Research And Development Of The System Of Thickness Measurement By Virtual Capacitance Sensor

With great development of modern industry, the demands of flimsy nonmetal products are increased enormously, such as plastic film, all kinds of papers and medical ointment, etc. In these products, thickness and uniformity are the most important technical indexes, and they are measured by method of off-line in our country. When this method is used, time and manpower are wasted, big errors and low efficiency are produced, it can't adapt to the modern extensive production. While the automatic level of dynamic thickness measurement is high in foreign countries, the systems'price is also high, that is hard to be accepted by most of our enterprises. Therefore, a sort of on-line system of thickness measurement is needed in market, which is cheap, reliable, and easy to operate.In this thesis, virtual instrument technique and capacitance micrometer were adopted, and a system of measuring flimsy nonmetal products'thickness to meet industrial requirements was developed. The main work of this paper is as follows:1. Started from the basic principle of capacitance sensor, the advantages, disadvantages and feasibility to measure nonmetal materials'thickness with capacitance sensor were analyzed. The edge effect was researched theoretically by FEM (Finite Element Method) emulation and precise capacitance calculation, while the parameter design of capacitance sensor's dimension was optimized.2. To cooperate with columnar-parallel-plane capacitance sensor with five layers, amplitude modulation circuit with model of capacitance operation amplifier was chosen as signal conversion circuit. Meanwhile,all relevant measuring circuits were designed.3. Virtual instrument technique was applied to the system of thickness measurement. Based on USB data collection, virtual instrument system was constructed. Virtual panel and relevant application programs were designed by LABVIEW.4. By the experiments of empty load test and mica paper's thickness measurement, performance indexes of system were assessed, meanwhile,the measuring errors were analyzed and solutions were presented. The system of measuring mica paper's thickness was perfect proved by experiment, and it could be also extended to other nonmetal products'thickness measurement.