Showing papers on "Pressure measurement published in 1988"

Enhanced pressure measurement flow control system

Abstract: The present invention provides a system for measuring flow of a fluid through a line. In the system, a region (15) of fluid along the line is isolated from pressure effects outside of the region. A source region (12) contains a measurement gas in communication with the isolated region, such that the source means and the isolated region together define a fixed volume, and such that a change in volume of fluid in the isolated region produces a complementary change in the volume of the source means with a resulting change in the pressure of the measurement gas contained in the source region. Further provided is a reservoir (11) in communication with the source means for containing a known volume of measurement gas, and means (25) for pumping measurement gas from the reservoir. The pressure of the measurement gas in the reservoir and the source region is monitored. This pressure data is then analyzed to determine the volume of fluid in the isolated region.

A multisensor employing an ultrasonic Lamb-wave oscillator

Abstract: Initial experimental, analytical, and numerical evaluations of a microsensor that uses ultrasonic Lamb waves propagating in a thin plate supported by a silicon die are presented. Changes of oscillator frequency indicate magnitudes of the variables sensed. Because it is sensitive to many measurands, the device could operate as a microphone, biosensor, chemical vapor or gas detector, scale, pressure sensor, densitometer, radiometer, or thermometer. Because it is based on the use of Lamb waves, the sensor has selective response and sensitive operation in the low-megahertz frequency range in vacuum, in a gas, or while immersed in a liquid. >

An ultraminiature solid-state pressure sensor for a cardiovascular catheter

Abstract: An ultraminiature solid-state capacitive pressure sensor that can be mounted in a 0.5-mm OD catheter suitable for multipoint pressure measurements from within the coronary artery of the heart is described. The transducer consists of a silicon 290*550*1.5- mu m/sup 3/ microdiaphragm surrounded by a 12- mu m-thick silicon supporting rim, both defined by the boron etch-stop technique. The transducer process features a batch wafer-to-glass electrostatic seal followed by the silicon etch, which eliminates handling of individual small diaphragm structures until die separation and final packaging. A hybrid interface circuit chip provides a high-level output signal and allows the sensor to be compatible with use on a multisite catheter having only two leads. >

Simultaneous planar measurements of velocity and pressure fields in gas flows using laser-induced fluorescence.

Abstract: The development of a nonintrusive spectroscopic technique is reported which permits simultaneous spatially resolved measurements of two velocity components and pressure in a plane of a compressible gaseous flow field. The technique is based on the detection of fluorescence from an absorption line excited with a narrow-bandwidth laser. Doppler shift and pressure broadening of the line are exploited to extract velocity and pressure information, respectively. The fluorescence is detected at a 90° angle with an image-intensified 100 × 100 element photodiode-array camera which is interfaced with a laboratory computer. Results of the implementation in a Mach 1.5 underexpanded supersonic jet are presented.

A diamond anvil cell for the investigation of superconductivity under pressures of up to 50 GPa: Pb as a low temperature manometer

Abstract: A single-crystal diamond anvil cell is described which has been successfully cycled down to liquid helium temperatures in numerous experiments Superconducting transitions are detected by a low frequency AC technique employing a radially compensated gradient coil and a commercial RF SQUID system The pressure is determined at room temperature by the ruby fluorescence technique with a focused laser beam Pressure changes between room temperature and low temperature are minimised A recalibration of the superconducting critical temperature, Tc, of Pb as a function of pressure has been carried out The so-called Pb manometer turns out to be a very suitable pressure gauge up to about 30 GPa At higher pressures the Tc of Pb is suppressed below 12 K and hence, for normal purposes, is inconveniently low At the present limit of resolution the Pb I-II phase transition at 13 GPa is not reflected in the smooth Tc-P dependence

Ultraminiature pressure sensor and method of making same

Abstract: A capacitive pressure sensor suitable for making highly sensitive, low pressure measurements is disclosed. The sensor may be mounted into a 0.5 mm OD catheter suitable for multipoint pressure measurements from within the coronary artery of the heart. The sensor employs a transducer which consists of a rectangular bulk silicon micro-diaphragm several hundred microns on a side by two microns thick, surrounded by a supporting bulk silicon rim about 12 microns thick. Both the diaphragm and the rim are defined by a double diffusion etch-stop technique. The transducer fabrication process features a batch wafer-to-glass electrostatic seal followed by a silicon etch, which eliminates handling of individual small diaphragm structures until die separation and final packaging. An addressable read-out interface circuit may be used with the sensor to provide a high-level output signal, and allows the sensor to be compatible for use on a multisite catheter having only two electrical leads.

Variable gas volume flow measuring and control methods and apparatus

Abstract: A method and apparatus for measuring gas flow volume in a system (of the kind in which the amount of gas flowing in a duct can vary in response to the variation of area of a variable area orifice in a duct and/or in response to changes in the total pressure of the gas upstream of the orifice) references the total pressure upstream of the orifice to the static pressure downstream of the orifice to produce a first signal representative of the differential pressure between the total pressure upstream of the orifice and the static pressure downstream of the orifice. The method and apparatus produce a second signal corresponding to the area of the opening in the orifice. The first and second signals are supplied to a gas flow volume database which is correlated to the sensors and to the orifice in the duct. The gas flow volume occurring in the duct at the first and second signals is read out from the database.

Subsurface formation testing apparatus

Abstract: Apparatus for collecting a plurality of samples of fluids in earth formations traversed by a wellbore includes a pressure sensor for deriving a pressure measurement and a temperature sensor for simultaneously deriving a temperature measurement. The pressure measurement signals and the temperature measurement signal are transmitted to processing circuitry using a narrow band frequency modulated scheme. The temperature measurement is used to provide a real time temperature compensated pressure measurement.

Thermodilution and pressure transducer balloon catheter

Abstract: A multi lumen balloon catheter suitable for pulmonary artery catheterization incorporating both pressure and temperature measurement functionalities by means of a forward facing transducer strain gauge device located axially of the inflated balloon for pressure measurement and means for sensing the temperature of the fluid surrounding the exterior of the catheter in use

Absolute capacitance manometers

Abstract: A single fluid-pressure transducer unit, of the type in which sensed electrical capacitance is varied in accordance with electrode deflections induced by pressure changes, is rendered capable of characterizing a wide range of pressures extending from near-vacuum to atmospheric levels, with the aid of a distinctive composite-electrode capsule which interacts uniquely with a conventional type of sheet-metal diaphragm. While sensing relatively low pressures, the exhibited capacitance of the transducer is essentially that appearing between the diaphragm and a nearby electrode carried by the capsule, but, at or near atmospheric pressure, the diaphragm physically engages and deflects that electrode, which is elastically deformable, causing it to vary a further capacitance appearing between that deformable electrode and a companion stationary electrode which is also part of the capsule.

Effects of the separating shear layer on the reattachment flow structure Part 1: Pressure and turbulence quantities

Abstract: The effect of the separating shear-layer thickness and shape on the structure of the flow in the reattachment region of a backward-facing step is examined using wall static-pressure profiles and turbulence data for a range of Reynolds number (800 < ReH< 40,000) and upstream boundary-layer thickness (0 < δ/H < 2). The reattachment pressure and the peak pressure in the reattachment zone decrease in a continuous manner as the upstream boundary layer thickens. The thinnest boundary layers follow the correlation of Roshko and Lau. Using the pressure data, correlations are developed which can be used to predict the level of turbulent shear stress in the near-wall region at reattachment, a location in which experimental data are extremely difficult to obtain.

Wideband external pulse recording during cuff deflation: a new technique for evaluation of the arterial pressure pulse and measurement of blood pressure.

Abstract: Analysis of the external brachial pulse recorded during standard blood pressure cuff deflation with use of a transducer with a wide frequency response has revealed a reproducible pattern with three distinct components that we have labeled K1, K2, and K3. K1 is a low-amplitude, low-frequency signal that is present with cuff pressures above systolic pressure. K2 is a triphasic signal appearing at systolic pressure and disappearing at diastolic pressure, which approximately corresponds to the audible Korotkoff sound. K3 appears with cuff pressure between systolic and diastolic pressure and continues to be present below diastolic pressure. Intra-arterial pressure recordings made with a high-fidelity Millar catheter-tip manometer revealed K2 and K3 analogs. K3 resembles the intra-arterial pressure waveform and when calibrated according to the pulse pressure, noninvasive dK3/dt determinations correlated well with intra-arterial dP/dt measurements. The appearance/disappearance property of K2 was designated as the "K2 algorithm" and represents a new, objective noninvasive method for measurement of blood pressure. The K2 algorithm compares favorably with intra-arterial measurements, is more accurate than the auscultatory technique, and may be especially useful in clinical situations in which the auscultatory technique does not work well.

CFD and transonic helicopter sound

Abstract: A computational method which predicts far-field impulsive noise from a transonic motor blade is demonstrated. This method couples near-field results from a full-potential finite-difference method with a new Kirchhoff integral formulation to extend the finite-difference results into the acoustic far-field. This Kirchhoff formula is written in a blade-fixed coordinate system. It requires initial data from the potential code on a plane at the sonic radius. A recent hovering rotor experiment is described where accurate pressure measurements were recorded on the sonic cylinder and at 2 and 3 radii. The potential code prediction of sonic cylinder pressures is excellent. Acoustic far-field pressure predictions show good agreement with hover experimental data over the range of speeds from 0.85 to 0.92 tip Mach number, the latter of which have delocalized transonic flow. These results are some of the first successful predictions for peak pressure amplitudes using a computational code.

Pressure flow characteristics of commonly used heat-moisture exchangers.

Abstract: Heat-moisture exchangers or “artificial noses” are commonly used to humidify the inspired air in intubated or tracheostomized patients. These devices add resistance to breathing that may be significant in critically ill and weak patients, especially when the devices are humidified. Three of each six commonly used types (Portex, SH 150, SH 151, NCC, Engstrom, and Pall) were tested to define the pressure flow characteristics. Known flows were passed through these devices, and the pressure drops across them were measured. The devices were tested when they were dry and when they were humidified with 100% saturated water vapor for 8, 16, and 24 h. The amount of water added to the devices was measured. The pressure flow characteristics of the devices could be described by a power function: P = ab, where P is pressure, is flow, and a and b are constants determined by the characteristics of the devices. In addition, the resistance increased with the increasing weight of the devices from added moisture clogging th...

A conductive polymer pressure sensor

Abstract: The authors have characterized the performance of the commercially available Interlink pressure sensor. The sensor costs less than $1. It is 0.25-mm thick, is light and flexible, and can be customized for a wider range of applications. The resistance-versus-pressure characteristic of the sensor is logarithmic. The operating range is from 0 to 2 MPa. The hysteresis is 8% and the nonrepeatability is less than 7% of full scale. The temperature drift is -0.5%/ degrees C of full scale. Using the Interlink sensors and electronics, the authors developed a portable data acquisition system to monitor the pressure under the bony prominences of the feet during normal gait. The advantages and drawbacks of the sensor are indicated. >

Foot pressure measurement system

Abstract: An improved foot pressure measurement system wherein pressure measurements are obtained from the variation of light output from an illuminated glass or transparent plate. A reflective material on the top surface of the plate causes an increase in light intensity escaping from the plate when pressure is applied to the reflective material. The accuracy and resolution of the pressure measurements are improved by obtaining a reference measurement of the background light intensity and distribution before pressure is applied and subsequently subtracting this background light from the light patterns produced when pressure is applied. The reflectance characteristics of the system are improved by using a photographic paper as the reflective material.

Capacitive sensors for measuring the pressure between the foot and shoe

Abstract: A test was conducted of a Hercules Orthoflex capacitive sensor used to measure pressure distribution under the foot for gait analysis and sensory substitution. Maximal nonlinearity for the sensor is 16%, and maximal hysteresis is 10% over the pressure range 0 to 1.3 MPa. Seven transducers in each shoe determine the distribution of pressure. >

Simultaneous determination of capillary pressure and relative permeability by automatic history matching

Abstract: This paper presents a new method for the simultaneous determination of capillary pressure and relative permeability that is a modification of the porous-plate capillary pressure experiment. The modifications involve the use of thin core samples and thin plastic filtration membranes, resulting in a significantly faster experiment. Relative permeabilities are determined from the experimental data by the use of an automatic history-matching simulator. The new method is found to be particularly well suited for the measurement of small oil relative permeabilities in gas/oil systems.

Miniature silicon resonant pressure sensor

Abstract: An absolute barometric pressure sensor which has shown exceptional performance is described in the paper. It consists of a mechanical resonator whose resonant frequency is changed by strain induced by applied pressure. The active element is formed in one piece, from single-crystal silicon, by microengineering techniques. It has a range from vacuum to a pressure of over 1 bar (105 Pa) and can resolve less than 1 part in 105 of full scale.

Pressure measurements correlated with electrical explosion of metals in water

Abstract: Time profiles of underwater shock wave pressure, current, and voltage were measured for exploding aluminum, aluminum‐lithium alloy, and copper wire in water when an inductive energy store was discharged through the wire. A linear relationship existed between the peak voltage across exploding wire and the underwater shock wave pressure generated by the wire. The aluminum‐lithium alloy reached a highly resistive state more quickly than pure aluminum wire at the same heating rate. The chemical reaction between the exploding wire material and the surrounding water plays a small role in the generation of detonation wave.

Tire-mounted air pressure gauge assembly

Abstract: The present invention is an improvement to a tire mounted air pressure gauge for use on vehicles having inflatable tires. The air pressure gauge has a dial face, with a coiled pressure responsive spring expandable to indicate the pressure detected by the gauge. The gauge is mounted directly onto the valve stem of a tire to detect the pressure in the tire, or is mounted onto the valve steam via an L-shaped conduit. The conduit contains a lug adapted to depress the conventional valve core of the valve stem and release air pressure within the valve stem and tire. An arc-shaped or cylindrical retainer is provided on the dial face to limit radial expansion of the coiled spring due to centrifugal forces of the rotating tire and other jarring forces exerted on the pressure gauge during use of the tire.

Semiconductor pressure sensor with casing and method for its manufacture

Abstract: A semiconductor pressure sensor and method for its manufacture. Preferably, the pressure sensor is used as an absolute pressure sensor. The pressure sensor includes a pressure sensor chip of semiconductor material, the pressure sensor chip including a piezoresistive diaphragm. The pressure sensor is arranged in a casing which has an aperture for transmitting the ambient pressure to the diaphragm of the pressure sensor chip. The pressure sensor chip is fastened on a conductive tape and the conductive tape is a component of the casing. The casing consists of a hard synthetic material and contains the pressure sensor chip. The casing is configured so that the method of manufacture and tooling for manufacture allow cost-efficient production. The casing also offers protection for the pressure sensor during testing, equipping and during application in a circuit. The pressure sensor also includes a soft elastic material for covering the pressure sensor chip and transmitting ambient pressure from the aperature to the diaphragm.

Experimental and numerical studies of shock wave focusing in water

Abstract: The focusing of plane shock waves and spherical blast waves in water by parabolic and ellipsoidal reflectors is studied experimentally and numerically. The numerical computations are performed by a second order method based on an extension of Godunov's method, which is called piecewise-linear method. Tests of this method and a comparison with pressure measurements show a strong dependence of the maximum pressure attained in the focal region on the mesh size. Outside this focal region, however, good agreement between the pressure measurements and the result of the numerical computation is found. Furthermore it is shown by numerical computation, that non-linear effects in the focusing process may be partly avoided by an optimized reflector contour which depends on the strength of the incident shock wave. This modification provides that the maximum pressure is attained at the geometric focus and not at a location between reflector surface and geometrical focus.

Optical determination of the characteristics of a pulsed-gas jet

Abstract: A pulsed‐gas jet with interesting properties has been developed. A typical pressure obtained at the output of this pulsed‐gas jet is 25 Torr for a backing pressure of 150 Torr. At a repetition rate of 10 Hz, the background pressure stays below 1.5×10−4 Torr. Laser‐induced fluoresence measurements permit one to determine the pressure and the divergence of the gas jet accurately.

Thermal conductivity of five normal alkanes in the temperature range 283–373 k at pressures up to 250 MPa

Abstract: Experimental data on the thermal conductivity of five liquid n-alkanes-hexane, heptane, octane, decane, and dodecane-are presented in the temperature range from 283 to 373 K at pressures up to 250 MPa or the freezing pressures. The measurements were performed on an absolute basis by an automated transient hot-wire apparatus. The uncertainty of the reported data is estimated to be within ±1%. The thermal conductivity of each alkane decreases almost linearly with rising temperature at a constant pressure and increases with increasing pressure at a constant temperature. Both the temperature coefficient of the thermal conductivity ¦(∂λ/∂T)p¦ and the pressure coefficient (∂λ/∂P)T decrease with increasing carbon number of alkanes. The experimental results were correlated with temperature and pressure by a similar expression to the Tait equation. It is also found that both the dense hard-sphere model presented by Menashe et al. and the modified significant structure theory proposed by Prabhuram and Saksena provide good representations of the present experimental results.

Novel optically excited resonant pressure sensor

Abstract: A novel pressure sensitive microresonator structure has been fabricated by anisotropic etching of silicon. An intensity modulated laser beam is focused onto the resonator and generates transverse vibrations, which are detected using optical heterodyne interferometric techniques. The pressure and temperature dependence of the resonant frequency of this structure is reported.