An apparatus for measuring a flow velocity of a fluid in a pipe includes: a housing in which a first ultrasonic transducer and a second ultrasonic transducer are arranged at a predefined distance to each other, the first ultrasonic transducer including a first sound transmitting element and a transmitter/receiver unit mounted thereto which emit first ultrasonic pulses at different angles, the second ultrasonic transducer receiving the first ultrasonic pulses and generating a first electronic output signal, the second ultrasonic transducer including a second sound transmitting element and a transmitter/receiver unit mounted thereto which emit second ultrasonic pulses at different angles, the first ultrasonic transducer receiving the second ultrasonic pulses and generating a second electronic output signal; and a control and evaluation unit electrically coupled to the first and second transducers, the control and evaluation unit tuning the first transducer to generate a first electronic output signal of a maximum amplitude.