Design And Development Of Null Cable And Integrated Capacitive Micro Displacement And Vibration Measurement System

With the development of science and technology, now high precision measurement for the micro displacement and micro vibration has been widely used in scientific research, industrial processing, aerospace, high-end equipment manufacturing and other fields. The accuracy of measurement will directly affect the quality of products and processing accuracy. At present, the capacitive sensor is most widely used in the micro displacement and vibration measurement, although it has many advantages such as high precision, good stability, simple structure, etc., but due to the measured parameters are both micro/nano levels, so stronger ability of anti-interference is needed in the system.The research status of the capacitance measurement is analyzed in this paper. The principle of micro displacement and vibration measurement is studied. On this basis, the integral scheme of null cable and integrated capacitive micro displacement and vibration measurement system is designed. In order to achieve high precision measurement, the factors affecting the measurement accuracy of capacitive sensing system are analyzed from the aspects of sensor, transmission cable, measuring circuit and so on, the corresponding solutions are given.The measurement circuit of the capacitive sensing system designed in this paper includes:capacitance/voltage conversion circuit, modulation and demodulation circuit, low pass filter circuit, zero modulation circuit, and data acquisition and communication circuits based on Cortex-M3. In the circuit, in order to prevent the interference, the special designed shielding box is adopted, and the signal conversion of the capacitance/ voltage is completed by selecting the appropriate grounding point. Due to the existing of resistors, capacitors and other components in the circuit, the phase shift of the carrier signal and the modulated signal might occur. In this case, the specific value of phase shift cannot be determined. Therefore, error caused by the phase shift cannot be eliminated. This will reduce the accuracy of micrometer. In order to eliminate the impact of the phase shift, the phase-locked-loop (PLL) circuit is employed. The schematic design of the hardware circuit is completed by using Altium Designer. The related programming software is compiled and debugged by Keil uVision4 and Microsoft Visual Studio 2010. Communication with the host computer and data display and other functions are realized. The whole system test is carried out, the relevant measurement data are obtained, and the data are analyzed and processed, the performance parameters of the whole system are obtained.In this paper, the design and development of null cable and integrated capacitive sensing system for the micro displacement and vibration measurement is completed. Under the condition of ensuring the accuracy and stability of the system, the volume of the system is reduced and the system’s intelligence and integration are enhanced. This capacitive sensing micrometer system has a wide range of applications prospects.