Showing papers on "Pressure measurement published in 1990"

Luminescent barometry in wind tunnels

Abstract: A flexible and relatively inexpensive method and apparatus are described for continuous pressure mapping of aerodynamic surfaces using photoluminescence and imaging techniques. Platinum octaethylporphyrin (PtOEP) has a phosphorescence known to be quenched by oxygen. When dissolved in a silicone matrix, PtOEP may be distributed over a surface as a thin, uniform film. When the film is irradiated with ultraviolet light, the luminescence intensity provides a readily detectable, qualitative surface flow visualization. Moreover, since the luminescence intensity is found to be inversely proportional to the partial pressure of oxygen, a quantitative measure of pressure change may be obtained using a silicon target vidicon or a charge-coupled device video sensor to measure intensity. Luminescent images are captured by a commercial frame buffer board. Images taken in wind tunnels during airflow are ratioed to images taken under ambient 'wind-off' conditions. The resulting intensity ratio information is converted to pressure using calibration curves of I0/I vs p/p0, where I0 is the intensity at ambient pressure p0 and I is the intensity at any other pressure p.

Ultraminiature pressure sensor with addressable read-out circuit

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

Silicon pressure sensor integrates resonant strain gauge on diaphragm

Abstract: A novel silicon pressure sensor has been developed which will enable high-precision pressure measurement. The sensor, which is based on a new concept, is fabricated from a single silicon crystal and has two resonant strain gauges which are held in vacuum cavities on the surface of the diaphragm to isolate them from the surrounding fluid. The two oscillating frequencies of the resonant strain gauges are differentially modulated by pressure. The sensor's measuring principle, features, its amplitude-controlled self-oscillation circuit, and the results of experiments are given.

Measurements of base pressure in the wake of a cylinder at low Reynolds numbers

Abstract: Measurements have been made of the base pressure coefficients of long circular cylinders at low Reynolds numbers from 35 to 1100 in a cross flow. The variation of "base suction" (negative base pressure coefficient or - C_(pb)) with Reynolds number shows a remarkably good correspondence with the variation of the Strouhal number. It is also possible to relate the variation in suction with the physical modes of wake formation found in previous studies. It is shown that the level of base suction is affected in only a minor fashion by whether parallel or oblique shedding is present, and it is found that the data are independent of the base pressure hole sizes and cylinder diameters that were used. The base suction is essentially constant along the span of a cylinder (outside of regions extending about 20 diameters in from each end), and the results arc independent of cylinder aspect ratio (L/D) provided that one exceeds a critical value of L/D.

Pump diagnostic system

Abstract: A method and apparatus to evaluate the performance of an implanted medication delivery device such as pumps and ports is described. In the case of a pump, the system measures ambient pressure and obtains two pressure measurements from the implanted device. One of these measurements is device reservoir pressure and the other is based on a disturbance pulse injected into the system at a point downstream of the reservoir. Based on those measurements and input calibration data, an expected flow rate is determined. The expected flow rate together with device refill data is in turn used to determine a normalized flow rate for the in-vivo device. Determinations are then made as to the performance of the reservoir, its pump and the condition of the outlet catheter without explant of the device. In the case of a port, the system measures the catheter resistance based on decay time of a disturbance pulse.

Capacitive pressure sensor

Abstract: A capacitive pressure sensor includes a set of facing electrodes arranged with a cavity disposed therebetween and having insulation layers respectively formed on the surfaces thereof. The contact area between the facing electrodes varies directly with the applied pressure, and variation in the contact area causes variation in the capacitance which is detected as a pressure measurement. Since the capacitance variation is proportional to the applied pressure, a pressure signal which is substantially linear can be obtained. Therefore, the capacitive pressure sensor of this invention can measure pressure with high precision.

Versatile, overpressure proof, absolute pressure sensor

Abstract: A non membrane-based overpressure proof gas pressure microsensor. It is not a membrane-based microsensor but is based on an open microbridge sensor structure. A method and apparatus is described to determine gas pressure from thermal conductivity, k, and volumetric specific heat, c pu , as well as pressure, P, using a microbridge sensor.

Sensor for pressure measurement in a liquid medium

Abstract: Pressure measurement. The sensor is characterised in that the electric charges appearing in line with the polarised region on the two faces of the membrane are conveyed in the case of at least one of them by a liquid or paste with electrically conducting nature towards electrodes situated outside the pressure region. Application to the measurement of pressure in lithotrity.

An umbilical data-acquisition system for measuring pressures between the foot and shoe

Abstract: An umbilical data-acquisition system has been developed for measuring pressure between the foot and shoe during walking. It consists of pressure sensors in the insoles of shoes, amplifier circuits, umbilical cables, a 12-b analog-to-digital converter, and a graphics display card in an IBM PC for real-time data collection and display. The applied pressure on a sensor decreases its resistance, which causes the output voltage of the amplifier circuit to increase. Seven sensors were attached to the surface of each insole of a pair of extra-depth shoes and calibrated in the insole before and after each test using a load cell as a reference. The IBM PC samples the outputs from the sensor and the load cell and stores a piecewise-linear lookup table for use in compensation for the nonlinearity of the sensor. On the PC's graphics display, two programs provide displays of foot pressures as real-time bar graphs or as analog pressure versus time curves. >

Pressure Sensors: Selection and Application

Abstract: This practical handbook provides the knowledge needed to specify and apply the best piezoresistive pressure sensors to interface with microprocessors and computers. Eliminating the details of semiconductor physics, it clarifies the three kinds of pressure measurement, explains silicon sensor design

Wind Tunnel Investigation and Flight Tests of Tail Buffet on the CF-18 Aircraft,

Abstract: : Investigations of tail buffet on the CF-18 have been conducted at the National Aeronautical Establishment (NAE) and the Aerospace Engineering Test Establishment (AETE). Flow visualization of the vortex burst phenomenon was carried out in a low speed water tunnel using a modified 1/72 scaled plastic model. In wind tunnel tests, a rigid 6% model was used for measurements in the NAE 5ft x 5ft Trisonic Tunnel. Unsteady pressure measurements on the vertical fin were made by means of 24 fast response transducers on each surface. Results of the acceleration experienced by the fin are presented Vortex flow structure was studied with the aid of a 49 pressure-sensor-rake mounted behind the fin. In addition to measuring steady pitot pressure values to deduce pressure contours, unsteady pressure fluctuations were obtained from 13 fast response transducers. The LEX was also instrumented with pressure orifices and fast response transducers. The investigation was carried out with LEX fences 'on' and 'off' to note their effect on tail buffet loads. Flight tests have been conducted at AETE on a test aircraft with accelerometers installed on the vertical fins and horizontal stabilators and strain gauges mounted on the aft fuselage structures and fin root attachment stubs. Flight test data are presented showing the effectiveness of the LEX fence in reducing aft fuselage structural to buffet loads.

Surface pressure measurement by oxygen quenching of luminescence

Abstract: Methods and compositions for measuring the pressure of an oxygen-containing gas on an aerodynamic surface, by oxygen-quenching of luminescence of molecular sensors is disclosed. Objects are coated with luminescent films containing a first sensor and at least one of two additional sensors, each of the sensors having luminescences that have different dependencies on temperature and oxygen pressure. Methods and compositions are also provided for improving pressure measurements (qualitative or quantitive) on surfaces coated with a film having one or more types of sensor.

Pressure feed paint cup

Abstract: An improved pressure feed remote paint cup for use with a spray gun. The cup consists of a pressure tank with a large opening for filling and cleaning and a lid for closing the opening. The lid is secured to the tank with a separate threaded ring. The lid has an integral handle which facilitates holding from a point of balance during use. A pressure regulator and a pressure gauge are mounted on the handle.

Lubrication monitoring system

Abstract: Control system for measuring/detecting transient fluid flow in a positive displacement pump lubrication system using time-differential pressure measurements. A pressure-actuated transducer for a captive oil column in the injection circuit imparts a proportional voltage signal to an electronically differentiating high pass filter, rendering it independent of any base line steady-state component. The resultant signal is fed into a comparator used to discriminate rates of pressure change against a preset reference level, thereby sensing transient spike pressures covering a wide range of adjustable frequencies and pump displacement strokes to thereby confirm required lubrication flow. The same transducer voltage signal transmitted during a steady-state portion of the pump cycle between injections is monitored for high and low set points such as incident to downstream blockage or system leakage.

Semiconductor pressure sensor

Abstract: A semiconductor chip with a gauge pressure sensor section and an absolute pressure sensor section is anodically bonded, in a vacuum, to a glass mount with an evacuated space between the absolute-pressure sensor section and the mated surface portion of the glass mount. The pressure to be measured is received by the reverse surface of the gauge pressure sensor section. Since no complicated package is mounted within the outer package, the assembly of the sensor is easy. Further, since the pressure sensor has two sensor sections, namely, the gauge pressure sensor section and the absolute pressure sensor section, the sensor can be used as an absolute pressure sensor of the reverse-surface pressure-receiving type.

Cavitation Regimes in Squeeze Film Dampers and Their Effect on the Pressure Distribution

Abstract: High speed motion pictures have revealed several operating regimes in a squeeze film, damper. Pressure measurements corresponding to these distinct regimes were made to examine their effect on the performance of such dampers. Visual observation also revealed the means by which the pressure in the feed groove showed higher amplitudes than the theory predicts. Comparison between vapor and gaseous cavitation are made based on their characteristic pressure wave, and the effect this has on the resultant force in the squeeze film. Presented at the 44th Annual Meeting in Atlanta, Georgia May 1–4, 1989

Simultaneous measurements of velocity, temperature, and pressure using rapid CW wavelength-modulation laser-induced fluorescence of OH

Abstract: In high speed flows, laser induced fluorescence (LIF) on Doppler shifted transitions is an attractive technique for velocity measurement. LIF velocimetry was applied to combined single-point measurements of velocity, temperature, and pressure and 2-D imaging of velocity and pressure. Prior to recent research using NO, LIF velocimetry in combustion related flows relied largely on the use of seed molecules. Simultaneous, single-point LIF measurements is reported of velocity, temperature, and pressure using the naturally occurring combustion species OH. This experiment is an extension of earlier research in which a modified ring dye laser was used to make time resolved temperature measurements behind reflected shock waves by using OH absorption an in postflame gases by using OH LIF. A pair of fused-silica rhombs mounted on a single galvanonmeter in an intracavity-doubled Spectra-Physics 380 ring laser permit the UV output to be swept continuously over a few wave numbers at an effective frequency of 3kHz.

Apparatus and method for measuring pressure in a fluid line for detecting an occlusion in said fluid line

Abstract: The apparatus and method for detecting pressure and occlusion in a fluid line (12) is for use with a fluid line being operated upon by a positive displacement, peristaltic pump (10) having several cam follower fingers (30, 32) pressing against the fluid line sequentially to force fluid through the line peristaltically. A sensor follower finger (36) is mounted to the cam shaft of the pump (10) among the other peristaltic fingers (30, 32) in order to cyclicly press against the fluid line with a certain degree of force and displacement as the cam shaft rotates. The sensor follower finger (36) includes a strain gauge mounted on the sensor finger to generate a signal indicating the degree of force being applied by the sensor finger against the tubing, and a signal processor unit which receives this force signal and determines the pressure within the fluid line based upon the signal. The signal processor compares the measured pressure with an upstream reference value during an upstream pressure measurement mode, and compares the measured pressure with a downstream reference value during a downstream pressure measurement mode. An alarm may also be provided for indicating if there is an occlusion condition either upstream or downstream when the measured pressure varies significantly from these reference values.

Absolute pressure sensors by air-tight electrical feedthrough structure

Abstract: A new electrical feedthrough structure for silicon absolute pressure sensors has been developed, and has been applied to an integrated capacitive pressure sensor, a piezoresistive pressure sensor and a piezoresistive force sensor array for tactile imaging. The feedthrough structure is constructed from Pyrex glass, which has narrow through-holes engraved by electrochemical discharge drilling, and silicon, which has the diffused electrical feedthrough from the reference cavity. The reference cavity is hermetically sealed by glass-silicon anodic bonding. The metal contacts to the diffused feedthrough at the bottom of glass holes are made by CrCuAu evaporation through a metal mask. Using this structure, an electrical feedthrough from the reference cavity can be made without any air leakage. This structure is useful for the fabrication of absolute pressure sensors, acceleration sensors and so on.

Ultra-high temperature stability Joule-Thomson cooler with capability to accommodate pressure variations

Abstract: A Joule-Thomson cryogenic refrigeration system capable of achieving high temperature stabilities in the presence of varying temperature, atmospheric pressure, and heat load is provided. The Joule-Thomson cryogenic refrigeration system includes a demand-flow Joule-Thomson expansion valve disposed in a cryostat of the refrigeration system. The expansion valve has an adjustable orifice that controls the flow of compressed gas therethrough and induces cooling and partial liquefaction of the gas. A recuperative heat exchanger is disposed in the cryostat and coupled to the expansion valve. A thermostatically self-regulating mechanism is disposed in the cryostat and coupled to the J-T expansion valve. The thermostatically self-regulating mechanism automatically adjusts the cross-sectional area of the adjustable valve orifice in response to environmental temperature changes and changes in power dissipated at a cold head. A temperature sensing and adjusting mechanism is coupled to the cold head for adjusting the temperature of the cold head in response to the change in heat flow in the cold head. The temperature sensing and adjusting mechanism comprises a temperature sensitive diode, a wound wire heater, and an electrical feedback control circuit coupling the diode to the heater. An absolute pressure relief valve is interposed between the output of the cryostat and an exhaust port for maintaining a constant exhaust temperature of the refrigeration system, independent of changes in atmospheric pressure.

Gas dissolving system and method

Abstract: An improved gas dissolving and releasing system involving the use of multistages of porous gas dissolving media at the center and near the wall of a pressure vessel is described. The gas dissolving system includes a liquid pressure pump, a pressure vessel with tangential inlet and outlet, a gas injector, an inlet nozzle assembly, a center gas dissolving tube, one or more wall-mounted gas dissolving plate assembly, a gas compressor, gas regulators, gas flow meter(s), pressure gauge(s), safety valve(s), sight tube(s), a bleed-off point, a pressurized water release unit, and a liquid flow meter. The liquid flow pattern inside of the pressure vessel is controlled to be of either swirling upflow, swirling downflow or swirling horizontal flow at a rotation speed of over 2,500 rpm. A set of special nozzles with different orifices is designated for precise liquid flow control and liquid rotation speed control. More than one gases introduced at different inlets are dissolved simultaneously and efficiently in the pressure vessel under controlled pressure at 2-7 atm. The improved gas dissolving system is compact, simple and cost-effective, and is applied to ozonation, chlorination, recarbonation, oxygenation, nitrogenation, aeration, and flotation processes.

A balanced resonant pressure sensor

Abstract: A new type of resonant pressure sensor in silicon is described. The pressure sensitive part consists of a square dual-diaphragm cavity structure which vibrates in a balanced torsional mode. The selected torsional mode in combination with a suspension along the two crossing node lines of the electrostatically vibrated part yields a high Q factor of 2400 in air and 80 000 in a vacuum. The pressure sensitivity is a result of a pressure change-induced flexure of the two diaphragms which changes the torsional stiffness and hence the resonance frequency. The pressure sensitivity of the differential and absolute pressure sensor was 19%/bar and 14%/bar respectively. The basic structure showed an inherent uncompensated low temperature sensitivity of − 16 ppm/°C. The fabrication process involving anisotropic silicon etching and silicon thermal bonding is described. The improved design which increased the Q factor in air to 3300 is also presented.

Variations in urethral and bladder pressure during stress episodes in healthy women.

Abstract: Pressure variations in the urethra and bladder during stress episodes and their time separations were investigated in 30 healthy female volunteers. The pressure was measured by means of a double microtip transducer catheter with the distal sensor in the bladder and the proximal sensor at the bladder neck, the mid-urethra and the distal urethra. In advance of the pressure spike during cough a pressure rise was demonstrated in the bladder and at all 3 sites of measurement in the urethra. The urethral pressure increments preceding and following the pressure spike were statistically significantly higher in the mid-urethra than the corresponding bladder pressures. This active urethral pressure generation in the mid-urethra and distal urethra was initiated 200 ms before the bladder pressure began to rise. The pressure in the urethral high pressure zone was higher than the bladder pressure in all cases. Passive pressure transmission to the urethral high pressure zone can take place only insignificantly due to a continuous higher pressure inside the urethra than in the bladder and due to the location of the high pressure zone in the demarcation of the abdominal cavity. It was concluded that the urethral pressure rise in the high pressure zone during stress episodes is mainly generated actively by intra- and/or peri-urethral structures.

A balanced dual-diaphragm resonant pressure sensor in silicon

Abstract: The design and fabrication of a resonant differential pressure sensor is described. The vibrating part consists of a dual-diaphragm structure suspended inside a frame. Anisotropic silicon etching and thermal silicon bonding techniques are used to fabricate the device. The sensor is electrostatically excited to vibration in a torsional balanced mode which yields a high Q factor of 2400 in air. The pressure sensitivity is based on a torsional stiffness change of the vibrating element. Measurements show a pressure sensitivity of 19%/bar over the range -0.5 to +0.5 bar and a very low temperature sensitivity of the resonance frequency of -16 p.p.m./ degrees C. >

Control apparatus or system for purged and pressurized enclosures for electrical equipment

Abstract: A control apparatus or system for purged and pressurized electrical equipment provides rapid, controlled exchange of pressurizing or purging gas to an electrical enclosure. The control system or apparatus for NFPA Type Y and Type Z electrical equipment enclosures has a source of pressurizing gas, a rapid exchange pressure control filter/regulator, rapid exchange pressure gauge, vent control valve and a manual inlet valve providing for rapid exchange of purging gas to the electrical enclosure during start up, an enclosure control valve, enclosure pressure indicator, a venturi providing controlled leakage from the system, and a pressure loss control alarm or switch. Another embodiment of the control system or apparatus for NFPA Type X electrical equipment enclosures has a rapid exchange pressure control filter/regulator, rapid exchange pressure gauge, vent control valve and an automatic inlet valve providing for rapid exchange of purging gas to the electrical enclosure during start up, and enclosure control valve, enclosure pressure indicator, a venturi providing controlled leakage from the system, and a pressure loss control alarm or switch.

Biological pressure transducer zeroing and levelling reference apparatus

Abstract: A medical pressure measurement device which employs a reference transducer linked to an atmospheric pressure sensitive device while also connected in immediate proximity to a single or several pressure measurement transducers which allows for automatic correction for hydrostatic transducer height difference from patient point to reference (usually some point on the patient's external anatomy equivalent in vertical height to the right atrium of the heart) to transducer position; while providing a constant zero pressure reference, i.e., ambient atmospheric pressure to the monitoring device via said reference transducer system.

Method and apparatus for transient measurement of gas permeability in closed-cell foam insulation

Abstract: Method and apparatus are provided for accurately and more rapidly measuring the permeability of various test gases in cellular polymeric materials with very low permeation rates, comprising a constant volume test chamber sealed with indium gaskets, said chamber being connected to a gas inlet valve and test gas reservoir with pressure gauge, gas outlet valve and oil check valve, an absolute pressure transducer to track the change in pressure in the test chamber, and said chamber being submerged in a water bath for strict temperature control. A thinly cut foam sample is placed in the test chamber surrounded by the test gas, where the gas inside the sample is first allowed to reach equilibrium with the surrounding gas; the pressure of the surrounding gas is then raised or lowered, and the rate at which the sample takes up or gives off the test gas is recorded over time as a change in pressure of the test gas around the foam. From this pressure variation the desired permeability coefficient may be measured, and achieved more quickly due to the reduced thickness of the sample. Unlike standard prior art transmission-method devices, this new sorption method and apparatus also allows for separate determination of the diffusion and solubility coefficients; it further allows for the use of much thinner foam samples than can be reliably used in prior art methods, resulting in a substantial reduction in testing time. The effective diffusion coefficient is used as an input to a computational model which predicts the rate of aging in a foam insulation panel. The effective solubility coefficient is used primarily to understand the behavior of the blowing agent in the foam system.

Exposure apparatus with a substrate holding mechanism

Abstract: A substrate holding device includes a holding table having a reduced pressure passageway; a pressure gauge for measuring a value related to the pressure in the reduced pressure passageway; a pump for producing a pressure difference between a first surface of the substrate to be attracted to the holding table and a second surface of the substrate not to be attracted to the holding table; a valve which can be opened/closed for control of the pressure in the reduced pressure passageway; a pressure control system for controlling the opening/closing of the valve on the basis of an output corresponding to the value measured by the pressure gauge; and a temperature control system for controlling the temperature of the holding table.