Conventional digital method for low frequency measurement based on counting the pulses over a fixed amount of time requires abnormally large time. On the other hand, if the reciprocal of the time period is measured, the time is reduced to one period only. Based on this principle, a method is presented for low-frequency measurement with reasonable accuracy over a narrow band of frequencies. The method is verified experimentally. This will find many applications such as measurement of power frequency changes.
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