Signal Processing And Its Implementation Method For System Of Remotely Measuring Rotational Velocity With Spatial Filtering Technique

Rotational-velocity measurement is closely related to industrial productions,national defense and scientific researches etc.System for remotely measuring rotational velocity with spatial filtering technique should have wider application prospect,because of its non-contact,simple structure and telemetry.The basic principle of the this system is using the extracted center frequency from spatial filtering signal to calculate the rotational velocity.Therefore,it is a key point to extract center frequency from the output signal of spatial filter accurately and instantaneously.However,the amplitude and phase of the spatial filtering signal has a certain randomness,and it is a time varying narrow-band signal.All these features add to difficulty in extracting the center frequency from the signal instantaneously and accurately by conventional methods.To solve this problem,According to the characteristics of the spatial filtering signal and the time-frequency localization characteristics of wavelet transform,this paper propose a center frequency extracting method based on complex-wavelet transform.In this method,we first construct a series of complex wavelet with different center frequency on the basis of the predicted center frequency of the spatial filtering signal.Then,we implement the complex-wavelet transform on this signal,and take The central frequency of the complex wavelet with the maximum module as the center frequency of the signal.The implementation in data acquisition and processing system of this center frequency extracting method is also analyzed.To simply and effectively implement complex wavelet transform,using the m-th and(m+1)-th order derivatives of Gaussian function as a pair of orthogonal wavelets,and taken them as the real and imaginary parts to construct a complex wavelet.The m-th derivative of Gaussian function is efficient obtained by the inverse discrete Fourier transformation.In order to verify the center frequency extraction method and it's performance,we carried out both simulation experiments and practical tests with spatial filtering signal.In the simulation experiments,using the studied center frequency extraction method in this paper to extract the frequency from the sinusoidal signal of known frequency,The results show that the the center frequency can be extracted effectively by compare with the FFT method and CZ method.In the practical tests respectively using symmetrical real wavelet(including odd and even symmetric real wavelet)and complex wavelet extraction centerfrequency,by comparing with FFT method and CZ method known that the the center frequency cannot be extracted effectively by using the real symmetric wavelet(including odd-symmetric and even-symmetric wavelet).It also implies that the proposed extracting center frequency method based on the complex-wavelet transform is more accurate than the FFT method and the CZ method.Thus,this paper effectively solve the difficult problem of extracting the center frequency of spatial filtering signal instantaneously and accurately.Thus,this paper effectively solve the difficult problem of extracting the center frequency of spatial filtering signal instantaneously and accurately.