Papers by Author: F.L. Luo

Abstract: It is important to improve the reliability of the eddy current non-destructive testing. It is generally difficult to reduce the probability of non-detection and the number of false alarms same time. Model Based Measurement (MBM), including estimation of state, failure diagnosis and trend analysis, has excellent results on general estimation. Actual results of MBM vary with the application domain, mathematical model and data processing. The time series model is a description of system in time domain based on equivalent output. The Kalman filter is an efficient method for suppressing the disturbance and improving the state estimation. A new method, called as eddy current testing (ECT) using a model based measurement, is presented. Two time series models are used for the normal status and the abnormal status in ECT. The Kalman filter on these models is applied to give useful information for decision making. Results of the experiment on aluminum plates demonstrate that this method is useful to improve the detection reliability.

Abstract: A direct digital synthesis (DDS) waveform generator for electromagnetic non-destructive testing (NDT) is presented in order to improve the measurement quality. The advantage and disadvantage of analogue and digital circuit waveform generators are analyzed. The DDS technique is preferred. The principle of DDS technique is introduced and the hardware and software design of a DDS waveform generator is described. The characteristics of the waveform generator based on a DDS chip AD7008 are that the signal frequency is of high stability, high precision and high resolution. Furthermore, the amplitude, frequency and phase can be continuously adjusted. An experimental electromagnetic NDT system is built and the testing results are analyzed. The system uses digitally generated sine waves as exciting, reference and demodulation signals. Experimental results show that the DDS waveform generator improves the signal-to-noise ratio. This kind of wave generation circuit is used not only in NDT but also in other instruments, such as electrical impedance tomography (EIT), which need signals with high stability, high precision and high resolution.

Abstract: Research achievements in a high speed attraction type magnetic levitation vehicle experimental system are reported. The high speed attraction type magnetic levitation vehicle constitutes a typical long stator linear synchronous motor. The study on levitation and propulsive electromagnetic fields is of great importance and is studied. Owing to the influence of the stator grooves and the material discontinuousness, the magnetic field distribution is very complex to be analyzed in analytical forms. The magnetic fields in the air gap are determined using the finite element method. The levitation force and thrust produced by the levitation magnetic field and the propulsive magnetic field are calculated. They are found to vary following the change of the air gap and exciting current. A magnetic field strength measurement system based on a hall sensor is designed. Experimental results are compared with the results from the magnetic field analysis.