Patent ID: 7073395

Claim:
An ultrasonic flowmeter comprising: first and second ultrasonic transducers that send and receive an ultrasonic wave and are arranged so as to form a propagation path for the ultrasonic wave in a flow path of fluid; a transmission unit and a reception unit that drive the first ultrasonic transducer and the second ultrasonic transducer such that the ultrasonic wave is sent and received in two ways between the first ultrasonic transducer and the second ultrasonic transducer, and receive the ultrasonic wave; a zero-cross detection unit that measures a propagation time of the ultrasonic wave by subjecting a received signal generated by the ultrasonic wave received in the reception unit to zero-cross detection; and a correction unit that reduces an error in the zero-cross detection caused by noise superimposed on the received signal, wherein the correction unit includes: a level detection unit that measures amplitude of a predetermined wave of the received signal; and a correction data storage unit that stores data indicating a relation between the amplitude of the predetermined wave and the propagation time of the received signal, and the correction unit corrects the propagation time according to a magnitude of the amplitude of the predetermined wave dn the basis of the data, and the ultrasonic flowmeter calculates a flow volume of the fluid on the basis of the propagation time.