Sensitive Pressure Transducer Research Articles

A new oscillating bubble technique for measuring surface dilational properties

A new oscillating bubble device has been developed and used for measuring the surface dilational properties of surfactant, protein and surfactant/protein adsorption layers in the frequency range 1–300 Hz. Within a closed measuring chamber, a small hemispherical bubble is produced at the tip of a capillary. A piezoelectric driver generates sinusoidal oscillations of the bubble volume, and consequently produces changes in the surface area and the radius. The piezoelectric driver can also produce arbitrary changes of area. This method allows the measurement of the pressure difference across the curved bubble surface, due to changes in the radius and surface tension. The pressure amplitudes are monitored by a sensitive pressure transducer which is mounted at the bottom of the chamber. One obtains information on the deformation from the pumped volume, on the change in surface tension from the pressure amplitudes, on the rate of deformation from the frequency and on the phase angle Φ between deformation and surface tension. This novel technique can also be used for adsorption kinetics studies at the air/water and oil/water interfaces. Experimental results on the frequency dependence of the dilational elasticity of cetyltrimethylammonium bromide solutions are in good agreement with a diffusional exchange of matter theory. Gelatin behaves as an almost insoluble layer; no frequency dependence was observed in the studied frequency interval. A mixed gelatin/anionic surfactant adsorption layer shows an almost linear dependence of Δγ(f) in the frequency range 50–300 Hz. This increase in the stress amplitude (Δγ) with the deformation rate is a characteristic feature of an intrinsic viscosity.

A capillary flow meter for measuring the hydraulic conductivity of clay under low gradients

The measurement of water flow through clay at low hydraulic gradients (<1) is a very difficult task requiring several months to accomplish in a laboratory. A capillary flow meter, capable of measuring extremely low flow rates through clay samples under low imposed hydraulic gradients, has been designed and tested. Flux as low as 10–12 m·s–1 was successfully measured using this flow meter. To minimize the contaminatiion effects, perchloroethylene, which has self-cleaning ability, mixed with Sudan IV was used as the bubble liquid in the capillary flow meter. Glass and Teflon® valves were fused to the inflow and outflow capillary tubes to permit these components to be flushed with cleaning agents and distilled water. The movement of the menisci through the capillary tube was used as a measure of the volume flow rate through the sample. A sensitive differential pressure transducer was connected between the inflow and outflow end of the clay sample to measure the imposed hydraulic head difference. This flow meter has been independently calibrated against a conventional constant head permeameter. Once the clay samples have stabilized in a permeameter, oedometer, or a triaxial cell, multiple flow measurements under low hydraulic gradients can be done in less than an hour. Key words: nonlinear flow, saturated hydraulic conductivity, non-Darcy flow, ultra-low flow meter.

Surface Rheological Data for a Polymeric Surfactant Using a Pulsed Drop Rheometer

Measurements of dynamic interfacial tension of adsorbed layers of the oil-soluble polymeric surfactant E5 have been made using a pulsed drop rheometer. The pulsed drop rheometer is based on the instantaneous expansion of a water droplet in oil. After perturbation an interfacial relaxation occurs and is followed from the drop profile. The difference in pressure across a curved interface and the interfacial tension are directly related. The decay of pressure change, and hence the interfacial tension decay, is followed as a function of time using a sensitive pressure transducer. Concentrations of E5 above and below the CMC were investigated at then-decane/water and Isopar M/water interfaces. The interfacial tension decays obtained were fitted to known relaxation mechanisms. Fourier transforms were calculated over a complete frequency spectrum to obtain the dilational elasticity and viscosity. Above the CMC, the interfacial relaxation of E5 at both then-decane/water and Isopar M/water interfaces was shown to be due to the diffusion of micelles to the interface and the subsequent lowering of the interfacial tension. From the calculated diffusion coefficient and micelle size, the micellar aggregation number could be calculated. Below the CMC, both diffusion and reorientation contribute to the interfacial relaxation. It was not possible to determine the parameters for each process because the characteristic frequencies for the two processes are of similar magnitude.

Effects of a Ground Plate on Magnus Effect of a Rotating Cylinder.

We present the effects of a ground plate (stationary or moved) on the Magnus effect of a rotating circular cylinder. Measurements were carried out for Reynolds number Re=6.6×104 and velocity ratio α=1. The surface pressure distributions on the cylinder were measured with a highly sensitive pressure transducer for the various clearances between the cylinder and the ground plate. The drag and lift forces on the cylinder were calculated from those surface pressure distributions. As a result, it was found that the lift suddenly changes at a certain clearance, and this behavior is not caused by the transition of the boundary layer from laminar to turbulent. This phenomenon is related to a change in the flow pattern, and each pattern was measured with a hot-wire anemometer. These flow patterns show that one of the flows through the clearance is along the cylinder surface, and another is along the ground plate. It is interesting that this phenomenon is unstable and hysteretic

On-line low flow high-precision gas metering systems

The paper describes a high precision gas meter suitable for low rates of flow (< 5 cm 3 min −1) which can be interfaced with data acquisition software for continuous on-line measurement. The meter used the highly sensitive pressure transducers currently available, operated with a very small back pressure, and had an accuracy around 0.5%. A frequency to voltage converter was developed and built into the gas meter. This allowed direct connection to a data logger/computer without prior computation.

An automatic apparatus for measuring interfacial and film tension under static and dynamic conditions

A fully automated and computer controlled apparatus is described that measures the interfacial tension (IFT) of fluid interfaces and the film tension of liquid films. The fluid interface is formed as a nearly spherical drop at the tip of a capillary which is immersed into another immiscible fluid. The size of the interface is controlled and measured by controlling the size of the drop and the capillary pressure is monitored by a sensitive pressure transducer. The interfacial tension is calculated by the Young–Laplace equation. The drop at the capillary tip can also be covered with a cap shaped liquid film and then the film area can be controlled and the film tension measured. This apparatus is useful for measuring equilibrium interfacial tension or film tension, the adsorption kinetics by stress relaxation experiment and the dynamic interfacial tension or dynamic film tension under both interface expansion or contraction conditions. The capabilities of this versatile, automatic instrument are illustrated with typical experimental results.

Profiler Measurements of Vertical Velocity Fluctuations in the Ocean

Abstract A method is described for measuring the vertical component of velocity fluctuations due to three-dimensional turbulence in the ocean from a freely falling microstructure profiler. The dynamic pressure measurement relies on a commercially available and very sensitive piezoresistive differential pressure transducer. At nominal profiler fall speeds of 0.9 m s−1, the noise limit in vertical velocity fluctuations is ∼3 mm s−1. Scaled turbulence spectra from shear probes and from the new sensor demonstrate the validity of the measurement. Although hydrodynamic noise (eddy-shedding) at frequencies near the peak in the dissipation spectrum precludes full resolution of the high wavenumber portion of the spectrum, the high end of the inertial subrange of the turbulence is resolved. At low wavenumbers, the measurement is limited by the finite size of the profiler. It is anticipated that the method will be useful in examining turbulent fluxes using an eddy-correlation technique.

Low volume perfusion-superfusion system for measurement of transmitter release from blood vessels in vitro

An in vitro technique has been developed for the simultaneous recording of vasoconstriction and transmitter release from small perfused blood vessels. To avoid excessive dilution of the released substances, 6–12-mg segments of rabbit ear arteries or rat tail arteries were mounted in 0.5-mL tissue chambers and perfusedsuperfused in a closed system. Drug administration and removal were performed by timer-controlled solenoid valves. Oscillation in the baseline generated by the roller pump was dampened by delivering Krebs' solution through a 4-mL buffer vial filled partly with air. Vasoconstriction was elicited by electrical stimulation and detected by pressure sensitive transducers. Transducer-generated electrical signals were amplified, digitalized, and recorded by a computerized system. Release of norepinephrine was measured after the tissue was preloaded with [ 3H]norepinephrine. This system allowed us to measure minimum vasoconstrictions of 1–2 mm Hgand [ 3H]norepinephrine efflux evoked by 4–8 electrical pulses. There was a good linear correlation ( r = 0.98) between the contractile responses and tritiated norepinephrine release. Endogenous norepinephrine released by electrical stimulation into the perfusion media was determined by high-performance liquid chromatography (HPLC) in the low picogram range (80–100 pg). Our novel experimental setup permits computerized data acquisition and automated in vitro pharmacological experiments on isolated blood vessels.

Measuremeat of in vivo lung acoustic impedance for animals using random noise and the two microphone technique

The in vivo acoustic impedance of rats' lungs was measured using random noise and the two microphone transfer function method for calculating impedance. This method eliminates the need for the sensitive pressure transducers used in the conventional measurement of respiratory impedance. Measurements were performed on control rats and rats that had, 5 months prior to the experiments, been exposed to coal dust for 2 weeks. Random noise, flat to 6.4 kHz, was propogated down a three section impedance tube. The experiments began with the insertion of a tracheal tube through the rat's mouth to a depth of approximately 3/4 in. into the trachea. Sound traveling through the impedance tube and tracheal tube and reflecting from the lung was measured with the two microphones and recorded by a two channel FFT analyzer. The analyzer calculated the transfer function between the microphones and, from this transfer function, the complex lung acoustic impedance was calculated. The impulse response was also computed from the transfer function, and was further processed, by the Ware-Aki area inversion algorithm, to produce the effective airway cross-sectional area as a function of depth into the lung from the trachea.

Unsteady pressure measurements on an oscillating cylinder in narrow annular flow

This paper describes experiments on the unsteady pressure field generated in annular flowwhen the central cylinder (centre-body) in the annulus is subjected to angular oscillations about a hinge. The oscillations were generated by a shaker and the fluid was air. The unsteady pressure was measured differentially on two diametrally opposed points in the annulus, in the plane of oscillation, on both the oscillating centre-body and on the coaxial outer duct, by means of a sensitive pressure transducer; the angular oscillation was measured by an internally mounted accelerometer. Both accelerometer and pressure-transducer signals were processed through an FFT signal analyser. Experiments were conducted for various positions of the hinge, frequencies of oscillation and flow velocities, and measurements taken along the length of the centre-body. Agreement between the measured pressure and theoretical values obtained from a previously developed theory was good, except near the body extremities, where end effects” related to the peculiarities of the apparatus come into play.

Prediction of moisture transfer in mixtures of solids: transfer via the vapor phase

A mathematical method has been developed and tested to predict the final relative water vapor pressure in a closed system for a multicomponent mixture of solids knowing the initial water content for each component. From the final relative pressure and individual sorption-desorption isotherms, it is then possible to estimate the extent to which moisture redistributes via the vapor phase among the various components. The model utilizes any equation which describes the moisture sorption-desorption isotherm of each component over the entire range of relative pressures and includes as variables the initial dry weight and moisture content of each component, head space volume, and temperature. Experimental studies were carried out in a vacuum rack assembly linking various solids via the vapor state and measuring relative pressures of water vapor before and after redistribution using a sensitive pressure transducer at a known temperature and head space volume. Both the mathematical simulations and experiments were carried out with various combinations of corn starch, microcrystalline cellulose, gelatin capsules, and silica gel. Pharmaceutical situations where such information might be useful are discussed.

A simple, sensitive and versatile solid-state pressure transducer.

ABSTRACT Sensitive and accurate pressure transducers are useful in many areas of biology. Two common applications are the measurement of pressure changes within the respiratory system of an animal, and quantification of the small pressure fluctuations that accompany the humidification and warming of inspired air in whole-body closed-system or open-system flow-through plethysmography (see Malan, 1973; Bucher, 1981). The design of such transducers is often complicated by the requirement to measure very small pressure fluctuations in the presence of a substantial pressure offset. Moreover, such pressure offsets often vary slowly with time. Frequent adjustments are then required to keep the output of the pressure transducer from saturating in either direction.

Touch dynamics signal generator for electronic musical instruments

The touch dynamics of the operation of keys of an electronic musical instrument are determined through the use of pressure sensitive transducers associated with the keys, the transducers each including a magnetic field responsive semiconductor device and providing signals which are analyzed to determine their variation in magnitude as a function of time. Additionally, after a pre-selected time period, if a key remains operated and the pressure exerted thereon is varied, the output voltage of the key associated transducer will be further analyzed to determine if the player is calling for the reproduction of a secondary effect.

Effect of size distribution of condensation nuclei on pressure in an expansion counter

Pressure in the sample chamber of a pressure defined expansion type nucleus counter and optical attenuation are measured using a sensitive pressure transducer, an optical sensor and an electronic recorder for different samples of aerosols. It is observed that first and second derivatives of pressure, as a function of time, display inflections characteristic of the samples. Details of the experimental work, theoretical background and an analysis of results are presented in this paper. It is concluded that the inflections are likely to indicate the number of modes in the size distribution of condensation nuclei in the sample. Measurements of optical attenuation and its derivative as a function of time support the interpretation.

Thermodynamic and structural aspects of the dehydration of smectites in sedimentary rocks

AbstractThe diagenetic conversion of smectite to illite in shales has been proposed as a mechanism for generating overpressure (fluid pressure above hydrostatic) in sedimentary basins. However, the mechanism and rate-controlling factors of the reaction and the magnitude of the resulting volume change are not known. In this paper the thermodynamics of the reversible hydration/dehydration of smectite are analysed in the pressure/temperature regime of sedimentary rocks. If the interlamellar water is more dense than bulk water, and the pressures on the solid and fluid phases are equal, the dehydration temperature should increase with increasing confining pressureviathe Clapeyron-Clausius equation. However, either fluid pressures below the pressure on the solid matrix or high pore-fluid salinities can reduce the dehydration temperature. Experiments on Ca2+-montmorillonite compacted in the presence of distilled water in a steel autoclave fitted with a sensitive pressure transducer failed to detect any overall volume change due to dehydration up to 185°C and 1400 bar. This finding, which is consistent with recent high-pressure DTA and XRD studies on Na+-montmorillonite, suggests that reversible loss of the last two water layers does not occur in sedimentary basins except as part of the more complex diagenetic conversion of smectite to illite. Some recent evidence from high-resolution TEM and microprobe analyses regarding the mechanism of the reaction is also discussed.

Molecular weight distribution of polyphenylene sulfide by high temperature gel permeation chromatography

AbstractPoly(phenylene sulfide) (PPS) has been characterized using a novel high temperature gel permeation chromatograph (GPC). Samples were injected in slurry form at ambient temperature, and redissolved by an in‐line precolumn heater at 250°C. A viscometer consisting of a capillary tube with inlet and outlet taps connected to a sensitive differential pressure transducer was used as sole detector, with deflections converted to concentration using the column calibration. Columns and viscometer were operated at 210°C. Universal calibration was carried out using intrinsic viscosity/molecular weight relations for polystyrene and PPS, determined by light scattering. Satisfactory operation was confirmed by agreement between intrinsic viscosity calculated from GPC with independently measured values, and comparisons with melt flow data. Samples of PPS tested were found to be of relatively narrow distribution, with Mw/Mn typically less than two.

Small sensitive pressure transducer for use at low temperatures

A sensitive diaphragm-type pressure transducer suitable for use at very low temperatures is described. This device was optimized for pressures up to 3.5 MPa, but sensors for other pressure ranges can be readily manufactured. The external pressure deflects two sapphire disks which causes a change in capacitance between the platinum electrodes sputtered on the disks. The transducer can easily resolve changes of 1 Pa at 3.5 MPa, while reproducibility and hysteresis, though not fully tested yet, are better than 10 Pa. The transducer is 610 μm thick and 8 mm diameter.

Low gradient permeability measurements in a triaxial system

Permeability measurements were conducted with the flow-pump method on sand, sandy silt and silty clay specimens in a conventional triaxial system by introducing and withdrawing water at known constant flow rates into the base of a specimen with a flow-pump, and by monitoring the head difference induced across the length of the specimen with a sensitive differential pressure transducer. The results show that the previously reported advantages of the flow-pump method, compared with conventional constant head and falling head methods, were realized for permeability measurements in conventional triaxial equipment. These advantages are that direct flow rate measurements are avoided together with the associated errors that arise from the effects of contaminants on capillary menisci and the long periods of time involved in flow rate measurements; permeability measurements can be obtained much more rapidly and at substantially smaller gradients; errors from the small intercept in the otherwise linear flow rate versus hydraulic gradient relationship, and also from seepage-induced permeability changes, can easily be recognized and avoided or minimized. The results further show that the initial transient response of a specimen that precedes the steady state condition needed for a permeability measurement can require a substantial period of time. In this study the response times varied from a fraction of a minute for a sand specimen to more than 200 minutes for a silty clay specimen. Errors in permeability measurements from this transient response can easily be avoided with the flow-pump method but not with constant head and falling head methods. Des mesures de perméabilité ont été effectuées par la méthode de la pompe à écoulement sur des échantillons de sable, de limon sableux et d'argile sableuse dans un système conventionnel triaxial par introduction et soutirage de débits constants prédéterminés dans la base de l'échantillon à l'aide d'une pompe à écoulement en mesurant la différence de charge induite le long de l'échantillon à l'aide d'un capteur sensible de pression différentielle. Les résultats obtenues confirment les avantages connus de la méthode de la pompe à écoulement par rapport aux méthodes conventionnelles de la charge constante et de la charge variable pour les mesures de perméabilité avec les systèmes triaxiaux conventionnels. Ces avantages sont les suivants: on évite des mesures directes de débit aussi bien que les erreurs associées qui sont le résultat des effets des polluants sur les ménisques capillaires et on diminue le temps indispensable aux mesures de débit; on peut obtenir des mesures de perméabilité beaucoup plus vite et pour des gradients beaucoup plus faibles. Il est possible de déceler et par conséquent d'éviter ou de minimiser facilement des erreurs causées par le petit intercept dans la relation débit-gradient hydraulique non linéaire et aussi par des changements de perméabilité dus à la percolation. Les résultats montrent aussi que la réponse initiale transitoire d'un échantillon qui précède l'état station-naire nécessaire pour une mesure de perméabilité peut exiger une période de temps considérable. Dans cette étude les temps de réponse ont varié depuis une fraction de minute dans le cas d'un échantillon de sable jusqu'à plus de 200 minutes dans le cas d'un échantillon d'argile sableuse. Avec la méthode de la pompe à écoulement il est possible d'éviter dans les mesures de perméabilité des erreurs causées par cette réponse transitoire, mais pas avec les méthodes de charge constante ou de charge variable. Notation A cross-sectional area of the specimen kpermeability kapp apparent permeability Llength of the specimen Qvolumetric flow rate generated by the flow-pump t time u pore pressure in the specimen in excess of atmospheric pressure &amp;gri head difference across the specimen length induced by an externally controlled constant flow rate &amp;grt total head difference across the specimen length &amp;gro head difference across the specimen length for the zero-flow condition σc′ effective consolidation stress in the specimen

The Effect of Immobilization Devices on the Load Distribution Under the Foot

The load distribution under the foot was investigated under various conditions by means of pressure-sensitive transducers. Weight-bearing pressures at the first and third metatarsal heads and at the heel were measured while subjects ambulated barefoot and while wearing numerous immobilization devices. The proportion of body weight imposed on the plantar surface of the foot is dependent on the specific gait pattern displayed during barefoot walking. Maximum reduction of forefoot loads was achieved by means of a short-leg walking cast or an ankle boot cast with a posteriorly placed flat rubber heel. A centrally placed rocker heel leads to increased forefoot loads, especially under the first metatarsal head. Casting devices used in conjunction with cast shoes were not as effective in pressure reduction as the same cast with a posteriorly placed heel, but they were more effective than the rocker heel. The height of the cast and configuration of the sole of the cast shoe had little effect on the observed patterns of force distribution. The wooden-soled post-operative shoe did decrease weight-bearing pressures as compared with barefoot walking and casts with a rocker heel but was less effective than the other devices studied. Peak loads measured at the sole of the foot were dependent on the position of the ankle and subtalar joints at the time of cast application.

A technique for continuously measuring filtration resistance at constant pressure

A device for continuously measuring, at constant pressure, the filtration resistance of different liquid suspensions is described. It is made up of two main parts: flowmeter system and electronic circuit. The flowmeter consists of a capillary tube and a sensitive pressure transducer, and has a time response of 100 ms and a linearity of +/- 1% from 1 uls-1. The electronic part allows the calculation and recording of flow versus time and filtration resistance versus the volume which passes through the filter. Principle, technical characteristics of the system and examples of recording with several Red Blood Cell populations are reported.