Modification of the Frequency Measurement Method Based on the Application of the Amplitude Spectrum Samples Ratio

The frequency measurement technique by analyzing the amplitude spectrum is one of the most popular methods of measuring it. The widespread use of the method is due to a number of its advantages: the weak influence of harmonics, flicker and noise of the signal. It is known that the main reason for the measurement error for this method is related to the so-called “spectrum leakage” effect. As a result, approaches related to superimposing windows on the input signal are being applied. However, this approach leads to an increase in the complexity of subsequent calculations to determine the frequency due to the increased complexity of the analytical relationships linking the magnitude values of the spectral samples of the input wave and the values of its frequency. Besides, it is extremely difficult to obtain such mathematical dependencies for a number of windows, as a result of which windows that are effective in reducing the “spectrum leakage” effect are not used to measure frequency using this method. In this publication, we research a technique for power frequency assessment which is applied the values of its amplitude spectrum and ways to improve its accuracy. The influencing quantities of the “spectrum leakage” effect are considered: the input wave initial phase, frequency, sampling time and amplitude of the main spectral component. A universal approach is proposed - the power frequency assessment technique which applied the amplitude spectrum samples, which makes it possible to measure the frequency for the application of virtually any window function. The method consists of using the ratio of the two largest spectral samples to determine the exact standing of the main sample of the spectrum. To compensate the effect of frequency deviation and the input wave initial phase value on the frequency measurement error, approximation by a first-order polynomial (linear function) and approximation by a harmonic function are used, respectively. The paper discusses the most popular window