| The ultrasound has been widely used in medical and flow measurement and it has special advantages. When transmitting in the fluid, the ultrasound has no influence on the flow field and no pressure loss. When the sensor is installed outside of the pipe,the direct contact between the fluid and the sensor can be avoided. This article makes a research on the ultrasonic measurement used in two phase flow.When ultrasonic measurement used in two phase flow measurement, the main problem is that: The ultrasound will reflect and scatter because of the inhomogeneity of two phase flow when transmitting in the fluid. As a result, the signal is full of chaos and the signal-to-noise ratio is very low.The article includes three parts:(1) In order to satisfy the requirement of two phase flow measurement, the article researches on coded signals and pulse compression. In consideration of practical application, this article uses linear frequency modulation coded excitation and pulse compression in consideration of practical application, the article researches the influence of time-bandwidth and chooses a suitable signal for two phase flow using ultrasonic testing technology.(2) The ultrasonic testing system that based on coded excitation and pulse compression signal is designed and implemented using FPGA. This system realizes coded signal generation, high speed A/D conversion, digital signal processing and communication based on PCI. This testing system provides a hardware platform for further study.(3) The article sets up an experimental test platform, and use ultrasonic attenuation method to test the size of gas bubbles in liquid. The experimental results show that the coded excitation signal can be used to test the size of bubbles in gas liquid two phase flow, and a higher signal-to-noise ratio and resolution can be got. This work validates the ultrasonic testing technology based on the pulse compression with coded excitation signal applied in two phase flow process parameters measurement. |
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