Research On Secondary Instrument Of High Pressure Bi-directional Elliptical Gear Flowmeter

Elliptical Gear Flowmeter is widely used in petroleum industry, chemical industry and hydraulic industry due to its advantages such as high precision, simple installation, stable performance and excellent repeatability. But the elliptical gear flowmeters made in China can be used only in low pressure situation at present because they don't endure high pressure, thus we have no choice but to use the high pressure flowmeters imported in high pressure situation. Therefore, the research on high pressure elliptical gear flowmeter will be conducive to widen the application of elliptical gear flowmeter and promote the development of flow metrology in China.Combining with domestic and foreign literatures, the thesis discusses the classification and operating principle of flowmeter, emphasizes on discussion of the operating principle, typical structure, advantages and disadvantages of elliptical gear flowmeter and summarizes the classification and development trend of the secondary instrument of flowmeter. Analyzing the structure of high pressure bi-directional elliptical gear flowmeter and considering the requirements of manufacturer, a structural design of secondary instrument with no CPU is put forward. The design adopts the measurement period method to measure flow, realizes multiplication and division operation by programming the EPROM which stores and outputs data in BCD code, and adopts the method of detecting electrical level to judge the direction of flow. The following research work is to design the function modules of the secondary instrument, introduce their composition and working principle in detail and analyze the characteristics of cascaded synchronous counters circuit, control-pulses-producing circuit and direction judgment circuit. Finally, the secondary instrument is developed, and experimental systems are designed and constructed to test the function of secondary instrument. The experimental studies shows that the secondary instrument works with fast time response, good linearity and big measurement range ratio which reaches 1000, realizes the judgment of flow direction and can compensate flow by firmware in the EPROM.The main content of each chapter is as follows:In chapter 1, based on the domestic and foreign literatures, the classification and operating principle of the flowmeter is introduced, and the operating principle, typical structure, advantages and disadvantages of the elliptical gear flowmeter are discussed emphasizly. The classification and development trend of the secondary instrument of flowmeter is summarized. In chapter 2, the structure of the high pressure bi-directional elliptical gear flowmeter and sensor are analyzed. The type of the detecting element is selected.In chapter 3, based on the condition that the flow signal is detected by magnetic-sensing sensor, the methods to measure flow and judge the direction of flow are theoretically analyzed.In chapter 4, a structural design of secondary instrument with no CPU is put forward. The secondary instrument of the high pressure bi-directional elliptical gear flowmeter is designed and developed. The composition and working principle of each function module of the secondary instrument are introduced. The circuits of the function modules are simulated.In chapter 5, experimental systems are designed and constructed to test the function of secondary instrument.