Analysis of the Effect of Air Gap on the Performance of Self-inductance Displacement Sensor

Inductive displacement sensor is one kind of the common sensors widely used in magnetic bearing system. In this paper, the working principle and output characteristics of the self-inductance displacement sensor are analyzed. For magnetic levitation rotor with a shaft diameter of 44.2mm, self-inductance displacement sensors with different air gaps are respectively designed. The magnetic field distribution and output characteristics of the designed sensor are simulated by finite element analysis method. Theoretical analysis and simulation results both show that there is a very good linear relationship between the output voltage and the rotor displacement of differential self-inductive displacement sensor when the displacement of rotor is in the range of -0.4 to 0.4(mm). Simulation results show the sensitivity of the self-inductance sensor is inversely proportional to the equilibrium air gap. With the increasement of air gap , the relative change value of total inductance is decreasing. When the rotor displacement is small relative to the equilibrium air gap, the relative change of total inductance is smaller and it can be considered unchanged. At this time, the amplitude of the current in the coil is basically unchanged when the voltage amplitude of the driving power is unchanged.