Abstract: Transducers are mounted in a housing or vessel to propagate signals along a fluid measurement path, and a plurality of massive elements are placed between transmitting and receiving transducers in the acoustic propagation path through the solid body of the housing or vessel to remove crosstalk. In a preferred embodiment, the elements are rings, which are attached to, or are machined from a thicker cylinder to leave a thin-walled cylinder that holds the transducer off from a conduit wall. Preferably the rings are closely spaced or contiguous, but contact each other only along a small point-like region, so that substantially all ringing acoustic energy flows to the rings via the thin-walled stand-off. In one embodiment, a thick-walled tube is formed with plural radially oriented slots to yield an equivalent structure of alternating masses. In a related embodiment, inner and outer thick-walled tubes so formed are joined at one end to provide a longer path.

Abstract: A snap-on flow measurement system includes a block which attaches to a conduit and positions at least one transducer for launching and receiving acoustic signals along a precisely defined path through a flowing fluid. In one embodiment adapted to small tubes, two transducers are coupled to the tube and launch acoustic interrogation signals along an axial path within the tube. In another embodiment adapted to larger conduits, the transducers launch oblique signals which follow a zig-zag path through the fluid, reflecting off an inner wall of the conduit. In both embodiments, a channel defines a fixed position to hold the conduit aligned with the transducers.

Abstract: Methods and apparatus for ultrasonically measuring selected physical parameters of a test material or structure are achieved by selecting and configuring waveguides for transmitting extensional, longitudinal, shear, Rayleigh and Lamb waves into media in a marginally dispersive manner. Marginally dispersive transmission is defined by specific criteria of velocity and waveguide diameter. Methods and apparatus for acoustically isolating the waveguides to permit leakage are included, as well as a method of extension to flexural mode conversion to launch flexural waves into a medium.

Abstract: A guided torsional wave sensor has a cross-section with a strong interaction of torsional wave energy and the surrounding fluid, such that a wave propagates in the sensor with a functional dependence on a single fluid characteristic. In one embodiment, the sensor body is optimized for fluid density. Diamond, polyhedral and curved-sided embodiments are described. In another embodiment, the sensor body responds to fluid viscosity. This embodiment is preferably hollow, and may include threaded, fractal or roughened surface features to enhance viscous coupling. Different systems include further sensors, sensors with portions of differing profile, and special mounting or activation structures.

Abstract: An apparatus and method for measuring fluid flow parameters operate under conditions wherein the composition of the fluid flow can change rapidly thereby changing the speed of sound within the fluid and wherein the actual flow rate can change rapidly thereby further changing the transit time of acoustic energy traversing an interrogation path within the fluid. The apparatus determines the speed of sound in the fluid and the fluid flow velocity by measuring an upstream and a downstream transit time of acoustic energy within the fluid. The fluid is typically flowing within a conduit, and the transducers for transmitting and receiving the acoustic energy are precisely and carefully installed in the conduit. The measurements also allow an estimate to be made of the average molecular weight of gases passing through the conduit and hence of the mass flow rate of a gas.

Abstract: A flow meter, or flow path intervalometer, transmits a transmission signal modulated with digital pseudo-noise or similar code. The received signal is correlated with the transmitted signal at successive times to produce a correlation function having a peak at a time to equal to the propagation time. The code is selected such that the side lobes of the correlation function are small. An interpolator determines a precise time of maximum correlation. In one embodiment, upstream and downstream correlation functions are defined and are correlated to determine an upstream-downstream propagation time difference interval .DELTA.t. In a preferred embodiment the digital code is a Barker code, and the transmitted signal is a finite interval wave which is phase modulated by the Barker code. In another embodiment, the received signal is a reflected signal which is range gated so as to represent flow data originating from a desired region within the conduit.

Abstract: A clamp-on ultrasonic transducer assembly for making ultrasonic measurements on solid materials in a temperature far removed from ambient. An electroacoustic transducer is coupled to the solid surface through an elongated buffer element enclosed within a housing which is mechanically coupled to the buffer element only in the region of contact between the buffer and the solid material to be measured.

Abstract: An apparatus and method for measuring fluid flow parameters operate under conditions wherein the composition of the fluid flow can change rapidly thereby changing the speed of sound within the fluid and wherein the actual flow rate can change rapidly thereby further changing the transit time of acoustic energy traversing an interrogation path within the fluid. The apparatus determines the speed of sound in the fluid and the fluid flow velocity by measuring an upstream and a downstream transit time of acoustic energy within the fluid. The fluid is typically flowing within a conduit, and the transducers for transmitting and receiving the acoustic energy are precisely and carefully installed in the conduit. The measurements also allow an estimate to be made of the average molecular weight of gases passing through the conduit and hence of the mass flow rate of a gas.

Abstract: A method and apparatus for measuring fluid characteristics use a non-invasive ultrasonic system for generating spatially extended signals into a volume of a fluid and detecting said signals for measuring the characteristic of the fluid. The generated waves are Rayleigh-like surface waves creating, in effect, an extended aperture transducer from which the waves leak into the fluid. The Rayleigh-like surface wave operates in an environment wherein the plate or other structure on which the surface wave is generated has a thickness, normal to the primary direction of propagation of the wave, of less than four Rayleigh wavelengths and greater than approximately one-half of a Rayleigh wavelength. The extended aperture has a length of at least about ten Rayleigh wavelengths. The excitation for the system is generally a short pulse interrogation in order to avoid those interferences which may cause Lamb waves to be set up in the solid material.

Abstract: An apparatus and method for measuring fluid flow parameters operate under conditions wherein the composition of the fluid flow can change rapidly thereby changing the speed of sound within the fluid and wherein the actual flow rate can change rapidly thereby further changing the transit time of acoustic energy traversing an interrogation path within the fluid. The apparatus determines the speed of sound in the fluid and the fluid flow velocity by measuring an upstream and a downstream transit time of acoustic energy within the fluid. The fluid is typically flowing within a conduit, and the transducers for transmitting and receiving the acoustic energy are precisely and carefully installed in the conduit. The measurements also allow an estimate to be made of the average molecular weight of gases passing through the conduit and hence of the mass flow rate of a gas.

Abstract: An intervalometer for determining the arrival time of a bandwidth limited energy pulse employs an integrated threshold arming apparatus and method for conditioning an event recognition circuit. The event recognition circuit, which is typically a zero crossing detector, responds to the conditioning signal for detecting a predetermined event after occurrence of said conditioning signal. The integrated threshold arming circuit employs a signal integration circuit responsive preferably to a rectified signal input, and comparison means for determining when the integrated value crosses a predetermined threshold. A dual threshold implementation can also be employed to further discriminate against false noise signals. The apparatus and method are preferably employed in connection with volumetric flow measurements of turbulent and time-varying fluids by ultrasonic pulse interrogation.

Abstract: An intervalometer for determining the transit time of an ultrasonic energy pulse through a fluid medium employs an automatic gain control amplifier circuit for amplitude stabilizing the electrical signal derived at a receiving transducer. The automatic gain control circuit tracks both a rapidly increasing and a rapidly decreasing signal amplitude. In various embodiments, synchronous switching can be employed in conjunction with a single amplifier and a plurality of storage elements to rapidly scan a plurality of signal paths and for providing automatic gain control capability on each path. The intervalometer further has a "slipped cycle" capability for accurately determining arrival time when is is known that the signal pulse will be within a certain range of times. In addition, the relative time difference between two arriving signal pulses can be accurately determined using this method so long as the range of time difference is sufficiently small.

Abstract: Waveguide antennas for ultrasonic flowmeters are described in which at least one pair of antennas is used to interrogate a flowing fluid. The waveguides are parallel, each pair defining a plane of interrogation which is parallel or nearly parallel to the flow.Some preferred embodiments use elongated waveguides which effectively interrogate the flow simultaneously along a sufficiently large number of parallel paths so that non-axial components of flow tend to be cancelled. Non-axial components are thereby suppressed or eliminated as significant error sources. The large number of effective paths, over a distributed planar area, also contributes to reliable operation even when the fluid is not single phase, especially if interrogating wavelengths are used which are large compared to scatterer dimensions. Several configurations are disclosed wherein the waveguides or their shields may be maintained clean and free of deposits without interrupting their use in the measurement of flow.

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.

Abstract: An ultrasonic flowmeter for determining fluid flow velocity within a conduit by determining the difference in transit time between interrogating ultrasonic pulses transmitted upstream between a pair of transducers and transmitted downstream between them. A high frequency clock pulse operating for one or more cycles of interrogation allows for accurate digital computation.

Abstract: An ultrasonic transducer assembly for making measurements within a fluid, the assembly including a transducer, a backing member and a matching member all supported within a cylindrical metal housing with the transmitting face of the housing being sealed with a thin sealing element formed of a non-resilient relatively high impedance material encasing a matching layer having an acoustic impedance intermediate between that of the transducer element and the fluid. The thickness of the sealing element is between 1/10 and 1/1000th of a wavelength at the center frequency of the wave emitted by the transducer.

Abstract: A clamp on ultrasonic transducer having a clamping element which can be positioned around a conduit with the inner portion of the clamping element being formed to fit closely against the outer wall of the conduit, thus defining at a selected position along the conduit a transverse reference plane. The clamping element carries on it one or more channels extending parallel to the axis of the conduit with ultrasonic transducing elements adjustably mounted on those channels such that their contact pressure with the conduit can be independently adjusted. The ultrasonic transducing elements then form a path of ultrasonic interrogation in a plane parallel to the axis of the conduit and at a position defined by the transverse reference plane.

Abstract: An ultrasonic densitometer for measuring the density or a density related parameter of a fluid has at least one transducer assembly that transmits and receives torsional waves guided in an axially extending sensor that is at least partially immersed in the fluid. The sensor has a noncircular cross section, typically rectangular, with dimensions, aspect ratio, frequency and bandwidth selected to limit dispersion. This non-circularity creates an inverse and substantially linear relation between the density of the fluid and the velocity of the torsional wave in the sensor. To meet special requirements, the sensor can take a variety of forms including axially curved, axially profiled, segmented or longitudinally composite. This densitometer, alone or in combination with conventional auxiliary ultrasonic measuring systems, can measure fluid density, density profiles, liquid level, viscosity, mass flow rate, gas pressure, and boiling or condensation, including measurements of flowing fluids in small conduits.

Abstract: A device for performing ultrasonic measurements on liquid flowing within a duct includes a pair of transducers communicating along an acoustic path within the duct. The acoustic path includes at least one midradius chord of the duct, the projection of that chord on a plane parallel thereto and including the duct axis being tilted with respect to the axis.

Abstract: A device for performing ultrasonic measurements on liquid flowing within a conduit having walls of relatively high acoustic impedance material. The conduit is split into two separate segments with the emitting transducer in one segment and a receiving transducer in the other segment. The space between segments is filled with a sealant material having relatively low acoustic impedance characteristics to provide an acoustic mismatch and hence attenuation to ultrasonic energy traveling through the conduit wall from the transmitter to the receiver. Because of the separation between segments ready access is provided to the internal walls of the conduit, allowing transducer configurations to be employed, which configurations require machining or assembly to be performed on the interior walls.