Design Of Multi - Parameter Adaptive Gas Vortex Flowmeter Based On ARM

Based on Karman vortex street principle, the vortex flow meter has advantages on low pressure loss, good stability and high adaptability on a variety of medium, which is widely used for measuring liquid, gas and steam flow. However, there are two major problems of vortex flow meter. First, signal could not be accurately measured in low flow rates, making the range more than limited. Second, the products on the market are both complement usage with fixed measuring range and diameter. We have to customize the secondary instrument in consequence of different diameter and medium in engineering applications, which increase the using cost. For those two problems, we design a multi-parameter adaptive vortex flow meter based on ARM which uses method of combining analog filtering and digital spectrum analysis for output signal acquisition and processing of the vortex sensor, enhancing the measurement accuracy, reducing the measurement limit, meeting the requirements of different instrument and medium.This paper analyzes the characteristics of output signal and noise from the piezoelectric vortex sensor. According to the signal characteristics, design Preamplifier circuit, including a charge amplifier, programmable gain amplifier, low pass filter, Schmitt shaping circuit and light-coupled circuit. Preamplifier circuit pre-treat the Q/V conversion, amplification, filtering, shaping of the output signal of vortex sensor, then output two signals:one is the vortex signal near-sinusoidal by low-pass filter; another is the square wave pulse equal to vortex signal frequency by Schmitt circuit. The control circuit used low-cost, low-power STM32F107VCT6 core processor of Cortex-M3 as the controller to complete the function of signal acquisition, analysis, calculation and display.The software mainly complete the function of the vortex signal acquisition, spectral analysis, program-controlled adjustment of magnification and the frequency calculation, Correction and display. Development tools are IAR Embedded Workbench for ARM with C language programming. Combining the characteristics of vortex signal with frequency, amplitude span a wider range of features, use of fixed sampling points, variable sampling frequency FFT algorithm, calculated power spectrum and Spectrum Correction according to FFT calculation results. The last and then work out frequency of vortex signal according to power spectrum information, not only reduce the measurement lower limit, but also meet the requirements of low power system.This project is achieved the idea of the design implementation of a hardware circuit, completed the writing and debugging of system software, furthermore, the gas flow in the laboratory test results show that:the advantages of the system are anti-interference ability, high accuracy, expanding the range limit, suitability to measure small flows and a wider range of application.