Showing papers on "Pressure measurement published in 1999"

Implantable medical device for sensing absolute blood pressure and barometric pressure

Abstract: An implantable barometric pressure sensor (220) coupled with an implantable medical device (IMD) provides a barometric pressure related, referenced pressure value for use in combination with an absolute pressure value measured by an implantable absolute pressure sensor (20) coupled to the IMD. In one embodiment, the barometric pressure sensor (220) is formed as part of a connector module (180) of the IMD or extends from the connector module (180). A percutaneous access device (360) is implanted to extend through the skin and subcutaneous tissue layer of the patient and is coupled with the barometric pressure sensor (220). The barometric pressure sensor (220) is preferably enclosed within an air chamber (170) of the implantable medical device, and a catheter (310) extends between the air chamber (170) of the implantable medical device and the percutaneous access device (360). Or the barometric pressure sensor (220) is enclosed within an air chamber (368) of the percutaneous access device, and a lead extends between the barometric pressure sensor (220) and the implantable medical device.

Pressure dependence of subharmonic signals from contrast microbubbles.

Abstract: Noninvasive pressure estimation in heart cavities and in major vessels would provide clinicians with a valuable tool for assessing patients with heart and vascular diseases. Some microbubble-based ultrasound contrast agents are particularly well suited for pressure measurements because their substantial compressibility enables microbubbles to vary significantly in size in response to changes in pressure. Pressure changes should then affect reflectivity of microbubbles after intravenous injection of a contrast agent. This has been demonstrated with a galactose-based contrast agent using 2.0-MHz ultrasound tone bursts. Preliminary results indicate that, over the pressure range of 0-186 mmHg, the subharmonic amplitude of scattered signals decreases by as much as 10 dB under optimal acoustic settings and the first and second harmonic amplitudes decrease by less than 3 dB. An excellent correlation between the subharmonic amplitude and the hydrostatic pressure suggests that the subharmonic signal may be utilized for noninvasive detection of pressure changes.

Method for wide range gas flow system with real time flow measurement and correction

Abstract: A gas delivery system accurately measures and optionally regulates mass flow rate in real time. A fluid conduit connects an inlet valve, calibration volume, flow restrictor, and outlet valve in series. Pressure and temperature sensors are coupled to the calibration volume. One or more pressure sensors may be attached across the flow restrictor. Alternatively, an absolute pressure sensor may be attached upstream of the flow restrictor. One embodiment of differential pressure sensors comprises a floating reference differential pressure sensor, including a first transducer attached to the fluid conduit upstream of the flow restrictor and a second transducer attached to the conduit downstream of the flow restrictor. In this embodiment, each transducer receives a reference pressure from a reference source, and optionally, after the calibration volume is charged, the floating reference differential pressure transducers are calibrated. When gas flow is initiated, differential and/or absolute pressure measurements are repeatedly taken, and a measured mass flow rate calculated thereon. Gas flow is adjusted until the measured mass flow rate reaches a target mass flow. Using the temperature/pressure sensors at the calibration volume, repeated calculations of actual flow rate are made to uncover any discrepancy between actual and measured mass flow rates. Whenever a discrepancy is found, the manner of calculating measured mass flow is conditioned to account for the discrepancy; thus, the measured mass flow rate more accurately represents the actual mass flow rate thereby providing an actual mass flow rate more accurately achieving the target mass flow rate.

Measurements and modeling of PS/supercritical CO2 solution viscosities

Abstract: This paper presents a technology to determine the melt viscosity of a PS/super-critical CO 2 solution using a linear capillary tube die mounted on a foaming extruder. CO 2 was injected into the extrusion barrel and the content of CO 2 was varied in the range of 0 to 4 wt% using a positive displacement pump. Single-phase PS/CO 2 solutions were formed using a microcellular extrusion system and phase separation was prevented by maintaining a high pressure in the capillary tube die. By measuring the pressure drop through the die, the viscosity of PS/CO 2 solutions was determined. The experimental results indicate that the PS/CO 2 solution viscosity is a sensitive function of shear rate, temperature, pressure, and CO 2 content. A theoretical model based on the generalized Cross-Carreau model was proposed to describe the shear-thinning behavior of PS/CO 2 solutions at various shear rates. The zero-shear viscosity was modeled using a generalized Arrhenius equation to accommodate the effects of temperature, pressure, and CO 2 content. Finally, the solubility of CO 2 has been estimated by monitoring the pressure drop and the absolute pressure in the capillary die.

Direct Measurement of Xylem Pressure in Leaves of Intact Maize Plants. A Test of the Cohesion-Tension Theory Taking Hydraulic Architecture into Consideration

Abstract: The water relations of maize (Zea mays L. cv Helix) were documented in terms of hydraulic architecture and xylem pressure. A high-pressure flowmeter was used to characterize the hydraulic resistances of the root, stalk, and leaves. Xylem pressure measurements were made with a Scholander-Hammel pressure bomb and with a cell pressure probe. Evaporation rates were measured by gas exchange and by gravimetric measurements. Xylem pressure was altered by changing the light intensity, by controlling irrigation, or by gas pressure applied to the soil mass (using a root pressure bomb). Xylem pressure measured by the cell pressure probe and by the pressure bomb agreed over the entire measured range of 0 to -0.7 MPa. Experiments were consistent with the cohesion-tension theory. Xylem pressure changed rapidly and reversibly with changes in light intensity and root-bomb pressure. Increasing the root-bomb pressure increased the evaporation rate slightly when xylem pressure was negative and increased water flow rate through the shoots dramatically when xylem pressure was positive and guttation was observed. The hydraulic architecture model could predict all observed changes in water flow rate and xylem. We measured the cavitation threshold for oil- and water-filled pressure probes and provide some suggestions for improvement.

The effects of chamber pressurization on soil‐surface CO2 flux and the implications for NEE measurements under elevated CO2

Abstract: Soil and ecosystem trace gas fluxes are commonly measured using the dynamic chamber technique. Although the chamber pressure anomalies associated with this method are known to be a source of error, their effects have not been fully characterized. In this study, we use results from soil gas-exchange experiments and a soil CO2 transport model to characterize the effects of chamber pressure on soil CO2 efflux in an annual California grassland. For greater than ambient chamber pressures, experimental data show that soil-surface CO2 flux decreases as a nonlinear function of increasing chamber pressure; this decrease is larger for drier soils. In dry soil, a gauge pressure of 0.5 Pa reduced the measured soil CO2 efflux by roughly 70% relative to the control measurement at ambient pressure. Results from the soil CO2 transport model show that pressurizing the flux chamber above ambient pressure effectively flushes CO2 from the soil by generating a downward flow of air through the soil air-filled pore space. This advective flow of air reduces the CO2 concentration gradient across the soil–atmosphere interface, resulting in a smaller diffusive flux into the chamber head space. Simulations also show that the reduction in diffusive flux is a function of chamber pressure, soil moisture, soil texture, the depth distribution of soil CO2 generation, and chamber diameter. These results highlight the need for caution in the interpretation of dynamic chamber trace gas flux measurements. A portion of the frequently observed increase in net ecosystem carbon uptake under elevated CO2 may be an artifact resulting from the impact of chamber pressurization on soil CO2 efflux.

Tire pressure indicator including pressure gauges that have a self-generating power capability

Abstract: A tire pressure indicator comprises a set of pressure gauges (1) respectively installed in the tires of a vehicle, and receiver circuit means (5) installed in the vehicle adjacent to the tires. Each pressure gauge (1) includes a power supplying device (20), a pressure-sensing unit (30), and a transmitter circuit (40). The power-supplying device (20) has a self-generating voltage unit (21) forced by a piezoelectric element (210), a spring element (211), and a weight (212). The spring element (211) is vibrated when the tires of the vehicle are in motion, thereby causing the piezoelectric element (210) to generate power supply. The pressure-sensing unit (30) includes a capacitor means (300) formed by a motion member (31), a conductive member (33), and a converting circuit (34). The motion member (31) is made of electrically conductive material and is moved relative to the conductive member(33) subject to the air pressure of the respective tire, so as to change the capacity of the capacitor means, enabling the converting circuit (34) to output a first signal to the transmitter circuit (40) subject to RC oscillation waveform detected. The transmitter transmits a second signal into the air by radio upon receipt of the first signal.

Cylinder pressure based optimization control for compression ignition engines

Abstract: The performance of a compression ignition internal combustion engine is improved by optimizing a cylinder pressure-dependent parameter on a full time, full range basis using in-cylinder pressure measurements to determine the actual value of the parameter to be optimized. The basic procedure is to determine the desired or optimum value of the parameter, determine the actual value of the parameter or a related parameter, and then adjusting an engine operating characteristic such as air/fuel ratio to maintain the controlled parameter at its optimum value. The preferred parameter is a cylinder pressure ratio (CPR) obtained by dividing first and second values of cylinder pressure, and sensed at different points in a thermodynamic cycle, by one another. The sensed values are preferably a first value Po, obtained during the compression stroke, and a second value Pa, obtained after combustion is complete. Direct in-cylinder pressure measurements can also be used for other purposes such as knock detection, determination of maximum cylinder pressure (MCP), and engine controls dependent thereon.

Noninvasive measurement of the hydrostatic pressure in a fluid-filled cavity based on the disappearance time of micrometer-sized free gas bubbles.

Abstract: A new method for noninvasive pressure measurement, based on the disappearance time of micrometer-sized free gas bubbles, is described in this article. An ultrasound (US) contrast agent, consisting of encapsulated gas bubbles, is used as a vehicle to transport the free gas bubbles to the desired region where the pressure is to be measured. The small free gas bubbles are generated at the region of interest (e.g., heart chambers), from the encapsulated gas bubbles, which rupture when they are exposed to a single low-frequency (e.g., 0.5 MHz), high acoustic amplitude US burst. The released gas bubbles persist for only a few ms and dissolve in the liquid, depending on their size, the gas, the liquid characteristics and ambient parameters such as temperature, gas concentration and pressure. A pressure-disappearance time relationship is determined using a sequence of high-frequency (e.g., 10 MHz), low acoustic amplitude US pulses. From in vitro experiments, reproducible results show a significant difference between the disappearance time of the bubbles as function of the local pressure, resulting in a quicker disappearance of the bubble for higher values of the pressure. The sensitivity of the method to small pressure changes (50 mmHg) is demonstrated.

Measurement of intracompartmental pressure with use of a new electronic transducer-tipped catheter system.

Abstract: Laboratory and clinical tests were carried out to determine the clinical usefulness, validity, and safety of a new self-calibrating, battery-powered monitoring system for the measurement of intramuscular pressure with use of an electronic transducer-tipped catheter. The eight probes accurately recorded applied pressures ranging from zero to 160 millimeters of mercury (zero to 21.33 kilopascals). The system registered little temperature-induced drift (maximum, 1.25 millimeters of mercury [0.17 kilopascal]) between dry room temperature and 40 degrees Celsius. There were also minimum variations (range, -0.14 to 0.81 millimeter of mercury [0.02 to 0.11 kilopascal]) in the pressures recorded during a twenty-four-hour period. The resting pressure in the tibialis anterior muscle of twenty volunteers who had normal limbs was a mean (and standard deviation) of 13.1 ± 8.3 millimeters of mercury (1.75 ± 1.11 kilopascals). There was a good correlation between externally applied pressures (zero, twenty, forty, sixty, eighty, and 100 millimeters of mercury [zero, 2.67, 5.33, 8.00, 10.66, and 13.33 kilopascals] applied with use of antishock trousers) and the pressures measured in the tibialis anterior muscle of four volunteers (r = 0.997 to 0.999). The injection of sterile saline solution into the tibialis anterior muscle of a volunteer and the use of high-frequency recording during muscular activity showed a high degree of responsiveness and sensitivity to changes in intramuscular pressure. We also prospectively evaluated the clinical usefulness of the system and found it to be easy to assemble, calibrate, and use. Thus, this reusable, electronic transducer-tipped catheter system, which is based on a noninfusion technique, is simple, minimally traumatic, and highly precise. It is free of hydrostatic pressure artifacts and provides dynamic responses to changes in intramuscular pressure.

Barometric pressure sensor for use with implantable absolute pressure sensor

Abstract: A barometric pressure sensor (260) for deriving reference pressure data for use in combination with absolute pressure data derived by an implantable medical device (IMD) is disclosed The barometric pressure sensor (260) is located in a sensing module (200) having a module housing (222) enclosing an air chamber (230) which encloses the barometric pressure sensor (260) An air vent (220) extends through the module housing (222) for venting the air chamber (230) to atmospheric pressure outside the housing A protective vent cover (240) extends across the air vent (220) formed of a material capable of air passage and capable of inhibiting passage of moisture, liquids, and particulate contaminants into the air chamber (230) The sensing module (200) is worn or carried by the patient and includes operating circuitry and a power supply for periodically storing sensed atmospheric pressure values as reference pressure data In another embodiment, the sensing module (200) comprises a percutaneous access device (300) which is adapted to be implanted in the skin and subcutaneous tissue layer of the patient

Low power integrated pressure sensor system for medical applications

Abstract: A new low power integrated pressure sensor system with digital output (1 bit PDM signal) for medical applications is presented. The absolute pressure sensor comprising 400 nm thick surface micromachined polysilicon membranes for capacitive pressure detection and a monolithic integrated 2nd order sigma–delta-modulator including voltage reference and timing generator is extremely miniaturized on an area of approximately 3 mm 2 . For protection and biocompatibility reasons the sensor is coated with a silicone elastomer of up to 100 μm thickness, which does not influence the sensor's performance. The sensor system was tested in vitro in physiological NaCl solution, showing excellent results compared to a commercial available reference sensor. The sensor system is working well down to a supply voltage of 2.2 V with a power consumption of 0.5 mW. The resolution is better than 12 bit. Due to the small chip area, low power consumption and cost effective production process, the sensor is ideal for medical applications, e.g., in combination with telemetric power and data transmission [J. Zacheja, B. Clasbrummel, J. Binder, U. Steinau, Implantable Telemetric Endosystem for Minimal Invasive Pressure Measurements, MedTech95, Berlin, Germany, (1995)] as an implantable sensor to reduce the mortality risk of intensive care patients.

Pressure sensing cannula

Abstract: A cannula is provided with one or more pressure transducers for measuring fluid pressure interiorly or exteriorly of the cannula. The pressure transducers may be mounted integrally with the tubular wall defining the main lumen of the cannula, or they may comprise differential pressure transducers mounted in dedicated lumens in communication with the main lumen. The pressure measurements from the transducers is used to determine fluid flow rate.

Fluid mechanics analysis of a spring-loaded jet injector

Abstract: A syringe jet injector is a device designed to administer a drug quickly and painlessly through the skin. Though syringe jet injectors have been in use for almost 50 years, current designs still suffer from inconsistent performance. To better understand the fluid mechanics of jet injection and gain insight into how the design might influence performance, two theoretical analyses to determine the fluid pressure profile at the exit orifice were conducted. The first was a continuum analysis assuming static incompressibility. Results demonstrated that the maximum jet pressure was highly sensitive to the spring constant, initial piston velocity, and piston cross-sectional area while the time to achieve the maximum pressure was most sensitive to the injection chamber length, initial piston velocity, bulk modulus of the injectant, and the piston cross-sectional area. The second analysis was a shock wave analysis. Results demonstrated a stepwise pressure-time plot that was similar in magnitude to that for the continuum analysis assuming static incompressibility. Results from these two investigations are useful for design modification of the jet injector to achieve desired pressure-time profiles at the orifice. Control of pressure-time profiles may help to achieve a more consistent and effective injection process.

Rigid encapsulation package for semiconductor devices

Abstract: A rigid encapsulation package for semiconductor sensors, actuators, and devices is described. In one embodiment, a semiconductor pressure sensor includes a sensor element having a deformable diaphragm for measurement of pressure, and a cap that includes a recess. The cap is attached to the sensor element to form a cavity therebetween. The pressure sensor further includes a leadframe, interconnecting bond wires, a pressure port that is coupled to the sensor element, and a nominally rigid material formed over the sensor element, cap, leadframe, and bond wires. The material may include one or more of the following: epoxy, RTV, resins, and gel. The sensor element may include a built-in stress isolation flexible region. A second pressure port may optionally be attached to the housing for providing differential or gage pressure measurements.

Surface Pressure Measurements in Supersonic Transverse Injection Flowfields

Abstract: Pressure-sensitive paint (PSP) was used to examine the surface pressures in flowfields generated by transverse injection of air through circular and elliptical nozzles into a supersonic freestream. Four jet-to-freestream momentum flux ratios (J) were investigated for each jet. Two different pressure paints (pyrene-based and PtOEP-based) were examined. Results of the paint comparison show that the PtOEP-based paint is significantly more temperature-sensitive than the pyrene-based paint. This results from its longer phosphorescence lifetime as compared to pyrene's short fluorescence lifetime. A comparison of the PSP results with conventional pressure measurements indicates good agreement between the two with no special fitting of the paint data. Results further show that jet operating conditions and injector geometry significantly affect the surface pressure field around a transverse jet. Increases in J dramatically alter the wall pressure field upstream and downstream of the injector. Injector geometry strongly affects the upstream extent of the separation region and the bow shock, and the character of the wake region downstream of the jet. Also, the effective back pressures computed from the PSP data for the elliptical injector cases are significantly higher than for the circular injector cases presenting a possible explanation for recently observed differences in transverse penetration.

Flush Airdata Sensing (FADS) System Calibration Procedures and Results for Blunt Forebodies

Abstract: Blunt-forebody pressure data are used to study the behavior of the NASA Dryden Flight Research Center flush airdata sensing (FADS) pressure model and solution algorithm. The model relates surface pressure measurements to the airdata state. Spliced from the potential flow solution for uniform flow over a sphere and the modified Newtonian impact theory, the model was shown to apply to a wide range of blunt-forebody shapes and Mach numbers. Calibrations of a sphere, spherical cones, a Rankine half body, and the F-14, F/A-18, X-33, X-34, and X-38 configurations are shown. The three calibration parameters are well-behaved from Mach 0.25 to Mach 5.0, an angle-of-attack range extending to greater than 30 deg, and an angle-of-sideslip range extending to greater than 15 deg. Contrary to the sharp calibration changes found on traditional pitot-static systems at transonic speeds, the FADS calibrations are smooth, monotonic functions of Mach number and effective angles of attack and sideslip. Because the FADS calibration is sensitive to pressure port location, detailed measurements of the actual pressure port locations on the flight vehicle are required and the wind-tunnel calibration model should have pressure ports in similar locations. The procedure for calibrating a FADS system is outlined.

Sintered pressure sensor for a pressure transmitter

Abstract: A transmitter in a process control system transmits a pressure over a process control loop. The transmitter includes I/O circuitry, compensation circuitry and an absolute pressure sensor. The I/O circuitry transmits information over the process control loop. Compensation circuitry receives a pressure related signal and responsively control's the I/O circuitry to transmit pressure information on the loop. The absolute pressure sensor includes a cavity which deforms as the sensor deflects in response to an applied pressure. A sensor in the cavity provides the pressure related signal to the compensation circuitry in response to the deformation.

Various applications of resonant pressure sensor chip based on 3-D micromachining

Abstract: An accurate and stable resonant pressure sensor fabricated using 3-D micromachining process was developed. Two resonators are located on the surface of the diaphragm and applied pressure is measured from the difference of two resonant frequencies. The resonators are encapsulated into the micro-vacuum cavities in order to isolate them from surrounding fluid and to get stable resonance. Three components, namely, the diaphragm, the resonators, and the vacuum cavities, are all single crystalline and monolithically structured on the 6.8×6.8-mm wide, 0.5-mm thick silicon chip. The resonator, having a high Q -value of 50 000, was obtained owing to the vacuum isolation and resulted in superior characteristics such as resolution, repeatability and long-term stability. In the next place, the developed pressure sensor was successfully applied to the differential pressure transmitter for industrial process, and several further applications were accomplished successively.

Fault-Tolerant Neural Network Algorithm for Flush Air Data Sensing

Abstract: A fault-tolerant neural network algorithm was successfully developed for use with flush air data sensing systems. This algorithm is composed of a combination of aerodynamic and neural network models used to translate a discrete pressure distribution from the nose of an aircraft into a set of air data parameters, including static pressure, dynamic pressure, Mach number, angle of attack, and angle of sideslip. Techniques were developed to detect and eliminate the effect of a lost signal from the measured pressure distribution. This system was evaluated with archived data, and its performance was compared with a signal processing system based completely on aerodynamic models

A single computer-controlled mechanical insufflation allows determination of the pressure-volume relationship of the respiratory system.

Abstract: Objective. To evaluate and further develop a method for determination and mathematical characterisation of the elastic pressure-volume (Pel-V) relationship in mechanically ventilated human subjects during one single modified insufflation with simultaneous determination of resistance of the respiratory system. Subjects. Eight adult non-smoking human subjects without heart, lung, or thoracic cage disease scheduled for non-thoracic surgery. The study was performed in anaesthetised and muscle-relaxed subjects. Measurements and Main Results. The Pel-V curve was determined with a computer-controlled Servo Ventilator 900C during a modified insufflation with either constant or sinusoidally varying flow. Pressure and flow were measured with the built-in sensors of the ventilator. Tracheal pressure (Ptr) was calculated by subtracting the pressure drop over the tracheal tube. The elastic recoil pressure in the peripheral lung, Pel, was obtained from the calculated Ptr by subtracting the pressure drop over the airways. Ptr was also directly measured through a catheter. The calculated Ptr gave similar results as the directly measured Ptr, thus indicating the reliability of the signal originating from the ventilator sensor for computation of downstream pressures. The inflection points of the sigmoidal Pel-V curve and the compliance of the linear segment were determined with high reproducibility. Conclusions. Using one single modified insufflation allows a fast and accurate determination of respiratory mechanics. The Pel-V curves were determined with high reproducibility and were adequately described by a three-segment model of the curve incorporating a linear segment between two asymmetrical non-linear segments.

System for manufacturing a semiconductor device

Abstract: A gas supply system for supplying a gas into a reaction chamber is provided with a pulse valve, a mass flow controller and a back pressure controller. The mass flow controller includes a flow meter and a variable flow control valve, and the back pressure controller includes a pressure gauge and a pressure control valve. The pulse valve, the mass flow controller and the back pressure controller are connected to a controller so that operations thereof are controlled by this controller.

Non-intrusive pressure/multipurpose sensor and method

Abstract: Method and apparatus are provided for determining pressure using a non-intrusive sensor that is easily attachable to the plumbing of a pressurized system. A bent mode implementation and a hoop mode implementation of the invention are disclosed. Each of these implementations is able to non-intrusively measure pressure while fluid is flowing. As well, each implementation may be used to measure mass flow rate simultaneously with pressure. An ultra low noise control system is provided for making pressure measurements during gas flow. The control system includes two tunable digital bandpass filters with center frequencies that are responsive to a clock frequency. The clock frequency is divided by a factor of N to produce a driving vibrational signal for resonating a metal sensor section.

Remote query pressure measurement using magnetoelastic sensors

Abstract: Two magnetostriction-based methods for measuring atmospheric pressure are presented. Each technique correlates changes in pressure with the characteristic resonant frequency of a magnetoelastic magnetostrictive thick-film sensor. In each case the sensor is monitored remotely, using an adjacently located pickup coil, without the use of physical connections to the sensor.

Miniature fiber optic pressure sensor for turbomachinery applications

Abstract: Development of pressure sensors for the instrumentation of experimental aerodynamic facilities has traditionally concentrated on electrical techniques. An improvement in the currently attainable temporal and spatial resolution in pressure measurement would be beneficial in the characterization of turbulent flows behind turbine rotor stages, for example. We present results obtained in a turbine test rig from a fiber optic pressure sensor based upon the interferometric response of an extrinsic cavity formed between the interrogation fiber and a reflective diaphragm. We discuss the design trade offs, optical interrogation and temperature sensitivity of such a configuration, and demonstrate the success of the design in small-scale shock tube experiments. We then describe the application of the sensor in a full scale turbine test facility in which pressure signals with frequency components exceeding 200 kHz were obtained.

Field observations of wave setup

Abstract: Wave setup is assumed to be a balance between the cross-shore convergence of the onshore flux of momentum (wave radiation stress Sxx) in the surfzone and a cross-shore pressure gradient. Oceanic observations between the 2- and 8-m isobaths near Duck, North Carolina, provide a test of the wave setup balance without assuming that wave height in the surfzone is proportional to water depth. Analysis of data from a cross-shore array of 11 pressure gauges and 10 sonar altimeters deployed during the fall of 1994 indicates the wave setup balance holds to at least the accuracy of the pressure measurements (a few centimeters). The correlation between the two terms in the setup balance is 0.93, and the linear regression slope is 1.05±0.19. Accurate estimates of the cross-shore pressure gradient require density measurements to adjust pressure measurements taken at different depths to the same level. The assumption that pressure and bathymetry are linear between the 2- and 8-m isobaths (or the more common assumption that the height of normally incident, shallow water waves is proportional to the water depth) introduces errors of up to 6 cm for the conditions considered here. Given this assumption, 3.5 years of data from pressure gauges in 2 and 8 m of water indicate that the wave setup balance is valid for a wide range of conditions (correlation 0.71 and regression slope 0.98±0.08).

Dual pressure monitor

Abstract: A remote pressure sensor includes a probe having a chamber for holding a liquid. A flexible membrane is mounted in the probe. A conduit joins a reference cell to the chamber for holding the liquid. And, a reference pressure gauge is operatively joined to the conduit for measuring pressure of the liquid therein for use in referencing a primary pressure sensor through which fluid flows.