Research On A New Type Of Column Magnetic Reversible Level Meter With Capacitance Array Sensors

It is very important to detect the liquid level in boiler accurately in order to make the boiler work safely. Over-higher or over-lower level will cause bad quality steam or deteriorative water circulation and then arouse some accident. Column magnetic reversible level meter is credible with high tight,lacking of leaking character, which is often used to detect level of boiler. However the dry reed sensor which is used to transforming the physics signals into electric signals can only work in the condition with temperature lower 120 OC . Therefore we need to design a new kind of sensor to solve this problem.In this dissertation, a new type of column magnetic reversible level meter with capacitance array sensors has been proposed. Instead of dry reed sensor, capacitance array sensors are used for transmission. The accuracy of those sensors will affect the detecting result. In order to obtain an optimal sensor, far-element method and Trefftz-FEM are utilized to build the sensor's math model. After comparing their simulation result with the experiment value, Hybrid-Trefftz FEM is proved to be an effective way with the relative error 3.3%. ANSYS is the software for analyzing four different electrode structures of capacitance sensors and then an optimal electrode structure parameter has been gained. Based on the optimal structure parameter, the prototype of these sensors is produced.The capacitance value between electrodes is only several pfs. In order to detect the micro-capacitance, a detection circuit based on the charging and discharging principle is selected. MSP430 is used for controlling those capacitance sensors, sampling and processing. Then output PWM wave which is turned into two-line-wire 4-20MA current signal by subsequent circuit.We use this system to detect and analyze its temperature character. The result proves that the sensors can recognize every column's situation which means the sensors can judge whether the columns turn around or not. The repeatability of different electrodes is different. The better is 0.035% and the worse is 8.9%. Temperature character of system is depended on sensors and detection circuits. Capacitance array...