Absolute Pressure Transducer Research Articles

Burnett Method with Absolute Pressure Transducer and Measurements for PVT Properties of Nitrogen and Hydrogen up to 473 K and 100 MPa

A measurement method for PVT properties of high-temperature and high-pressure gases was developed by simplifying the Burnett method and revising the data acquisition procedure. Instead of a differential pressure transducer, which is traditionally used, an absolute pressure transducer is used in the present method, and the measurement of pressure becomes easier. However, the absolute pressure transducer is placed outside the constant temperature bath because of the difficulty of its use in high-temperature surroundings, and some parts with different temperatures from the sample vessels exist as dead space. The present method takes into account the effect of the dead space in the data acquisition procedure. Nitrogen was measured in the temperature range from 353 K to 473 K and at pressures up to 100 MPa to determine the apparatus constants, and then, hydrogen was measured at 473 K and up to 100 MPa. The determined densities are in agreement within uncertainties of 0.07% to 0.24% (k = 2), both with the latest equation of state and existing measured data.

A Capillary Tube Viscometer Designed for Measurements of Hydrogen Gas Viscosity at High Pressure and High Temperature

A capillary tube viscometer was developed to measure the dynamic viscosity of gases for high pressure and high temperature. The apparatus is simple and designed for safe-handling operation. The gas was supplied to the capillary tube from a high-pressure reservoir tank through a pressure regulator unit to maintain a steady state flow. The measurements of a pressure drop across the capillary tube with high accuracy under extreme conditions are the main challenge for this method. A differential pressure sensor for high pressures up to 100 MPa is not available commercially. Therefore, a pair of accurate absolute pressure transducers was used as a differential pressure sensor. Then the pressure drop was calculated by subtracting the outlet pressure from the inlet one with a resolution of 100 Pa at 100 MPa. The accuracy of the present measurement system is confirmed by measuring the viscosity of nitrogen as a reference gas. The apparatus provided viscosities of nitrogen from ambient temperature to 500 K and hydrogen from ambient temperature to 400 K and for pressures up to 100 MPa with a maximum deviation of 2.2 % compared with a correlation developed by the present authors and with REFPROP (NIST).

Thermodynamic studies on Ba 2.875UO 5.875(s)

The Gibbs energy of formation of Ba 2.875UO 5.875(s) has been determined using manometric technique. The equilibrium CO 2(g) pressures over the three phase mixture: {Ba 2.875UO 5.875(s) + Ba 3UO 6(s) + BaCO 3(s)} have been measured using an absolute pressure transducer in the temperature range 1030–1220 K. The corresponding Gibbs energy expression as a function of temperature can be given as: Δ f G m ° ( T ) ( B a 2 .875 U O 5 .875 , s, T ) ( kJ mol − 1 ) ± 5 = − 3153.1 + 0.5573 ( T / K ) Δ f H m ° (298.15 K) and S m ° (298.15 K) data have been calculated from the above Gibbs energy expression using required values from the literature. The corresponding values are −3143.4 ± 2 kJ mol −1 and 270.8 ± 4 J K −1 mol −1, respectively. The Δ f H m ° (298.15 K) value has also been calculated from third law method as −3137.7 ± 4 kJ mol −1.

Differential precisely controllable piezoresonant absolute pressure transducer with a manifold increase in sensitivity

A new system is developed for a multiple increase change in the output of transducer frequency that leads to an increase in its sensitivity. The system does not disturb the vacuum and it makes it possible to perform precise micrometric control of absolute pressure.

Performance Evaluation of Honeywell Silicon Piezoresistive Pressure Transducers for Oceanographic and Limnological Measurements*

Abstract Simultaneous calibrations of three temperature-compensated piezoresistive ruggedized precision “absolute” pressure transducers (Honeywell model PPTR0040AP5VB-BD), which have been designed specially for long-term coastal oceanographic and limnological measurements, have been carried out at four differing temperatures (10°, 20°, 30°, and 40°C) to evaluate their suitability for such applications. The full-scale pressure range of these shallow water absolute pressure sensors is ≈ 2800 hPa (equivalent to water depth of ≈ 18 m). Measurement results have been used to examine the transducers’ performance indicators, such as zero-point offset, accuracy, linearity, hysteresis, temperature sensitivity, and slope. Differing piezoresistive ruggedized precision absolute pressure transducers (PPTRs) exhibited differing zero-point offset values, ranging from 2 to −79 hPa. Temperature sensitivity of zero-point offset was ≈0.3 hPa over the temperature range 10°–40°C. The mean hysteresis over the full-scale absolute pressure range (≈2800 hPa) varied from approximately 2 to 8 hPa over the temperature range 10°–40°C. The slope of the least squares–fitted linear graph (taking the mean of ascending and descending pressures) was close to the ideal value of unity (deviation from 1 over the temperature range 10°–40°C was in the range of −0.001 to +0.005). Linearity was excellent, its mean over the entire pressure range being between ≈ −0.006% and 0.008% of full-scale (FS) over the above temperature range. The worst performance was exhibited at input pressures below ≈1500 hPa. Zero-point offset has played a significant role in deteriorating the accuracy of the PPTR, the mean accuracy (within ≈0.1% and −5%) having been exhibited by those transducers having offsets of 2 and −79 hPa, respectively. The mean accuracy exhibited temperature sensitivity of ≈1% in the range 10°–20°C and negligible sensitivity beyond 20°C. Use of a calibration equation significantly improved the mean static accuracy obtainable from the PPTR, to between −0.04% and 0.01% of FS. Evaluation results have indicated that a suitably calibrated temperature-compensated Honeywell PPTR provides an alternate cost-effective means for pressure measurements for coastal oceanographic and limnological studies.

Low cost navigation system for UAV's

This paper describes the development of a navigation system for SIVA family of UAVs that incorporates measurements from low cost solid state IMU and magneto-resistive magnetometer, single receiver inexpensive GPS, and absolute and differential pressure transducers. The navigator is composed of three modules: an attitude estimator, a position and velocity estimator and a mission management module. All the UAV navigation, guidance, control and communication algorithms and processes run on a PC-104 Pentium I processor. The attitude estimator algorithm is a computationally-inexpensive nonlinear observer developed using Lyapunov theory that computes angular velocity corrections from two vector measurements: Earth's magnetic field and gravity, guaranteeing global Input to State Stability. The position and velocity estimator consists of a set of three static linear Kalman filters that correct the integration of local level components of acceleration with GPS, pressure derived altitude and airspeed measurements. The autonomous navigation is performed by means of pre-programmed mission data, composed by a set of mission elements which define the trajectory to guide the UAV through a safe path. Mission data, mission phases and ground control modes are managed by the mission management module.

Energy Analysis of Flow Induced Harmonic Motion in Blood Vessel Walls

Energy is transferred between the flowing blood and the vessel walls during pulsatile blood flow (a normal pulse cycle) resulting in storage and dissipation of elastic energy. This allows the elastic and muscular arteries to act as an auxiliary pump to propel the blood fluid forward during systole and maintain a basal blood pressure during diastole. The pulsatile flow pattern caused by the contraction of the left ventricle sets up a state of harmonic motion in the blood vessel walls throughout the arterial vasculature. In this paper, we report on a kinetic energy analysis of pressure and flow velocity waveforms, which characterize energy transfer between the blood and the blood vessel walls at different frequencies of pulsatile flow and pressure. Porcine carotid arteries were tested under simulated physiologic pulsatile flow and pressure conditions in a model water bath system and compared to measurements in vivo on human carotid arteries. Fluid and wall pressures were monitored on the porcine vessels in situ using an absolute differential pressure transducer (fluid) and by a low-pressure volumetric balloon transducer (wall), respectively. A continuous-wave Doppler ultrasonic transducer monitored flow velocity and measurements were made both in vitro and in vivo at frequencies of 1.2 Hz (72 cycles per minute) and 2.1 Hz (125 cycles per minute) for comparison purposes. The areas under the pressure versus time and flow velocity versus time curves were used to calculate the relative change in work and kinetic energies. The calculations of the ratios of the relaxation slopes versus the impact slopes showed that the vessel wall absorbed more energy at the frequency of 1.2 Hz than at the 2.1 Hz frequency. The results of these calculations indicate that energy of the pulse pressure at rest pulse rates is absorbed and dissipated in the vessel wall and the surrounding extracellular matrix. At higher pulse rates and pressures, the vessel wall becomes increasingly elastic, and therefore, transmits or reflects most of the energy of the pressure pulse back to the blood fluid. As the vessel wall becomes less compliant with aging or disease, the energy absorbing and dissipating properties of the arterial wall at rest pulse rate diminish.

Multiphase flows sensor response database

The requirement for reliable and yet cost effective multiphase meters has recently become increasingly more important. Multiphase meters are especially needed in cases when several operators share the use of production and transportation facilities in the exploitation of marginal oil and gas reserves. The employment of a sensor array comprising a combination of conventional instrumentation is seen as a cost effective and reliable solution to multiphase metering due to their simplicity, robustness and reliability. As part of the UK National Flow Programme, Cranfield University, working in conjunction with the National Engineering Laboratory (NEL), has collected the response from a range of sensors when subjected to three phase (oil/water/gas) flow conditions. The ultimate objective of the project is to enable the industry to develop novel signal processing techniques so that the flow rates of the three individual phases can be determined from simple, robust sensors. This database is available to industry and academia for the evaluation and development of signal analysis and measurement strategies from the Flow Programme via Cranfield University. This paper presents the detail of the sensor spool piece, experimental arrangement and tests that were carried out. The sensor spool piece comprising of two capacitance meters, two conductance meters, a gamma densitometer, an absolute pressure transducer, two differential pressure transducers and a thermocouple, was designed and assembled by Cranfield University. After the initial commissioning trials, the spool piece was transferred to NEL. Data was collected over a wide range of flow conditions with two salinity levels of 50 and 100 g/l MgSO 4. Tests were also carried out at two different locations in the flow loop so that the user can explore possible installation effects on the data. A total of 531 data test series are in the database.

Modelling of subsurface vortex vibrations

During 2001 the Paris Dam (South Africa) was constructed in the Buvaan River to augment the flow for the extension of irrigation downstream from the dam. The dam has a height of 42 m, and an active storage capacity of 80 * 106 m3. The wall is a double arch concrete structure. During the first filling in February 200 1, the water level was lowered by releasing water through the bottom outlets to allow access for the last construction work to be completed. Water was released through the two 1200 mm diameter outlets, controlled by a sleeve valve at the end of the line. In the outlet structure, water entered the outlet works through the bottom sluice gate (4 m2), while the gates at the upper two levels were closed. In the outlet pipe, just upstream from the sleeve valves, full-bore butterfly valves were installed as maintenance valves for the sleeve valves. Unfavourable inlet conditions resulted in subsurface vortices leading to vibrations in the outlet pipe with extensive pressure fluctuation across the discs of the butterfly valves. These valves failed after a short period of time and the outlet control chamber was flooded. The outlet structure was modeled to an undistorted scale of 1:15 (Froude uniformity) and the pressure fluctuation was measured with (absolute) pressure transducers at a number of positions along the outlet pipe. Changes to the outlet were incorporated and the reduction on the pressure fluctuations was measured. Within the constraints of the existing structure, alterations were implemented and modeled, succeeding in eliminating the creation of the subsurface vortex and unwanted pressure fluctuations. Model investigation provided a valuable contribution to quantify and solve the fluid structure problem associated with the creation of the subsurface vortex. The changed developed in the model study was incorporated in the prototype. Physical vibration measurements on the structure indicated that the improvements to the structure reduced the vibrations.

Improved Design of Differential Precision Vibrating-Wire Absolute Pressure Transducer

The symmetric design of a power transmitting transducer system ensures high thermal stability and shock and vibration resistance. By applying a special sleeve and regulating element it is possible to substantially simplify the technology involved in the production of tension in the wires and linearization of the characteristics of the transducer. The error of the transducer is significantly reduced.

絶対圧計を用いたヘリウム４蒸気圧温度目盛の実現

絶対圧計を用いたヘリウム４蒸気圧温度目盛の実現

Performance of the US quench detection systems in the QUELL experiments

The Quench of Long Length (QUELL) experiments have been completed. The US contribution was to develop and implement both conventional and novel techniques in quench detection. The results of the quench detection experiments demonstrate that all US systems functioned as expected. The most important criteria for the comparison of the various quench detection systems were the time constant of the response and noise rejection by the system. The novel US internal (inside the CICC) sensors included; (1) a cowound voltage sensor, and (2) a fiberoptic temperature sensor. The internal sensors combined fast response with high noise rejection capacity, and proved to offer potentially high reliability for ITER. The conventional sensors, namely the absolute pressure transducer and Venturi flowmeters, confirmed inherent thermo-hydraulic time response limitations in measurements of pressure and flow that excludes them as quench detectors for ITER and other large scale CICC applications.

Identifying and Removing Barometric Pressure Effects in Confined and Unconfined Aquifers

AbstractFailing to account for barometric pressure effects in water level measurements can introduce errors by misestimating the total head and by adding noise to water level measurements. For determining the total head in an aquifer, we assert that the air pressure head at the water surface in the well must be added to measured water levels (equivalent to using an absolute pressure transducer) even though the resulting values may have larger temporal and spatial variability than the original water level measurements. At the Savannah River Site in South Carolina, the average barometric pressure variation is 6 to 7 cm, with a range of over 30 cm. Failure to account for barometric pressure variability could result in misestimation of the direction and magnitude of the hydraulic gradient at the site. We also demonstrate procedures for removing barometric effects, such as to reduce noise during an aquifer pumping test, and to identify mechanisms by which barometric pressure affects water levels. Three mechanisms are summarized including: an instantaneous response for confined aquifers; a delayed response due to borehole storage in confined and unconfined aquifers; and a delayed response in unconfined aquifers due to the passage of barometric pressure changes through the unsaturated zone. Using data from the Savannah River Site, barometric efficiencies are estimated using linear regression and a modification of Clark's Method. Delayed responses are estimated using regression deconvolution. The type of barometric effect provides diagnostic information about whether the aquifer is confined or not, the presence of borehole storage or skin effects, and the air diffusivity coefficient within the unsaturated zone. We also show how removal of barometric pressure effects improves the ability to observe otherwise unnoticeable effects.

Gas leak through ultrathin radiation entrance windows

The permeation rates through an ultrathin radiation entrance window membrane have been measured for several common detector gas components, as well as for some atmospheric gases, by collecting the permeated gas into a clean volume equipped with an absolute pressure transducer. The dependence of the leak rate on the differential pressure (1.0 bar in most of the measurements) has also been discussed. Formulas with the permeation rate as a function of the molecular diameter or the molecular mass are presented. They give a rough estimate for the dependence of the permeation rate on the gas properties. The structure of the window membranes used in the measurements is presented.

Cavity differential-absolute-pressure transducer with frequency output

A new construction of the differential resonator microwave transducer is considered, having a number of advantages over other transducers: high sensitivity, protection against interference, simple construction, high mechanical strength, etc. The very simple electrical measuring circuit gives, without amplification, a frequency output signal of sufficiently large amplitude. The differential principle makes it possible to exclude a number of errors associated with temperature, vibro-shock loading, etc., playing a large role in absolute pressure transducers used in flying equipment, working in challenging climatic conditions and under severe vibro-shock loading.

Silicon microsensors: Construction, design and performance

Sensors are devices which convert non-electronic variables to currents or voltages. They become microsensors when they are fabricated by modified integrated circuit techniques. Microsensors fall into two classes: replacements for existing devices with physically smaller, higher performance and lower cost structures; and novel sensors which can only be constructed by using micromechanics. These ideas can be illustrated by the results of a major effort in surface micromachined pressure transducers which started with the goal of producing designable, economicaly viable absolute pressure sensors with a scaling reduction factor of at least 100 over existing devices. Since an absolute pressure transducer consists of a vacuum sealed pill box which deforms with applied pressure and a sensing scheme which converts deformation with applied pressure to electronic signals, reliable pill box construction must be addressed first. Mechanical considerations in conjunction with the desired scaling lead to the conclusion that a pill box wall thickness of roughly 2 micrometers would be required. This implies the use of thin films and because of thermal consideration leads to the selection of polysilicon as the most attractive film for pill box construction. High packing densities, a requirement for novel sensors, leads to a pill box construction technique which uses surface micromachining with silicon dioxide as a sacrificial layer which is etched laterally as the technology of choice. This choice becomes defendable if the mechanical properties of polysilicon can be determined and if process design can be implemented to produce repeatable, predetermined built-in strain, Young's modulus, and tensile strength.

Surface micromachined pressure transducers

Typical IC processing is fundamentally two dimensional; sensors are three-dimensional structures. In surface micromachining, two-dimensional IC processing is extended to sensor structures by the addition of one or more sacrificial layers which are removed by lateral etching. The resulting sensor structures involve the substrate and one or more deposited films which form the intended micromechanical component. The concepts of this type of sensor manufacturing are readily demonstrated by considering absolute pressure transducers in some detail. Absolute pressure transducers involve a vacuum-sealed cavity and a deformation sensing technique. The cavity is formed from the substrate and a low-pressure chemical vapor deposited polycrystalline silicon film. The mechanical properties of this film must be controlled well enough to allow the device to be designed. This implies morphological control during processing. Optimized films which do exhibit controlled compressive or tensile strains exclude oxygen or nitrogen and are therefore not modified by extended hydrofluoric acid etches. Their mechanical behavior is monitored by micromechanical test structures which measure Euler buckling and thereby determine the value of the built-in strain. The cavity vacuum is established by reactive sealing. Long-term vacuum integrity is achieved by a low-stress silicon nitride barrier which also acts as a dielectric isolation barrier. Sensing is accomplished via deposited polysilicon resistors. These devices behave like metal resistors in terms of their temperature coefficient of resistance and noise figure. Their piezoresistive behavior is larger than that of typical metal film structures and smaller than that of single-crystal resistors. Pressure sensors with four diaphragms, two active and two inactive, have been constructed and optimized towards manufacturability. The measured performance is excellent and agrees with the predictions of the design algorithm.

In-flight measurement of static pressures and boundary-layer state with integrated sensors

Advanced wing designs for transport aircraft using adaptive geometries for performance optimization and load control need reliable integrated sensors for feedback to the control system. More efficient air data sensing, eliminating the pitot-static piping, is also required, as in highly integrated modern flight management systems. Absolute pressure transducers from different manufacturers were tested and adapted to the flight-test environment. In laboratory and different flight tests, their applicability for steady measurements was proven in comparison to scanivalves. It was shown that sensing of pressure fluctuations in the buffet regime will improve the prediction of operational buffet limits. The pressure transducers were also used to investigate the laminar/ turbulent transition in the attachment-line flow of a swept wing in comparison to hot-film probes and were found to be an effective tool for such an experiment.

SHOOT flowmeter and pressure transducers

A venturi flowmeter has been designed and constructed for the Superfluid Helium On-Orbit Transfer (SHOOT) experiment. The calibration results obtained from the SHOOT venturi demonstrate the ability of the flowmeter to meet the requirements of the SHOOT experiment. Flow rates as low as 20 dm 3 h −1 and as high as 800 dm 3 h −1 have been measured with the flowmeter. The pressure drop in the flowmeter is measured by two Validyne differential pressure transducers. The ranges of the two transducers are 0.86 kPa (0.125 p.s.i.d.) and 8.62 kPa (1.25 p.s.i.d.). The low range transducer measures flow rates less than 200 dm 3 h −1, whereas the high range transducer measures flow rates greater than 200 dm 3 h −1. The repeatability of the flowmeter at the nominal flow rate of 500 dm 3 h −1 is within ±1% of the flow rate. Performances of the SHOOT differential and absolute pressure transducers, which have undergone calibration and vibration tests, are also included. Throughout the tests, the responses of the transducers remained linear and repeatable to within ±1% of the full scales of the transducers.

Contracts

An order worth in excess of £100,000 for absolute air pressure transducers has been received by the Aerospace Department, Farnborough Division of Solartron Transducers, from Smiths Industries in Cheltenham. These transducers will be the primary sensors in air data computers being manufactured for Sea Harrier aircraft of the Royal Navy.