Qili Hou

Gas–Liquid Two-Phase Flow Correction Method for Digital CMF

There are large measurement errors in Coriolis mass flowmeter (CMF) when it is used to measure gas-liquid two-phase flow without compensation. In particular, the flowtube of CMF may stall when using analog transmitters and CMF cannot operate normally because of the high damping caused by gas-liquid two-phase. To solve above problems, a gas-liquid two-phase flow rig is developed to perform the two-phase flow experiments. A digital drive method using multiplying digital-to-analog converter and direct digital synthesizer is applied to CMF to maintain the flowtube oscillation under two-phase flow condition. A digital zero-crossing detection method based on Lagrange interpolation is adopted to calculate the frequency and phase difference of the sensor output signals in order to synthesize the digital drive signal and realize the flow measurement. The artificial neural network using back propagation algorithm is applied to correct measurement errors. A digital Coriolis mass flow transmitter is developed with a digital signal processor to control the digital drive, and realize the two-phase flow measurement and correction. By connecting the developed transmitter with a CMF025 type primary instrument, the gas-liquid two-phase flow experiments are conducted to validate the performance of the transmitter. The testing results show that the transmitter can maintain the flowtube oscillation and reduce the metering errors.

Development of Coriolis mass flowmeter with digital drive and signal processing technology.

Coriolis mass flowmeter (CMF) often suffers from two-phase flowrate which may cause flowtube stalling. To solve this problem, a digital drive method and a digital signal processing method of CMF is studied and implemented in this paper. A positive-negative step signal is used to initiate the flowtube oscillation without knowing the natural frequency of the flowtube. A digital zero-crossing detection method based on Lagrange interpolation is adopted to calculate the frequency and phase difference of the sensor output signals in order to synthesize the digital drive signal. The digital drive approach is implemented by a multiplying digital to analog converter (MDAC) and a direct digital synthesizer (DDS). A digital Coriolis mass flow transmitter is developed with a digital signal processor (DSP) to control the digital drive, and realize the signal processing. Water flow calibrations and gas-liquid two-phase flowrate experiments are conducted to examine the performance of the transmitter. The experimental results show that the transmitter shortens the start-up time and can maintain the oscillation of flowtube in two-phase flowrate condition.