Study And Application Of The Mechanism Of The Magnetostrictive Linear Position Sensor

The magnetostrictive linear position sensor (MLPS) is a kind of sensor that can get the distance between the measured point and the receiving point by measuring the time difference between the excitation and the receipt of elastic waves. In the MLPS system, an impact load can be generated in the magnetostrictive wire due to the joint effect of the permanent magnet and the exciting magnetic field, and at the same time, the arisen elastic waves propagate to two ends of the wire. The propagation of elastic waves can cause a local distortion in the magnetostrictive wire, and under the effect of the inverse magnetostrictive effect, the magnetic domains deflexion brings about the change of output signals of the pick-up coil. Through our calculations, we have established a mathematic model of the generation, propagation and detection of the elastic waves. We have described in a mathematic way the conversion process of electromagnetic energy to mechanical energy, the propagation process of mechanical energy in magnetostrictive wire, the transformation process of mechanical energy into electromagnetic energy and at last its conversion to the voltage signals. In Chapter II, according to the working principle of the MLPS, we have analysed the magnetostrictive performance as well as other characteristics of Ni-Span-C used in MLPS, and we have discussed the magnetization of domains in the magnetostrictive wire. In our study, we have made some experiments, analysed the space distribution of the permanent magnet's field, studied the characteristics of the magnetic domain's deflexion in the wire under the effect of different outer magnetic fields, and we have analysed the electromagnetic phenomena in MLPS system.In Chapter III, from the joint effect of the permanent magnet's field and the circumferential magnetic field induced by the driver pulse current, as well as the deflexion characteristics of the magnetic domains, we have studied the generation mechanism of the induced waves in MLPS. From the point of view of the load on particles in the magnetostrictive wire, in reference to the elastic kinetics theory, we have explained the generation mechanism of the elastic waves in MLPS and analysed the characteristics of the torsional waves. We have proved in our experiments that the elastic waves are the joint effect of the waves drived by positive edge and those by negative edge. We have analysed the local magnetic force of the elastic waves in MLPS and established the resultant torque mathematical model. According to the propagation mechanism of the elastic waves, we have analysed in a mathematic way the energy conversion in the detection of the elastic waves. From the point of view of the conservation of energy, we have analysed the phenomenon that the elastic waves can show different amplitudes under the effect of an outer magnetic field on the magnetostrictive wire. We have designed a driver pulse current circuit in the MLPS. According to the generation condition of the elastic waves and our experiment data, we have determined the parameters of the driver pulse current.In Chapter IV, on the basis of our study about the mechanism of the MLPS, we have made a test platform, tested the performance of the MLPS and given the precision analysis. We have made an analysis of the results after having tested the induced waves and the elastic waves of several magnetostrictive wires made in China and abroad.