| 摘要 |
An ultrasonic apparatus measures the concentration and flow rate of a sample gas by calculating a possible propagation time range on the basis of the gas temperature, determining whether or not the phases at which two firs t trigger signals, respectively generated on the basis of forward and backward waveforms of the ultrasonic waves, coincide with each other, processing the zero-cross signals so that the phases coincide with each other, obtaining reference zero-cross time instant by calculating mean value of the forward a nd backward zero-cross time instants, obtaining an ultrasonic reception point b y subtracting an integral multiple of the cycle of the ultrasonic waves so tha t the results of the subtraction falls into a possible propagation time range and estimating the ultrasonic propagation time on the basis of the ultrasoni c reception point.
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