The Fault Location Of Aircraft Cables Based On Chaotic Test Signals

Spread Spectrum Time Domain Reflectometer (SSTDR) has been demonstrated tobe effective technology for locating intermittent faults on a wire. In this method, thepseudo-random sequence is modulated by a cosine wave signal has been widely used asthe SSTDR test signal. The failure can be located by detecting the cross correlationbetween the reflected signal and the test signal. The low testing signal levels and highnoise immunity of this testing method makes it well suited to detect intermittent faults.However, because the weak reflected signals caused by small intermittent faults arelikely to be drown by the noises of the system, we can not identify them even throughcorrelation, thus can not detect them. Moreover, the current widely used PN codes cannot fully meet the requirements of intermittent cable faults’ detection and localization.The good autocorrelation of test signals is particularly important to SSTDR testingmethod, we can choose better test signals to improve the efficiency of the method.Firstly, this paper describes SSTDR based on Max Length (ML) sequences, andpoints out that the testing system is sensitive to noise on the wire. The reason is that thenature of MLsequences is not enough good. Secondly, through the comparative study ofthe logistic and cubic mapping’s nature, this paper draw a conclusion that the chaoticsequences’ characteristics are more compliance with the requirements of the SSTDRdetection method. Finally, according to digital simulation, we have found when the testsignals generated by logistic mapping are applied to SSTDR detection system, thesystem’s capability of anti-noise will be improved.