分段式液位测量变送器的研究仪器科学与技术专业论文.docxVIP

哈尔滨工业大学工学硕士学位论文 哈尔滨工业大学工学硕士学位论文 - - II - Abstract Some industries such as petrochemistry imminently need a new kind of liquid-level measuring instrument, which can detect whole range of many lays, can indicate the oil-water interface and the thickness of mixed lay. The liquid- level measuring instrument based on divided-into-segments capacitor sensor just satisfies this kind of need. Divided-into-segments liquid-level measuring instrument divides measuring range into different lays(every lay corresponds to a fixed space height) using equal-structure physical electrodes, combines analog circuit technology, digital circuit technology and singlechip technology to detect capacitor lay by lay. If same mediums are measured, the digital collections from every lay should be same or near, otherwise should be rather different. Utilizing this phenomenon, the lay where the interface is can be judged, the interface or liquid-level height can be calculated. The transducer in divided-into-segments liquid-level measuring instrument is the main research content of this paper. Firstly, the whole scheme of the transducer is designed, the transducer includes capacitance/voltage converting, ripple-control capacitor switching, magnify-multiple switching, A/D converting, singlechip, photoelectric isolation and RS-485 serial communication, etc. The measurement of microcapacitor is the key technology of transducer. After comparing many methods of capacitor measurement, the method of stray-immune microcapacitor measurement based on charge-discharge method is used, so the theory and advantage of this method are especially analyzed. Based on the whole scheme design and theory analyze, every part in hardware and software aspects is designed in details, including hardware circuit and software flow. Finally through debugging and experiment in the locale and data analyze, it is proved that the transducer has good performance, reachs the required technology standard, at the same time the places nee