Showing papers on "Pressure measurement published in 1994"

Intra-abdominal pressure measurement using a modified nasogastric tube: Description and validation of a new technique

Abstract: This study assessed the accuracy of an intragastric method of measuring intra-abdominal pressure (IAP). Prospective sequential study with simultaneous paired measurement of gastric and urinary bladder pressures. Operating theatre, University Teaching Hospital.Patients: 9 patients undergoing laparoscopic cholecystectomy were studied. Intraperitoneal pressures were monitored during peritoneal insufflation at laparoscopy up to a pressure of 20 mmHg. Intra-abdominal pressure measurements were recorded simultaneously using a gastric balloon and urinary catheter. Gastric pressure may be up to 4 mmHg higher or 3 mmHg lower than urinary bladder pressure. Intra-abdominal pressure can be measured easily in this new fashion, allowing a continuous pressure trend to be obtained without interfering with urinary output estimation.

Diode-laser absorption technique for simultaneous measurements of multiple gasdynamic parameters in high-speed flows containing water vapor

Abstract: A distributed-feedback InGaAsP diode laser, emitting near 1.38 μm, was used to acquire spectrally resolved absorption profiles of H2O lines in the ν1 + ν3 band at a repetition rate of 10 kHz. The profiles were used for simultaneous measurements of flow parameters in high-speed, one-dimensional (1-D) transient flows generated in a shock tube. Velocity was determined from the Doppler shift, which was measured with a pair of profiles simultaneously acquired at different angles with respect to the flow direction. Temperature was determined from the intensity ratio of two adjacent lines. Pressure and density were found from the fractional absorption. From these primary gasdynamic variables, the mass and momentum fluxes were determined. Experiments were conducted with three different gas mixtures in the shock tube: pure H2O at initial pressures lower than 3 Torr, up to 6% of H2O in O2 at initial pressures below 120 Torr, and up to 8% of H2 in O2 at initial pressures below 35 Torr. In the third case, pyrolysis of H2/O2 behind incident shocks produced known yields of H2O. With all three mixtures, results compare well with 1-D shock calculations. This H2O diagnostic strategy shows promise for applications in both ground and flight testing.

Dual pressure sensing catheter

Abstract: This invention is an apparatus for determining pressure at one or a number of intermediate points along a catheter (10) inserted into a closed cavity. Fiberoptic cables (34) extend from the proximal end of the catheter (12a) to the intermediate points at which pressure measurements are taken as well as to the distal tip of the catheter (12d).

Experimental Study on the Aerodynamic Performance of a Savonius Rotor

Abstract: The aerodynamic performance of a Savonius rotor has been studied by measuring the pressure distributions on the blade surfaces at various rotor angles and tip-speed ratios. It is found that the pressure distributions on the rotating rotor differ remarkably from those on the still rotor especially on the convex side of the advancing blade, where a low pressure region is formed by the moving wall effect of the blade. The torque and power performances, evaluated by integrating the pressure, are in close agreement with those by the direct torque measurement. The drag and side force performance is also studied.

Integrated optical ring resonator with micromechanical diaphragms for pressure sensing

Abstract: An optical pressure sensor has been fabricated which uses an integrated-optical ring resonator to measure the strain induced in a micromachined silicon diaphragm. A silicon substrate is etched from the side opposite the silicon oxynitride optical waveguides to produce a rectangular diaphragm whose long edge lies underneath a straight section in the ring. Pressure-induced changes in the resonant frequency of the ring are measured using a frequency swept laser diode. A linear response to pressure is observed for the TM mode with a sensitivity of 0.0094 rad/kPa. This pressure sensor is rugged, is amenable to batch fabrication, and it provides a link-insensitive readout. >

Determining cardiac velocity fields and intraventricular pressure distribution from a sequence of ultrafast CT cardiac images

Abstract: A method of computing the velocity field and pressure distribution from a sequence of ultrafast CT (UFCT) cardiac images is demonstrated. UFCT multi-slice cine imaging gives a series of tomographic slices covering the volume of the heart at a rate of 17 frames per second. The complete volume data set can be modeled using equations of continuum theory and through regularization, velocity vectors of both blood and tissue can be determined at each voxel in the volume. The authors present a technique to determine the pressure distribution throughout the volume of the left ventricle using the computed velocity field. A numerical algorithm is developed by discretizing the pressure Poisson equation (PPE), which Is based on the Navier-Stokes equation. The algorithm is evaluated using a mathematical phantom of known velocity and pressure-Couette flow. It is shown that the algorithm based on the PPE can reconstruct the pressure distribution using only the velocity data. Furthermore, the PPE is shown to be robust in the presence of noise. The velocity field and pressure distribution derived from a UFCT study of a patient are also presented. >

Pressure Compartments in Sedimentary Basins: A Review

Abstract: Pressure compartments are found in sedimentary basins throughout the world. They are defined primarily by hydraulic potentials calculated from pressure measurements but may be indicated by differing brine and hydrocarbon chemistries; by mineralogic differences; by electrical resistivity, sonic velocity, and density of the shales; and by mud weight requirements and drilling rate changes. Pressure compartments are characterized by an effective seal, in three dimensions, that prevents pressure equilibration to normal hydrostatic pressure. A pressure seal, as opposed to a capillary seal, restricts flow of both hydrocarbon and brine and is formed where the pore throats become effectively closed, i.e., the permeability approaches zero. A leaking pressure seal, called a "rate seal," occurs when the pressure difference caused by subsidence-sedimentation or uplift-erosion or other pressure source is greater than the seal pressure leakage. When the internal fluid pressure in the compartment exceeds the fracture pressure of the seal, the seal will fracture and fluids will escape from the compartment. The fracture and resealing may occur repeatedly. Multiple pressure seal origins must be invoked to explain their geometric and stratigraphic occurrence. Certainly some pressure seals appear to be stratigraphically controlled with perhaps more or less diagenetic enhancement. Some seals, particularly those that cross stratigraphy, appear to be entirely diagenetic. The lateral seals, which appear to be subvertical to vertical, are possibly due to faulting and fracturing or to lateral facies changes. An extensive investigation of seal origin, recognition, and duration is being undertaken by a consortium of universities under the sponsorship of the Gas Research Institute.

A valve having means for generating a wireless transmittable indicating signal in case of a pressure drop within vehicle tires

Abstract: A valve which includes signal generating means for generating a signal representing a pressure drop occurring within a vehicle tire. The valve includes an absolute pressure sensor coupled to measure the pressure within the tire. A microprocessor is provided which upon activation following operation of the valve stores a value of the electric pressure signal from the pressure sensor in a memory. During operation of the vehicle, the stored reference electric pressure signal is compared with periodic measurements of pressure within the tire. The transmitter is activated at periodic intervals, whenever a given ratio between the compared values and a threshold value exceeds an upper or a lower limit. The system is activated by an acceleration sensor which can detect when the vehicle is moving, thus avoiding power consumption when the vehicle is stopped.

Apparatus for determining the volume of a bellows reservoir for medication in an implantable infusion system

Abstract: In a method and apparatus for determining the volume of a bellows reservoir for medication in an infusion system which is implantable in a patient, the pressure in the reservoir is measured and the corresponding volume is determined from a predetermined relationship between pressure and volume. A pressure gauge is disposed for measuring the pressure in the bellows reservoir, and a signal corresponding to the measured pressure is supplied to a memory unit wherein a corresponding volume is determined from the measured pressure value by means of the predetermined relationship between pressure and volume being stored in the memory unit.

Tactile sensor with 3-axis force and vibration sensing functions and its application to detect rotational slip

Abstract: This paper concerns a new tactile sensor with both 3-axis force sensing and slip sensing functions. The first three axis force sensing is achieved with tactile heads, each of which is supported by three pressure sensing elements. The pressure sensing function is achieved with arrays of pressure transducers that measure a change in the contact resistance between a specially treated polyimide film and a resistive substrate. The slip sensing function is achieved through the use of a stress-rate sensor that responds to small-scale variations in a surface profile with roughness. Static and dynamic analyses of the new tactile sensor were made and compared with experimental results. Further experiments were conducted with an algorithm to detect rotational slip. >

Comparison of intraarterial with continuous noninvasive blood pressure measurement in postoperative pediatric patients.

Abstract: Objective. The purpose of this study was to estimate the accuracy, bias, and frequency response of continuous blood pressure monitoring using finger photoplethysmography in children.Methods. To compare arterial blood pressure measured using the Finapres device with simultaneously measured intraarterial blood pressure we studied 27 randomly selected postoperative pediatric patients who were receiving a variety of inotropic and vasoactive agents at a cardiac intensive care unit in university-affiliated pediatric hospital.Results. Sixty-two of 66 attempts (94%) to obtain a noninvasive blood pressure measurement were successful. A total of 37,351 paired blood pressure measurements from 53 records were compared, revealing a measurement bias of −18.6 mm Hg for systolic blood pressure and −13.4 mm Hg for diastolic blood pressure. The measurement bias increased proportionately to blood pressure, with systolic and diastolic gains between the noninvasive and intraarterial techniques of 0.86 and 0.75 mm Hg/mm Hg, respectively. The variation bias during each recording epoch, as measured by standard deviation of bias, was low (mean σsystolic=2.9 mm Hg; mean σdiastolic=2.0 mm Hg). The frequency response between the intraarterial and noninvasive pressure waveforms was flat to 10 Hz and approximately equal to 1.Conclusions. Substantial measurement bias exists between this noninvasive blood pressure measurement technique and intraarterial blood pressure. Measurements of the intrapatient variability and frequency response analysis suggest that the noninvasive technique accurately tracks intraarterial blood pressure over the short term. This technique may have useful applications in settings where intraarterial monitoring is undesirable or unobtainable.

Micro‐Pirani vacuum gauge

Abstract: A Pirani vacuum sensor has been fabricated by the silicon micromachining technique. A square glass membrane was formed on (100) silicon substrate with a platinum‐film resistor coated. The membrane is suspended by its four leads extended to the corners of an etched cavity. This structure can provide both low thermal loss through leads to the substrate and large active area for gaseous heat conduction. It thus can be used as a highly sensitive vacuum sensor. The fabricated sensor has shown a linear response of pressure from 8×10−5 to 6 Torr with constant‐temperature operation. It is found that the low‐pressure limit of the vacuum sensor was caused by the noise of the instrument used in the experiment. A new terminology called ‘‘noise equivalent pressure’’ thus is definable due to this finding. The physical limit of the noise equivalent pressure is analyzed. Optimization of the device structure and the noise equivalent pressure are also discussed in detail. A new method of ambient‐temperature compensation is...

The Operational Stability of a Centrifugal Compressor and Its Dependence on the Characteristics of the Subcomponents

Abstract: A centrifugal compressor was tested with three different diffusers with circular-arc vanes. The vane inlet angle was varied from 15 to 30 deg. Detailed static wall pressure measurements show that the pressure field in the diffuser inlet is very sensitive to flow rate. The stability limit regularly occurred at the flow rate giving the maximum pressure rise for the overall stage. Mild surge arises as a dynamic instability of the compression system. The analysis of the pressure rise characteristic of each individual subcomponent (impeller, diffuser inlet, diffuser channel,...) reveals their contribution to the overall pressure rise. The diffuser channels play an inherently destabilizing role while the impeller and the diffuser inlet are typically stabilizing. The stability limit was mainly determined by a change in the characteristic of the diffuser inlet. Further, the stability limit was found to be independent of the development of inducer-tip recirculation.

Density compensated gas flow meter

Abstract: A mass flow meter for a gas dispenser (100) includes an apparatus and method for determining specific heat ratio of a gas as a function of two pressure measurements in relation to a sonic nozzle (52) and for determining mass flow rate as a function of the specific heat ratio, the two pressure measurements in relation to the nozzle (52), and a density measurement of the gas. A stagnant pressure is measured by transducer (96) just upstream of the sonic nozzle and dynamic pressure is measured at the nozzle (52) by a pressure transducer (310). The stagnant pressure, dynamic pressure and density are used to determine the specific heat ratio of the gas and then to determine the mass flow rate.

MR measurements of pulsatile pressure gradients.

Abstract: A magnetic resonance (MR) imaging method for evaluating pulsatile pressure gradients in laminar blood flow is presented. The technique is based on an evaluation of fluid shear and inertial forces from cardiac-gated phase-contrast velocity measurements. The technique was experimentally validated by comparing MR and manometer pressure gradient measurements performed in a pulsatile flow phantom. Analyses of random noise propagation and sampling error were performed to determine the precision and accuracy of the method. The results indicate that a precision of 0.01-0.03 mmHg/cm and an accuracy of better than 8% can be achieved by using standard clinical pulse sequences in tubes exceeding 6 mm in diameter. The authors conclude that MR measurement of pressure gradients is feasible and that additional hemodynamic information may be derived from conventional phase-contrast imaging studies.

Capacitive absolute pressure sensor

Abstract: A capacitive absolute pressure sensor. The sensor includes a substrate having an electrode deposited thereon and a diaphragm assembly disposed on the substrate. As pressure increases, the diaphragm deflects, touches the electrode (in the touch mode), and changes the capacitance of the sensor. The changed capacitance is sensed to thus sense pressure changes. A buried feedthrough is used to sense the change in a capacitance in a chamber under the diaphragm and thus determine the pressure sensed. A vacuum in the chamber is maintained by proper selection of a thickness of a sensing electrode and an insulating layer, exposition thereof to a thermal cycle, and the hermetic bonding of the diaphragm assembly to the substrate.

Differential pressure measurement arrangement utilizing dual transmitters

Abstract: A two-wire transmitter (2) senses differential pressure, absolute pressure, and process temperature of a process fluid. The information can be used to provide an output representative of mass flow through a pipe (4). The transmitter (2) has an electronics module housing (14) attached to a sensor module housing (16).

Dual absolute pressure sensor and method thereof

Abstract: A dual absolute pressure sensor independently converts first and second external pressures to first and second electrical signals respectively. A package body has first and second openings for receiving the first and second external pressures to outside surfaces of first and second sensor die attached to opposite surfaces of an internal glass substrate that separates the first and second openings. The first sensor die includes a first cavity having a reference pressure to measure against the first external pressure and develop a first differential pressure. A first piezoelectric network converts the first differential pressure to the first electrical signal representative of that pressure. The second sensor die includes a second cavity having a reference pressure to independently measure against the second external pressure and develop a second differential pressure. A second piezoelectric network converts the second differential pressure to the second electrical signal representative of that pressure.

Development of prototype fiber-optic-based Fizeau pressure sensors with temperature compensation and signal recovery by coherence reading

Abstract: A range of prototype fiber-optic-based Fizeau interferometric pressure sensors with temperature compensation and signal recovery by dual-wavelength coherence reading have been developed. A separate fiber-optic-based Fizeau temperature sensor with similar cavity length was incorporated into the pressure sensor to allow the pressure measurement to be corrected for the temperature dependence of the pressure probe. The pressure and temperature probes were multiplexed spatially. For the low-pressure sensor, the obtained range to resolution ratio and the accuracy were /spl sim/6.7/spl times/10/sup 3/:1 and better than /spl plusmn/1 percent over a pressure range of 0-0.48 bar, respectively. For the medium pressure sensor, the achieved range to resolution ratio and the overall accuracy were 3.6/spl times/10/sup 4/:1 and /spl plusmn/0.15 percent over a full-pressure range of /spl sim/10 bar. For the high pressure sensor, a range to resolute ratio of /spl sim/1.67/spl times/10/sup 4/:1 and an overall measurement accuracy of /spl plusmn/0.69 percent over a pressure range of /spl sim/1000 bar have been achieved. Due to the universality of the signal-processing scheme based on the dual-wavelength coherence-reading technique, the signal-processing box can be compatible with a range of sensors illuminated by the sources with similar central wavelengths. This study would be readily used to develop a range of commercial fiber-optic pressure sensors with similar optical path differences, interrogated by a universal signal-processing box, for different applications. >

Simultaneous pressure measurement and high-speed photography study of cavitation in a dynamically loaded journal bearing

Abstract: Cavitation of the oil film in a dynamically loaded journal bearing was studied using high-speed photography and pressure measurement simultaneously. Comparison of the visual and pressure data provided considerable insight into the occurrence and nonoccurrence of cavitation. It was found that (1) for the submerged journal bearing, cavitation typically occurred in the form of one bubble with the pressure in the cavitation bubble close to the absolute zero; and (2) for cavitation-producing operating conditions, cavitation did not always occur; with the oil film then supporting a tensile stress.

Formation permeability determination by micro or mini-hydraulic fracturing

Abstract: This paper presents a theory and its application for post-fracture pressure-transient analyses. The proposed procedure, known as impulse fracture test,'' is an injection/falloff test designed for the determination of formation permeability and reservoir pressure. The hydraulically induced fracture can pass the near wellbore damaged zone and expose a larger formation area to flow. The permeability and reservoir pressure determined are therefore more representative of the reservoir. The theory is based on the distribution of sources with variable intensity along the fracture trajectory. For field applications, asymptotic solutions are derived to give the type-curve'' capability for the estimation of formation permeability and reservoir pressure. Assorted slope behaviors, such as [minus]1, [minus]2, +1/2 and +1 slopes, are predicted from various pressure and pressure derivative plots. Analyses of data from two wells which were inadvertently fractured support these behaviors.

Pressure measurement apparatus having a reverse mounted transducer and overpressure guard

Abstract: A novel pressure measurement apparatus for measuring fluid pressures generated within a fluid passageway is disclosed. The apparatus includes a semiconductor pressure transducer which is mounted to a chip carrier comprised of a ceramic substrate layer. The semiconductor pressure transducer is reverse mounted to the substrate layer by way of a series of electrically conductive epoxy bond points. The semiconductor pressure transducer is enclosed within a gel cap containing an incompressible gel medium. Fluid pressures generated within the fluid passageway are communicated to the transducer via the gel medium.

Apparatus for sensing a physical condition in a living subject

Abstract: An apparatus for determining a physical condition in a living subject by determining peripheral resistance to flow is wherein peripheral resistance to flow is determined by measuring changes in the pressure drop characteristic in an artery during diastole. The pressure drop characteristic can be determined by measuring absolute pressure, relative pressure or dimensional changes in the artery during diastole. The apparatus can advantageously be used in a rate-responsive heart stimulator.

Evaluation of a fiberoptic system for airway pressure monitoring

Abstract: Objective..Our objective was to evaluate the accuracy of a novel fiberoptic system for airway pressure measurement at the carinal end of the endotracheal tube in an in vitro pediatric lung model.Methods. A fiberoptic pressure measuring system was compared to the conventional method of measuring airway pressure with a pneumatic transducer using a test lung model. Pressure measurements were obtained using four endotracheal tubes of various internal diameters (ID) (3 to 6 mm) during simulated spontaneous and mechanical ventilation. Airway pressure was measured using both methods simultaneously and the results were compared by statistical analysis.Results. Airway pressure measured by the fiberoptic system was not significantly different from measurements obtained by the pneumatic transducer except when using the 3-mm and 4-mm ID endotracheal tubes during mechanical ventilation.Conclusions. We conclude that the fiberoptic system provides accurate and precise measurement of airway pressure during spontaneous and mechanical ventilation. Additionally, the statistically significant differences obtained for 3- and 4-mm tubes are not large enough to be clinically significant. The fiberoptic system offers advantages over the pneumatic system for measuring the airway pressure. These advantages include decreased chance of false pressure measurement secondary to occlusion with water or mucous, less chance of kinking, and, possibly, more rapid response to pressure changes due to the mechanical ventilator.

A small-size silicon microphone for measurements in turbulent gas flows

Abstract: For the first time a silicon microphone specially designed for measurements in turbulent gas flows has been fabricated and tested. The new design, based on surface-micromachining techniques, has a very small pressure-sensitive polysilicon diaphragm of 100 μm side length and 0.4 μm thickness with polysilicon piezoresistive strain gauges. The small diaphragm makes it possible to resolve and measure the pressure fluctuations of the smallest eddies in a turbulent flow. In order to achieve a sufficiently high acoustic pressure sensitivity, a relatively deep (3 μm) cavity is formed below the diaphragm by using the sacrificial-layer etching technique. A special vent channel is designed to give an equalization of the static air pressure between the cavity and the ambient without degrading the dynamic pressure response of the microphone. The device has a very flat frequency-response curve within ±2 dB between 10 Hz and 10 kHz and an acoustic sensitivity of 0.9 μV Pa−1 for a supply voltage of 10 V. It has been shown that the new sensor fulfils the requirements for pressure measurements in turbulence. The microphone frequency response has been calculated using an electrical analogy. Comparisons with experimental data are presented.

Determination and Characteristics of the Transition to Two-Phase Slug Flow in Small Horizontal Channels

Abstract: Two-phase pressure drop and fluctuating static pressures were measured in a small horizontal rectangular channel (hydraulic diameter = 5.44 mm). The two-phase fluid was an air/water mixture at atmospheric pressure tested over a mass flux range of 50 to 2,000 kg/m[sup 2] [center dot] s. Two-phase flow patterns were identified and an objective method was found for determining the flow pattern transition from bubble or plug flow to slug flow. The method is based on an RMS static pressure measurement. In particular, it is shown that the transition is accompanied by a clear and abrupt increase in the RMS pressure when plotted as a function of mass quality. Use of the RMS pressure as a two-phase flow pattern transition indicator is shown to have advantages over pressure-versus-time trace evaluations reported in the literature. The transition is substantiated by a clear local change in slope in the curve of two-phase pressure drop plotted as a function of either Martinelli parameter of mass quality. For high mass fluxes, the change in slope is distinguished by a local peak. Some degree of substantiation was found in previous work for both of the results (the RMS static pressure change and the local pressure dropmore » change) at the transition to slug flow.« less

Three and a Half Centuries Later - The Modern Art of Liquid-Column Manometry

Abstract: After three and a half centuries the Torricellian mercury manometer remains the most accurate pressure standard. State-of-the-art manometers achieve parts-per-million total uncertainties near atmospheric pressures and imprecisions as low as 0,01 Pa. The total uncertainty is determined primarily by uncertainties in the measurement of the height of the mercury surfaces and the average mercury density. The latter is limited generally by the uncertainty of the average temperature of the mercury. The techniques used to locate the mercury surfaces and determine their heights not only determine the imprecision and accuracy of the height measurement, but can also have a significant effect on the maintenance of a stable and uniform mercury temperature. This review discusses the factors important in high-accuracy manometers with particular emphasis on surface detection and height measurement techniques. Specifically discussed are capacitance detection, white-light fringes, optical interferometry, with and without floats, and ultrasonic measurements.

Device for measuring pressure with replaceable connector element

Abstract: A transducer assembly for measuring pressure or differential pressure includes an oxide ceramic pressure measurement cell removably retained inside a connection housing by an annular set ring on a first side and by a cup packing located on a second side. The pressure measurement cell is held at a fixed distance inside a connection housing from a connector element. The connection housing removably connects to a main housing, allowing for release and replacement of any of the elements within the assembly, thus enabling adaptation of the device to different applications without recalibration.

No touch pulse measurement by optical interferometry

Abstract: Arterial pulsatility was measured using an optical interferometer. As opposed to laser Doppler flow meters, the prototype system the authors evaluated can detect pulsation profiles of major arteries with potentially useful information including pulse wave velocity, profile of pulse pressure, etc. >