Showing papers on "Pressure measurement published in 1992"

The Physical Basis of Ultrahigh Vacuum

Abstract: Contents: Molecule-Molecule and Molecule-Interactions. Collision Processes in Gases. Interaction of Charged Particles with Surfaces. Interaction of Radiation with Surfaces. Mechanical Properties of Materials at Very Low Pressures. General Considerations of Pressure Measurement. Total Pressure Gauges. Partial Pressure Gauges. Processing Techniques for Ultrahigh Vacuum. Pumps for Ultrahigh Vacuum. Examples of Ultrahigh Vacuum Systems.

Implantable pressure sensor lead

Abstract: A pressure sensing lead, wherein a hollow needle extending from the distal end of the lead is coupled to a pressure transducer. The hollow needle may be coiled and adapted to be screwed into human tissue, for example through the ventricular septum from the right ventricle into the left ventricle of a patient's heart, or through the wall of the heart into the pericardial sac. Alternatively, the hollow needle may be straight and a separate coiled needle mounted around the straight needle may be provided to affix the lead to body tissue. Pressure gradients are communicated from the tip of the hollow needle to its base and applied to the pressure sensor, allowing, for example, left ventricular pressure measurements to be taken from the right ventricle or pericardial sac pressure measurements to be taken from within the heart without the necessity of the pressure sensor itself passing through the heart wall.

Pressure measurement device with selective pressure threshold crossings accumulator

Abstract: A pressure measurement device (10) with a selective altitude threshold crossings accumulator and method therefor provides for selective accumulation of relative pressure thresholds. A pressure sensor (12) measures atmospheric pressure and provides analog pressure signals (30) representing measured atmospheric pressures. A digital-to-analog converter (14) converts the analog pressure signals (30) to digital pressure signals (32) for a computer (16) which then computes altitudes corresponding to the measured atmospheric pressures. The computer (16) assigns a threshold flag value which corresponds to the relative direction (e.g. 'up' or 'down') from a first (e.g. lower) altitude to a second (e.g. higher) altitude when the magnitude of the first-to-second altitude differential exceeds a first threshold. The computer (16) then generates a unit count (34) when both the relative direction from the second altitude to a third (e.g. lower) altitude opposes the first-to-second altitude direction and the magnitude of the second-to-third altitude differential exceeds a second threshold. An accumulator (18) accumulates the unit counts (34), and the accumulated count (36) is displayed on a display device (20, 22).

Ultraminiature single-crystal sensor with movable member

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 microdiaphragm 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.

Doppler assessment of prosthetic valve orifice area. An in vitro study.

Abstract: BACKGROUND Although Doppler echocardiography has been shown to be accurate in assessing stenotic orifice areas in native valves, its accuracy in evaluating the prosthetic valve orifice area remains undetermined. METHODS AND RESULTS Doppler-estimated valve areas were studied for their agreement with catheter-derived Gorlin effective orifice areas and their flow dependence in five sizes (19/20-27 mm) of St. Jude, Medtronic-Hall, and Hancock aortic valves using a pulsatile flow model. Doppler areas were calculated three ways: using the standard continuity equation; using its simplified modification (peak flow/peak velocity); and using the Gorlin equation with Doppler pressure gradients. The results were compared with Gorlin effective orifice areas derived from direct flow and catheter pressure measurements. Excellent correlation between Gorlin effective orifice areas and the three Doppler approaches was found in all three valve types (r = 0.93-0.99, SEE = 0.07-0.11 cm2). In Medtronic-Hall and Hancock valves, there was only slight underestimation by Doppler (mean difference, 0.003-0.25 cm2). In St. Jude valves, however, all three Doppler methods significantly underestimated effective orifice areas derived from direct flow and pressure measurements (mean difference, 0.40-0.57 cm2) with differences as great as 1.6 cm2. In general, the modified continuity equation calculated the largest Doppler areas. When orifice areas were calculated from the valve geometry using the area determined from the inner valve diameter reduced by the projected area of the opened leaflets, Gorlin effective orifice areas were much closer to the geometric orifice areas than Doppler areas (mean difference, 0.40 +/- 0.31 versus 1.04 +/- 0.20 cm2). In St. Jude and Medtronic-Hall valves, areas calculated by either technique did not show a consistent or clinically significant flow dependence. In Hancock valves, however, areas calculated by both the continuity equation and the Gorlin equation decreased significantly (p less than 0.001) with low flow rates. CONCLUSIONS Doppler echocardiography using either the continuity equation or Gorlin formula allows in vitro calculation of Medtronic-Hall and Hancock effective valve orifice areas but underestimates valve areas in St. Jude valves. This phenomenon is due to localized high velocities in St. Jude valves, which do not reflect the mean velocity distribution across the orifice. Valve areas are flow independent in St. Jude and Medtronic-Hall prostheses but decrease significantly with low flow in Hancock valves, suggesting that bioprosthetic leaflets may not open fully at low flow rates.

Temperature dependence of the ruby luminescence method for measuring high pressures

Abstract: Pressures in diamond‐anvil high‐pressure cells often are determined by measuring ruby emission spectra because the R1 luminescence has high quantum efficiency and frequency of the R1 band shifts almost linearly with pressure, independent of temperature. To more than 600 K, pressures can be precisely determined by measuring luminescence spectra at ambient and high pressures at the same temperature. The temperature dependence of the frequency of the R1 line is not simple, and empirical approximations have been developed so that a pressure at a known temperature might be estimated from measurements of spectra at that P and T and at ambient pressure and one temperature; that is, without measuring the R1 line at ambient pressure at each temperature. Measurements reported here show that, between 100 and 260 K, pressures computed by using empirical approximations calibrated near ambient temperature may be in error from 0.1 to several GPa. The temperature dependence of the R1 line is accurately described by the f...

A system for wireless intra-ocular pressure measurements using a silicon micromachined sensor

Abstract: A system for wireless intraocular pressure measurements using a silicon micromachined sensor

Method for compensating errors in a pressure transducer

Abstract: Disclosed is a method of compensating any of a plurality of different pressure transducers for their characteristic pressure sensitivity, zero pressure offset, and self-heating error The method comprises selecting a gain resistor that adjusts the gain of an output signal of the pressure transducer in use so that the pressure transducer appears as an ideal pressure transducer to a pressure monitor The self-heating error is compensated by measuring an initial bridge voltage that drives the transducer and an initial output signal of the pressure transducer when the transducer is first energized After a period of time a second bridge voltage and a second output signal are determined The self-heating error is determined as a function of the difference between the initial and second values The zero pressure offset is compensated by determining the output signal of the pressure transducer at zero gauge pressure after the pressure has been compensated for the self-heating error

Site of pressure measurement during spontaneous breathing with continuous positive airway pressure: effect on calculating imposed work of breathing.

Abstract: OBJECTIVE To describe the importance of measuring pressure at the tracheal end of the endotracheal tube during spontaneous breathing with continuous positive airway pressure in order to correctly assess: a) the changes in airway pressure and b) the work imposed by the breathing apparatus. DESIGN Multitrial tests under simulated clinical conditions using a mechanical lung model. SETTING A research laboratory at a university medical center. INTERVENTIONS Spontaneous breathing with continuous positive airway pressure, at peak sinusoidal inspiratory flow-rate demands of 30 and then 60 L/min with sizes 6, 7, 8, and 9 mm internal diameter endotracheal tubes at each flow rate. MEASUREMENTS AND MAIN RESULTS Pressure, flow rate, and inhaled and exhaled volumes, during simulated spontaneous ventilation with continuous positive airway pressure were measured. Pressure was measured alternately at the "Y" piece of the breathing tubing of the continuous positive airway pressure system and at the tracheal end of the endotracheal tube to calculate the work imposed by the breathing circuit, endotracheal tube, and the total breathing apparatus. Greater changes in pressure and work were measured at the tracheal end of the endotracheal tube than at the "Y" piece of the breathing tubing for all test conditions. For example, at a peak inspiratory flow-rate demand of 30 L/min when pressures measured at the tracheal end of endotracheal tubes were compared with pressures measured at the "Y"piece, the total work imposed by the breathing apparatus increased by approximately 145% with a 6-mm tube, 95% with a 7-mm tube, 50% with an 8-mm tube, and 40% with a 9-mm tube (p less than .05). Measuring pressure at the "Y" piece of the tubing results in significant underestimations of the changes in pressure and the work imposed, especially when the endotracheal tube has a small internal diameter and/or when the peak inspiratory flow-rate demand is high. CONCLUSIONS The results indicate that pressure should be measured as close to the patient's airway as possible, i.e., at the tracheal end of the endotracheal tube, rather than using the traditional approach of measuring pressure and assessing work at the inspiratory or expiratory limbs, or "Y" piece of the breathing tubing.

Capacitive melt pressure measurement with center-mounted electrode post

Abstract: A melt pressure measurement probe for insertion through wall of melt-containing vessel has a pressure-deflectable end portion for contact with pressurized melt. Pressure-resistant securing means fixes the end surface in a non-flow obstruction relationship. A seal surface on the probe prevents exposure of the melt to the securing means. Pressure detection means internal of the probe, responsive to deflection of the probe end surface to detect melt pressure, comprises a temperature-compensated capacitive sensor, one capacitor plate defined by the end portion and an opposite capacitor plate in the probe with a capacitive gap in-between. Electronic circuitry remote from the melt-exposed end, including circuitry within the probe to generate a signal proportional to the capacitance, compensates for change of temperature of the capacitor to generate an output signal proportional to melt pressure.

Comparison of the pressure‐induced frequency shift of Sm:YAG to the ruby and nitrogen vibron pressure scales from 6 to 820 K and 0 to 25 GPa and suggestions for use as a high‐temperature pressure calibrant

Abstract: The pressure‐induced frequency shift of the Sm:YAG Y1 peak at elevated temperature is calibrated against the temperature‐corrected Raman shift of the nitrogen vibron and, at temperatures less than 673 K, the R1 shift of ruby. The results presented here indicate that pressure can be determined from the Y1 and Y2 peak frequencies, without temperature correction, from 6 to 820 K and from 1 bar to 25 GPa by using the equations: P(GPa) =−0.12204 (ωY1obs−16187.2) and P(GPa)=−0.15188 (ωY2obs−16232.2). However, pressure determinations based on Y2 are less accurate, especially at high temperature. At elevated temperature, the Sm:YAG Y1 and Y2 peak frequencies are most accurately determined by curve fitting a spectral window at least 400 cm−1 wide. The spectral range was chosen in order to include the decay of the intensity of the Lorentzian Y1 peak to a background value and incorporate a third peak at 16360 cm−1.

Subsea well pressure monitor.

Abstract: A pressure measuring device will measure pressure in a subsea tubular member. The device includes a stationary unit mounted to the exterior of the tubular member and a movable unit that will be lowered into position next to the stationary unit whenever pressure is to be monitored. The stationary unit has a strain gage which will monitor pressure by measuring strain in the tubular member. The stationary unit has a light emitter which will emit pulses corresponding to pressure measured. The stationary unit has a photocell which will receive a light beam from the movable unit. The light beam and photocell provide power for the stationary unit. The movable unit has a receiver which receives any light pulses from the light emitter and correlates them to a pressure measurement.

Time-Averaged Heat Transfer and Pressure Measurements and Comparison With Prediction for a Two-Stage Turbine

Abstract: Time-averaged Stanton number and surface-pressure distributions are reported for the first-stage vane row and the first-stage blade row of the Rocketdyne Space Shuttle Main Engine two-stage fuel-side turbine. These measurements were made at 10 percent, 50 percent, and 90 percent span on both the pressure and suction surfaces of the component. Stanton-number distributions are also reported for the second-stage vane at 50 percent span. A shock tube is used as a short-duration source of heated and pressurized air to which the turbine is subjected. Platinum thin-film gages are used to obtain the heat-flux measurements and miniature silicone-diaphragm pressure transducers are used to obtain the surface pressure measurements. The first-stage vane Stanton number distributions are compared with predictions obtained using a quasi-3D Navier-Stokes solution and a version of STAN5. This same N-S technique was also used to obtain predictions for the first blade and the second vane.

Pressure-measuring method and needle system for hemodialysis

Abstract: A method and devices for measuring pressure within blood vessels used for hemodialysis and also for flow of blood into or from such blood vessels during hemodialysis. In one aspect of the method, a currently available hemodialysis set is used. This set comprises a tube (14) attached at one end to a hollow needle (12) and closed at the other end by a cap (19) which covers a proximal connector (18). The method comprises puncturing the blood vessel with the needle (12), measuring the distance to which blood flows under pressure into tube (14), calculating that pressure from that distance, and finally using the hemodialysis set for flow of blood in the performance of hemodialysis. In other aspects of the method, the improved devices of the invention are used. In one embodiment a proximal portion comprising a hollow needle (12), tube (14) with calibrated markings (16) and a proximal connector (18) are attached to a distal portion comprising a male connector (32) with lumen occluded by a hollow needle with a capillary lumen (34) and closed cylinder (24). The improvements in this embodiment increase the length of tube filled by blood and decrease the fluctuation in that length as a result of change in pressure between systole and diastole. In another embodiment a one-way flap valve (50) allows measurement of the maximum or systolic pressure within the blood vessel. In other embodiments pressure measurements are normalized for different atmospheric pressures at different altitudes. After the measurement of pressure, the needle, tube, and proximal connector are used for withdrawal or return of blood for a hemodialysis treatment.

System for monitoring pressure and temperature of pneumatic tires on a moving vehicle

Abstract: A tire pressure and temperature monitoring system for measuring tire inflation pressure and anomalous temperature of rotating tires in a moving vehicle by means of optoelectronic devices located in the stationary structure of the vehicle and an elastic diaphragm that rotates with the wheel and tire. The combined use of optoelectronic components and elastic diaphragms, provides a marked improvement in performance, reliability and cost over previously disclosed magnetic or radio frequency pressure measurement systems. The optoelectronic detector elements are also used to identify those tires whose side wall temperature is significantly higher than the side wall temperature of the other tires. In addition, the system can also be used as a measurement of individual wheel rotational speed and related wheel motion. Alternatively, fiber optic cables can be used to transmit light from a single light source to lenses mounted adjacent each tire and to transmit the reflected energy to remotely located optoelectronic devices.

Kontrollvorrichtung fuer den luftdruck von luftbereiften fahrzeugraedern

Abstract: A device for monitoring the air pressure in pneumatic tyres comprises a transmitting device fitted to each wheel of a vehicle and rotating with it, and a receiver which is built into the vehicle or accommodated in a separate housing. The transmitting device mounted in the wheel comprises a pressure gauge for measuring the tyre pressure, a transmitter and a signal generator which generates an identification signal unique to each transmitter and transmitted before or after the pressure signal. The receiver processes received signals only when the identification signal received matches a reference identification signal stored in the receiver. This facilitates reliable operation of the monitoring device and prevents false alarms.

Air pressure gauge with self contained adjustable alarms

Abstract: A diver's air tank pressure gauge having audible and visual alarms, an alarm pointer for indicating the pressure at which the alarms will activate, and a crank assembly for changing the position of the alarm pointer. The pressure gauge dial has a cutout for limiting the travel of the alarm pointer between acceptable high and low pressure limits. When the air tank pressure equals a preset alarm pressure, an electrical circuit is completed which activates the alarms. The diver can then turn off the alarms by resetting the alarm indicator to a lower pressure setting and continue the dive at a shallower depth.

Direct sampling of engine emissions for instantaneous analysis

Abstract: A method and associated apparatus for on-line gas analysis of a multicomponent gas emission flow, comprising: continuously withdrawing and regulating the pressure of a first sample flow from the emission flow, continuously withdrawing a second sample flow from the first sample flow, the second flow sample being diluted with mass controlled amounts of diluent (N2 or air) to lower the dew point of the gas sample to below room temperature; controlling the absolute pressure of the diluted sample to the range of 920-950 mbar; frequently periodically analyzing the diluted sample flow, controlled as to pressure, by fourier-transform infrared spectrometric techniques to render a concentration measurement for each desired gas species; and correcting each concentration measurement for dilution to derive an undiluted concentration measurement representative of the actual exhaust gas, said correction being accomplished by measuring the actual air/fuel ratio of the gas emission flow to provide a theoretical carbon concentration in the undiluted exhaust gas and thereafter ratioing the theoretical total carbon concentration to the measured carbon concentration in the sample to provide the needed correction factor.

A pressure regulator for the cuff of a tracheal tube.

Abstract: A regulator is described for the maintenance of a constant pressure difference above airway pressure during positive pressure ventilation in a cuffed tracheal tube. It comprises a tubular threshold valve which is powered by the anaesthetic gas supply source to a breathing system. The valve is interposed between the anaesthetic gas supply machine and the breathing system creating a pressure differential. The upstream pressure is transmitted to the pilot tube supplying the cuff of a tracheal tube via an upstream connection. The valve is suitable only for breathing systems that require a constant gas supply. The regulator was evaluated during anaesthesia, using a modified Mallinkrodt Hi-Lo jet ventilation tube to obtain simultaneous pressure measurements within the cuff and the lumen of the tracheal tube. A greater pressure was demonstrated in the cuff than in the airway and the two traces were approximately parallel throughout the respiratory cycle. The device should prevent excessive cuff inflation pressure and solves the problem of forgetting to let the cuff down before extubation.

3-dimensional pressure sensor.

Abstract: Use of ultrasonic stimulation together with a pressure sensitive piezoelectric material in a sensor makes it possible to obtain three dimensional pressure measurements on an object in one operation. A piezoelectric material which is manufactured with a conductive surface on both sides, and shear orientation (i.e. piezo voltage produced by pressure on the material is sensitized in a single axis of the shear plane), and generates a proportional voltage when stretched or compressed (and tension and compression is sensed by the generation of opposite polarity voltages), makes it possible to measure normal forces by ultrasonic stimulation, and shear forces by the generation of piezo voltages, using the same sensor. In a preferred embodiment, multiple sensors are disposed in a high density array, and the various axes for the three dimensional measurements are obtained by varying the orientation of each sensor relative to an adjacent sensor. In an alternative embodiment, at least two differently oriented layers of film are included in each sensor.

Vacuum Technology and Space Simulation

Abstract: Contents: 1. Vacuum Nomenclature. 2. Pressure. 3. Pressure Measurement. 4. Pumping Speed. 5. Gas Flow in Components and Systems. 6. Pumping Systems. 7. Cryogenic Pumping. 8. Gas Load. 9. Outgassing of Materials. 10. Systems. 11. Leak Detection.

Testing apparatus for pressure gauges implementing pneumatic feedback to control stepless regulating valve

Abstract: A testing apparatus for in situ calibration of various types of pressure gauges is provided for measuring absolute pressure, manometric pressure or differential pressure. The apparatus includes a reference chamber where a desired pressure can be established with very high accuracy. Pressure regulation is based on an output signal from a calibrated electronic pressure sensor connected to the reference chamber, and on a reference signal (V ref ), these signals being supplied to an electronic control circuit which controls a regulating valve. The regulating valve controls gas pressure within the reference chamber so that the pressure is established on the desired valve.

Unsteady viscous flow in a high-speed core compressor

Abstract: A probe incorporating a miniature high-frequency response pressure transducer has been traversed behind the first three stages of a high-speed multistage compressor operating at throttle settings corresponding to near choke, peak efficiency, and near surge. A novel method of compensating for transducer temperature sensitivity was employed. Consequently, time-averaged pressures derived from the transducer were found to be in good agreement with pneumatic pressure measurements. Analysis of the unsteady pressure measurements revealed both the periodic and random fluctuations in the flow field. This provided information on rotor-rotor interaction effects and the nature of viscous blade wake and secondary flows in each stage.

System and method for the measurement of mechanical properties of elastic materials

Abstract: A system and method for measuring the biomechanical properties of a healing wound in a specimen which utilize a chamber for applying an increasingly negative pressure over time to an area of tissue containing the wound, markings on the area for facilitating measurement of expansion of the area, a pressure measurement device for measuring the pressure in the chamber as a function of time, one or more cameras for obtaining multiple views of the area over time, a digitizer for generating a digital representation of each of the views, and a processor for determining a strain value from each digital representation and for correlating each strain value with a pressure measurement corresponding to the same point in time to provide a stress-strain relationship.