Research On Ultrasonic Real-time Measurement For Gas-liquid Two-phase Flow-rate Based On FPGA

With the rapid development of petroleum, chemical industry, construction andother industries as well as the increasing demand of the human for environmentalprotection, the demand for precision and measurement range of two-phase flow hasbecome more and more high in modern industry. At the present, the detectionprecision of two-phase fluid has not yet reached the industry standard, due to thecomplex characteristics of two-phase fluid. So the measurement of two-phase fluid isstill a problem. In this paper ultrasonic technology is applied to two-phase fluidmeasurement, and cross-correlation algorithm is used to analyze ultrasonic signal toachieve high-precision, adjustable range and real-time flow rate measurement oftwo-phase fluid.The adjustable range ratio measurement is the main innovation of this paper. Thepeak position of cross-correlation result is difficult to precisely determine, thereforethe measurement error is caused, and the measurement range is limited. To solve thisproblem, according to the principle of ultrasonic pulse cross-correlation technology,the method of adjusting time interval of pulse strings and sampling is proposed in thispaper. The main contents are represented as follows:Firstly, according to the solidification flow pattern hypothesis proposed byG.I.Taylor, the mathematical model of cross-correlation measurement is established.The simulation of cross-correlation of ultrasonic signal is performed by MATLAB.The realization process of cross-correlation based on FFT and IFFT is fully analyzed,and the programming and optimizing method of FFT algorithm is introduced. Themethod of expanding rang ratio of measurement is proposed based on the theory errorin the cross-correlation measurement.Secondly, the hardware system of ultrasonic measurement is designed, includingthe FPGA chip and peripheral circuits. The peripheral circuits are composed oftransmitting circuit, receiving circuit and signal acquisition circuit. The ultrasonicsignal transmission, signal receiving and acquisition are controlled by FPGA. Thirdly, the design, simulation and debugging of FPGA programming system areperformed. The system function is composed of pulse generation module,cross-correlation detection module and adjustable range module and so on. TheQuartus II development software is applied to design program, and the ModelSimsoftware is applied for simulation. The complexity of programming is much simplifiedwith the various megafunction of Quartus II. In order to ensure the calculation resultaccuracy of digital signal processing, this part is calculated in the form of floatingpoint.Finally, according to the flow rate measurement studied in this paper, theexperiment system of two-phase fluid in vertical pipe is constructed. The fluid noisesignal is acquired and analyzed. An appropriate calibration method is proposed for themeasurement result of ultrasonic cross-correlation method.