A new method of vortex flow meter based on variable gain amplifier and band pass switched-capacitor active filter is designed. The singlechip processor measures the range and frequency of the vortex flow meter output signals by the inner analog to digital converter (A/D), and the gain of the variable gain amplifier is controlled by the digital to analog converter (D/A) of the processor, then the relative stable active signal is provided to the subsequent measurement circuits. The band pass switched-capacitor active filter traces the frequency of the variable gain amplifier output signal, it is guaranteed that the center frequency of the band pass filter is near to the signal frequency, so the favourable filter result is obtained. The frequency of the filtered signal and the flux of the liquid are calculated by the processor. The experimental results show that the complex amplifier circuit due to the large variable range of the vortex flow meter output signal is replaced, and the discontinuous problem of the signal is solved. The noise of the signal is effectively restrained because that the center frequency of the band pass filter is adjusted by the processor.
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