Patent ID: 6931945

Claim:
A Doppler type ultrasonic flowmeter, comprising: an ultrasonic transmitting means provided with an ultrasonic transducer for emitting ultrasonic pulses and adapted to direct the ultrasonic pulses from the ultrasonic transducer into a fluid to be measured that is flowing in a fluid pipe; a flow velocity profile measuring means for receiving an ultrasonic echo of the ultrasonic pulses entered into the fluid to be measured, said ultrasonic echo being reflected from a measurement region in the fluid pipe and measuring a flow velocity profile of the fluid to be measured in the measurement region; a fluid flow rate computing means for calculating the flow rate of the fluid to be measured on the basis of the flow velocity profile of the fluid to be measured; and a frequency selecting and setting means for automatically selecting a fundamental frequency of an ultrasonic wave from the ultrasonic transducer that causes a resonant transmission phenomenon to take place with respect to a pipe wall of the fluid pipe, wherein said frequency selecting and setting means controls the operation of the ultrasonic transmitting means so that an ultrasonic wave of a selected optimum frequency is emitted from the ultrasonic transducer.