Showing papers on "Pressure measurement published in 1981"

Pressure and temperature dependence of electrical resistivity of Pb and Sn from 1-300K and 0-10 GPa-use as continuous resistive pressure monitor accurate over wide temperature range; superconductivity under pressure in Pb, Sn and In

Abstract: The dependence of the electrical resistivity of Pb on hydrostatic pressure is determined over major portions of the temperature and pressure ranges 1-300K and 0-10 GPa (100 kbar), respectively, and for Sn at 300K. The results are compared with a simple Bloch-Gruneisen law including volume changes due to thermal contraction. It is demonstrated that both Pb and Sn are ideally suited for use as accurate resistive manometers, enabling a reliable continuous determination of pressure over a wide temperature range. The agreement between the pressure at low temperatures indicated by both resistive and superconducting (Tc) Pb manometers is excellent. Tc(P) calibration curves are given to 22 GPa for Pb and to 5 GPa for Sn and In. A general method is presented which shows how pressure can be used to test for the presence of electron-electron scattering; in the temperature range studied, T>or=7.2K, electron-phonon scattering constitutes the dominant scattering mechanism in Pb, as expected.

Compartmental pressure measurements: an experimental investigation using the slit catheter.

Abstract: A new catheter employing a different technique to monitor compartmental pressure has been developed. The accuracy of the catheter was compared to a wick catheter and to the needle manometer technique for monitoring compartmental pressure. The slit catheter is the most accurate of the three techniques for continuous pressure monitoring for periods of up to 24 hours in the experimental canine model. The slit catheter is as accurate as the wick catheter for pressure measurements from 0 through 10 mm Hg. The needle technique has proven to be the least accurate of the three.

Integral hermetic implantable pressure transducer

Abstract: A hermetically sealed pressure transducer suitable for implantation in a human body. A pressure sensitive circuit is fabricated using contemporary silicon technology. The pressure sensitive circuit is sealed in an oil-filled chamber formed within a titanium cylinder having a glass substrate bottom and a thin titanium top. According to one embodiment, the pressure sensitive circuit contains a sealed inner chamber at a known pressure, thereby measuring pressure relative to a known value. A second embodiment vents the pressure sensitive circuit to produce a relatively pressure measurement. A grill protects the assembly and aids insertion into the desired area. A lead connects the transducer to an implantable sensing circuit.

Oscillating Flow of a Viscous Compressible Fluid Through a Rigid Tube: A Theoretical Model

Abstract: The forced oscillation technique used to determine the impedance of the respiratory system has been modified by measuring, instead of pressure and airflow at the mouth of the subject, the transfer function over a rigid tube. An exact description of the aerodynamic characteristics of a cylindrical conduit is needed in this method. Therefore, a line model was developed, describing the tube as a pneumatic transmission line and taking into account the axial pressure losses, the gas compressibility, and the thermal conductivity of the tube wall. The quality of this model was verified by measuring velocity profiles at the end of an open tube at various frequencies. The agreement with the predictions of the model was satisfactory.

Influence of cerebrospinal fluid on epidural pressure.

Abstract: Summary The pressure in the epidural space was measured with a water manometer in 40 women receiving elective epidural for pain relief in labour, and in three patients who were undergoing lumbar puncture. Injection of a small volume of fluid in the epidural space produced a positive pressure in all subjects, with a mean of 14 cmH2O (range 6·5–20 cmH2O). Pressure varied with posture, respiration, cough and jugular venous compression. The variations in pressure agreed closely with those reported for cerebrospinal fluid (CSF) pressure. It is suggested that in the lumbar region the dura fills the vertebral canal and is both compressible and expansile. When fluid is injected into the epidural space, the dura acts as a movable membrane and pressures on either side of it tend to equalise. Measurement of epidural pressure may provide a less traumatic way of estimating CSF pressure than traditional methods.

Building Internal Pressure: Sudden Change

Abstract: The change of the internal pressure of a building caused by the sudden opening of a window or door under the action of wind is analyzed using the Bernoulli equation of fluid mechanics. The problem is treated at several levels of sophistication, from the simplest quasi-steady isothermal incompressible solution to the most complex solution assuming unsteady isentropic compressible flow with due regards to the inertia effect. Following the break of a window or door by wind, the internal pressure reaches the external pressure at the opening rather rapidly. After the internal pressure has reached the external pressure, there is an overshoot and subsequent oscillation of the internal pressure, in spite of the constancy of the external pressure under a steady wind. The results are compared to solutions obtained from the Helmholtz resonator model of acoustics.

Pressure measurement at high temperatures in the diamond anvil cell

Abstract: The frequency shift of the R1 ruby fluorescence peak has been measured in the diamond anvil cell along the ice/water melting curve in the temperature interval 25–200 °C and pressure interval 0–40 kbars. The temperature and pressure coefficients of the frequency shift were found to be independent in this region. Using a least‐squares‐fitting program to find the fluorescence peak positions, we could reproducibly measure pressures to ±0.2 kbar at 25 °C and to ±0.5 kbar at 300 °C. The temperature coefficient of the frequency shift of R1 in the interval 25–300 °C was determined to be −0.149 cm−1/°K. Large systematic errors in the pressure determination were found to arise when nonuniformity of temperature in the diamond anvil cell caused uncertainty in the ruby temperature.

Gauge pressure sensor

Abstract: An atmospheric differential pressure sensor is disclosed comprising a pressure transducer, having a diaphram, mounted within a two piece protective transducer housing. An ambient atmospheric pressure receiving cavity is formed by the housing and coupled to the transducer diaphragm by a pressure transmitting tube that has a isolating oil drop within the tube to keep atmospheric contaminants away from the diaphram. The atmospheric pressure receiving cavity has external openings extending peripherally over more than 180° of rotation about a central axis of said housing, and the ambient cavity provides a non-linear directional path between the end of the tube connected to the cavity and the exterior of the housing.

Instrumentation for Aerated Flow on Spillways

Abstract: Instruments that have been used for measuring air concentration and velocities in self-aerated flow are examined. For air concentration measurements it is shown that the conductivity probe is satisfactory. For the velocity measurement the concentration measurements together with a pressure cell measuring the total head was attempted but the measurements were difficult to interpret. A correlation probe which detected the air water interface as it passed between two needles proved satisfactory for mean velocity measurements and the signal from a single resistance probe was used to estimate the bubble size. All of the probes were tested in the laboratory and on Aviemore spillway and based on this experience suggestions are made for future instruments.

A new approach to noninvasive manometry: interaction between ultrasound and bubbles.

Abstract: Fairbank andScully (1977) have suggested using the interaction between ultrasound and air bubbles in noninvasive manometry. In this paper, an extension of this concept is introduced, which avoids the error caused by variations in bubble volume. This is accomplished by means of a modulation of the ambient pressure, realised in practice by a low frequency ultrasound wave of known amplitude. It is further suggested that use be made of the pulse-echo amplitude from a single bubble as the primary parameter from which the hydrostatic pressure can be derived. The new method has been analysed theoretically and by a model experiment. Problems expected in clinical applications are discussed. The most promising areas for its application are intracranial and intrauterine pressure measurements.

Pressure measurement sonde

Abstract: A pressure measurement sonde of the type comprising two piezoelectric detectors, one being used for pressure measurements and the other being used as a reference detector. The latter is used to compensate at least partly, the effects due to temperature variations. This sonde includes means for favoring the heat exchanges of said detectors with the surrounding medium and for substantially balancing the heat exchange rates of each of said detectors with the surrounding medium. The sonde is particulary adapted to the carrying out of pressure measurements in oil wells.

Method for liquid chromatography

Abstract: To stabilize flow rate in a single-stroke, syringe-type high pressure pump to a constant value after turn-on, a control system increases the pump speed until equilibrium conditions are reached and then pumps at the preset rate. In one embodiment, the control system senses the maximum rate of change of pressure, detects a pressure when the rate of change is two-thirds of the maximum, increases the pump rate until the pressure is three times that at the value of the detected pressure and begins pumping at the preset constant flow rate. In other embodiments: (1) a pumping system is operated at a flow rate ten times the preset flow rate and, when the time derivative of the pressure has dropped to nine tenths of its maximum, the pump motor speed is reduced to the preset flow rate; (2) the outflow of the column is measured under no load conditions at the desired flow rate and when a column is connected, the pumping speed is increased until the same outflow results before reducing the pumping rate; and (3) the system is operated in a constant pressure mode to a point at which the pressure is estimated to provide the desired flow rate, the flow rate measured, and if the flow rate is not the preset one, a new pressure measurement is set and the procedure repeated. In a constant pressure system, the speed of a recording chart is adjusted to the pumping speed to provide a chromatogram with abscissae of flow rate units.

Self-correcting electronically scanned pressure sensor

Abstract: This invention is a multiple channel high data rate pressure sensing device for use in wind tunnels, spacecraft, airborne, process control, automotive, etc., pressure measurements. This device offers data rates in excess of 100,000 measurements per second with inaccuracies from temperature shifts less than 0.25% (nominal) of full scale over a temperature span of 55° C. This device consists of thirty-two solid state sensors 11, signal multiplexing electronics to electronically address each sensor, and ditital electronic circuitry to automatically correct the inherent thermal shift errors of the pressure sensors and their associated electronics.

Measurement of instantaneous shut-in pressure in crystalline rock

Abstract: A method is defined which was found useful, not only for determining the instantaneous shut-in pressure (ISIP) during fracture creation, but also for determining the pressure inside the fracture, near the exit and entrance wellbores, when a circulation of fluid through a fracture is taking place. The basic assumption of the Muskat method is that, after a short transient period, the shut-in pressure approaches an asymptotic value, Pa, in an exponential fashion, i.e., if Pa is subtracted from P at each time, t, and the result is plotted, ln (P-Pa) vs t will be a straight line. Various values of Pa are tried until the best straight line fit is found. Two Muskat analyses are shown. (MHR)

Excess pressure losses in a slit

Abstract: Excess pressure losses in a slit are reported for the flow of viscous fluids under a large range of the Reynolds number. Four types of fluids were used: Newtonian, inelastic shear-thinning, elastic shear-thinning and approximately second-order fluids. The excess pressure losses were obtained from pressure measurements with ten flush-mounted transducers, hence eliminating hole errors and differentiating between entrance and exit losses. The contribution of the viscous dissipation to the excess pressure losses was calculated from a macroscopic energy balance, correcting for the kinetic energy losses and the normal stresses arising in the fully developed flow region. Entrance losses are very important when the fluid exhibits both elastic and shear-thinning properties. In the absence of shear-thinning properties, the entrance losses are smaller or close to values obtained with Newtonian fluids. The exit losses present the same patterns as the entrance losses, but their magnitudes are only 20—40% of the entrance losses. Our results confirm that the assumption of fully developed flow down to the exit is unacceptable, in consequence the exit pressure cannot be used to evaluate the primary normal stress difference.

Emitter Discharge Sensitivity to Pressure and Temperature

Abstract: The discharge sensitivities to pressure and temperature of three types of emitters (helical long-path, labyrinth and vortex-type emitters) were determined in the laboratory. The measured discharge sensitivity to pressure was used to calculate the maximal permissible pressure variation in a field for the various emitters. The relative discharge distribution along an experimental pipe with helical long-path emitters was calculated on the basis of the measured temperature distribution and the computed pressure distribution. The resulting relative discharge distribution was curvilinear, in good agreement with the measured values. Under field conditions where water is heated as it flows in pipes exposed to solar radiation, emitter discharge along the second half of the pipe is determined by its specific discharge sensitivity to temperature.

Multiple shock reverberations in a layer structure observed by particle‐velocity and pressure gauges

Abstract: Multiple reverberations of shock waves in a layer structure have been observed by means of a particle‐velocity gauge using electromagnetic induction and a manganin pressure gauge. Changes in the particle velocity observed are in good agreement with estimates from the published Hugoniot data centered on the normal state. The shock pressure measured indicates that there are significant differences from the usual estimate, above. Attenuation of shock pressure and the suppression of thermal pressure accompanying the shock reverberations are considered to explain the differences. The reverberation shock pressures calculated using the Mie‐Gruneisen equation of state, which correspond to the recentered Hugoniot values for the previous state, are in good agreement with the observed ones.

Accuracy of an ultrasound Doppler servo method for noninvasive determination of instantaneous and mean arterial blood pressure.

Abstract: A new noninvasive method for determining arterial blood pressure is presented. Using a fast servo system, the pressure in the arm cuff is controlled so that the flow is maintained at a low value. Transcutaneous ultrasound Doppler techniques are used to detect flow to the artery. Comparison with invasive pressure measurements demonstrated that the servo method reproduced beat-to-beat variations in arterial blood pressure faithfully. Mean arterial blood pressure was determined from the noninvasive recordings using the same mathematically valid procedure as was used for the invasive recordings. The deviation between the invasive and the noninvasive determinations of this measurement was -0.6 +/- 2.2 mm Hg (mean +/- SD) in 23 subjects.

Auto-zero system for pressure transducers

Abstract: An apparatus for automatically compensating for deviation of a capacitance manometer reading from true pressure. The capacitance manometer is connected to a source of pressure having a value less than the pressure the capacitance manometer is capable of reading and the indicated pressure is stored as a correction factor. Thereafter, each pressure read by the manometer is adjusted by the correction factor.

Pressure regulating transducer

Abstract: A pressure regulating transducer for providing a regulated output pressure in response to an electric input signal in which a proportional solenoid operates a valve, and the output pressure from the valve operates against the force generated by the solenoid to establish the position of a valve element for a regulated fluid output pressure. The position of the valve element will vary in response to flow changes, absolute pressure changes, and changes in the inlet or outlet pressures caused by leaks or restrictions, to maintain the designated outlet pressure for the input signal provided. Thus, a predetermined outlet pressure is maintained for each current input value, regardless of flow and/or absolute pressure changes.

Piezoresistive pressure cell

Abstract: The pressure cell has a front end cell wall embodied by a metering diaphragm which contains at least one resistor applied by coating and passes over at its backside into an annular cylinder barrel which is closed by a rear cell wall cemented to the same by plastic material adapted to be stressed under elastic elongation and shear. The rear cell wall consists of a material which differs from that of the metering diaphragm. Yet the pressure cell is practically free of any external stress under normal ambient conditions because of the elasticity of the plastic material used for cementing. The pressure cell may be used, for example, in electronic sphygmo-manometers, in carburetors of internal combustion engines for automatic adjustment of the same, and the like. Absolute pressure and reference pressure measurements may be taken. By virtue of the small hysteresis, pressure variations in rapid succession can be measured. The preferred pressure measuring range lies between 0.1 and 2 bar, with pressure ranges up to 1000 bar being permissible as well. Also lower pressure ranges can be achieved.

Subsonic tests of an all-flush-pressure-orifice air data system

Abstract: The use of an all-flush-pressure-orifice array as a subsonic air data system was evaluated in flight and wind tunnel tests. Two orifice configurations were investigated. Both used orifices arranged in a cruciform pattern on the airplane nose. One configuration also used orifices on the sides of the fuselage for a source of static pressure. The all-nose-orifice configuration was similar to the shuttle entry air data system (SEADS). The flight data were obtained with a KC-135A airplane. The wind tunnel data were acquired with a 0.035-scale model of the KC-135A airplane. With proper calibration, several orifices on the vertical centerline of the vehicle's nose were found to be satisfactory for the determination of total pressure and angle of attack. Angle of sideslip could be accurately determined from pressure measurements made on the horizontal centerline of the aircraft. Orifice pairs were also found that provided pressure ratio relationships suitable for the determination of Mach number. The accuracy that can be expected for the air data determined with SEADS during subsonic orbiter flight is indicated.

Vacuum leak detector and method

Abstract: Apparatus and method for detecting leakage in a vacuum system involves a moisture trap chamber connected to the vacuum system and to a pressure gauge. Moisture in the trap chamber is captured by freezing or by a moisture adsorbent to reduce the residual water vapor pressure therein to a negligible amount. The pressure gauge is then read to determine whether the vacuum system is leaky. By directing a stream of carbon dioxide or helium at potentially leaky parts of the vacuum system, the apparatus can be used with supplemental means to locate leaks.

Pressure measurement method

Abstract: A method of determining the pressure applied to a limb by an inflatable garment by placing a flexible pressurizable cuff between the garment and the limb to receive the compressive garment forces and then determining the pressure in the cuff due to those compressive forces alone. The cuff pressure component due to compression of the garment is determined by extrapolating from a plot of cuff pressure versus bias pressure. The bias pressure is required to obtain an accurate reading of cuff pressure and is eliminated as a component in determining the garment pressure by means of the extrapolation. A preferred transducer for converting cuff pressure to electrical signals employs a manometer tube extending between two plates of a capacitor.

Method of and apparatus for inspecting liquid storage tanks for leaks by means of pressure decrease and increase

Abstract: A method of inspecting storage tanks for leaks by means of pressure decrease and increase in the tanks, in which a part of a liquid 6 stored in a tank 1 is discharged to put the tank 1 under vacuum and variations in the pressure in the tank 1 with time are checked, the pressure in the tank 1 is thereafter increased to the level of the atmospheric pressure, and then the liquid which was discharged from the tank is poured back thereinto to put the tank under pressure and variations in the pressure in the tank with time are checked. The method is done by an apparatus designed for inspecting storage tanks for leaks by means of pressure decrease and increase in the tanks, having an air pipe (2), a measuring pipe (3), a liquid feed pipe (4), a liquid suction pipe (5) and an air-tight container (7), which are communicated with a tank (1) to be inspected, a pressure regulator pump (8) connected to the air-tight container (7), and a manometer (11) and a recording air gauge (10) connected to the measuring pipe (3).

Direct measurements of acoustic admittance using laser Doppler velocimetry

Abstract: Research was directed at making measurements of oscillatory velocities in propane/air and solid propellant flames using laser Doppler velocimetry (LDV) instrumentation. Combustors were developed to impose controlled periodic pressure disturbances on burning solid propellants and to excite a propane/air flame. A tracking system was developed to maintain the LDV control volume at a fixed position above the regressing propellant surface so that a large number (over 10,000) of velocity realizations could be recorded. The research demonstrated that unsteady velocities (up to 1000 Hz) could be measured for propane/air flames seeded with micronsized particles and for solid propellant flames. The simultaneous velocity and pressure measurements were used to obtain acoustic admittances over a range of excitation frequencies, amplitudes, and pressures.

Pressure measurement system with a constant settlement time

Abstract: The invention provides a pressure measurement system with a substantially constant settlement time. The invention includes a closed loop pressure measurement system having an input impedance configuration and a feedback impedance configuration where a signal from the feedback impedance configuration is used to null or balance a signal from the input impedance configuration. The error between the signals is integrated in a digital integrator to generate a measurement of the sensed parameter. The invention further comprises a means for varying the feedback loop gain of the system as a function of pressure in a manner to compensate for the gain change produced in the system in response to a pressure change.