Ultrasonic anemometer

A signal processing apparatus for a fluid velocity measuring system, including:

• a plurality of electroacoustic transducing means mounted in spaced apart relation to one another within a fluid flow, said transducing means cooperating to define a set of linear bidirectional acoustic signal propagation paths comprised of one of said propagation paths between each pair of the transducing means;
• a first signal generating means for generating a first electrical signal in the form a continuous wave;
• a second signal generating means for generating a second electrical signal in the form of a an individual pulse;
• a coupling means for selectively electrically coupling the first signal generating means and the second signal generating means with the transducing means to cause the transducing means to generate a continuous wave acoustic signal in response to receiving the first electrical signal and, alternatively, to generate an acoustic pulse in response to receiving the second electrical signal;
• wherein each the transducing means, in response to receiving the acoustic continuous wave signal and the acoustic pulse, respectively generates a third electrical signal in the form of a continuous wave and a fourth electrical signal in the form of an individual pulse;
• a detecting means coupled to the transducing means and to the first and second pulse generating means, for sensing the first, second, third and fourth electrical signals;
• a counting means coupled to the detecting means for generating a plurality of values with respect to each of the propagation paths, including first and second values representing acoustic signal propagation times along the associated path in first and second opposite directions, and third and fourth values representing propagation time of the pulse in the first and second directions;
• and
• a computing means coupled to the counting means for calculating, with respect to each propagation path, a composite signal propagation time in said first direction based upon the first and third values, and a composite signal propagation time in the second direction based upon said second and fourth values.

In a fluid flow measurement system including at least three spaced apart electroacoustic transducers defining a plurality of linear, co-planar and bidirectional acoustic signal propagation paths in at least three non-parallel directions between adjacent pairs of the transducers, a process for measuring fluid flow velocity and direction in the plane of the signal propagation paths, including the steps of:

• causing each one of the transducers to generate acoustic signals and alternatively to receive acoustic signals generated by at least one of the other transducers;
• determining respective signal propagation times corresponding to propagation of the acoustic signals in first and second opposite directions along each of the propagation paths;
• computing a fluid velocity value V along each of the signal propagation paths, each value V being a vector in the direction of its associated signal propagation path and computed based on the signal propagation times in the first and second directions along the associated path;
• determining whether any of the vectors V is at least substantially aligned with the direction of fluid flow, to identify each of the vectors V as either so aligned or non-aligned;
• and
• combining only the non-aligned vectors V to provide a single resultant vector representing fluid flow velocity and direction.