High-precision Pressure Sensor Research Articles

Spatial variability of wind-induced air pressure fluctuations responsible for pressure pumping

Small air pressure fluctuations in the atmosphere are responsible for the pressure pumping effect, which leads to an enhancement of soil gas transport. To investigate the spatial variability of these air pressure fluctuations, several high-precision differential pressure sensors were installed at the floor of a Scots pine forest. The alignment of the pressure sensors allowed for the determination of the propagation direction and speed of the observed air pressure fluctuations. Below-canopy and above-canopy airflow characteristics were monitored to find possible links between the air pressure fluctuations and the airflow. Results show that the propagation direction of the air pressure fluctuations observed at the forest floor correspond to the above-canopy and not to the below-canopy wind direction. Moreover, propagation speed of the air pressure fluctuations is higher than the below-canopy wind speed and corresponds to above-canopy wind speed. These findings indicate a connection between below-canopy air pressure fluctuations and above-canopy airflow. The air pressure fluctuations were found to be well correlated up to a distance of 15 m. With increasing distance, the correlation strongly decreases. However, the calculated pressure pumping coefficient, which quantifies the strength of the pressure pumping effect, yields similar values up to a distance of 90 m. This allowed specifying the range of influence of the air pressure fluctuations.

Development and simulation of microfluidic Wheatstone bridge for high-precision sensor

In this work we present the results of analytical modeling and 3D computer simulation of microfluidic Wheatstone bridge, which is used for high-accuracy measurements and precision instruments. We propose and simulate a new method of a bridge balancing process by changing the microchannel geometry. This process is based on the “etching in microchannel” technology we developed earlier (doi:10.1088/1742-6596/681/1/012035). Our method ensures a precise control of the flow rate and flow direction in the bridge microchannel. The advantage of our approach is the ability to work without any control valves and other active electronic systems, which are usually used for bridge balancing. The geometrical configuration of microchannels was selected based on the analytical estimations. A detailed 3D numerical model was based on Navier-Stokes equations for a laminar fluid flow at low Reynolds numbers. We investigated the behavior of the Wheatstone bridge under different process conditions; found a relation between the channel resistance and flow rate through the bridge; and calculated the pressure drop across the system under different total flow rates and viscosities. Finally, we describe a high-precision microfluidic pressure sensor that employs the Wheatstone bridge and discuss other applications in complex precision microfluidic systems.

Long‐term observations of North Atlantic Current transport at the gateway between western and eastern Atlantic

AbstractIn the western North Atlantic, warm and saline water is brought by the North Atlantic Current (NAC) from the subtropics into the subpolar gyre. Four inverted echo sounders with high precision pressure sensors (PIES) were moored between 47°40′N and 52°30′N to study the main pathways of the NAC from the western into the eastern basin. The array configuration that forms three segments (northern, central, and southern) allows partitioning of the NAC and some assessment of NAC flow paths through the different Mid‐Atlantic Ridge fracture zones. We exploit the correlation between the NAC transport measured between 2006 and 2010 and the geostrophic velocity from altimeter data to extend the time series of NAC transports to the period from 1992 to 2013. The mean NAC transport over the entire 21 years is 27 ± 5 Sv, consisting of 60% warm water of subtropical origin and 40% subpolar water. We did not find a significant trend in the total transport time series, but individual segments had opposing trends, leading to a more focused NAC in the central subsection and decreasing transports in the southern and northern segments. The spectral analysis exhibits several significant peaks. The two most prominent are around 120 days, identified as the time scale of meanders and eddies, and at 4–9 years, most likely related to the NAO. Transport composites for the years of highest and lowest NAO indices showed a significantly higher transport (+2.9 Sv) during strong NAO years, mainly in the southern segment.

Experimental Investigation of Pressure Load Exerted on a Downstream Dam by Dam-Break Flow

The failure of a natural or an artificial dam often leads to catastrophic flooding downstream. Studies have been conducted to investigate the mechanisms of single dam failure and the propagation of dam-break flood wave. However, little attention has been paid to the cascade failure of two or more sequential dams. In this article, consequences of a dam-break flood wave down a channel exerting pressure load on a downstream dam with different backwater effects were studied experimentally. Three typical flood patterns were observed for different downstream reservoir water depths. High precision pressure sensors were employed to measure the pressure load at different heights on the dam. Changes of the maximum pressure load were measured as the bed slope and the upstream and downstream reservoir water depths varied. An empirical formula was obtained by linear regression to predict the maximum pressure load. Additionally, a sinusoidal attenuation function was introduced to describe the time evolution of pressure load exerted on the downstream dam, and its parameters were determined using the measurement data in different cases.

High precision pressure sensors based on SAW devices in the GHz range

In this paper, an AlN/free-standing nanocrystalline diamond (NCD) system is proposed in order to process high frequency surface acoustic wave (SAW) resonators for sensing applications. The main problem of synthetic diamond is its high surface roughness that worsens the sputtered AlN quality and hence the device response. In order to study the feasibility of this structure, AlN films from 150nm up to 1200nm thick have been deposited on free-standing NCD. We have then analysed the influence of the AlN layer thickness on its crystal quality and device response. Optimized thin films of 300nm have been used to fabricate of one-port SAW resonators operating in the 10–14GHz frequency range. A SAW based sensor pressure with a sensibility of 0.33MHz/bar has been fabricated.

Pressure Sensor Monolithically Integrating MEMS and CMOS-LSI with CMOS Compatible "Back-end-of-line MEMS processes"

Back-end-of-line (BEOL) MEMS processes for a compact, high-precision pressure sensor was developed. A CMOS-LSI-integrated capacitive pressure-sensor was fabricated with a chip size of 0.72 mm2 using developed BEOL MEMS processes. Multi-sensor chip (with a size of 1.7 by 1.9 mm2) which consists of pressure sensor, temperature sensor and high-precision measurement circuits was also fabricated, and precise atmospheric pressure measurement (∼ 10 Pa) was demonstrated. As the sensitivity of pressure sensor can be easily changed by the size of its MEMS capacitors, the pressure sensor is thus suitable for various pressure-range applications.

HIGH-CYCLE FATIGUE DEVICE FOR LOW STIFFNESS COMPONENTS

The long-term reliability of small electroplated bellows made of a thin Ni/Cu/Ni layered material is sought. The design criteria are related to their stiffness and airtightness as they are used to convert a (very) small pressure variation into a displacement in a high-precision pressure sensor. Yet, in the above-mentioned cases, the airtightness cannot be assessed easily. It is proposed to develop a special setup to directly test bellows in their ‘‘environment'' (i.e., they are welded onto A304L(N) stainless steel holders). Furthermore, as high-cycle fatigue behavior is sought, that is, at least 1–10 million cycles are necessary to obtain the endurance properties, up to 10 samples may be tested simultaneously to save time.

Fatigue Limit Evaluations of a Complex Structure by Using Temperature Measurements

The study deals with the long-term reliability of a high precision pressure sensor using bellows mainly made of electroplated Ni. The bellows are expected to stay in service for many decades. Their high cycle fatigue behavior has to be known to assess the probability of airtightness loss. A specific high cycle fatigue setup, put in a resonant machine that is displacement-controlled, has been designed. An infrared thermographic technique is used to determine the mean fatigue limit of bellows. Increases in the mean temperature of the bellows with the displacement range are monitored. Several authors empirically relate the mean fatigue limit of a flat specimen to a rapid temperature change. A similar analysis is performed in the present case by using the bellows mean temperature. Finite element computations allow us to estimate a mean fatigue limit for electroplated Ni. This result is compared with those obtained mechanically in a Woehler diagram.

A Unified Series of High-Precision Pressure Sensors for Automatic Regulation and Monitoring Systems

A number of high-precision pressure sensors for automatic regulation and monitoring systems are presented. The design-technological principles used in the sensors, which ensure their operating capability under severe operating conditions, are considered. A comparative analysis of the technical level of the sensors and their foreign analogs is given.

Thermomechanical properties and fatigue of nanocrystalline Ni/Cu electrodeposits

AbstractThis study deals with the long-term reliability of a high precision pressure sensor using bellows mainly made of electroplated Ni. Thermomechanical properties of this deposit are obtained by several experiments and compared to theoretical models, computations and other authors' results. Bellows are expected to stay in service for many decades, thus their high cycle fatigue behavior has to be known. Stress-life fatigue curve for crack initiation and fatigue crack growth in the electroplated Ni are measured and identified using numerical computations. Results are compared with other results obtained on similar Ni electrodeposits. Normalized stress-life fatigue curve shows no specific nanosize effects.

Solubility of hydrogen sulfide in pure water and in NaCl solutions, from 20 to 320°C and at saturation pressures

The solubility of hydrogen sulfide in pure water and in NaCl solutions has been studied experimentally from 20 to 320°C and at saturation pressures. Hydrogen sulfide solutions in equilibrium with their vapor phase were contained in a pressurized titanium bellows of known total volume. The bellows transmitted inside-vapor pressures via a thermally stable oil (pressure medium) to a high-precision pressure sensor. Temperatures were measured by a sheathed thermocouple immersed into the oil surrounding the bellows. Values for the Henry constants were derived from measurements of equilibrium vapor pressure, volume, temperature, and bulk composition. The Henry constants agree well with previously published data up to about 200°C, but then deviate towards lower values (higher solubilities) at higher temperatures. Henry constants from 20 to 320°C and at saturation pressures may be obtained from the correlation log k H ( T, P sat,1 ) = +0.6342702616 e + 3 + 0.2709284796 e + 0 · T − 0.1 113202904 e − 3 · T 2 − 0.1671907660 e + 5/ T −0.2619219571 e + 3 · log T, where k h is in units of bar/molality and T in Kelvin. The experimental Henry constants have been fitted to a scaled particle theory model and have been tested by a recently proposed linearization procedure. The salting-out effect of NaCl on H 2S solubility is nearly independent of temperature up to about 250°C, but then increases sharply as temperatures approach the critical point of water. Skeleton tables to 365°C and for ionic strengths μ = 0, 1, 2, 3 have been prepared.

Thermodynamics of Aqueous H2S Solutions at Elevated Temperatures: Solubility and First Dissociation Constant

The solubility of hydrogen sulphide in pure water and in NaCI solutions has been studied experimentally from 20 to 320~ and at saturation pressures. Hydrogen sulphide solutions in equilibrium with their vapor phase were contained in a pressurized titanium bellows of known total volume. The bellows transmitted inside-vapor pressures via a thermally stable oil (pressure medium) to a highprecision pressure sensor. Temperatures were measured by a sheathed thermocouple immersed into the oil sourrounding the bellows. Values for the Henry constants were derived from measurements of equilibrium vapor pressure, volume, temperature, and bulk composition. The Henry constants agree well with previously published data up to about 200~ but then deviate towards lower values (higher solubilities) at higher temperatures. Henry constants from 20 to 320~ and at saturation pressures may be obtained from the correlation