Abstract: This paper presents the measurement of the frequency of a single sinusoid by counting the zero crossings and extends it above the Nyquist limit. For this purpose, two sets of samples are acquired, at two different but close sampling frequencies. Based on the count of zero crossings obtained in each case and on the two sampling frequencies, four coefficients are computed. Then, the most appropriate coefficient from those four is used for calculating the frequency. The less the difference between the two sampling frequencies, the higher the maximum measurable frequency. The relative error is of the order of 0.0001, and the measurement time is about 100 ms. The method was experimentally tested using a National Instruments PCI 6023 data acquisition board.
Keywords: Frequency, sampling frequency, Nyquist limit, zero crossings, maximum measurable frequency.