The Research On Non-Contact Variational Diameter Of Pipeline Detection Technology

The geometric distortion of the pipeline is one of the important reasons that cause the oil and gas pipeline leak. As one important method of pipeline inside detection technology, internal diameter testing is mainly used to detect the pipeline's geometric distortion caused by external pressure or other reasons, to evaluate the service life of the pipeline, provide the reasons based on for whether repair the pipeline or replace the pipeline whose life has reached its life limit. So, there is very important practical significance that detecting the pipeline inside termly.In order to overcome the breakage to the pipline and other negative effects caused by traditional contact methods such as the mechanical displacement testing, in this paper, the non-contact eddy current displacement sensor is used in variational diameter of pipeline detection technology. Application for the special needs of the environment, the optimum design of current displacement sensor and the design of the large displacement eddy current sensor testing circuit are put forward.The static and time-varying electromagnetic field are analysed and discussed, and the electromagnetic field theory, namely Maxwell's equations is put forward systematically in this paper. Then the "skin effect", the sensor impedance, the mutual inductance between the measured body and sensor and other issues are all summarized in depth. On the basis of the basic working principle of the eddy current sensor, the detailed analysis of the equivalent circuit is carried out. Refering to the subject requirements, mathematical mode of the sensor is established, the optimal design method for the objective function and the sensor structure parameters are chosen. Using the MatLab, a computer software, the objective function is optimized by the single model method and the ideal sensor structural parameters are found. The constant frequency AM measurement circuit is designed and produced, which is mainly divided into single-chip control circuit, DDS (Direct Digital Frequency Synthesis) signal source circuit, the former amplify and detector filter circuit, the linear compensation circuit, analog to digital conversion and data display, etc.The experiments show that the design of the large eddy current displacement sensor testing circuit in this paper could Detect up to 1.5 times of the sensor's diameter and meet the requirements of the application for testing variational diameter of pipeline, it also validate the stability of the system, and make the design reach the expectant effect. However, some technical details such as the accuracy of the system need to be further improved, and in the end of the paper some improvement advice is advanced.