Improvement And Implementation Of Digital Signal Processing Method For Coriolis Mass Flowmeter

Coriolis mass flowmeter is a high-performance instrument，which can measurethe mass flow directly with high accuracy. It has wide range of applications andbroad application prospect. To overcome the shortages of previous algorithm inpractical applications, advanced digital signal processing method has been appliedto Coriolis mass flowmeter, and the system software has been developed based onhigh-speed digital signal processor.According to the characteristic of U type tube signal under the frequentstarting stopping flow condition, a mutation-signal model of Coriolis mass sensorsignal is proposed to describe the change patterns of signal parameters with thesudden change of flow. The existing algorithm is improved to apply to processingof the mutation signal, and the fast response system software is developed based onthe DTFT algorithm. The improved algorithm has both fast dynamic response andhigh measurement accuracy, and the precision can reach the degree of0.1underboth stable flow and mutate flow.To solve the problem of micro-bend type Coriolis mass flowmeter’s pooraccuracy in the measurement of small flow, a method consisting of two-stage filterand digital zero-crossing detection using four-point lagrange interpolation isproposed for high-precision measurement, and the whole algorithm is implementedin real time on a Coriolis mass flow transmitter developed with TMS320F28335chip. Two-stage filter can filter out the noise outside of the natural frequency of thesensor signal more thoroughly, and four-point lagrange interpolation with a smallamount of calculation can detect zeroes more accurately. Thus the algorithm isconducive to high-precision measurement of small phase difference.For the processing of high-frequency signal, the TMS320C6726chip, whichhas both powerful computing capability and high processing speed, is chosen as thecore processor of the new Coriolis mass flow transmitter. And the system softwarebased on zero-crossing detection and DTFT algorithm is developed in real time.Then the real-time demand can be met even if the sample frequency is increased forhigh-frequency signal.Finally, system tests and experimental calibrations are done to test theperformance of the digital transmitter based on TMS320C6726chip. Electrical signal test results show that the measurement accuracy of the transmitter reaches0.1%for both301Hz and701Hz signals with noise. And the experimentalcalibration results show that for the CMF025type primary instrument, themeasurement accuracy of the transmitter is greater than0.07%with the turn-downratio of15:1; for the micro-bend type tube, the measurement accuracy of thetransmitter reaches0.1%with the turn-down ratio of10:1.