Ultrasonic system for measuring fluid impedance or liquid level
First Claim
1. An ultrasonic system for measuring at least one selected impedance related parameter of a fluid comprisinga solid member capable of supporting the propagation of moderately directional, bulk SV shear waves without mode conversion,transducer means acoustically coupled to said member for generating and detecting said SV waves propagated along a multiply-reflected path that includes at least two reflections in a region of said member remote from said transducer means and is at least partially immersed in said fluid to form a solid-fluid interface, said reflections having an angle of incidence that exceeds the first critical angle by at least five degrees and is at least ten degrees less than the second critical angle,said path lying in a portion of said member that is substantially homogeneous and flaw free and said SV waves having a frequency that lies in the range of 0.5 to 5 MHz to minimize energy loss by absorption and maximize energy loss by coupling to said fluid at said reflections in said remote region, andmeans for sensing the attenuation of said waves along said path at said interface to measure said selected impedance related parameter.
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Abstract
An ultrasonic system that measures either the impedance of a fluid or liquid level utilizes moderately directional, bulk SV mode sound waves generated by a transducer and propagated in a homogeneous, flaw-free solid member. The SV wave propagates in the solid along a zigzag path that reflects at a solid-fluid interface in at least two areas and at an angle of incidence that exceeds the first critical angle by at least five degrees and is less than the second critical angle by at least ten degrees. The attenuated amplitude of the wave due to acoustic coupling between the solid and the fluid measures the impedance or an impedance related parameter of the fluid. The system preferably includes a second acoustic path that serves as a reference to compensate for changes in parameters such as temperature, the nature of the fluid, the transducer, the transducer coupling, and residues or corrosion at the solid-fluid interface. In another form, the reference mechanism is a series of reflections from notches in the solid member. For liquid level measurement desensitized to variations in the liquid impedance, the solid is an elongated member that is oriented at an oblique angle, or is parallel to, the surface of the liquid. Other liquid level measurement systems utilize multiple receivers or reflectors located at the points of reflection of the zigzag wave.
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Citations
54 Claims
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1. An ultrasonic system for measuring at least one selected impedance related parameter of a fluid comprising
a solid member capable of supporting the propagation of moderately directional, bulk SV shear waves without mode conversion, transducer means acoustically coupled to said member for generating and detecting said SV waves propagated along a multiply-reflected path that includes at least two reflections in a region of said member remote from said transducer means and is at least partially immersed in said fluid to form a solid-fluid interface, said reflections having an angle of incidence that exceeds the first critical angle by at least five degrees and is at least ten degrees less than the second critical angle, said path lying in a portion of said member that is substantially homogeneous and flaw free and said SV waves having a frequency that lies in the range of 0.5 to 5 MHz to minimize energy loss by absorption and maximize energy loss by coupling to said fluid at said reflections in said remote region, and means for sensing the attenuation of said waves along said path at said interface to measure said selected impedance related parameter.
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18. An ultrasonic system for measuring at least one selected impedance related parameter of a fluid comprising
a solid member capable of supporting the propagation of moderately directional, bulk SV shear waves without mode conversion, first transducer means acoustically coupled to said member for generating and detecting at least said SV waves propagated along a multiply-reflected first path that includes at least two reflections in a region of said member remote from said transducer means and is at least partially immersed in said fluid to form a solid-fluid interface, said reflection having an angle of incidence that exceeds the first critical angle by at least five degrees and is at least ten degrees less than the second critical angle, said first path lying in a portion of said member that is substantially homogeneous and flaw free and said SV waves having a frequency that lies in the range of 0.5 to 5 MHz to minimize energy loss by absorption and maximize energy loss by coupling to said fluid at said reflections in said remote region, means for sensing the attenuation of said waves along said first path at said interface to measure said selected impedance related parameter, and desensitizing means for rendering said measurement substantially insensitive to variations in other parameters which could influence said measurement.
Specification