Technology And Application Research For Concentration Measurement Of Magnetic Suspension Based On Electromagnetic Induction

Non-destructive testing(NDT) technologies become more and more important in the industry of railway equipment manufacturing, operation and maintenance, especially with the development of high-speed rail technology. Nowadays, NDT serves as an indispensable procedure for quality control in all the fields related to railway equipment, meanwhile, it is also a key technique to guarantee the safe operation of the railway.In this thesis, we focus on the magnetic particle testing method, which is one of the most important NDT technologies. It is well known that measuring the concentration of magnetic ink is the critical step of this type of testing method. We started with an investigation of the drawbacks of existing concentration measuring approaches for magnetic ink, and then we proposed a novel concentration measuring method based on the concept of electromagnetic induction. In this new method, we proposed to make use of the magnetic precipitation, instead of the conventional natural precipitation methods. Finally, we developed an electromagnetic induction-based measuring instrument, which is able to efficiently obtain quantitative results for the concentration of magnetic ink. Furthermore, we investigated practical methods to calibrate our developed instrument. It turns out that the developed instrument has the advantage of simple structure and easy for application.In order to further exploit the applicability of our instrument, we conducted a series of calibration experiments for different fluorescent magnetic particle. We found that the resulting calibration curves significantly vary from each other. We then investigated the reasons for these differences.Measurement repeatability and reliability(error) are two important characters of a newly developed instrument. Experimental results demonstrate that our developed instrument achieves a measurement repeatability(represented by the relative standard deviation) less than 5%, and a measurement error less than 1.5%. Moreover, a large numbers of in situ measurements were considered to validate the experimental results in the laboratory. We made use of different concentrations of magnetic ink, and carefully compared the corresponding appearances after reaction for artificial specimens and natural defects. As our developed instrument can provide quantitative results for the concentration measurement, it is significantly different from conventional approaches, which generally rely on visual inspection.In summary, the instrument developed in this paper can provide quantitative measurement results in quasi real time, and can be used for the magnetic particle testing and optimal control of production processes in various industries, especially in the fields of railway vehicles, cars, trucks and high speed trains.