A flow measuring apparatus (300, 500) measures a fluid flow (130) within a conduit (120) including a wall (110). The apparatus (300, 500) includes a
transducer arrangement including at least two transducers (100A, 100B) for alternately emitting and receiving
ultrasonic radiation through the conduit wall (110) and the flow (130). The apparatus (300, 500) also includes a
signal processing arrangement (310) for generating signals to excite the
transducer arrangement (100A, 100B) and for
processing received signals provided by the
transducer arrangement (100A, 100B) for generating output signals from the
signal processing arrangement (310) indicative of properties of the flow. The transducer arrangement (100A, 100B) in cooperation with the conduit (120) provides a first path (200) for Lamb-wave
ultrasonic radiation coupling directly from a first of the at least two transducers (100A, 100B), to a second of said at least two transducers to generate a first received
signal. The transducer arrangement (100A, 100B) in cooperation with the conduit (120) provides at least one second path (210) for
ultrasonic propagation along the wall (100) via
Lamb waves coupling to at least a portion of the flow (130) from a first of the at least two transducers (100A, 100B) to a second of the at least two transducers (100A, 100B) to generate a second received signal. The
signal processing arrangement (310) determines from said first and second received signals
ultrasonic radiation propagation time periods through the first path (200) and through the at least one second path (210), and to perform computational operations on the
propagation time periods to determine properties of the flow including, but not limited to, at least one of: fluid flow velocity (v) in the conduit (120), a sound velocity (c) through the fluid (130).