Capacitive sensors use various types of capacitors as sensing elements to convert the measured physical quantity or mechanical quantity into capacitance variation conversion device. Capacitive sensors have the advantages of simple structure, high temperature resistance, radiation resistance, high resolution, good dynamic response characteristics, so they are widely used in pressure, displacement, acceleration, thickness, vibration, liquid level. Proximity sensors have the characteristics of reliable work, high accuracy of repeated positioning, no mechanical wear, no noise, strong vibration resistance and so on. In automatic control system proximity sensors can be used as limit, count, positioning control and automatic protection link. They are widely used in machine tools, metallurgy, chemical industry, textile and printing industries.