Optimal Design Of Parallel Multi-Channel Far-Field Eddy Current Rapid Detection System

Compared with other non-destructive testing technologies,non-destructive testing technology based on eddy current effect has the advantages of simple detection,non-contact and in-service detection,and is widely used in the field of metal pipeline detection.The far-field eddy current detection technology can analyze the thickness and defects of metal casing by transmitting low frequency and slow test excutation.The kind of exciting signal leads to the slow running speed of the instrument,so the parallel multi-channel processing method is adopted in the receiving part to realize the rapid detection of metal casing thickness and micro-defects.The casing testing instrument developed using far-field eddy current testing technology sends out test excitation from the transmitting circuit.Its receiving ciucuit needs to be designed specifically with a far-field synchronous receiving circuit,in which the digital phase-sensitive detection algorithm and the orthogonal sampling method are adopted to identify the pipe thickness and the internal and external defects.The signal receiving circuit described in the thesis is divided into analog circuit and digital signal processing circuit.In the analog circuit part,multiple parallel channels adopt the same signal conditioning structure to amplify and filter the high and low frequency signals received by the sensor,which simplifies the hardware circuit and provides the digtal acquisition system with a high signal-to-noise ratio.The digital signal processing circuit adopts the cooperative processing mode of FPGA and DSP,makes use of the parallel processing characteristics of FPGA to realize the synchronous configuration of ADC and parallel processing of sampled data,and uses the strong data processing ability and high speed of DSP to realize the digital filtering and phase difference algorithm calculation.The effective combination of the two makes it realized that the synchronous receiving circuit efficiently complete the signal acquisition and phase calculation.Compared with the previous far-field unit receiving system,the thesis proposes a parallel multi-channel signal processing mode and distinguishing function of internal and external defects to realize the parallel processing of 16 signals.Compared with the channel switching processing methods,the acquisition time can be reduced to one fifth of the original design effectively,and the measuring speed of the instrument underground is improved.In addition,the identification of internal and external defects can effectively locate the damage location of the casing and increase the measuring accuracy of the instrument.In order to verify the function of the instruments,the results of laboratory debugging and field operation are given at the end of the thesis.The debugging results have confirmed the corresponding relationship between the test phase difference and the metal casing thickness,and the field operation results have effectively verified the instrument's ability to detect metal casing thickness and micro-defects.