Research On Measuring Technique Of Mass Flowmeter

Coriolis Mass Flowmeter (CMF) is a type of direct mass flowmeter, which is named with Coriolis, a French scientist. It is based on the principle that while liquid flows inside an oscillating pipe, the Coriolis Force generates in a direct ratio to the mass flux of the liquid. CMF products take the advantage of measuring directly the mass and density of liquid and being not disturbed by form and conglutination of liquid. Due to the restriction on technique, up to now, our nation's CMF products have default of low precision and obvious zero drift, so our CMF products comes mainly from import.In CMF system, the signal process of phase difference is a key technology having an effect upon precision of measurement. After a analyzing of measure principle and development status, the paper deeply researches the signal process of phase difference in CMF system. A linear interpolation algorithm used in phase difference measurement is presented after analyzing and comparing several method of phase difference measurement. Its basal principle is to find two corresponding point with close amplitude and compute their time difference, which can indicate the phase difference. These two sampling points are around at the zero of two sinusoidal curves which are near to linearity around their zero-points. The algorithm can eliminate the effects of high-frequency noise and zero drift well from the analysis of simulation result. Otherwise, in the designing process of excitation circuit, it can make the vibration generator change after the sounding pipe changes with frequency tracking. This gives support for accuracy of phase difference measurement and CMF system. Based on the algorithm a type of hardware system is developed and data acquisitions, CPLD design and single chip design are presented in detail. Next, the hardware system is experimented and debugged.A signal process algorithm in CMF system based on digital phase-lock loop (DPLL) is presented in the article after a great many documents are consulted. The result of simulation and analysis indicates the algorithm can eliminate the effects of the high-frequency noise and fixed-frequency disturb very well. The algorithm supplies the theory reference on developing the CMF system with digital signal processor (DSP) to improve the performance of CMF products.