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Abstract

In using a fast Fourier transform for correction of a pulsation error in a conventional air flow rate measuring device, the correction is delayed due to the observation time and computation time required for the fast Fourier transform, leading to difficulty in following changes in the pulsation state at high speed. The air flow rate measuring device according to the present invention comprises an air flow rate detector that generates an output signal in accordance with an air flow rate being measured, an amplitude detector that detects a pulsation amplitude from the output signal, a low-pass filter in which the cut-off frequency changes in accordance with the value of the pulsation amplitude, and a waveform arithmetic unit that computes the waveforms of the output signal from the low-pass filter and the output signal. The waveform arithmetic unit is constituted from multipliers, an adder, and a condition determination process. The low-pass filter is constituted from a subtractor, a multiplier, an adder, and a delay element, with the cut-off frequency changing in accordance with the pulsation amplitude by changing the gain of the multiplier with the pulsation amplitude.

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First Claim