Coriolis mass flowmeter (CMF) is a kind of flow measurement instrument, which can directly measure the high-precision transient mass flow parameters. Also, the vibration characteristic of the U-shaped measuring tube inside is one of the important factors that determine the measuring accuracy. The pulsating flow through the measuring tube will lead to the motion component except for the main vibration frequency, which will affect the phase difference calculation and reduce the measurement accuracy of the mass flowmeter. This article presents a method to improve the accuracy of U-tube CMF based on variable step-size least-mean-square (LMS) filter and Hilbert transform with interval shifting under pulsating flow. Experimental work was conducted on a dynamic experimental platform of pulsating flow. Experimental results show that the stability and accuracy of the proposed algorithm are better than that of the traditional CMF phase difference calibration method. The mean time difference error is $9.0525~\mu \text{s}$ , and the mean time difference relative error is 5.806%. The calibration effect is more than 88.0934% better than other traditional algorithms. It is verified that it has a good error calibration effect for pulsating flow at various frequencies.

Error Analysis and Accuracy Calibration Method of U-Tube Coriolis Mass Flowmeter Under Pulsating Flow

As an increasingly popular flow metering technology, Coriolis mass flowmeter exhibits high measurement accuracy under single-phase flow condition and is widely used in the industry. However, under complex flow conditions, such as two-phase flow, the measurement accuracy is greatly decreased due to various factors including improper signal processing methods. In this study, three digital signal processing methods—the quadrature demodulation (QD) method, Hilbert method, and sliding discrete time Fourier transform method—are analyzed for their applications in processing sensor signals and providing measurement results under gas-liquid two-phase flow condition. Based on the analysis, specific improvements are applied to each method to deal with the signals under two-phase flow condition. For simulation, sensor signals under single- and two-phase flow conditions are established using a random walk model. The phase difference tracking performances of these three methods are evaluated in the simulation. Based on the digital signal processor, a converter program is implemented on its evaluation board. The converter program is tested under single- and two-phase flow conditions. The improved signal processing methods are evaluated in terms of the measurement accuracy and complexity. The QD algorithm has the best performance under the single-phase flow condition. Under the two-phase flow condition, the QD algorithm performs a little better in terms of the indication error and repeatability than the improved Hilbert algorithm at 160, 250, and 420 kg/h flow points, whereas the Hilbert algorithm outperforms the QD algorithm at the 600 kg/h flow point.

Improvement of signal processing in Coriolis mass flowmeters for gas-liquid two-phase flow

Coriolis flowmeters are designed based on the Coriolis force principle. It has high accuracy in mass flow measurement and provides additional multi-parameter measurements such as density, temperature, and volume flow. It is widely used in industrial flow measurement. Under the condition that the flowrate of single-phase flow is stable, the control and real-time tracking of most Coriolis flowmeters can meet the measurement requirements and obtain accurate real-time flow measurement results. However, when the flow conditions change rapidly, the converter system is often unable to track the flow changes in real time, and the measurement results may lag behind or even be erroneous. In this paper, a new prototype based on Zynq for the Coriolis flowmeter converter is developed in order to solve the problem of lagging behind in the measurement results. The fast sampling rate and more computational power from Zynq can realize the real-time measurement for rapidly changing flow. An experimental study using the prototype system was carried out under water flow conditions. Preliminary results showed that the repeatability under various test conditions down to one-second batch runs is within 0.1%. This verifies that the prototype system can measure rapidly changing flows.

Design of a Fast Response Coriolis Flowmeter Converter Based on Zynq

Image Processing of Gas-Liquid Two-Phase Flow in High-Speed Photography Based on Reconstruction Algorithm

Under two-phase flow conditions, the performance of Coriolis mass flowmeters is significantly affected. A critical signal processing technique in Coriolis flowmeters is the estimation of resonance frequency and phase difference from sinusoidal vibration signals. This paper reviews three typical digital signal processing methods used to calculate phase difference, including Quadrature Demodulation, Hilbert Transform and Discrete Fourier Transform (DFT). These three methods are compared using simulated signals based on experimental results under two-phase flow conditions up to high GVFs (gas volume fractions) and low flow rate. The results indicate that, under two-phase flow conditions in particular for high GVFs and low flow rate, the three methods are affected in different degrees, and may need further modification to achieve better results under two-phase flow conditions.

Jiarong Liu

Papers

Signal processing of coriolis mass flowmeters under gas-liquid two-phase flow conditions

Improvement of signal processing in Coriolis mass flowmeters for gas-liquid two-phase flow