Patent ID: 8141434

Claim:
A flow measuring apparatus ( 300 , 500 ) for measuring a flow of a fluid ( 130 ) within a conduit ( 120 ) including one or more walls ( 110 ), said apparatus ( 300 , 500 ) including a transducer arrangement ( 100 A, 100 B) including at least one transducer for emitting ultrasonic radiation into the flow ( 130 ) and at least one transducer for receiving ultrasonic radiation from the flow ( 130 ) in operation, and a signal processing arrangement ( 310 ) for generating signals to excite the transducer arrangement ( 100 A, 100 B) and for processing received signals provided by the transducer arrangement ( 100 A, 100 B) for generating output signals from the signal processing arrangement ( 310 ) indicative of properties of the flow, characterized in that said transducer arrangement ( 100 A, 100 B) in cooperation with said conduit ( 120 ) is operable to provide a first path ( 200 ) solely via said one or more walls ( 110 ) for Lamb-wave ultrasonic radiation coupling directly from the at least one transducer for emitting ultrasonic radiation to said at least one transducer for receiving ultrasonic radiation to generate a first received signal; said transducer arrangement ( 100 A, 100 B) in cooperation with said conduit ( 120 ) is operable to provide at least one second path ( 210 ) for propagation of ultrasonic radiation within said one or more walls ( 100 ) via Lamb waves coupling to at least a portion of said flow ( 130 ) from the at least one transducer for emitting ultrasonic radiation to the at least one transducer for receiving ultrasonic radiation to generate a second received signal; and said signal processing arrangement ( 310 ) is operable to determine from said first and second signals ultrasonic radiation propagation time periods through the first path ( 200 ) and through the at least one second path ( 210 ) in upstream and downstream flow directions, and to perform computational operations on said propagation time periods to determine said properties of the flow in respect of at least one of: a flow velocity (v) of the fluid ( 130 ) in the conduit ( 120 ), a velocity of sound (c) through the fluid ( 130 ).