to drive MOSFET and very narrow pluseswere generated with many types of widths to ensure enough detecting range. Todecrease the bias and shorten dead zone, the paper analysed reflected plusefeatures and high speed data acquisition and processing system, and setted thesingle channel repeatedly data acquisition methods with50MSPS sampling rateat one time, then saved the data from AD outputs into embedded RAM inEP3C25. Denoising the reflected pluse with using wavelet transform method, themodulus maximas of wavelet coefficients of the test and the reflected pluses werefound out with modulus maxima algorithm, and the number of sampling intervalscan be counted out between the modulus maximas. So the time the reflective plusspent in the cable can be figured out. And then the distance between the test andthe fault points could be calculated according to distance formula. STM32readsdistance data from dual-port RAM in EP3C25and drove LCDs to display thedistance numbers to inspector. In this thesis, MOSFET drive circuit, AD converting circuit, theinterconnected circuit between STM32and EP3C25and their peripheral circuitwere designed, the system logical control, sampling process, system clock andthe timing of data process were simulated, and the reflected pluse data wasdenoidesed. The results show: this system can reach100MSPS sample rate and1m error system performance index in the condition of200m/μs wave speed. Thewhole system has the features of high accuracy, small dead zone and widemesearment range and it is easy to operate. And it’s appropriate to detect andlocate the cable fault.