Pressure Compensation Research Articles

Novel carbon dioxide gas sensor based on infrared absorption

The feasibility of sensing carbon dioxide with a IR single- beam optical structure is studied, and a novel carbon dioxide gas sensor based on IR absorption is achieved. Applying the Lambert-Beer law and some key techniques such as current stabilization for IR source, using a high-quality IR detector, and data compensation for the influences of ambience temperature and atmosphere total pressure, the sensor can measure carbon dioxide with high precision and efficiency. The math- ematical models for providing temperature and pressure compensation for the sensor are established. Moreover the solutions to the models are proposed. Both the models and the solutions to the models are verified via experiments. The sensor possesses the advantages of small volume, light weight, low power consumption, and high reliability. Therefore it can be used in many associated fields, such as environmental protection, processing control, chemical analysis, medical diagnosis, and space en- vironmental and control systems. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)01708-6)

MODELLING AND SIMULATION OF PROPORTIONAL MOBILE VALVES

A modern mobile valve is a complex entity which consist of several integrated valve functions such as pressure compensation, pump flow sharing (anti-saturation), pressure relief and anticavitation. Main spool is either electrically or hydraulically pilot operated with load sensing ability so the valve can be used with LS-pumps.In this paper the methods of modelling multifunctional mobile valves are presented. The proposed modelling technique is numerically efficient since small internal oil volumes of the valve can be ignored and mathematical stiffness of the model is significantly decreased. The usability of the model is taken into account by means of easy parameterization. The model can be identified using data available in the manufacturers' catalogues.

Peripheral blood flow response to step-wise increase of arterial pressure in conscious rats.

In conscious rats, changes in renal or superior mesenteric flow were observed when arterial pressure was elevated by occluding the terminal aorta. Blood flow was measured with an implanted electromagnetic flow probe and terminal aorta occlusion (TAO) was induced with an implanted pneumatic occluder. Arterial pressure was recorded with an indwelling catheter in the common carotid. Each TAO lasted for 20 seconds and flow and pressure at the end of this period were noted as those during TAO. After elimination of the reflexive compensation of arterial pressure by ganglionic blockade, the renal flow increase during TAO was slight but significant (p <0.01), although the relative increase in flow was less than that in pressure. In other words, renal autoregulation, constancy of renal blood flow in the face of arterial pressure change, was imperfect. After further pentobarbital anesthesia, however, renal autoregulation was more complete to such an extent that the renal flow increase was insignificant during TAO. In contrast, the relative increase in superior mesenteric flow during TAO was larger than that in pressure with or without anesthesia.

Downhole acoustic transducer

An acoustic transducer comprises two pairs of opposite elongate segments (20) placed inside a deformable tube (14). Drive means (22) operable to expand in a direction orthogonal to the axis of the tube are disposed between the segments of each pair. The drive means occupy a substantial portion of the inside volume of the tube. A preferred arrangement includes drive means for a pair of segments longitudinally displaced from the drive means for the other pair. Drive means may be constituted by stacks of piezoelectric pellets (24) extending radially relative to the axis of the tube. A pressure compensation system is provided to keep the pressure inside the tube (14) substantially equal to the external pressure. Longitudinal flutes (14a) are formed inside the tube (14) between the segments (20) to facilitate tube deformation and amplify volume variation.

Dynamic plantar pressure measurement in 49 patients with diabetic neuropathy with or without foot ulcers

Summary We compared plantar pressures under selected areas of the foot in 49 diabetic patients with neuropathy using the F-scan system — in their own shoe (with and without an insole), in a jogging shoe (with and without an insole) and in an extra depth orthopaedic shoe with a small metatarsal bar. Patients with current or previous plantar ulcers ( n =30) were compared to those with no such history ( n =19). There was very little decrease in plantar pressure between the patients' shoes and the jogging shoes, although non-ulcer patients put more weight on the lateral toes and more on the medial side after adjustments. In most cases the orthopaedic shoe increased pressure under the forefoot significantly. Large standard deviations between patients made comparisons between groups impossible. Integrated peak pressure values were not often significantly different from peak pressure values alone, suggesting some compensation of pressure by time. Standard extra depth shoes did not give the reduction of pressure anticipated. Close attention must be paid to the location of the bar. The reliability of the F-scan system allows for variation of up to 30% between different measurements, and calibration is difficult in these patients; this limits its use in scientific studies. The accuracy is adequate for visual appraisals of changes in pressure.

飛行制御系における空力的不確かさのモデル化とロバスト制御器への動圧補償の導入

This paper first describes a modeling method for the uncertainty of aerodynamic coefficients in a linear state-space aircraft model. Second, a design method of robust flight control systems based on the model is also presented. The proposed method is applied to the structure of the uncertainty for the μ-analysis and has the following characteristics: 1) the variations of the altitude and the velocity are explicitly treated as real repeated scalar perturbations since all dimensional derivatives are the function of the altitude and the velocity, and as a result 2) a gain-scheduled controller using the dynamic pressure compensation which satisfies the robust performance for a comparatively wider flight envelope can be designed. Simulation study is carried out to indicate that the proposed method is less conservative and satisfies the robust performance for a wider flight envelope than those of the H∞ design and the μ-synthesis where all aerodynamic coefficients are assumed to be individually perturbed.

Reentrant radio-frequency resonator for automated phase-equilibria and dielectric measurements in fluids

A reentrant rf cavity resonator has been developed for automated detection of phase separation of fluid mixtures contained within the cavity. Successful operation was demonstrated by redetermining the phase boundaries of a CO2+C2H6 mixture in the vicinity of its critical point. We developed an accurate electrical model for the resonator and used helium to determine the deformation of the resonator under pressure. With the model and pressure compensation, the resonator was capable of very accurate dielectric measurements. We confirmed this by remeasuring the molar dielectric polarizability Aε of argon and obtained the result Aε=(4.140±0.006) cm3/mol (standard uncertainty) in excellent agreement with published values. We exploited the capability for accurate dielectric measurements to determine the densities of the CO2+C2H6 mixture at the phase boundaries and to determine the dipole moment of 1,1,1,2,3,3-hexafluoropropane, a candidate replacement refrigerant. Near the operating frequency of 375 MHz the capacitor in the resonator has an impedance near 14 Ω. This low impedance is more tolerant of electrical conductivity within the test fluid and in parallel paths in the support structures than comparable capacitors operating at audio frequencies. This will be an advantage for operation at high temperatures where some conductivity must be expected in all fluids. Of further value for high-temperature applications, the present rf resonator has only two metal–insulator joints. These joints seal coaxial cables; neither joint is subjected to large mechanical stresses and neither joint is required to maintain precise dimensional tolerances. The resonator is rugged and may be operated with inexpensive electronics.

Pressure Compensation and the Bottom Boundary Layer

Abstract It is an observed characteristic of oceans that velocities and horizontal pressure gradients are larger new the ocean surface than they are in deeper water. This is conventionally labeled “pressure compensation” whereby baroclinic structure, comprising sloping isopycnal surfaces, is adjusted so that surface pressure gradients are reduced in deeper water. In this paper, a two-dimensional flow in a channel is numerically modeled to demonstrate the baroclinic adjustment process and its relationship to the bottom boundary layer. A simple analytical model is also developed and defines the timescale of the adjustment process.

Pressure compensation of the temperature shift of the emission wavelength of a distributed-feedback laser

A new method of the emission wavelength stabilisation was proposed and developed for a holographic distributed-feedback laser with a dye solution. This method was based on pressure compensation of the temperature-induced change in the refractive index of the active solution. The compensation was achieved in a hermetically sealed two-section cell: one section was filled with the active dye solution and the other, separated from the former by a flexible impermeable membrane, was filled with a pressure-compensation liquid. A correct selection of the thermophysical characteristics of the components ensured that a temperature rise in both sections increased the pressure more rapidly in the active medium than in the absence of the compensator. This device made it possible to stabilise the refractive index of the active medium and to reduce the temperature drift of the emission wavelength by more than two orders of magnitude.

SURGE IN A PRESSURE-COMPENSATED POSITIVE DISPLACEMENT VANE-PUMP

In this paper, we revealed a factor causing the remarkably large amplitude delivery-pressure oscillation with quite low frequency, occurring often in pressure-compensated variable displacement vane pumps under deadhead conditions. It was found experimentally and theoretically that the pump instability originates in the fact that the gradient, ∂A/∂E is significantly negative, where A is time-averaged effective area for the internal pressure compensation force and E is the cam ring eccentricity. Also this phenomenon is regarded as same as surging of the turbo-fan.

Hydrostatic pressure compensator for measuring gas diffusion coefficients

An apparatus is described for determining gas diffusion coefficients by the stationary flow method, which contains a pressure-balancing system to balance out the pressure difference at the ends of the diffusion channel and which enables one to alter the nondiffusional component of the mass transport. A device is described based on compensating the pressure difference from the dependence of the pressure on the height of the liquid column, not on the form of the diffusing gases.

Determination of sugars by capillary electrophoresis with electrochemical detection using cuprous oxide modified electrodes

The separation by capillary electrophoresis and off-column amperometric detection of underivatized sugars has been studied. A palladium-metal union was used as grounded cathode to decouple the high separation voltage before detection. With a second piece of capillary the field decoupler was connected to a home-made T-shaped detection cell. Cuprous oxide modified microelectrodes were prepared and evaluated. For the detection of sugars they were operated at a constant potential of + 0.60 V. The peak-height reproducibility with these electrodes over a period of 18 h (25 injections) was within 7% absolutely and within 4% when one of the analytes was regarded as internal standard. To preserve the flat electroosmotic flow profile in the separation capillar, pressure compensation was applied. The contribution of various sources to the system zone variance was studied. Under optimized conditions plate numbers of over 100 000 were obtained. For the baseline separation of a mixture of sugars 0.10 mol l −1 sodium hydroxide solutions had to be used as background electrolyte. Detection limits of 1–2 μ mol l −1 were found for various carbohydrates.

海洋音響トモグラフィー用２００Ｈｚ低周波音源

At first, required conditions for the source of the acoustic tomography of 1000km scale are estimated by the use of the sonar equation. The results obtained are as follows; the frequency is 200Hz, sound pressure level is 190dB and Q is below 4. Using the cylinder source of pulsating barrel type with several driver units and vibrating masses, conditions to realize the sound pressure level above 190dB and the source diameter within 1 m are calculated. At the result of the estimation with the physical parameters of several kinds of magneto-strictive materials, it is shown that the super magneto-strictive material is the only material to satisfy the required conditions. After constructions of the source for pressure balance in deep sea are discussed experimentally, the air cavity is added inside the cylinder source and the pressure compensator is adopted to compensate the pressure change in the air cavity according to the water depth.Next, sea trials of the developed sound source are carried out in Suruga Bay, and obtained results are as follows; the change of the resonant frequency relative to water depth agrees well with the calculated value, and then it is shown that the change is corresponding to the stiffness in the air cavity. It is shown that the sound pressure level above 190dB is obtained in the range of the water depth between 800m and 1200m and the frequency between 180Hz and 240Hz. And it is confirmed that the Q of the source is below 4 at the resonant frequency in the each depth. At last, the long distance propagation test of 621km was carried out in the east of Izu-Ogasawara area, and receiving signal was obtained with sufficient SN ratio.

Multichannel Raman spectrometry system for weakly scattering materials at simultaneous high pressures and high temperatures

A Raman system is described which is suitable for rapid determination of Raman spectra of silicates and other weak Raman scatterers under simultaneous high-pressure and high- temperature conditions. Samples are pressurized with an argon pressure medium and Sm:YAG pressure standard in an Inconel 718 or rhenium Merrill–Bassett diamond–anvil cell that is externally heated in a vacuum oven equipped with quartz windows on either side. Raman spectra are excited and collected through the front window using ≊160° scattering geometry. A triple spectrometer in conjunction with a holographic notch filter, disperses the Raman scattered radiation onto a liquid-nitrogen-cooled CCD detector. Simultaneously measured Sm:YAG fluorescence spectra are collected through the rear window and routed via an optical fiber to a second multichannel spectrometer system equipped with a diode-array detector. The high sensitivity of the detectors and the simultaneous measurement technique enable detection of and compensation of pressure drifts occurring at high temperature. The performance of the system is demonstrated by measurement of the positions and linewidths of the high-frequency Raman modes of polycrystalline forsterite (α-Mg2SiO4) at temperatures up to 930 K at pressures of ∼8 GPa and up to 842 K at pressures in the range 12–14 GPa.

Mass flowmeter detecting fluctuations in lift generated by vortex shedding

Indirect measurement of mass flow rate has been widely used, combining volumetric flowmeters with the temperature and/or pressure compensation of fluid density. However, this approach has disadvantages, such as a complicated compensating algorithm, and is only applicable to ideal gases, except for highly pressurized and other gases. A flowmeter for direct measurement of mass flow is more suitable for overcoming the disadvantages of indirect measurement. The authors propose one approach to direct measurement using a vortex flowmeter. That is, Karman vortices are generated by a vortex shedder, and fluctuations in the lift and their frequency are detected by stress sensors built into the vortex shedder. The amount of lift is divided by the frequency to yield signals proportional to the mass flow rate. The proposed approach to sensing features simplicity both in principle and in sensor construction. Satisfactory results are obtained from applying this approach to water, air and other gases.

Off-column detection with pressure compensation in capillary electrophoresis

A theoretical description has been developed of the zone broadening in capillary electrophoresis when the electric field is decoupled before the detector. With off-column detection, the parabolic flow profiles induced by the electroosmotic flow contribute to zone broadening in the separation and the coupling capillary. Good agreement is found between the theory and the experimental data on zone broadening with on-column detection. With off-column detection a zone-broadening contribution equivalent to approximately 15 nL is not accounted for by the theory. This contribution may be attributed to the field decoupler

Pressure compensation for high current ion implanters

A multivariable method for determining optimum pressure compensation values for high current ion implanters is presented. The sheet resistance of implanted test wafers is correlated to the time averaged total endstation and beamline pressures and two respective pressure compensation factors. Pressures were varied by bleeding argon gas into the electron shower and by gas liberated from photo resist coated wafers. The correlation is used to determine the optimum pressure compensation values to ensure that sheet resistance does not vary with pressure. The multivariable method is compared to the manufacturer's suggested method and the method of intersecting lies. The effects of gas composition are considered second order effects in this analysis and are neglected.

Changes in Microsprinkler Discharges Resulting from Long-term Use

An experiment was conducted to determine if wear on emitter orifices over long periods of operation could significantly affect microsprinkler discharge rates. Twelve combinations of flow control method, base size, and operating pressure were used in the experiment. Flow control methods were by orifice control (OC), vortex control (VC), or by pressure compensation (PC). Blue-base emitters with nominal discharges of 38 L/h1 (10 gal/h1) and green-base emitters with nominal discharges of 57 L/h1 (15 gal/h1) using each emission method were operated at pressures of 138 and 207 kPa (20 and 30 psi) for a total of 2,000 h. Emitter discharges were individually measured from 20 emitters initially, and then after 500, 1,000, and 2,000 h. Green-base OC and VC emitters operated at 207 kPa (30 psi) had increases in discharge rates as much as 11% after 2,000 h of operation. After 500 h of operation, green-base PC emitters had reductions in discharge of about 7% when operated at 138 kPa (20 psi) and 18% when operated at 207 kPa (30 psi). Discharge rates from blue-base PC emitters, operated at either pressure, and blue- and green-OC emitters, operated at 138 kPa (20 psi), remained constant after 2,000 h of operation.

Triple controls of variable displacement pumps

The paper reports upon numerical simulation tests carried out on a variable displacement axial piston pump equipped with multiple automatic controls. The swashplate control circuit includes three 3-way valves: the pressure compensator, the flow compensator and the torque limiter. The dynamic response of the system is evaluated for both separate and combined control functions. The effect of changes in the design parameters is discussed in terms of both sensitivity analysis and conventional discrete search.

An improved-performance barrel-stave projector

Researchers at the Defence Research Establishment Atlantic (DREA) have been active since 1986 in the development of the barrel-stave flextensional projector. Intended primarily for use in sonar systems, the barrel-stave projector promises to be a small, light-weight projector with high power and low resonance frequency. This paper describes work in progress aimed at increasing the power output of the projector by nearly doubling the mass of ceramic in the drive element, and at improving operability at depth by implementing passive pressure compensation.