Abstract: An encapsulated or rigid bundle of rods forms a substantially non-dispersive buffer usable in extreme environments, operable over wide bandwidth, and in some implementations, easily repairable in the field. In one preferred configuration, suitable for measuring the flow of low-molecular-weight gases over a wide range of pressure, temperature and flow rates, the bundle is made of about one thousand stainless steel welding rods tightly packed inside a 1-inch diameter tube. The rigid encapsulated assembly is sealed at the end that is in contact with the gas and may be sealed into a high-pressure flange in a manner that yields broadband transmission characteristics. A second buffer bundle, aligned with the first bundle, may be pressure-coupled on the other side of the flange.

Abstract: A method of humidity measurement wherein a humidity responsive element is subjected to the measuring environment and its temperature coefficient is measured. A system operates a sensor element between a first temperature and a second temperature, determining its temperature coefficient, which is then compared to a previously compiled table. The differential measurement thus made automatically corrects for system error originating in equipment drift, cable capacitance change and various aging and slow hysteresis or sensor capacitance variations. In another embodiment, an occasional differential measurement is performed to detect errors in a set of stored curves and update the tables used for single-point humidity measurements, thus obviating the need for protocols involving reference gases or recalibration.

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, or sleeves which are attached to, or are machined from a thicker cylinder to leave a thin-walled cylinder with alternating masses. An isolation structure lightly sandwiches a flange between O-rings. This structure may be formed with flanged transducer casings, allowing the transducers to be closely spaced in solid conduits or on rigid frames without ringing. Alternatively, it may be formed in a separate framework or holder, providing precise positioning for interrogating gases in unconfined or loosely confined regions. Closed path sensor configurations measure circulation or swirl.

Abstract: A sensor system includes an ultrasonic transducer head with plural transducing elements. The elements are arranged in pairs with the first one of each pair lying in a first plane and the second one of each pair in a second plane spaced a half wavelength away. For transmission, the two are driven out of phase, while for reception their outputs are combined differentially. By changing the drive frequency the transmitted beam is steered to compensate for changes in transducer alignment, or changes in acoustic path caused by abnormal temperature, pressure or flow velocity. In another embodiment, an assembly has a plurality of transducers aligned along slightly divergent paths. Preferred systems employ an upstream and a downstream transducer assembly, each of which is used to alternately transmit and receive signal energy.

Abstract: A sensing system detects elastic waves propagated along a sensing path in a sheet to detect a characteristic of material contacting the other side of the sheet. An acoustic load applied between transducers discriminates characteristics in diverse environments. Different systems detect density, stiffness, presence, degree of coupling, thickness, or fill height of the material, with applications to areas as diverse as aircraft wing ice measurement, storage tank fill height detection, and mass flow detection. In one preferred embodiment a protective housing covers and protects the first side of the sheet over a region of the sheet encompassing the sensing path, and may secure transducers in defined positions. The housing preferably defines a closed reservoir that is temporarily filled to determine a normative measurement such as transit time or change in phase velocity.

Abstract: An apparatus and method for measuring gas flow velocity through a high stack employs ultrasonic transducers. The transducers are placed on opposite ends of a diameter several hundred feet up, with a small vertical separation L between the transducers. Apparatus for measuring acoustic velocity in the stack gas over short path lengths is also included.

Abstract: Transducers are mounted in a housing or vessel to propagate signals along a fluid measurement path, and received signals are temporally separated to remove crosstalk in the acoustic propagation paths of interest, which may be paths through the solid body of the housing or vessel or may be separate paths. These may be segments in a closed path circulation or swirl measurement, or different paths carrying combinations of possibly unrelated measurement signals. In a preferred embodiment, a single channel instrument processes signals from plural transducers which are connected in parallel to its processing input, greatly enhancing the effective system bandwidth and reducing equipment costs. Clamp-on circulation measurement or detection systems are described that allow easy evalution and set-up of flow conditioning loops.

Abstract: Apparatus for measuring the combustion characteristics of a gaseous fuel. Wobbe index and calorific value are measured with a fast response time by maintaining a stoichiometric mixture in a mixer supplied with the gaseous fuel at a constant pressure together with ambient air. The pressure of ambient air is controlled by measuring the residual oxygen from combustion of the mix and employing variations in that measured value to control the ambient air supplied to the mixer. The control signal for the ambient air is proportional to the Wobbe index. A separate measurement of the oxygen in the stoichiometric mix provides a signal proportional to the calorific fuel value.

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 zero compensation circuit particularly is used in an oxygen sensing apparatus and method employing a sensing cell including two pairs thermistors and a source of an inhomogenous magnetic field. One thermistor of each pair is electrically heated and is positioned inside the magnetic field, and the second thermistor of each pair is positioned adjacent to the respective first thermistor of each pair, substantially outside the magnetic field. When oxygen is present in the sensing cell, the thermistors inside the magnetic field generate a gas flow in the direction of the adjacent thermistors of each pair positioned outside the magnetic field, thus tending to reduce the temperature of the thermistors inside the field and increase the temperature of the thermistors outside the field.

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: Apparatus for measuring concentration of a paramagnetic gas in a gas mixture includes first and second magnet pole pieces positioned adjacent each other with a selected gap therebetween, for generating an inhomogeneous magnetic field. The pole pieces have a selected sectional shape, and a gap-facing surface with a selected configuration, that provide an elongated region of maximum magnetic field intensity in the gap. Electrically heated magnetic wind generating thermistors are positioned in the gap. Electrically heated magnetic wind sensing thermistors are positioned adjacent to the magnetic wind generating thermistors, proximate to the elongated region of maximum magnetic field intensity, such that a heated region associated with the wind generating and wind sensing thermistors is substantially encompassed by the elongated region of maximum magnetic field intensity.

Abstract: An ultrasonic transducer assembly for monitoring the quality of spot welds employs a transducer element joined to a support element and fitted within a conventional welding electrode assembly. The transducer assembly is biased against the interior surface of the welding electrode tip by a biasing element, preferably a compression spring. A sleeve, preferably composed of brass, surrounds the transducer element and is joined to the support element. A coaxial cable in communication with external instrumentation has a ground lead attached to the sleeve, and a signal lead attached to the transducer element.

Abstract: Oxygen sensing apparatus and methods utilize a sensing cell including two pairs of electrically heated thermistors and a source of an inhomogeneous magnetic field. One thermistor of each pair is positioned inside the magnetic field, and the second thermistor of each pair is positioned adjacent to the respective first thermistor of each pair, substantially outside the magnetic field. When oxygen is present in the sensing cell, the thermistors inside the magnetic field generate a gas flow in the direction of the adjacent thermistors of each pair positioned outside the magnetic field, thus tending to reduce the temperature of the thermistors inside the field and increase the temperature of the thermistors outside the field. The thermistors are connected in a measuring bridge circuit including elements for maintaining the temperature of the thermistors at a substantially constant level, thereby providing a signal that can be used to compensate for changes in the thermal characteristics of the background gases.

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.