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Showing papers on "Pressure measurement published in 1980"


Journal ArticleDOI
TL;DR: For the indirect measurement of beat-to-beat systolic and diastolic pressure in the human finger, a new hydraulic servocontrol system was designed to maintain the vascular volume in the unloaded state to evaluate the accuracy of this method.
Abstract: For the indirect measurement of beat-to-beat systolic and diastolic pressure in the human finger, a new hydraulic servocontrol system was designed to maintain the vascular volume in the unloaded state The servocontrol system consists of a compression chamber equipped with an occluding cuff and a photoelectric plethysmograph, an electromagnetic shaker, and a volume servo circuit The shaker connected to a diaphragm actuator is used for controlling the cuff pressure The vascular volume change in the finger is detected by the photoelectric plethysmograph The plethysmographic signal is fed into the servo circuit to control the cuff pressure, which is clamped at a proper value corresponding to the unloaded vascular volume At this state the controlled cuff pressure follows the intraarterial pressure The accuracy of this method was evaluated using an in vitro vascular model of the finger Comparisons with direct measurement were carried out successfully in four normotensive and six hypertensive subjects

143 citations


Journal ArticleDOI
TL;DR: In this article, an apparatus and technique for loading diamond anvil cells with gases at high pressure was devised. But this was done at room temperature with helium and hydrogen isotopes to initial densities exceeding those of the normal liquids.
Abstract: We devised an apparatus and technique for loading diamond‐anvil cells with gases at high pressure. Cells were filled quickly and conveniently at room temperature with helium and hydrogen isotopes to initial densities exceeding those of the normal liquids. We report preliminary values of 4He and D2 melting points based on the ruby pressure scale and compare them with extrapolations from our earlier melting curves measured to 20 kbar in a piston‐cylinder device. Our filling procedure now makes it possible to use 4He as a pressure medium in diamond cells. The technique is also useful for loading cells with gaseous mixtures.

127 citations


Patent
25 Feb 1980
TL;DR: In this article, a pressure sensor employing the piezoresistive effect of single crystal silicon resistors to measure the flexure of a semiconductor diaphragm is presented.
Abstract: A semiconductor pressure sensor employing the piezoresistive effect of single crystal silicon resistors to measure the flexure of a semiconductor diaphragm. In the preferred embodiment, a Wheatstone bridge composed of a first pair of resistors disposed on the center of the diaphragm and a second pair of resistors disposed on the periphery of the diaphragm is employed. Due to the nature of the diaphragm flexure, the first and second pairs of resistors exhibit piezoresistivity in opposite directions enabling pressure measurement with greater sensitivity. The diaphragm is mounted on and supported by a silicon clamp ring. The diaphragm and the clamp ring together form a unitary semiconductor structure. Because the piezoresistive effect which serves as a measure of the diaphragm flexure and hence as a measure of the pressure difference across the diaphragm is temperature dependent, the sensor also includes a temperature sensitive resistor, forming a part of the same unitary semiconductor structure, which provides a measure of the temperature of the piezoresistive elements. This measure of temperature enables external circuitry to correct for the temperature dependence of the piezoresistive effect thereby providing a pressure measurement of greater accuracy.

100 citations


Journal ArticleDOI
TL;DR: In this article, a simple clamp-type pressure apparatus was used for measurements of magnetic susceptibility and electrical resistivity at low temperatures, which was capable of generating hydrostatic pressures up to 30 kbar at room temperature and at least up to 25kbar at 4.2 K.
Abstract: A design of simple clamp type pressure apparatus utilized for measurements of magnetic susceptibility and electrical resistivity at low temperatures is presented. The cell consists of WC piston and Be–Cu cylinder which was autofrettage processed, and sample cavity consists of a teflon bucket and an electrode plug. In a temperature range from 300 K down to 77 K, pressure was determined by manganin gauge which was calibrated by Bi I→II transition pressure at room temperature and also the temperature dependence of pressure coefficient of manganin resistance was taken into account. As a result, the cell was capable of generating hydrostatic pressures up to 30 kbar at room temperature and at least up to 25 kbar at 4.2 K.

84 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported the direct calibration of a spinning rotor gas friction gauge (RG) against the multiple expansion vacuum pressure standard of the Physikalisch-Technische Bundesanstalt (PTB), Berlin, with HE, Ne, Ar, Kr, Xe, CH4, N2, and CO2.
Abstract: The paper reports the direct calibration of a spinning rotor gas friction gauge (RG) against the multiple expansion vacuum pressure standard of the Physikalisch‐Technische Bundesanstalt (PTB), Berlin, with HE, Ne, Ar, Kr, Xe, CH4, N2, and, via a membrane micromanometer, with H2, O2, CO, and CO2. It was found that in the pressure range 10−5–10−2 mbar (10−7–10−4 Pa) the macroscopic coefficient of tangential momentum transfer between gas molecules and the rotor surface, σ, is close to unity. The long term reproducibility of the new RG at p≳10−5 mbar as observed over two years with long intermediate periods of air exposure was within the limits of the total uncertainty of 1% for the comparison with the PTB standard. The RG thus seems recommendable for use as a reliable transfer standard, all the more since the only constituent of the new instrument that must be transferred is a small (typically 4.5‐mm‐diam) steel ball.

61 citations


Journal ArticleDOI
TL;DR: A weighted sum of the percentage difference between reference and recorded amplitudes of sinusoidal waveforms for several catheters and connecting tubings was calculated and found that when the connecting tubing was shorter than 3 feet long and no air bubbles were trapped readings were accurate.
Abstract: Direct measurement of blood pressure with a fluid-filled catheter and transducer is widely accepted in clinical practice. However, errors associated with the measurements are often not appreciated. The system frequently is unable to reproduce rapidly changing waveforms and overshoots to produce higher peak pressures. The most common causes of this phenomenon are trapped small air bubbles and long connecting tubing. To assess the inaccuracy in pressure measurements, we calculated the weighted sum of the percentage difference between reference and recorded amplitudes of sinusoidal waveforms for several catheters and connecting tubings. We found that when the connecting tubing was shorter than 3 feet long and no air bubbles were trapped readings were accurate. On the contrary, connecting tubings 7 feet long or longer, and/or air bubbles, were frequently associated with inaccurate results. For example, minimal air bubbles (0.25 ml) in a system exaggerated the systolic pressure measurement by 41 torr when simulated blood pressure was 150/50 torr.

59 citations


Patent
30 Jun 1980
TL;DR: In this article, a method of determining the pressure applied to a limb by an inflatable garment by placing a flexible pressurizable cuff between the garment and the limb to receive the compressive garment forces and then determining the cuff pressure in the cuff due to those compressive forces alone is presented.
Abstract: A method of determining the pressure applied to a limb by an inflatable garment by placing a flexible pressurizable cuff between the garment and the limb to receive the compressive garment forces and then determining the pressure in the cuff due to those compressive forces alone. The cuff pressure component due to compression of the garment is determined by extra-polating from a plot of cuff pressure versus bias pressure. The bias pressure is required to obtain an accurate reading of cuff pressure and is eliminated as a component in determining the garment pressure by means of the extrapolation. A preferred transducer for converting cuff pressure to electrical signals employs a manometer tube extending between two plates of a capacitor.

44 citations


Journal ArticleDOI
TL;DR: An implantable variable resistance pressure gauge has been constructed from a conductive elastomere in the form of a scleral buckle which is suitable for recording intraocular pressure in vivo continuously over an indefinite period of time.
Abstract: An implantable variable resistance pressure gauge has been constructed from a conductive elastomere in the form of a scleral buckle which is suitable for recording intraocular pressure in vivo continuously over an indefinite period of time. The similarity of the pressure transducer to the standard scleral buckles used to reduce retinal detachments suggests that it will be tolerated over a period of years without significant effect on intraocular pressure. The electrical output from these pressure gauges appears to be both well defined and of sufficient magnitude to operate a valve to control intraocular pressure.

37 citations


Journal ArticleDOI
TL;DR: In this paper, the applicability of a microwave Doppler shift technique for directly determining propellant response functions over the desired frequency range is presented. But the results of an investigation are presented on the applicable of a microwavesign technique.
Abstract: The results of an investigation are presented on the applicability of a microwave Doppler shift technique for directly determining propellant response functions over the desired frequency range. The investigation consisted of three phases. In Phase 1 the validity of the technique was established by comparing measured pressure-coupled response function data to existing data from T-burners and rotating valve tests. In Phase 2 a new microwave burner-pressure modulation system capable of achieving frequencies and mean chamber pressures of at least 1500 Hz and 10.5 MPa (1500 psia), respectively, was developed. During Phase 3 test firings are being carried out to define the frequency limit, response function resolution, and precision of the new design.

28 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used the spectrum from a neon light to provide an internal wavelength standard during the measurement of the ruby spectrum, which eliminated the stripchart error, a potential source of large errors.
Abstract: When measuring pressures in the diamond anvil cell, undersirable line broadening and wavelength shifts result if small ruby crystals are used in a calibration system designed for large ones. These effects can be eliminated through the proper choice of objective lens, condensing lens, and slit system. Using such a system, we obtained excellent results with samples as small as 30 μm. In addition, we describe the use of the spectrum from a neon light to provide an internal wavelength standard during the measurement of the ruby spectrum. This eliminates the stripchart ‐ wavelength drive synchronization error, a potential source of large errors. A calculation of the estimated error associated with a typical pressure measurement indicates that, for small ruby samples, the pressure can be determined with a precision of ±0.5 kbar.

25 citations


Patent
04 Jun 1980
TL;DR: In this article, a solution of a liquid in a gas is transported in a first conduit from a low elevation to a high elevation, whereby the absolute pressure and the temperature of the solution change.
Abstract: A method and system of energy conversion derived from temperature and pressure differentials that may be provided between high and low elevations. A solution of a liquid in a gas is transported in a first conduit from a low elevation to a high elevation, whereby the absolute pressure and the temperature of the solution change. Some of the liquid separates out of the solution in the first conduit in the form of particles suspended in the remaining solution to create a mixture of the separated particles and the remaining solution in the first conduit as a result of the changes in absolute pressure and temperature, so that at any particular position in the first conduit where the separation takes place, the average proportional density of the mixture after the separation has taken place is decreased in relation to the density of the solution at such position prior to the separation taking place. The mixture is transported into a separation chamber at the high elevation in response to pressure differentials created by the decrease in average proportional density of the mixture in the first conduit. At least of portion of the suspended particles are separated from the mixture in the separation chamber to create a separated liquid, and a dried gas; and the separated liquid is transported through a second conduit to a transducer at a lower elevation than the high elevation. The transducer converts the pressure and motion of the transported separated liquid into a useful form of energy.

Patent
15 May 1980
TL;DR: In this paper, a process and apparatus for measuring the catheter fluid pressure of a patient is described, where a pressure transducer is used to convert the pressure into an electrical signal and a pressure indicator indicates the pressure corresponding to the electrical signal.
Abstract: A process and apparatus for measuring the catheter fluid pressure of a patient wherein a pressure transducer is used to convert the pressure into an electrical signal and a pressure indicator indicates the pressure corresponding to the electrical signal. A turnable active filter is disposed in the signal path between the transducer and the pressure indicator and the frequency parameters of the filter are adapted to that of the catheter in real time.

Journal ArticleDOI
TL;DR: In this article, the authors present dimensionless solutions for pore-water pressure responses for different electrode geometry and drainage conditions at the electrodes, so that measurement of pore water pressure responses at the electrode as a function of time for a relatively short period should enable computation of the coefficient of consolidation, c sub v and the ratio of the coefficients of electro-osmotic conductivity to hydraulic conductivity,k sub e/k sub h.
Abstract: The basic concept involves incorporation of a simple electrode system in a field probe, measurement of pore-water pressure changes at the electrodes as a function of time in response to a DC field, and measurement of the electro-osmotic flow rate of water. Mathematical solutions for pore-water pressure responses for different electrode geometry and drainage conditions at the electrodes are presented dimensionless form, so that measurement of pore-water pressure responses at the electrodes as a function of time for a relatively short period should enable computation of the coefficient of consolidation, c sub v and the ratio of the coefficient of electro-osmotic conductivity to hydraulic conductivity,k sub e/k sub h. Unique solutions for k sub e, k sub h, and the coefficient of volume change, m sub v, are shown to be possible using measured electro-osmotic flow rate in a closed loop between electrodes and comparison with theory. (AUTHORS)

Patent
26 Sep 1980
TL;DR: In this paper, a linearly polarized beam is phase shifted in a birefringent plate, then passed through a photoelastic pressure sensor and a polarization analyzer.
Abstract: An apparatus for pressure measurement employs fiber optics to transport a broadband beam light to and from a remote electrically passive sensing head. In the sensing head, a linearly polarized beam is phase shifted in a birefringent plate, then passed through a photoelastic pressure sensor and a polarization analyzer. The wavelength for which the output light has an intensity minimum is a measure of the applied pressure.

Journal ArticleDOI
TL;DR: In this paper, the relationship between hole pressure and the first normal-stress difference for a range of Reynolds numbers where inertial effects are not negligible was investigated. But the results were restricted to Poiseuille flow of a second-order fluid over a slot cut into one wall of a straight channel.
Abstract: Liquid-filled holes used for pressure measurements of visco-elastic liquids give rise to systematic hole pressure ‘errors’Tanner andPipkin have presented an analysis for flows of a second-order fluid in which they derive a simple relation between the first normal-stress difference and the hole pressure for flow situations where Reynolds numbers are very small Implicit in the analysis is the assumption that the streamlines are symmetric about the hole center line In this paper, using a numerical solution, we investigate the relationship between the hole pressure and the first normalstress difference for a range of Reynolds numbers where inertial effects are not negligible The ratio of hole pressure to first normal-stress difference is found to vary from 025 to 016 as the Reynolds number is varied from 1 to 10 Streamline patterns are presented for Poiseuille flow of a second-order fluid over a slot cut into one wall of an otherwise straight channel Various geometries are considered The results naturally include those for an incompressible Newtonian liquid at non-zero Reynolds numbers

Patent
24 Mar 1980
TL;DR: A pressure measurement transducer for laminar pressure distributions consists essentially of an elastic material, whose electrical conductivity increases under the effects of pressure and electrodes attached to either side of the material.
Abstract: A pressure measurement transducer for laminar pressure distributions consists essentially of an elastic material, whose electrical conductivity increases under the effects of pressure and electrodes attached to either side of the material. It is simply constructed and enables measurement over large surfaces economically and with few connections. The elastic material is in the form of a mat (3) of size appropriate to the measurement surface. Two opposing electrodes are placed one on either side of the mat for each measurement point. The electrodes for each point of measurement consist of crossing points of conducting paths (1,2) running longitudinally on one side and transversally on the other. The thickness of the mat is between 0.1 and 5 mm., and pref. between 0.5 and 1 mm.

Journal ArticleDOI
TL;DR: In this paper, the melting point at 0 °C was determined for pressures up to 1200 MPa and the experimental data were fitted to a third order polynomial; this equation fits the melting line data much more closely than the Simon type heretofore recommended.
Abstract: The mercury melting line has been determined for pressures up to 1200 MPa. The change of electrical resistance in the mercury sample was used for detecting the equilibrium between the solid and liquid phases. Pressure measurements were made with highly stable manganin gages calibrated against two controlled clearance piston gages. Temperature measurements were made in the constant temperature bath by means of platinum resistance thermometry. Systematic errors in pressure and temperature were evaluated for all the measurements as well as the scatter due to the resolution of the equilibrium determination between the two phases of mercury. The mercury melting point at 0 °C is 756.84 ± 0.16 MPa which is in close agreement with the value obtained by Dadson and Greig. The experimental results are compared with previous melting lines. There are systematic differences when compared to Bogdanov's equation up to 1200 MPa but there is very close agreement with recent data obtained by Houck and Morris over the pressure range they covered. The experimental data were fitted to a third order polynomial; this equation fits the melting line data much more closely than the Simon type heretofore recommended and can be used up to 1200 MPa to increase the accuracy of a practical pressure scale based on the melting line of mercury.

Journal ArticleDOI
TL;DR: In this article, the design and performance of a compact, high precision, capacitive, vapor pressure gauge was described using a thin electrodeposited copper diaphragm.
Abstract: The design and performance of a compact, high precision, capacitive, vapor‐pressure gauge is described. The gauge was constructed using a thin electrodeposited copper diaphragm.

Journal ArticleDOI
TL;DR: In this article, a fast valve which can inject gas pulses with durations from 25 to 400 μs into a vacuum system is described, and a pressure rise time of ∼ 0.5 Torr/μs has been determined at the valve opening.
Abstract: A fast valve which can inject gas pulses with durations from 25 to 400 μs into a vacuum system is described. Quantities up to 5 Torr l can be injected. A pressure rise time of ∼0.5 Torr/μs has been determined at the valve opening. A fast opening time is achieved by having a magnetically accelerated ring collide with a disk which is used as a vacuum seal. Gas pulse parameters have been measured with a fast ionization gauge.

Patent
05 Jun 1980
TL;DR: In this article, a pressure gauge is constructed in which the socket and at least a portion of the movement for driving the pointer are initially formed integral of a molded polymeric plastic composition.
Abstract: Method and apparatus for constructing a pressure gauge in which the socket and at least a portion of the movement for driving the pointer are initially formed integral of a molded polymeric plastic composition.

Patent
08 Jul 1980
TL;DR: In this paper, the authors measured the pressure in the measuring tank under various conditions and determined the rate of leak from a test object, using a measuring tank, a pressure gauge, a vacuum pump and a device for removing vapor from the measurement tank.
Abstract: In measuring the rate of leak from a test object, a conduit system including branch lines interconnects the test object with a measuring tank, a pressure gauge, a vacuum pump and a device for removing vapor from the measuring tank. Valves in the conduit system permit the various parts to be selectively interconnected or separated. By measuring the pressure in the measuring tank under various conditions it is possible to determine the rate of leak.

Patent
08 Jan 1980
TL;DR: An improved pressure/temperature probe whose accuracy will not be affected by the pressures and temperatures to which it is subject or by the resistance of the connecting cables is presented in this paper, which includes a separate pressure transducer and temperature transducers which are connected in series to a constant current source.
Abstract: An improved pressure/temperature probe whose accuracy will not be affected by the pressures and temperatures to which it is subject or by the resistance of the connecting cables. The probe includes a separate pressure transducer and temperature transducer which are connected in series to a constant current source. In addition to the pressure reading taken by the pressure probe, a temperature reading of the pressure probe is derived from the pressure probe. This temperature reading provides the actual temperature of the pressure probe and permits highly accurate temperature correction. The pressure probe is constructed and arranged so as to have a high thermal time constant while the temperature probe is constructed and arranged to have a low thermal time constant.

Journal ArticleDOI
TL;DR: A simple optical cell for high-pressure studies of liquids and solutions to 5 kbar, and used in the 0-60 ˚C temperature range, is described in this paper, where convenient methods for pressure measurement, temperature control and isolation of the sample from the pressure fluid are presented.
Abstract: A simple optical cell for high‐pressure studies of liquids and solutions to 5 kbar, and used in the 0–60 °C temperature range, is described. Convenient methods for pressure measurement, temperature control and isolation of the sample from the pressure fluid are presented. This system is used to detect liquid‐solid phase transitions in benzene and trans‐decalin by scattered light measurements.

Journal ArticleDOI
TL;DR: In this paper, a pressure jump relaxation technique is described to study fast reactions in solution under pressure up to 15 kbar and the mechanical relaxation time of the instrument is 05 ms.
Abstract: A pressure jump relaxation technique is described to study fast reactions in solution under pressure up to 15 kbar The mechanical relaxation time of the instrument is 05 ms

Patent
09 May 1980
TL;DR: In this article, a gauged pressure sensitive device is applied to a muscle while pressure to the muscle is gradually increased to a point just short of the muscle breaking point, the applied pressure at this pre-breaking point is measured to provide an objective measure of muscle strength.
Abstract: A technique and apparatus for muscle strength testing. A gauged pressure sensitive device is applied to the muscle while pressure to the muscle is gradually increased to a point just short of the muscle breaking point. The applied pressure at this pre-breaking point is measured to provide an objective measure of muscle strength. The gauged pressure sensitive device may be an air bag connected to a pressure gauge, the air bag being placed between the pressure source and the muscle, thereby allowing the applied pressure to be measured.

Patent
02 Jan 1980
TL;DR: In this article, it has been found that if the cuff is properly designed, pressure corresponds very closely to diastolic blood pressure measured at the brachial artery with a standard arm cuff using a stethoscope.
Abstract: A cuff having a casing and an inflatable diaphragm is slipped over a portion of the body of the user, preferably a thumb or finger. The diaphragm is connected by a conduit to a pressure source and to a manometer. A preferred pressure source is as a cylinder similar to that of a syringe. A plunger in the syringe inflates the diaphragm. The pressure in the cuff is slowly increased until the subject first notices a slight localized throbbing sensation within the artery inside the cuff, the pressure corresponding to diastolic blood pressure, and this pressure is read. Use of a transducer or even a stethoscope is unnecessary. Further, it has been found that if the cuff is properly designed, pressure corresponds very closely to diastolic blood pressure measured at the brachial artery with a standard arm cuff using a stethoscope. For other cuff structures the pressure in the cuff may be calibrated to that in an arm by using these subjective sensations. The pressure is increased further until the subject senses the disappearance of the localized throbbing within the artery, a condition which corresponds to systolic blood pressure, such pressure again being noted.

Patent
24 Nov 1980
TL;DR: In this article, an apparatus and method for reducing the amount of gas consumed during welding operations is described, where a source of relatively high pressure inert gas is supplied to an individual welding station.
Abstract: An apparatus and method is described for reducing the amount of gas consumed during welding operations. A source of relatively high pressure inert gas is supplied to an individual welding station. At the station is a pressure regulator for substantially reducing the gas pressure and having an inlet in communication with the higher pressure gas supply and an outlet in communication with the inlet of a surge tank. The outlet of the surge tank is in communication with the welding apparatus. The volume of the surge tank is sufficient, and the apparatus functions, to supply a flow of gas, to the welding apparatus at the reduced pressure during transient when the welding apparatus is turned on, greater than that supplied during steady state conditions. In one embodiment, the apparatus of the invention includes a pressure gauge, pressure regulator, and surge tank within a sealed housing with the face of the pressure gauge positioned at one side thereof and visible externally of the housing. Access to the regulator for adjustment thereof is limited by means of a locked cover which, when opened, allows adjustment of the regulator through an opening with a suitable tool.

Journal ArticleDOI
TL;DR: In this article, a laser anemometer and high-response pressure probes were used to study the complex flow in a transonic axial compressor rotor at 20,000 rpm.
Abstract: A laser anemometer and high-response pressure probes were used to study in detail the complex flow in a transonic axial compressor rotor at 20,000 rpm. The investigation was aimed at providing complete data on the internal flowfield at the design speed for peak efficiency, near compressor surge, and choke. Useful information is presented on flow vectors, three-dimensional shock waves, oscillating total pressures, blade wakes, and losses downstream of the rotor.

Journal ArticleDOI
TL;DR: A technique for simultaneously retrieving pressure and temperature profiles using satellite-based narrow-band radiometer measurements of absorption in the CO(2) 4.3-microm band is described.
Abstract: A technique for simultaneously retrieving pressure and temperature profiles using satellite-based narrowband radiometer measurements of absorption in the CO2 4.3-micron band is described. Pressure and temperature profiles for earth's upper atmosphere on a global scale can be obtained with errors less than 3% and 3 K, respectively. The p-T information can be used not only for improving the accuracy of inverted gas concentrations in the same absorption experiment but also for investigating the upper atmosphere circulation.

Patent
10 May 1980
TL;DR: In this paper, the authors proposed to secure the measurement of the voltage to be detected with the absolute pressure by detecting the differential voltage between two units of the diaphragm using the semiconductor distortion gauge, one of which is made vacuum with the other detected to the atmosphere of the detected pressure.
Abstract: PURPOSE:To secure the measurement of the voltage to be detected with the absolute pressure by detecting the differential voltage between two units of the diaphragm using the semiconductor distortion gauge, one of which is made vacuum with the other detected to the atmosphere of the detected pressure. CONSTITUTION:Pellet 1 is joined onto the flat surface of Pyrex glass 2 via the anode junction method, and then diaphragm rooms 13a and 13b with semiconductor distortion gauges 11a and 11b formed on each upper surface are formed. And room 13a is kept under the vacuum state; while room 13b is connected to measured pressure Pi via hole 16 and pipe 4. On the other hand, gauges 11a and 11b are connected to electrodes 8a and 8b via resistance draw-around parts 12a and 12b, and electrodes 8a and 8b are connected to thick-film conductors 9a and 9b via lead wires 10a and 10b. And conductors 9a and 9b are connected to terminals 3a and 3b. The upper parts of these joint areas are covered with cap 15 containing hole 18 to introduce atmospheric pressure Ph to form a pressure sensor.