Abstract: A method for operating an ultrasonic flowmeter and an ultrasonic flowmeter are provided. The ultrasonic flowmeter comprises at least one emitting ultrasonic transducer for transmitting ultrasonic signals and at least one receiving ultrasonic transducer for receiving. A control and evaluation unit actuates the emitting ultrasonic transducer such that it emits the ultrasonic signal, the receiving ultrasonic transducer receives the emitted ultrasonic signal and the control and evaluation unit determines at least one indirect value for the flow rate of the medium through the measuring tube by evaluating emitted and received ultrasonic signals. A constant measurement quality is achieved by the control and evaluation unit adapting an ultrasonic signal frequency of the emitted ultrasonic signal such that a change in an opening angle of the sound beam of the ultrasonic signal caused by a change in the value of the sound velocity of the medium is at least partially compensated.

Abstract: A method for operating an ultrasonic flowmeter for measuring a flow through a measuring tube. A control and evaluation unit controls the emitting ultrasonic transducer such that it emits the ultrasonic signal. A receiving ultrasonic transducer receives the emitted ultrasonic signal and the control and evaluation unit in the measuring operation by evaluating emitted and received ultrasonic signals. At least one indirect value for the flow rate of the medium through the measuring tube is determined from a determined signal transit time of the ultrasonic signal. The method can react flexibly to changing measurement conditions in that the control and evaluation unit controls the emitting ultrasonic transducer such that a broadband ultrasonic signal is emitted. An optimum measuring frequency range is determined in an evaluation step. The received broadband ultrasonic signal is frequency filtered into a plurality of measuring frequency ranges of the received broadband ultrasonic signal.