Research On Injection Signal Technology Of Metal Pipeline Detection And Identification System

With the development of modern cities,most metal pipelines such as power cables and communication cables are mainly laid underground.During the construction of the project,the current situation of the layout of the underground metal pipelines must be known in advance to prevent unnecessary damage and prevent the normal operation of the city.In the process of metal pipeline detection,the target metal pipeline needs to be identified first,and then the path of the pipeline can be detected,and finally the fault point of the pipeline can be accurately located.Therefore,it is necessary to cooperate with multiple devices to accurately measure the position information of the target pipeline,but it is extremely inconvenient to frequently replace the devices on the construction site.In addition,the onsite construction environment is complex.For the portability of the equipment,battery power is generally used,which will lead to low power supply efficiency of the equipment and low transmission signal power,which also brings difficulties to the construction operation.In this thesis,the injection signal technology in the metal pipeline detection and identification system is deeply studied,and a small size and high power transmitter is designed to be used in the path detection,fault location and pipeline identification of metal pipelines.In this thesis,the detection of metal pipelines is studied based on the principle of electromagnetic detection method.Aiming at the problem of single transmitter function,a realization scheme of a multifunctional transmitter is proposed.According to the transmission characteristics of the signal in the metal pipeline,the signal transmission model of the transmitter in the path detection mode,the fault location mode and the pipeline identification mode is established,and the three output waveforms and the working principle of the transmitter in different modes are analyzed.In order to improve the output power of the transmitter,the advantages of the class D power amplifier compared with the traditional analog power amplifier were compared,and its basic working principle was studied.The principles of PWM modulation and sigma-delta modulation are analyzed,and pulse modulation is realized in FPGA by combining their characteristics.Aiming at the problem that the detection of metal pipelines in three modes requires different waveform signals,this thesis proposes a DDS technology based on the combination of lookup table scheme and CORDIC algorithm.The basic principle,basic structure and output spectrum of ideal DDS based on look-up table scheme are studied,the phase truncation error and amplitude quantization error are analyzed,and MATLAB software is used to simulate the output SFDR of DDS.By adopting Sunderland structure and phase-amplitude converter,the purpose of compressing ROM capacity is achieved,the basic principle and implementation of CORDIC are studied,and the signals generated by FPGA are simulated and verified by Model Sim software.The results show that the DDS module implemented by the combination of the look-up table scheme and the CORDIC algorithm can generate the original signals in three working modes.Then a digital modulation module is designed to modulate the PWM wave and use the differential pin to output.In order to solve the problem of low transmitter power,the transmitter hardware system using the principle of Class D power amplifier is designed and completed.the control system adopts the hardware architecture of ARM+FPGA,in which ARM is mainly responsible for the task of human-computer interaction,and FPGA is mainly responsible for generating target signals.The SPI protocol is used for communication between the two,and its IO transmission model is analyzed and the timing constraints are imposed.Firstly,a SEPIC topology switching power supply based on LM5022 is designed as the power supply module of class D power amplifier.Then the gate drive circuit based on IRS20957 S is designed,and the BTL circuit is used as the output stage of the class D power amplifier.Finally,the Butterworth filter and the output voltage detection circuit are designed.Through the construction of experimental site and prototype verification,the injection signal technology of the metal pipeline detection and identification system studied in this thesis is in line with practical applications.When the transmitter is powered by a 12 V power supply,it can emit sine waves,dual-frequency mixed waves and dual-frequency modulation waves with a peak-to-peak value of about 100 V in the metal pipeline path detection mode,fault location mode and pipeline identification mode respectively.