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The stress-type vortex flow meter,which based on Karman vortex street principle ,are widely used to measure liquid, gas and steam flow,because of its high sensitivity, good stability, low cost, and etc. However, there are two major problems of vortex flow meter: First, the signal can not be detected low flow rates, so making the range more than limited; Second, High power consumption, can not be used in harsh industrial environment field. For these two problems, we design a low-power vortex signal processing system based on STM32 which uses method of combining analog filtering and digital spectrum analysis for output signal acquisition and processing of the vortex sensor.Vortex flow meter system is the design category of secondary instrument, the object is to deal with the weak piezoelectric charge that output of piezoelectric sensor, This paper analyzes the characteristics of output signal and noise from the piezoelectric vortex sensor, according to the signal characteristics, we use low power operational amplifier TLV2252 and TLV2254 of TI to design Preamplifier circuit, including a charge amplifier, programmable gain amplifier, low pass filter and Schmitt shaping circuit, Pre-treat the Q/V conversion, amplification, filtering, shaping of the output signal of vortex sensor, then output two signals success: 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. Signal acquisition operation and the control circuit used ST’s low-cost, low-power STM32F103RBT6 core processor of Cortex-M3 as the control. The part of the circuit includes a STM32 processors circuit, serial communication circuit, LCD interface circuit to complete the signal acquisition, analysis, calculation, and control liquid crystal to display the results.This software to complete some function of the vortex signal acquisition, spectral analysis, and program-controlled adjustment of magnification, the frequency calculation and display. Development tools are IAR Embedded Workbench for ARM, using C language programming. The main control module by calling a variety of routines to accomplish specific functions. Vortex signal with frequency, amplitude span a wider range of features, use of fixed sampling points, variable sampling frequency FFT algorithm, calculated power spectrum according to FFT calculation results, the last and then work out frequency of vortex signal according to amplitude information, Not only meet the requirements of low power system, real-time, but also improves the measurement accuracy.This project is achieved the idea of the design implementation of a hardware circuit, completed the writing and debugging of system software, furthermore ,the water flow in the laboratory test results show that: the high system anti-interference ability, high accuracy, and expand the range limit, low power consumption, so it can be used to measure small flows.
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