Transient Response of a Novel Displacement Transducer for Magnetic Levitation System

Abstract

Problem statement: In magnetic levitation system, position sensors are used to obtain a voltage proportional to the position of the suspended object. This is an essential feedback signal for stabilizing the system. These sensors make the system clumsy and prone to failures. To eliminate any physical attachment on the levitated object for the purpose of measuring its displacement, a novel magnetic displacement transducer has been designed. Approach: Variation in inductance of the transducer with the position of the levitated object was used to detect the position of the object. Coil of the transducer was excited by a 5 kHz voltage and variation in phase angle of its current was measured by synchronous demodulation method. Transient response of this system was also obtained for step change in the position of the levitated object. Results: By simulation as well as by experiments it was observed that a minimum delay equal to one and a half times the cycle time of the exciting frequency was always present. The delay further increases with increase in order of the filter. In magnetic levitation applications, mechanical frequency of the levitated object was generally below 10 Hz and therefore a delay of around 300 micro seconds with an exciting frequency of 5 kHz was acceptable. Steady state characteristic of the transducer was nearly linear and it was further linearized by using a look up table and cubic interpolation. Signal output from synchronous demodulation circuit had been digitally processed for application to magnetically levitated system. Conclusion: A novel yet simple circuit for sensing the position of the moving object for electromagnetic levitation system is developed. The transient response of the developed system is also obtained and the simulation results are verified experimentally.