Showing papers on "Pressure measurement published in 2000"

Simultaneous pressure and temperature measurement with polymer-coated fibre Bragg grating

Abstract: It is shown, both theoretically and experimentally, that the pressure and temperature sensitivities of a fibre Bragg grating (FBG) can be increased by as much as 30 and 8 times, respectively, by coating the FBC with a polymer. A novel technique is then presented for coating an FBG with polymers so that a single FBG can be used for simultaneous measurement of pressure and temperature with good sensitivities.

Process pressure measurement devices with improved error compensation

Abstract: A device and method provide for improved error compensation in the measurement of process pressure. The device and method are able to compensate for diaphragm deformation (offset) and varying dielectric constants present in a process field environment. The pressure sensor (56), filled with a dielectric fill-fluid (95), includes at least three capacitor plates (144, 146, 148, 150), disposed about a diaphragm (102). At least two capacitor plates (144, 146) are placed on one side of a conductive diaphragm (102), and one capacitor plate (148, 150) is placed on the other side of the diaphragm (102). The method compensates for both diaphragm offset and variances in the dielectric constant of the fill-fluid (95). An error compensated measurement of differential pressure is a function of the amount of diaphragm deflection detected at the edge region (194) subtracted from the amount of diaphragm deflection detected at the center region (140). One way of measuring diaphragm deflection is to measure the changes in capacitances from two capacitors on each side of the diaphragm (102), and to combine these values to achieve an error compensated output (R) representative of the applied differential pressure.

A miniature pressure system with a capacitive sensor and a passive telemetry link for use in implantable applications

Abstract: A miniature telemetric pressure-measuring system is presented in this paper. The system uses passive telemetry to transfer power to the transponder and pressure data to the remote base unit. Such telemetric systems are becoming ever more important in the biomedical field as the interest for in-vivo measurements of different biological parameters both of humans and animals is increasing. A novel capacitive-type pressure sensor based on an SiGeB diaphragm is used as a sensing element. The merits of combining a capacitive pressure sensor and passive telemetry lies in the inherent low-power consumption of the sensor and the continuous availability of power through induction. The pressure sensor is connected to an integrated interface circuit, which includes a capacitance to frequency converter and an internal voltage regulator to suppress supply voltage fluctuations on the transponder side. In addition, the sensor and accompanying interface circuit take up very little space so as to be suitable for implantation.

Remote query measurement of pressure, fluid-flow velocity, and humidity using magnetoelastic thick-film sensors.

Abstract: Free-standing magnetoelastic thick-film sensors have a characteristic resonant frequency that can be determined by monitoring the magnetic flux emitted from the sensor in response to a time varying magnetic field. This property allows the sensors to be monitored remotely without the use of direct physical connections, such as wires, enabling measurement of environmental parameters from within sealed, opaque containers. In this work, we report on application of magnetoelastic sensors to measurement of atmospheric pressure, fluid-flow velocity, temperature, and mass load. Mass loading effects are demonstrated by fabrication of a remote query humidity sensor, made by coating the magnetoelastic thick film with a thin layer of solgel deposited Al2O3 that reversibly changes mass in response to humidity.

Pore pressure/stress coupling and its implications for seismicity

Abstract: Periodic pressure measurements made during the depletion of oil fields and virgin pressure measurements through normally- and over-pressured sequences in sedimentary basins both demonstrate that changes in pore pressure and minimum horizontal stress (σh) are coupled to one another. Pore pressure/stress coupling is predicted by poroelastic theory. Data from the North Sea (Ekofisk Field) and Texas (Travis Peak Formation of east Texas and Vicksburg Formation of south Texas) suggest that σh decreases at approximately 80% and 50% of the rate of depletion of reservoir pore pressure respectively. Virgin pressures in overpressured sedimentary basins suggest that σh increases at approximately 60-80% of the rate of increase in pore pressure in the Canadian Scotian Shelf, the Australian North West Shelf and the Gannet/Guillemot Fields area of the North Sea. The total vertical stress (σv) is given by the weight of the overburden and is unaffected by changes in pore pressure. Hence, contra to simple, uncoupled models of the effect of pore pressure on rock failure, differential stress in normal fault regime basins (σv - σh) increases as pore pressure decreases, and decreases as pore pressure increases. Increased differential stress with decreased pore pressure can account for depletion-induced seismicity, despite effective stresses increasing. Decreased differential stress with increased pore pressure implies that a greater increase in pore pressure can be withstood prior to failure than would otherwise be predicted, and increases the propensity of tensile, rather than shear failure, occurring with overpressure development.

Initial investigations on systems for measuring intraocular pressure

Abstract: Basic investigations on an intraocular implant system for continuous measurements of the intraocular pressure (IOP) are introduced. The system consists of a pressure sensor connected to transponder components integrated in the haptic of an artificial soft intraocular lens. External transponder components will be integrated in a spectacle and a hand-held unit. The influence of the lens material on the pressure sensor performance will be discussed in detail. Two pre-version of the concept mentioned will be introduced. In the first version, a pressure sensor was connected to a microwire. In a second version, the sensor was connected to transponder components for wireless data and energy transmission. Both versions were encapsulated in standard soft intraocular lens material. Pressure measurements show the same sensitivity before and after encapsulation. In addition, a small offset was observed due to the influence of the silicone coating. The performances of the sensors have the same precision as widely accepted gold standard for the determination of the IOP.

Unsteady Pressure Measurement

Abstract: Pressure measurement and turbomachinery have been intimately linked since flow field diagnosis was employed in verifying the operation of the first gas turbines. In the early years, time-mean pressures were required and extensive use of pneumatic connections between the measurement points and pressure transducers was made. Over the last two decades or so there has been a requirement to measure time-varying pressures in turbomachinery applications to bandwidths of order 100 kHz and the silicon piezoresistive pressure sensor has been the device which has been at the heart of many of the measurements. Although we mention other new developments in technology that are under way, this paper concentrates on the silicon piezoresistive sensor. The operation of the device in the context of gas turbine applications is outlined and some of the special issues which arise and must be addressed for accurate measurements are discussed. Following this, two example fields of the application of piezoresistive sensors are discussed in some detail, namely, rotating blade static pressure measurements and fast response aerodynamic probes. In both these cases instrumentation design considerations are discussed, technological implementation details given and sample data displayed and briefly discussed. Contemporary work elsewhere is included in the discussion. Finally, conclusions are drawn and the future context for the piezoresistive device is outlined.

Advanced hybrid integrated low-power telemetric pressure monitoring system for biomedical applications

Abstract: A new, highly miniaturized hybrid integrated solution for telemetric pressure measurement in biomedical applications is presented. The telemetrically powered ITES (Implantable Telemetric Endo-System) consists of a surface micro-machined capacitive type absolute pressure sensor fabricated in an eight-mask MOS-like process and two low-power ASICs for capacitance change read-out and telemetric data and energy transmission. An advanced flip-chip mounting and assembly technology is applied to overcome most of the drawbacks of hybrid integration and to fulfill space requirements of biomedical implants without monolithic sensor integration. This paper emphasizes system design considerations of the hybrid system such as its partitioning and the mounting and assembly technology. The pressure sensor design and its associated read-out is discussed in detail.

Steady and Periodic Pressure Measurements on a Generic Helicopter Fuselage Model in the Presence of a Rotor

Abstract: A wind tunnel test of a generic helicopter fuselage model with an independently mounted rotor has been conducted to obtain steady and periodic pressure data on the helicopter body. The model was tested at four advance ratios and three thrust coefficients. The periodic unsteady pressure coefficients are marked by four peaks associated with the passage of the four rotor blades. Blade passage effects are largest on the nose and tail boom of the model. The magnitude of the pulse increases with rotor thrust coefficient. Tabular listings of the unsteady pressure data are included to permit independent analysis. A CDrom containing the steady and unsteady pressure data presented in the report is available from the authors.

Vibro-acoustic method of transformer clamping pressure monitoring

Abstract: This paper presents a vibro-acoustic method of on-line monitoring of a transformer core and winding clamping pressure. The method based on the dependence of oscillating frequencies spectra on the clamping force allows to distinguish between the core and the winding clamping pressure drop. Special software was developed for its practical application. Examples of practical application are given.

Telemetric monitoring of blood pressure in freely moving mice: a preliminary study

Abstract: This paper describes for the first time the possibility for recording the systolic pressure (SP), diastolic pressure (DP), and the mean arterial pressure (MAP) as well as the heart rate (HR) and locomotor activity (LA) in freely moving mice, using a commercially available telemetry and data acquisition system. The system comprises a new, small radio-telemetry transmitter implanted in the peritoneal cavity, a receiver board placed underneath the home cage, a multiplexer and a computer-based data acquisition system. The signals from the receiver were consolidated by the multiplexer and were stored and analysed by the computer. The telemetered pressure signals (absolute pressure) were corrected automatically for changes in atmospheric pressure measured by an ambient pressure monitor. The effects of implantation on animal behaviour, and, after the animals had recovered, the effects of handling on the SP, DP, MAP and HR were examined. The radio-telemetry system for recording the SP, DP, MAP and HR provides an accurate and reliable method for monitoring the direct effects of handling on SP, DP, MAP and HR. In addition, by using this new blood pressure (BP) transmitter, we maintain that BP measurements in freely moving mice are more efficient, reliable, and less labour-intensive than the measurement techniques described in the literature thus far.

A wireless pressure measurement system using a SAW hybrid sensor

Abstract: A pressure measuring system based on surface acoustic wave (SAW) sensors is presented. Since SAW sensors are powered by the energy of the RF field no battery is required, which is a major drawback of conventional microcontroller based telemetry systems. A successful combination of a SAW reflective delay line with a high-Q capacitive pressure sensor is shown. With a new way of matching the sensor impedance to the SAW reflector impedance both a high signal-to-noise ratio and a high signal dynamic are achieved which supports accurate signal evaluation. As an example of realization the prototype of a tyre pressure sensor unit is presented.

Ball tonometry: a rapid, nondestructive method for measuring cell turgor pressure in thin-walled plant cells.

Abstract: In this article we describe a new method for the determination of turgor pressures in living plant cells. Based on the treatment of growing plant cells as thin-walled pressure vessels, we find that pressures can be accurately determined by observing and measuring the area of the contact patch formed when a spherical glass probe is lowered onto the cell surface with a known force. Within the limits we have described, we can show that the load (determined by precalibration of the device) divided by the projected area of the contact patch (determined by video microscopy) provides a direct, rapid, and accurate measure of the internal turgor pressure of the cell. We demonstrate, by parallel measurements with the pressure probe, that our method yields pressure data that are consistent with those from the pressure probe. Also, by incubating target tissues in stepped concentrations of mannitol to incrementally reduce the turgor pressure, we show that the pressures measured by tonometry accurately reflect the predicted changes from the osmotic potential of the bathing medium. The advantages of this new method over the pressure probe are considerable, however, in that we can move rapidly from cell to cell, taking measurements every 20 s. In addition, the nondestructive nature of the method means that we can return to the same cell repeatedly for periodic pressure measurements. The limitations of the method lie in the fact that it is suitable only for superficial cells that are directly accessible to the probe and to cells that are relatively thin walled and not heavily decorated with surface features. It is also not suitable for measuring pressures in flaccid cells.

Blast-pressure measurement with a high-bandwidth fibre optic pressure sensor

Abstract: A sensor to measure rapidly changing pressures in an explosive air blast requires high bandwidth and high spatial resolution. For such an application a low-cost, electrically isolated sensor is particularly attractive. We describe an optical fibre-based pressure sensor that meets these requirements. The sensor is subjected to an experimental explosive-blast measurement test and the results are discussed with respect to the sensor performance and compared with a simple blast-wave model and conventional pressure transducers.

Fluid-pressure controlled ink pressure regulator

Abstract: A pressure regulation system for an inkjet printer comprises a chamber (2) for containing ink, level sensing means (4) for measuring the level of ink contained in the chamber (2), a pressure source (3) for providing a fluid at a controlled positive or negative gauge pressure, and a pressure control means for controlling the pressure source. An ink supply regulating means (6) regulates the flow of ink and an ink flow control means (5) controls the ink supply regulating means (6) based on an output of the level sensing means (4). The pressure regulation system can be mounted close to the printhead (1).

Method for non-invasive blood pressure cuff identification using deflation pressure measurements

Abstract: An inventive apparatus and method as disclosed for the automatic identification of a given one of a predetermined plurality of cuff assemblies interconnectable to a sphygmomanometer for use in a blood pressure measurement procedure. The invention provides for the obtainment of a pressure measurement(s) during deflation of an inflatable cuff, and utilization of such measurement(s) to identify the cuff assembly. More particularly, each different cuff assembly may be provided with a corresponding gas-flow restrictor which allows the pressure measurement(s) made during deflation of a given cuff assembly to be correlated in fashion that allows for identification. Preferably, first and second pressure transducers are provided for automatic pressure measurements both upstream and downstream of a cuff assembly during the deflation portion of a cuff identification operation. The upstream and downstream pressure measurements may be utilized to calculate a sequence of ratio values which in turn may be employed in the cuff identification procedure.

Measurement of external pressures generated by nerve cuff electrodes

Abstract: When external pressures are applied to a peripheral nerve, tissue damage can occur via compression and blood flow occlusion, resulting in degeneration and demyelination of axons. Although many types of nerve electrodes have been designed to avoid or minimize this pressure during stimulation of the nerve or recording of its activity, the measurement of the pressure exerted by these cuffs has not been reported. Currently, only theoretical models are used to predict nerve cuff electrode pressures. The authors have developed a nerve cuff electrode pressure sensor to measure external pressures exerted by peripheral nerve cuff electrodes. The sensor has a high sensitivity, linear response with little hysteresis and reproducible output. Pressure measurements have been obtained for split-ring and spiral cuff electrodes. The measurements obtained are in agreement with theoretical predictions. Moreover, they indicate that the pressures exerted by cuffs currently used for stimulation generate only a small amount of pressure, which is below the pressure required to occlude blood flow in nerves. The results also suggest that this new sensor can provide reliable measurement of external pressures exerted by nerve electrodes and would be an important tool for comparing various nerve cuff electrode designs.

Micro coils for an advanced system for measuring intraocular pressure

Abstract: A miniaturised transponder system consisting of a chip and a micro coil for measuring intraocular pressure continuously is presented. The system will be integrated in the haptic of a soft artificial intraocular lens. Calculations show that the capacitance of the coil influences the DC voltage drop significantly. With respect to to reliable system function a 20 /spl mu/m thick coil with an outer diameter of 10.3 mm, an inner diameter of 7.7 mm, 16 windings and a gap of 20 /spl mu/m between the windings was selected. Measurements show a good agreement between calculated and measured values. Wireless pressure measurements were carried out showing a linear behaviour of the output signal with respect to the applied pressure.

Steam - Water Relative Permeability

Abstract: A set of relative permeability relations for simultaneous flow of steam and water in porous media have been measured in steady state experiments conducted under the conditions that eliminate most errors associated with saturation and pressure measurements. These relations show that the relative permeabilities for steam-water flow in porous media vary approximately linearly with saturation. This departure from the nitrogen/water behavior indicates that there are fundamental differences between steam/water and nitrogen/water flows. The saturations in these experiments were measured by using a high resolution X-ray computer tomography (CT) scanner. In addition the pressure gradients were obtained from the measurements of liquid phase pressure over the portions with flat saturation profiles. These two aspects constitute a major improvement in the experimental method compared to those used in the past. Comparison of the saturation profiles measured by the X-ray CT scanner during the experiments shows a good agreement with those predicted by numerical simulations. To obtain results that are applicable to general flow of steam and water in porous media similar experiments will be conducted at higher temperature and with porous rocks of different wetting characteristics and porosity distribution.

The plant cell pressure probe

Abstract: The pressure probe is a micro manometer for the simultaneous direct recording and manipulation of plant cell hydrostatic pressure. It is used to map in space and time the turgor pressures of individual cells within tissues and organs of intact plants. This is used to study the hydraulic architecture of tissues, tissue movement and the responses of tissues to water stress. The approach can be augmented by simultaneous measurement of individual cell osmotic pressure. This permits the hydraulic driving forces across selectively permeable membranes and walls to be assessed fully. By manipulating manually the pressure, cell wall elasticity and its properties can also be mapped. Under some conditions this can be extended to plastic behaviour.

Estimation of pressure gradients in pulsatile flow from magnetic resonance acceleration measurements

Abstract: A method for estimating pressure gradients from MR images is demonstrated. Making the usual assumption that the flowing medium is a Newtonian fluid, and with appropriate boundary conditions, the inertial forces (or acceleration components of the flow) are proportional to the pressure gradients. The technique shown here is based on an evaluation of the inertial forces from Fourier acceleration encoding. This method provides a direct measurement of the total acceleration defined as the sum of the velocity derivative vs. time and the convective acceleration. The technique was experimentally validated by comparing MR and manometer pressure gradient measurements obtained in a pulsatile flow phantom. The results indicate that the MR determination of pressure gradients from an acceleration measurement is feasible with a good correlation with the true measurements (r = 0.97). The feasibility of the method is demonstrated in the aorta of a normal volunteer. Magn Reson Med 44:66–72, 2000. © 2000 Wiley-Liss, Inc.

Pressure-sensitive paint measurements in a shock tube

Abstract: Surface pressures were measured in the short-duration, transient flow environment of a small-scale, low pressure-ratio shock tube using thin-film pressure-sensitive paint (PSP). Issues regarding coating formulation, measurement uncertainty, optical system design, and temperature and illumination compensation are discussed. The pressure measurements were acquired during steady flow conditions following the passage of normal shocks and expansion regions along a flat sidewall and a wedge sidewall. The PSP characteristic response time was 3 to 6 ms. Overall pressure uncertainty for the shock tube measurements ranged up to 5% over one atmosphere and compared well with theoretical estimates of uncertainty.

Medical device having precision interconnect

Abstract: An electrical device such as a pressure guide wire (700) which has a resistive pressure sensor, such as a piezoresistive sensor (208), uses a precision interconnect in order to provide proper pressure measurement readings. The precision interconnect helps avoid the effects of contact and line resistance on the measurement of the pressure sensor's resistors (402 and 404). The precision interconnect uses high input impedance device's such as differential operational amplifiers (902, 904) in order to overcome the effect of any changes in the contact resistance. Further, an interface switch (1110) which is responsive to a control signal (1106) automatically determines what type of pressure guide wire (10 or 700) is attached to the interface circuit (1200).

Resonance based pressure transducer system

Abstract: The invention relates to a resonance based pressure transducer system, insertable into a living body for the in vivo measurement of pressure. It comprises a pressure sensor ( 2 ) having a mechanical resonator ( 16 ), the resonance frequency of which is pressure dependent; and a source of ultrasonic energy ( 4 ). The sensor ( 2 ) is mechanically coupled to said source ( 4 ) of ultrasonic energy, and the sensor and the source of ultrasonic energy are provided on a common, elongated member ( 6 ) at the distal end thereof. A system for pressure measurement comprises an AC power supply, a resonance based pressure transducer system, and a control unit for controlling the supply mode of the AC power, and for analyzing a resonance signal emitted from the resonance based pressure transducer system.

The physics of sub-bandage pressure measurement.

Abstract: Compression therapy is the principal treatment for leg ulcers associated with venous disease. The extent of compression generally can be estimated from the general Laplace equation relating pressure, bandage tension and leg radius. This study aimed to investigate the physical forces under long stretch bandages applied under constant tensions to cylinders of three defined radii ('model limbs'). Force expressed as pressure was measured under one, two and three layers of eight long stretch bandages and a plastic film (control) using temperature-compensated, strain-gauge pressure transducers. The bandages were applied at the manufactures' recommended extensions/tensions and at constant tensions (2-10N) to three rigid plastic tubes of increasing size, covered with a layer of soft foam. Foams of different hardnesses ranging from 20 to 230N were assessed. The median applied pressure and observed bandage characteristics changed with bandage type. The median applied pressure also changed with tension, number of layers, tube radius and foam hardness. The inter-layer shear component also tended to increase with the number of layers. An increase in sub-bandage pressure was observed relative to the radius, tension, foam hardness and number of layers but the relationship was not directly proportional. The shear force tended to be associated with increased bandage layers.

Pressure-based mass flow controller system

Abstract: A pressure based mass flow controller includes a flow path for connection to a fluid source, a flow restrictor dividing the flow path into an upstream reservoir and a downstream reservoir, an upstream pressure measurement device connected to the upstream reservoir, and a flow valve connected to the flow path The controller also includes a control device programmed to receive a desired flow rate, an indication of upstream pressure from the upstream pressure measurement device, an indication of downstream pressure from a remote downstream pressure measurement device connected to the downstream reservoir

Development of High-Resolution N 2 Coherent Anti-Stokes Raman Scattering for Measuring Pressure, Temperature, and Density in High-Speed Gas Flows

Abstract: Mean and instantaneous measurements of pressure, temperature, and density have been acquired in an optically accessible gas cell and in the flow field of an underexpanded sonic jet by use of the high-resolution N2 coherent anti-Stokes Raman scattering (CARS) technique. This nonintrusive method resolves the pressure- and temperature-sensitive rotational transitions of the ν = 0 → 1 N2Q-branch to within Δω = 0.10 cm-1. To extract thermodynamic information from the experimental spectra, theoretical spectra, generated by a N2 spectral modeling program, are fit to the experimental spectra in a least-squares manner. In the gas cell, the CARS-measured pressures compare favorably with transducer-measured pressures. The precision and accuracy of the single-shot CARS pressure measurements increase at subatmospheric conditions. Along the centerline of the underexpanded jet, the agreement between the mean CARS P/ T/ρ measurements and similar quantities extracted from a Reynolds-averaged Navier–Stokes computational fluid dynamic simulation is generally excellent. This CARS technique is able to capture the low-pressure and low-temperature conditions of the M = 3.4 flow entering the Mach disk, as well as the subsonic conditions immediately downstream of this normal shock.