Cylindrical Measuring Method Based On Capacitance Sensor

Detection technology is a measure of the value of the measured object,to obtain useful infornation for the characterization,to provide the basis for the production control process.Detection technology's development is inseparable from the scientific and technological progress,they are both closely linked,supplenent each other. The advent of AD7747 chip solved parasitic capacitance effects of capacitance sensor, make capacitance sensor used more widely, promoted the development of detecting technology.The piston of compressor in automobile air conditioning is the core component of air conditioning system, its operation condition is more harsh than common air conditioning compressor. Meanwhile, car air-conditioning required to achieve durable, which requires air-conditioning compressor longer life.The size of compressor piston and the annual output are high,in order to meet its needs,this paper designed a measuring circuit to protect the factory requirements.The paper had four parts to describe this circuit.First,it disscussed the corresponding theory in detail,including capacitive sensor,the∑-△technology of ADC and the error evaluarion of cylindricity,providing a reliable theory foundation.Secondly,the hardware related to the measuring head of capacitance,external design and internal structure of AD7747,the section of SCM,etc,designed the circuit with measurement and controlling.Again,introduced the software design of the system,including I2C serial bus,the agreement between I2C bus and AD7747,the internal register of AD7747 and relevant setting in this paper,the program flow and so on.Finally,showed the feasibility of measuring circuit through an example,and compared with the tri-ordinate measuring machine data.The innovation of this paper was that it measured cylindricity using capacitance sensor exploratively,using capacitor sensor combined with AD7747 to measure cylinder-type specimens,evaluating cylindricity error with minimum area cylindrical method,the design circuit could detect the cylindricity of piston specimens.