| Vortex flowmeter has been widely used in the power industry and other industrial processes to measure the flow rate because it has many advantages,such as simple structure and long working life.It is applicable to measure the flow rate of a variety of media,including liquids,pure gases and saturated steam.However,the vortex flow sensor based on the principle of fluid vibration is very sensitive to the pipeline vibration,and in practical work,the vibration is ubiquitous.The pipeline vibrations can be divided into periodic sinusoidal vibration and transient impact.When the power of vibration noise is greater than that of vortex flow signal,it is difficult for common digital signal processing methods to eliminate the interference,which will seriously affect the measurement accuracy of vortex flowmeter.Therefore,it is very important to study the method of resisting strong vibration interference in order to enhance the reliability of vortex flowmeter under complex application conditions.Aiming at the periodic vibration interference,the collected data of the vortex flow sensor output signal are filtered,and the amplitudes of the filtered signal are extracted.The fluctuations of both the amplitude and frequency are analyzed and compared.The patterns of fluctuation features are extracted by calculating and analyzing the probability density function and the cycle differenced sequence.Combining with the features of the amplitude modulation and frequency modulation,the mathematical models of the vortex flow signal,periodic vibration interference and co-frequency signal are built,and the patterns between the frequency and model parameters are obtained.The effectiveness of the three types of signal models are verified through error analysis,then the reliability of the fluctuation patterns of signal amplitude and frequency are examined,which establishes the theoretical basis for digital signal processing method based on frequency variance.The accuracy of the frequency estimation is the key to ensure the reliability of the frequency-variance based antistrong periodic vibration interference method.Based on the ratio of the Fourier coefficients a method combining bilateral correction with weighted average(RWBWFCR)is proposed so as to improve the anti-noise performance of the frequency correction.The correction principle of this method is presented.The effects on the frequency correction of changing the initial phase,the frequency deviation,the calculation points of FFT,and the signal-to-noise ratio are analyzed.The theoretical accuracy of this method when there is stationary Gaussian white noise is deduced and verified.This method has some advantages,such as less computation load,small storage space,high correction precision,strong anti-interference ability,and is easy to be implemented by a microcontroller in real time.RWBWFCR method is applied to the low-power and antistrong periodic vibration type vortex flowmeter with single sensor to solve the problem of harmonic interference and improve the reliability of the digital signal processing method based on the frequency estimation.Aiming at the transient impact interference,the experimental setup of transient impact interference is developed,and a lot of experiments are carried out.Based on the experimental data,the time-domain and frequency-domain characteristics of the transient impacts outputted by vortex flow sensor are analyzed,and the pattern of this type of interference is extracted,that is,the signal amplitudes will suddenly increase and then attenuate gradually.The linear combination of multi-groups of damped elastic system with one-degree-of-freedom is utilized to build the model of the transient impact interference.The reliabilities of the elastic vibration pattern and the model of transient impact interference are examined by the quantitative validation of the model,which lays the foundation for the study of the antistrong transient impact interference method.In order to eliminate the transient impact interference,the method of seeking for the data segment that contains this type of interference is proposed on the basis of the elastic vibration pattern.Aiming at these data segments,a segmented Kalman filter based digital signal processing method is proposed to reduce the power of transient impact interference,so that the overall power of the vortex flow signal is dominant.Then the vortex flow rate is extracted from the noisy output signal by spectrum analysis.Based on a low-power microcontroller,the antistrong transient impact interference system for vortex flowmeter is built,and the digital signal processing method of the antistrong transient impact interference is implemented in real time.Both gas and water flow experiments have been conducted to verify the validity and reliability of this system and algorithm. |
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