Research On Digital Signal Processing Methods Of Vortex Flow-Meters

Vortex flow-meter is widely used because of its many advantages.However,it is subjected to noise disturb caused by pipe vibrations and fluid turbulence.The processing circuits in the vortex flow-meter are unable to ensure the measuring accuracy in industial fields.The span ratio of vortex flow-meter is lower than the theoretic value. One of the primary researches of vortex flow-meter is to dispose vortex signal with spectrum analysis. In theory, it can implement the right measurement when SNR is more than 1, but in practical application, because of the sampling in non-complete period of vortex flow-meter signal, suffering from the influence of frequency spectrum revelation and stockade effect,the FFT power spectrum is not accurate. To gain the credible measurement, in application, SNR is needed to be more than 1 by far, so the lower limit of measurement is limited. Spectrum correction theory is applied extensively in the field of machinery vibration signal analyzing and fauts diagnose in rencent years,but its application is seldom repoted in vortex flow-meter.It has important theoretical significance and practical value to engage the research on supplement the detection method of vortex flow-meter.From the viewpoint of improving the precision of vortex flow-meter parameters in detection,this paper first reviews the development process of detection mode, and introduces the character of the usual vortex flow-meter parameters detection method and different kinds of improving method based on FFT algorithm to enhance the analysis precision, and elucidates the research background. Secondly this paper details the basic theory, form of Fourier transform, and the problems which must be paid attention to in the practical application. The reasons of the error caused by the traditional vortex flow-meter parameter detection methods base on the windowed FFT are thoroughly analyzed.The analytic representation of the error caused by spectrum leakage and the numerical model of the correcting method are proposed.Mathematical derivation of the basic principle of many kinds of discrete spectrum correction method has been carried on. The detailed steps to realize the concrete algorithm are given in this paper.The characters of various methods and its applying condition in the vortex flow-meter parameters detection are discussed and compared.In view of the character of vortex flow-meter signal, the paper uses spectrum correction to improve the measurement precision, and extends the measurement range. The paper also proposes a new method, called correlation filter, based on the relation of frequency and amplitude of vortex signal. The simulation results are obtained by MATLAB language, the software of signal processing is written by C language,and the experimental tests are carried out. The experimental result proves that this method effectively picks up the vortex signal when SNR is less than 1.