Design And Realization Of Glass Surface Water Testing System Based On Capacitance Edge Effect

With the development of science and technology, the requirements of the glass surface water measurement technology, such as the measurement of the water volume on the surface of industrial instruments and the detection of the rainfall on the vehicles, have been increased remarkably in the field of industry and civilian. Precise measurements of water can not only reflect important information of instruments, but also promote the machine automation. To optimize the practical application of glass surface water measurement, capacitance sensors, which are non-invasive, non-radiative, and structurally simple, are used as measurement carriers in this thesis. In consideration of the good measurement capability of the capacitance sensors' fringe effect in measuring the thickness of non conductive objects, a series of researches of the design and implementation of glass surface water measurement system based on the capacitance sensors' fringe effect are preceeded.In this thesis, the fringe capacitance sensors' evaluation indexes are researched and evaluated by measuring the water volume on the glass surface, reading a large number of related literatures, and proceeding large numbers of experiments based on the capacitance sensors' fringe effect. The influences of the adjacent sensors' area, the plate distances, and the effective length of the plates on the sensors' performance indexes are analyzed. By using multi-physics simulation software COMSOL, the sensor performances of different kinds of fringe capacitance sensors, such as multi-ring, round arrays, flower, and other structures fringe capacitance sensors, are analyzed and compared. A new single-ring structure adjacent sensor is constructed and optimized based on the result of the analysis of the influences of the sensor structure on the capacitance sensor output. To enhance the weak output of the fringe capacitance sensors, a data acquisition/conversion circuit based on AD7142 and PIC8F452 is designed. Signal acquisition, de-noising, filtering, communication, display, and storage program are programmed in MPLAB IDE. A PIC-based experimental platform is built to research and analyze the measurement of water on the glass surface.Based on the experimental system and the program programmed in the MPLAB, a glass surface water measurement system is established. By using the measurement system, a series of experiments are proceeded to measure the water volume on the glass surface and the simulation results are proved to be similar with the experiment results. The error sources of the system and the error compensation methods are analyzed. All the experiments show that this glass surface water measurement system is effective and has a good precision in measuring water volume.