Research And Implementation Of Capacitive Micro-displacement Measurement System Based On AD7747

With the rapid development of science and technology and increasing demand for industrial production, people put forward higher and higher requirements for precision measurements. Capacitance micrometer technology as an important means of non-contact decay displacement measurement, due to the measuring instrument has the advantages of simple structure, high resolution, good dynamic characteristics, strong anti-jamming capability, which has been more and more widely used in the ultra precision machining, precision positioning, precision measurement, and other fields.This paper is based on the distance measurement principle of the changeable pole pitch type capacitive displacement sensor, combined with digital measurement circuit and related data processing method, we complete the development work of the capacitance displacement measurement system. Firstly, through the specific analysis we design and make out the sensor probe that can meet this paper's demand of actual measurement, analysis the advantages and disadvantages of several common capacitance measurement circuit, combined with the sensor designed in this paper has certain limitations in measuring the occasion, the actual demand of measuring circuit should be simplified, we put forward the digital measuring circuit with AD7747 chip as the core, and put it in the sensor probe, which can reduce the sensor size. Secondly, the displacement measurement system is divided into the main control module, signal isolation module, display module and data communication module, and design the corresponding hardware and software. In addition, the PC measurement software is divided into two modes: system debugging mode and system measuring model, and design the software of them respectively. Then we design and build a calibration platform of displacement measurement system, and complete the work of the calibration of displacement measurement system through the method of indirect calibration, then we get a group of capacitance- displacement data, and we process these data by spline interpolation, then get the capacitance-displacement measuring curve of displacement measurement system, and put forward the concrete calculation method of displacement. Finally, in order to improve the accuracy of the measurement system and reduce the measurement error of displacement measuring system in the specific measurement environment, obtain the capacitance displacement measuring curve can really applicable to the current measurement environment, this paper put forward respectively the data in debugging mode and measuring model of the displacement measurement system of compensation measures.At last, using the capacitance-displacement measuring curve, we put the displacement measuring system which has been completed in the laboratory environment, and make the linearity experiment, resolution experiment and repeatability experiment, we get the static performance of the measuring system through the experiment: the linearity of the capacitance micro displacement measuring system which is designed in this paper is better than 0.39%, the resolution can achieve 0.68?m, the repeatability is 0.63 ?m.