Dissertation
Dissertation > Industrial Technology > Machinery and Instrument Industry > Instruments, meters > Material testing machine and test equipment > Nondestructive flaw detector > Magnetic detector

Magnetic flux leakage detection system design based on LabVIEW

Author LiuHengDa
Tutor HuManLi
School Northwestern University
Course Oil and gas dynamics and detection technology
Keywords Ferromagnetic Materials Magnetic Flux Leakage Virtual Instrument Signal Acquisition and Processing Inspection System Design
CLC TH878.3
Type Master's thesis
Year 2011
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According to the magnetic flux leakage (MFL) properties, the MFL inspection system based on Lab VIEW was devised and the defects MFL testing of ferromagnetic materials was done to inspect their defects non-destructively for improving their reliability.There are 3 steps to test MFL:magnetization, sensing, data acquisition and processing. The magnetization was studied by two methods:equivalent magnetic charge method (EMC) and finite elements method (FEM). Three simplified defects’math-models were v-shaped defect, rectangular defect and hole. The MFL space distribution analytical expressions of these three defects were built by EMC method. The rectangular defects’MFL images were drawn on the basis of expressions. The relationship between rectangular defects and their MFL surface distribution were studied via images by modifying different parameters. The v-shaped defects’ magnetic field space distribution was analyzed using FEM software. The sensing principle and data acquisition and processing theory, especially the testing of the displacement was studied and the method of mouse displacement measurement technology was proposed.According to MFL testing theory, the MFL inspection system based on LabVIEW was also designed from three aspects. The panel’s magnetized design methods as well as axial and circumferential directions of pipeline’s magnetized design methods were studied. The system includes hall element and mouse for sensing MFL and displacement and data acquisition card (DAQ card) to collect data. Through LabVIEW programming, the mouse pointer borders set by graphical user interface were break away and the precise displacement determination without range limit was realized. The LabVIEW program of equidistant sampling in space, which offer the ability of control, collection and processing was designed with interface programs. The defects MFL signals were real-time displayed, conversed and stored and further intuitively displayed after de-noising by wavelet transform and differential analysis.The performance testing experiment using this MFL inspection system based on LabVIEW was done. Displacement calibration and performance analysis was done by stepper motor calibration experiment. The result demonstrates that this method can provide displacement measurement with accuracy of 0.1mm and with good linearity, high sensitivity and little error. The MFL feature standard through which judge defect signals was made in MFL inspection experiment. The MFL equidistant sampling in space inspection experiment demonstrates that the functions of data acquisition, real-time display and de-noising process can be realized conveniently and the MFL inspection technology based on LabVIEW can accurately inspect defects of ferromagnetic materials.

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