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Fault Detection For Electric Cable And Optical Fiber Using Microwave Chaos

Posted on:2016-12-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:H XuFull Text:PDF
GTID:1108330482966680Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
With the rapid development of global information, electric cable and optical fiber, important media of information transmission, play a more and more important role in the national economy and social progress. Their application has penetrated into every field of the society. Therefore, one important issue is how to rule out the cable and fiber fault in the shortest time at the lowest cost. At present, the existing detection technology of cable and fiber fault has some defects, including low accuracy, weak anti-interference ability, offline test only and the tradeoff between resolution and distance.Microwave chaos has the characteristics of broadband, noise-like waveforms and δ-like ambiguity function. When it is used for fault location of cable and fiber, the high spatial resolution with centimeter level can be obtained. In addition, the chaotic signal can also test the live wires benefiting from the strong anti-interference ability. Therefore, in this paper, the microwave chaotic signal generated by a nonlinear circuit such as Colpitts circuit and Boolean circuit is introduced into the cable and fiber detection. We propose the Colpitts-chaos time-domain reflectometry and Boolean-chaos time-domain reflectometry for cable fault detection and chaos optical time-domain reflectometry modulated by Colpitts circuit for fiber fault detection. The main work and results are summarized as follows.1) The existing detection techniques of cable and fiber were summarized and compared, and the challenges and problems were analyzed. In this paper, the microwave chaotic signal with broadband and good correlation property generated by nonlinear circuit was introduced into the fault detection.2) The typical production method of microwave chaotic signal using analog system and digital system was introduced. The nonlinear dynamic characteristics of the improved Colpitts circuit and the Boolean circuit were studied by simulation and experiment, including the route to chaos, the largest Lyapunov exponent, permutation entropy and peak noise ratio of correlation trace. The time domain, frequency domain and auto-correlation properties of the chaotic oscillation generated by the improved Colpitts circuit and Boolean circuit were analyzed.3) The Colpitts-chaos time-domain reflectometry was proposed to detect the cable faults. In this method, the microwave chaotic signal generated by the improved Colpitts circuit was used as the probe signal, combined with the correlation detection technology to realize the cable fault location. Simulation and experiment demonstrated the feasibility of the proposed method. The results showed that the Colpitts-chaos time-domain reflectometry could not only locate open circuits, short circuits, impedance discontinuities and shield layer breakage, but also had the ability to test live wires, which was not only immune to the influence of communication signal, but also had very small interfering effect on the communication signal. The measurement range and spatial resolution were 930 m and 7 cm, respectively.4) We proposed and demonstrated a Boolean-chaos time-domain reflectometry for detecting the cable faults. In this method, the microwave chaotic signal generated by the Boolean circuit was used as the probe signal, combined with the correlation detection technology to realize the cable fault location. Based on this principle, a prototype of Boolean-chaos time-domain reflectometry was developed, which could be used to detect the cable faults, such as open circuits, short circuits, impedance discontinuities and wet arcs. A spatial resolution of 0.3 m and a maximum range of about 1800 m could be achieved. In addition, it also had the ability of testing live wires.5) We proposed the chaos optical time-domain reflectometry using a laser directly modulated by the improved Colpitts circuit. The chaotic laser with a single wavelength was generated by a distributed feedback laser diode directly modulated by the improved Colpitts circuit for diagnosing a single fiber link. Further, we used this circuit to modulate the multiple-longitudinal-mode Fabry-Perot laser diode to realize the chaos optical time-domain reflectometry with wavelength tunable for diagnosing wavelength-division-multiplexing passive optical network. Experimental results showed that the unterminated fiber end, mismatch connector and fiber breakpoint could be preciously located using the proposed method. A range-independent spatial resolution of centimeter level could be achieved.
Keywords/Search Tags:time domain reflectometry, chaos, fault location, Colpitts circuit, Boolean circuit
PDF Full Text Request
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