Min Fang

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.

Mathematical Modeling of Ultrasonic Gas Flow Meter Based on Experimental Data in Three Steps

According to experimental data, the features of ultrasonic echo are studied, and a new mathematical model of ultrasonic gas flow meter is built so as to reflect the effects of the excitation signal and gas flow rate on ultrasonic echo. This mathematical model consists of three parts, and is established in three steps. An amplitude sub-model expressed as a polynomial is set up with the curve fitting method to express the non-linear relationship between the echo amplitude and the gas flow rate. A process sub-model described as an output-error model is established by the system identification method to reveal the influence of excitation on the echo shape. A delay time sub-model is built with piecewise fitting to obtain a relationship between the propagation time and the gas flow rate. These sub-models can quantitatively analyze the relationship between the excitation signals, gas flow rates, ultrasonic echo amplitudes, shapes, and propagation time.

Frequency-Variance Based Antistrong Vibration Interference Method for Vortex Flow Sensor

Vortex flowmeter is apt to be disturbed by pipe vibration in industrial applications. It is a very difficult problem to be solved, and affects the applications of vortex flowmeter. To solve this key problem, the frequency features of the flow signal and vibration noise are analyzed. A frequency-variance algorithm is proposed to deal with the vortex flow sensor output signal. A variance threshold is set to distinguish the vortex flow signal from the vibration noise interference. A signal processing system based on an ultralow-power microcontroller is developed to implement the algorithm and to extract the flow rate information from the signal containing strong vibration noise. At the same time, this system meets the requirements of low-power and two-wire mode, and can be used in process control. The strong vibration experiments are conducted to validate the effectiveness of both antistrong vibration algorithm and the system. Only one vortex flow sensor is required in the vortex flowmeter, which avoids the design and installation of the vibration sensor and saves the costs of meter.

Energy transfer model and its applications of ultrasonic gas flow-meter under static and dynamic flow rates

Most of the ultrasonic gas flow-meters measure the gas flow rate by calculating the ultrasonic transmission time difference between the downstream and upstream. Ultrasonic energy attenuation occurs in the processes of the ultrasonic generation, conversion, transmission, and reception. Additionally, at the same time, the gas flow will also affect the ultrasonic propagation during the measurement, which results in the ultrasonic energy attenuation and the offset of ultrasonic propagation path. Thus, the ultrasonic energy received by the transducer is weaker. When the gas flow rate increases, this effect becomes more apparent. It leads to the measurement accuracy reduced, and the measurement range narrowed. An energy transfer model, where the ultrasonic gas flow-meter under without/with the gas flow, is established by adopting the statistical analysis and curve fitting based on a large amount of experimental data. The static sub model without the gas flow expresses the energy conversion efficiency of ultrasonic gas transducers, and the dynamic sub model with the gas flow reflects the energy attenuation pattern following the flow rate variations. The mathematical model can be used to determine the minimum energy of the excitation signal for meeting the requirement of specific measurement range, and predict the maximum measurable flow rate in the case of fixed energy of excitation signal. Based on the above studies, a method to enhance the excitation signal energy is proposed under the output power of the transmitting circuit being a finite value so as to extend the measurement rage of ultrasonic gas flow-meter.

Feature Patterns Extraction-Based Amplitude/Frequency Modulation Model for Vortex Flow Sensor Output Signal

To solve the key problem that vortex flowmeter is susceptible to be disturbed by pipe vibration, the collected data of the vortex flow sensor output signal are filtered, and the amplitudes of the filtered signal are extracted. The fluctuations of both the amplitude and frequency are analyzed and compared so as to study antistrong vibration interference digital signal processing methods for vortex flowmeter. The patterns of fluctuation features are extracted by calculating and analyzing the probability density function and the cycle differenced sequence. Combining with the features of the amplitude modulation and frequency modulation, the mathematical models of the vortex signal, vibration interference, and cofrequency signal are built, and the patterns between the frequency and model parameters are obtained. The effectiveness of the three types of signal models is verified through error analysis, then the reliability of the fluctuation patterns of signal amplitude and frequency is examined, which provides the basis for digital signal processing methods based on fluctuation features.