To enhance accuracy in detecting sound wave propagation time in a passage by providing an acoustic sensor structure and a sound wave transmitting method for reducing distortion in transmitted or received sound wave, and to enhance the measurement performance and reliability of an acoustic gas flowmeter standing on the propagation time detection.
This acoustic gas flowmeter measures the temperature and flow velocity of a gaseous fluid to find a gas flow by detecting sound wave propagation time in the fluid flowing through a duct, wherein at least a pair of acoustic sensors are disposed on opposed wall surfaces of the duct. The sensors each constitute a transmitter/receiver for sound waves in the duct, having an acoustic structure comprising a speaker with a speaker vibrator, a cylindrical sound tube of a diameter not larger than that of the speaker and a length enough to shield heat from a high-temperature fluid with its sound wave incident end directly coupled to the vibrator, and a hyperbolic horn directly coupled to a sound wave exit end of the sound tube and designed to have a cutoff frequency not higher than one fifth of the carrier frequency of an M-series PRK(phase reverse keying) signal used as a transmission signal. The gas flow is measured by driving the speaker by a signal obtained by nulling the amplitude of a half-cycle of a sine-wave pulse immediately preceding a phase inversion portion where the phase of the PRK signal is 180 degrees inverted.
OKIMURA HITOSHI
KITAYAMA YOJI
ARIMITSU YASUYUKI
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