JPH02268230A - Pressure sensor and gas flowmeter using it - Google Patents

Abstract

PURPOSE:To remove noise components automatically and to make it possible to detect pressure highly accurately by applying a first pressure on one surface of each of two piezoelectric elements, applying a second pressure on the other surfaces of the elements, and obtaining the sum of the outputs of both elements. CONSTITUTION:A fluid pressure P1 from one outlet port of the element part of a flowmeter is introduced into one surface of each of piezoelectric elements 2 and 3 through a nozzle 29 and an introducing path 33. A pressure P2 from another outlet port is introduced to the other surfaces of the elements 2 and 3 through a nozzle 30 and an introducing path 36. Therefore, the pressures P1 and P2 are alternately applied to the elements 2 and 3, and the potential differences due to deformation are generated. The sum of the outputs of the elements 2 and 3 are sent into an amplifier 5, and the detected pressure fluctuation signal is outputted. Noise components due to pressure fluctuation and temperature fluctuation which are generated in the entire fluid are removed with the elements themselves. When the sum of the outputs is obtained, the sensitivity twice between than before is obtained. Thus, the highly accurate pressure detection can be performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is capable of detecting even minute pressure fluctuations, and detects the ratio of noise caused by vibration to output power (hereinafter referred to as SN ratio).
This invention relates to a pressure sensor ν that uses a piezoelectric element and has a high level of pressure and is optimal for use in a gas flow meter, etc., and a gas flow meter that uses the pressure sensor.

[Prior Art] Various types of pressure sensors have been known, such as a manometer, a Bourdon tube type, a capacitance type, a differential transformer type, and a body diaphragm type. These are-
They are used to detect large pressures within the shell, and are often large, complex, and expensive. Furthermore, since the pressure of the object to be detected is large, usually no consideration is given to noise caused by disturbances during imaging. Therefore, it cannot be used in applications that require detection of even minute pressures, or even if it is used, the noise ratio will be high and high-precision detection will be difficult.

Applications that are preferable to the extent that they can detect even minute pressures include, for example, full-bucks flowmeters and Karman vortex flowmeters that detect the flow rate of fluid through pressure detection (for example, JP-A-60-187814, JP-A-57-54809). Publication No.). In addition, a pressure sensor using a film-like piezoelectric element is known as a pressure sensor that is optimal for use in these flowmeters and can detect even minute pressure fluctuations (for example, in Japanese Patent Application Laid-Open No.
7-54809). As disclosed in Japanese Patent Application Laid-open No. 60-187814, the above-mentioned full-width flowmeter uses the Coanda effect to alternately direct the main stream of the fluid ejected from the ejection nozzle to a pair of partition walls in the flowmeter element part. A pressure sensor detects the pressure fluctuation that occurs when the flow changes, and the flow rate of the fluid is detected at the frequency of the pressure fluctuation that corresponds to the flow rate. As disclosed in Japanese Unexamined Patent Application Publication No. 57-54809, the Karman vortex flowmeter intermittently generates Karman vortices in the circulating fluid using a vortex generator provided in the flowmeter element. A pressure sensor detects the pressure fluctuation that occurs when the fluid passes through the fluid, and the flow rate of the fluid is detected by the number of Karman vortices generated depending on the flow rate.

It is desirable for a pressure sensor used in such a flow meter to have high sensitivity, that is, to be able to detect even the weakest pressure changes and pressure changes over a wide range of frequencies. must be made quite high.

In order to increase the signal-to-noise ratio, a pressure sensor disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 57-54809 is known as a pressure sensor that takes particular measures against vibration.

This pressure sensor uses a polymer piezoelectric material as a piezoelectric element, and two piezoelectric elements are attached like a bimorph type on each side of a lever that is branched into one for pressure detection and one for noise component correction. The element covers its surroundings and separates the pressure detection piezoelectric element from the atmosphere. Since the imaging noise component is applied to both the piezoelectric element for pressure detection and the piezoelectric element for noise component correction, the principle can be calculated by subtracting the signal from the piezoelectric element for noise component correction from the output signal from the piezoelectric element for pressure detection. In other words, noise caused by photographing is removed.

This method is the most common method called a differential type that corrects noise components other than those to be detected.

[Problems to be Solved by the Invention] However, in the structure of the pressure sensor described above, the piezoelectric elements for noise component correction and pressure detection are housed in locations with different structures and atmospheres. There is a problem in that the imaging and temperature propagation methods are different, and noise components cannot be removed accurately and sufficiently. In particular, since the piezoelectric element for noise component correction is isolated, it is difficult to remove noise related to fluid temperature fluctuations and noise components propagated throughout the fluid from a throttle valve or the like. In addition, since the piezoelectric element, which is mechanically weak, is exposed in the fluid flow path, foreign matter in the fluid easily adheres to the piezoelectric element, and the piezoelectric element may be damaged or damaged during the manufacturing, handling, and implementation processes. There is a problem that sensitivity tends to decrease.

The purpose of the present invention is to provide a high-speed sensor that can accurately correct not only noise caused by vibrations, but also all kinds of noise such as temperature fluctuations and miscellaneous noise propagated throughout the fluid, has an extremely high signal-to-noise ratio, and can detect even the slightest pressure fluctuations. The object of the present invention is to provide a pressure sensor that is sensitive, has a simple structure, and is highly reliable.

Another object of the present invention is to provide a highly accurate gas flowmeter using the above-mentioned high-performance pressure sensor.

[Means for Solving the Problems] The pressure sensor of the present invention that meets the above object is a pressure sensor that is configured by providing electrode layers on both sides of a membrane piezoelectric material and has two piezoelectric elements stretched in a planar manner. and an amplifier for amplifying the sum of the outputs of both piezoelectric elements, and the two piezoelectric elements are arranged so that both surfaces face in the same direction and the faces in the same direction have the same polarization. , the pressure detection section is provided with two inlet nozzles for introducing fluid pressure, and one of the inlet nozzles connects one surface of one piezoelectric element to the surface through a first fluid pressure introduction path. The other inlet nozzle communicates with one surface of the other piezoelectric element having a different polarization polarity, and the other inlet nozzle communicates with the other surface of the one piezoelectric element and the other piezoelectric element through a second fluid pressure introducing path. the one inlet nozzle and the first fluid pressure introduction path and the volume of the other inlet nozzle and the second fluid pressure introduction path in the pressure detection section are substantially equal to each other. .

The fluid to be measured by this pressure sensor can be both gas and liquid.

This pressure sensor is an optimal pressure sensor for use in gas flowmeters such as full-volume flowmeters and Karman vortex flowmeters, and the two inlet nozzles of the pressure sensor are It is connected to a flow meter element that generates pressure fluctuations in accordance with the flow rate of fluid flowing. In connection, it is preferable that the lengths of the two pressure guiding tubes be equal.

In this invention, the piezoelectric body used in the piezoelectric element is composed of a ceramic piezoelectric body represented by lead zirconium titanate (PZT), a polymer piezoelectric body, or a composite piezoelectric body in which PZT powder is mixed into a polymer. .

The polymer piezoelectric material is, for example, polyvinylidene fluoride and 3
Composed of a copolymer of fluorinated ethylene.

The film thickness is 10% in terms of sensitivity, strength, and ease of handling.
It is preferable to select from the range of ~100 μTrL. The film thickness can be easily and precisely controlled using well-known film forming techniques.

The electrode layers provided on both sides of the piezoelectric body are made of a material such as aluminum, copper, gold, nickel, or palladium, and are formed on the surfaces of the piezoelectric body by a metallizing method such as vapor deposition, sputtering, or plating.

It is preferable that each fluid pressure introducing path has a bent structure or a constricted structure so that the introduced fluid does not directly hit the piezoelectric element surface.

The polarization of the piezoelectric element is imparted during the process of manufacturing the piezoelectric body, and a well-known method can be applied to this imparting. The piezoelectric elements are arranged in the pressure detection section so that both surfaces face in the same direction, but they may be arranged in parallel or in series, as shown in the embodiments described below.

[Function] In the above pressure sensor, the pressure of the fluid taken out from a certain pressure outlet is simultaneously applied to one side of both piezoelectric elements through one inlet nozzle and the first fluid pressure introduction path. The pressure of the same fluid introduced and taken out from another pressure outlet is introduced to the other side of both piezoelectric elements through the other inlet nozzle and the second fluid pressure introduction path, and due to the differential pressure between the two sides. The resulting deformation of each piezoelectric element causes spontaneous polarization in the piezoelectric body, and the resulting potential difference between the two surfaces of the piezoelectric body is outputted via the electrode layer. Both piezoelectric elements are connected to an amplifier so that the sum of their outputs is input, and the amplifier amplifies and outputs the detected output from which the noise component has been subtracted.

Regarding the removal of noise components, this pressure sensor has (a) a structure that simultaneously guides fluid pressure to both sides of the piezoelectric element and detects the differential pressure; (2) substantially the same structure and the same atmosphere. By arranging two piezoelectric elements in parallel, all kinds of noise components are removed very precisely.

First, since fluid pressure is simultaneously introduced to both sides of the - piezoelectric elements, by connecting two inlet nozzles to different measurement positions for the same fluid to be measured, pressure fluctuations (noise components) of the entire fluid can be reduced. >, it is possible to simultaneously guide both sides of the piezoelectric element while guiding local pressure fluctuations corresponding to the measurement position from one path.The pressure fluctuations of the entire fluid are simultaneously transmitted to both sides of the two piezoelectric elements. Therefore, the two piezoelectric elements undergo the same deformation due to this fluctuation component, and the potential difference caused by the pressure fluctuation of the entire fluid is erased by the piezoelectric element itself, and the potential difference and the number of times the pressure difference occurs corresponds to the differential pressure component between the two surfaces. A signal with a corresponding frequency is output.The same applies to temperature fluctuations in the entire fluid, and temperature fluctuations are simultaneously transmitted to both sides of each piezoelectric element, so this fluctuation component causes the two piezoelectric elements to Noise components due to temperature fluctuations are automatically canceled by the piezoelectric element itself through the same deformation.

Therefore, by connecting this pressure sensor to the flowmeter element of a fluidics flowmeter or Karman vortex flowmeter, it is possible to automatically eliminate fluctuation components of the entire fluid that can become noise, while also Only the pressure fluctuation component caused by the vortex can be detected with high precision.

Then, pressure is introduced from the same path to the surfaces of the piezoelectric elements with different polarization polarities, which are arranged so that the polarization polarities are in the same direction, so that the deformation directions of both piezoelectric elements are in opposite phases. By outputting as the sum of both, an output signal from which noise components caused by fluctuations in the entire fluid have been removed can be obtained with twice as high sensitivity as in the case of a single piezoelectric element.

Further, noise components caused by imaging the entire pressure sensor and flowmeter are almost completely removed by the structure in which two piezoelectric elements are arranged side by side. Since the two piezoelectric elements are arranged facing the same direction, both piezoelectric elements vibrate at the same time and under the same conditions.

As mentioned above, both piezoelectric elements simultaneously detect the pressure to be measured in opposite phases, but when vibration is applied to both piezoelectric elements, the vibration causes one piezoelectric element to deform in a direction that reduces the detected pressure. If a force is applied to the piezoelectric element, the piezoelectric element being used will always experience a deforming force of the same magnitude in the direction of increasing the detected pressure. Since the output from the pressure detection section is taken as the sum of the detection outputs of opposite phases of both piezoelectric elements, the noise component accompanying the above-mentioned imaging is automatically erased, and only the pressure to be measured is detected. , as described above, is detected with twice the sensitivity.

[Embodiments] Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a pressure sensor according to one embodiment of the present invention, FIG. 2 shows the configuration of a piezoelectric element, and FIG. 3 shows a pressure sensor according to another embodiment in which the piezoelectric element is arranged differently. , 4th
The figure shows an example in which the pressure sensor is used in a full-volume flowmeter, and FIG. 5 shows an example in which it is used in a Karman vortex flowmeter.

In FIG. 1, reference numeral 1 indicates a pressure sensor body according to the present invention, and the pressure sensor 1 includes a pressure detection section 4 having two piezoelectric elements 2.3, and a pressure detection section 4 having two piezoelectric elements 2.3. It consists of an amplifier 5 that amplifies and outputs the amplified signal. The two piezoelectric elements 2.3 are stretched in a planar and deformable manner. As shown in an enlarged view in FIG. 2, the piezoelectric element 2.3 has a film-like piezoelectric body 6.7 made of a piezoelectric material coated with aluminum, copper, gold, nickel, palladium, etc., which has good corrosion resistance, on both sides. Electrode layers 8.9 and 10.11 made of metal are formed by vapor deposition, sputtering, plating, or the like.

Although the planar shape of these two piezoelectric elements 2.3 is circular in this embodiment, it is not limited to this. Piezoelectric body6.
Although various piezoelectric materials can be used as the material of 7, as in the above (e), in this example, a polymeric piezoelectric material made of a copolymer of polynylidene fluoride and ethylene trifluoride was used.

The thickness of the polymer piezoelectric film is suitably 10 to 100 μTn for a gas pressure sensor from the viewpoint of sensitivity, strength, and ease of handling, and in this example, the thickness was 15 μTn. However, the pressure sensor according to the present invention includes, of course, one for use with liquids, and the thickness of the polymer piezoelectric film and the structure of the electrode portions described below may be appropriately selected depending on the liquid to be measured. Although not shown, depending on the fluid to be measured and the magnitude of pressure fluctuation, it is also possible to attach a polymer piezoelectric film to a M metal or rubber diaphragm and treat it as a polymer piezoelectric film with reinforced suspension. It is.

The peripheral edge of the piezoelectric element 2.3 is connected to the holders 12.13 and 14.1 from both sides via the electrode layers 8.9 and 10.11.
It is held by 15. The piezoelectric elements 2.3 held in each holder are arranged in parallel so that both surfaces face in the same direction, and are arranged so that the faces in the same direction have the same polarity. . Boulder 12.
13.14.15, the whole or the surface of which is made of a conductive material such as brass, and each electrode layer 8.9.10.1
1 and function as output terminals of each piezoelectric element.

The holders 12 and 13 and 14 and 15 are insulated by piezoelectric bodies 6.7.

The boulders 12, 13, 14, 15 are formed in substantially the same shape to improve the S/N ratio, and pressure chambers 16, 17, 18, 19 are formed on both sides of the piezoelectric element 2.3. . Each holder 12.13.14.15 has an aperture 20 in the center.
．． 21, 22, 23, and the pressure chambers 16, 17, 18, 19 are connected to the corresponding front chambers 2 through the throttles.
4.25.26.27.

The pressure detection unit 4 is surrounded by an MB2 formed with a base 28 that accommodates and holds the holders 12.13 and 14.15, and two inlet nozzles 29.30 that introduce fluid pressure, and both are bonded together. It is bonded with adhesive to prevent internal leakage. The substrate 28 and the lid 31 may be made of engineering plastics such as epoxy resin or polyacetal resin that have good insulation and high mechanical strength, and in this embodiment, they are made of phenol resin.

The inlet nozzle 29 has a front chamber 24, an aperture 20. It communicates with one surface of the piezoelectric element 2 through the pressure chamber 16, and communicates with the other surface of the piezoelectric element 3 with different polarization through the front chamber 24, the communication path 32, the front chamber 27, the diaphragm 23, and the pressure chamber 19. is connected to. Therefore, a series of these paths constitutes the first fluid pressure introduction path 33 according to the present invention. The inlet nozzle 30 communicates with the other surface of the piezoelectric element 3 via the volume adjustment chamber 34, the front chamber 26, the baffle 22, and the pressure chamber 18, and
It communicates with the other surface of the piezoelectric element 2 via the volume adjustment chamber 34, the communication path 35, the front chamber 25, the diaphragm 21, and the pressure chamber 17. Therefore, this series of paths constitutes the second fluid pressure introduction path 36.

The volumes of the inlet nozzle 29 and the first fluid pressure introduction path 33 in the pressure detection unit 4 are made equal to the volumes of the inlet nozzle 30 and the second fluid pressure introduction path 36, and this volume adjustment is performed by the volume adjustment chamber 34. It is being carried out in

In the device shown in FIG. 1, a small hole is made in the board 28 and each lead wire 37, 38, 39 is passed through, and one end of the lead wire 37 is connected to the holder 13 by soldering or the like, and the other end is connected to the common power source. It is connected. The lead wire 38 is connected to the holder 12
and the holder 14 are connected. The lead wire 39 has one end connected to the holder 15 and the other end connected to the amplifier 5. The other input terminal of the amplifier 5 is connected to a common power supply via a lead wire 40. Reference numeral 41 indicates an output terminal from the amplifier 5.

The pressure detection section 4 and the amplifier 5 are housed in a shield case 42 made of metal or the like, which is a good electrical conductor, so that they are not affected by electromagnetic induction noise from a commercial power source. In addition, the case 4 is filled with epoxy filler 43 to prevent noise caused by the movement of wiring materials and electronic components.
The pressure sensor 1 is constructed by fixing the two and leaving no extra gaps inside. Note that from the viewpoint of noise removal, it is preferable to use a shielded wire for the output terminal 41.

The operation of the pressure sensor 1 configured as described above will be explained below along with the configuration and operation when the pressure sensor 1 is used in a full-volume gas flowmeter.

FIG. 4 shows a configuration in which the pressure sensor 1 is applied to a fluidic flowmeter, and 50 in the figure indicates a flowmeter element section in the fluidic flowmeter. The gas to be measured flows through the flowmeter element section 50 in the direction of the arrow. 5
Reference numeral 1 denotes a flow path reduction portion, from which a jet nozzle 52 at its tip ejects a jet stream with an increased flow velocity. Due to the Coanda effect, the main stream of the jet flows through the pair of partition walls 5 that constitute the enlarged flow path section 53.
4.55, the wall flow is redirected and directed from the control nozzle 56 (or 57) perpendicularly to the jet from the jet nozzle 52, and from the jet nozzle 52. A force is applied so that the jet flows along the other partition wall. As this is repeated, the gas flows alternately along the partition walls 54 and 55, and pressure fluctuations occur within the flowmeter element 50 in response to this flow change. Since the frequency of the above-mentioned flow change is proportional to the gas flow rate, the flow rate can be measured by detecting the frequency of pressure fluctuation. Note that 58 in the figure is a target for efficiently directing the jet toward one of the partition walls.

In the flowmeter element section 50 as described above, an internal pressure outlet 59.
60 are provided, and the internal pressure outlets 59, 60 are respectively connected to the inlet nozzles 29, 30 of the pressure sensor "J1" via pressure guiding tubes 61, 62 of equal length.

When the flow switches to the internal pressure outlet 59 inside the flow meter element 50, the fluid pressure near the internal pressure outlet 59 becomes higher than that near the internal pressure outlet 60, and conversely, the flow changes to the internal pressure outlet 60.
When switching to the side, the fluid pressure near the internal pressure outlet 60 becomes higher. The pressure (Pl) at this internal pressure outlet 59 is
The pressure is introduced into one surface of the piezoelectric element 2 and one surface of the piezoelectric element 3 through the pressure guiding tube 61, the inlet nozzle 29, and the first fluid pressure introduction path 33, and the pressure (P2) at the internal pressure outlet 60 is , pressure guiding tube 62, inlet nozzle 30,
The fluid pressure is introduced into the other surface of the piezoelectric element 2 and the other surface of the piezoelectric element 3 via the second fluid pressure introduction path 36 . Pressures Pl and P2 are applied alternately to both piezoelectric elements 2.3, and the piezoelectric elements are deformed by the pressure fluctuations, causing spontaneous polarization in the piezoelectric body, thereby creating a potential difference between both sides of the piezoelectric body itself. The sum of the outputs of both piezoelectric elements 2.3 is sent to the amplifier 5, where it is amplified and taken out from the output terminal 41 as a pressure fluctuation detection signal.

In the above detection, fluid pressure is simultaneously introduced to both sides of the piezoelectric element, and the differential pressure is detected by each piezoelectric element. Therefore, noise components due to pressure fluctuations and temperature fluctuations occurring in the entire fluid are Since the noise component is applied to both sides of the piezoelectric element at the same time, the piezoelectric element undergoes the same deformation due to the noise component, and the noise component is automatically canceled in the piezoelectric element itself. Then, the detection output of the pressure to be measured with the noise removed is taken out as the sum of the outputs from both piezoelectric elements 2.3, so compared to the case of - piezoelectric elements 2.3,
It is extracted with twice the sensitivity, allowing extremely high-precision detection.

Furthermore, when imaging is applied as a disturbance, the additional force acts on both piezoelectric elements 2.3 simultaneously as a force in the same direction.

Since the directions of deformation of the piezoelectric elements 2.3 due to the introduction of fluid pressure are opposite to each other, the amount of deformation of the two piezoelectric elements due to the above excitation force is as follows with respect to the direction of increasing and decreasing deformation:
Same direction.

Therefore, the increase/decrease in output due to this noise component is automatically canceled at the stage where the outputs of both piezoelectric elements 2.3 are shored.

The pressure sensor described above can also have a structure as shown in FIG. 3, and the pressure sensor of the present invention is not limited to a full-volume flowmeter, but can also be applied to other flowmeters such as a Karman eddy current meter as shown in FIG. Can be used.

In the pressure sensor 70 shown in FIG. 3, two piezoelectric elements 71 and 72 are arranged in series within the pressure detection section 73,
Both surfaces are arranged so that they each face the same direction, and the surfaces facing the same direction have the same polarization. The volumes of the inlet nozzle 74 and the first fluid pressure introduction path 75 are adjusted in the volume adjustment chamber 78 so that the volumes of the inlet nozzle 76 and the second fluid pressure introduction path 77 are substantially the same. The holder 80 is connected to a common power source through a lead wire 83, the holder 79 and the holder 81 are electrically connected through a lead wire 84,
A holder 82 is connected to an amplifier 86 via a lead wire 85. The other configuration is the pressure sensor 1 shown in Figure 1.
According to.

There is no superiority or inferiority in performance between the meat pressure sensor 1 and the pressure sensor 70, and the pressure sensor 70 also provides the same effect as described above.

FIG. 5 shows an example in which the pressure sensor according to the present invention is used in a Karman vortex flowmeter.

In FIG. 5, 90 indicates a flow meter element portion of the Karman vortex bottle body, and 91 indicates a vortex generator. The fluid flowing in the direction of the arrow in the figure hits the vortex generator 91, thereby intermittently generating Karman vortices 92 in its wake. One internal pressure outlet 93 is provided in the portion through which this Karman vortex 92 passes, and the other internal pressure outlet 94 is provided in the inner wall surface of the flowmeter element section 90. Both internal pressure outlets 9
3.94 is connected to the inlet nozzle 30, 29 of the pressure sensor 1 via a pressure guiding tube 95.96. Other configurations are similar to those shown in FIGS. 4 and 1.

In such a Karman vortex flowmeter, the number of Karman vortices generated per unit time changes in proportion to the fluid flow rate.
The flow rate is detected by measuring the number of Karman vortices passing through the internal pressure outlet 93.

Pressure fluctuations caused by the passage of the Karman vortex are introduced to one side of both piezoelectric elements 2.3 via the internal pressure outlet 93, the pressure guiding tube 95, and the inlet nozzle 30, and are introduced into one side of both piezoelectric elements 2.3 through the internal pressure outlet 94, the pressure guiding tube 96, and the inlet. Via the nozzle 29 the pressure and pressure fluctuations of the entire passing fluid are introduced onto the other side of the two piezoelectric elements 2.3. As the sum of the outputs of both piezoelectric elements 2.3, only the pressure fluctuation due to passage of the Karman vortex is detected with high precision, making it possible to measure the flow 1 with high sensitivity and precision. Other operations are similar to those of the full-volume flowmeter described above.

The above explanation is based on the full-width flowmeter, Karman vortex ff
1ri"f, the pressure sensor according to the present invention can be applied to other flowmeters as long as pressure fluctuation detection is essential.

[Effects of the Invention] As explained above, the pressure sensor of the present invention has one inlet on both sides of two piezoelectric elements arranged so that the faces in the same direction have the same polarization. By applying pressure from the nozzle and simultaneously applying pressure from the other inlet nozzle to the other side and taking the differential pressure between both sides, noise components due to pressure fluctuations and temperature fluctuations are automatically erased, and both piezoelectric By summing the outputs of the elements, the detection accuracy is doubled, and since the two piezoelectric elements are placed side by side under the same conditions, noise caused by one movement can be automatically eliminated. Therefore, only the pressure fluctuation to be measured can be detected with extremely high accuracy.

The minimum detectable pressure fluctuation range is 0.0001 to 0.
Very small at 1mmH2O, S/N ratio is 0,0001
ml-! 20dBV at 20, 60 at 0.1 H20
Very high dBV.

For this reason, it has become possible to detect minute pressure fluctuations in gases and liquids, which could not be detected in the past, without being affected by surrounding noise. With the current technology, minute pressure fluctuations of about 0.1 x 820 could only be measured with very large scale or expensive equipment, but the product of the present invention can be configured into a small sensor of about 20 x 20 x 10 x and is easy to measure. In addition, it can be used not only as a full-volume flowmeter or Karman vortex flowmeter, but also by being incorporated into other instruments or parts of machinery, so it can be expected to be used in a wide range of fields.

In addition, since the mechanically weak piezoelectric element is not exposed, foreign matter in the fluid will not adhere to it, making it easy to manufacture, handle,
It has a long lifespan as it does not cause damage or sensitivity loss during the process of implementation. Furthermore, the structure is simple and there are no parts that require advanced technology to manufacture, so it can be manufactured at low cost.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a pressure sensor according to one embodiment of the present invention, FIG. 2 is an enlarged partial sectional view of a piezoelectric element portion of the pressure sensor of FIG. 1, and FIG. 3 is a pressure sensor according to another embodiment. 4 is a schematic diagram of the configuration when the pressure sensor in Figure 1 is used in a full-build flowmeter, and Figure 5 is a schematic diagram of the configuration when the pressure sensor in Figure 1 is used in the Karman vortex flow rate h4. , is. 1.70...Pressure sensor 2.3.71.72...Piezoelectric element 4.73...Pressure detection section 5.86...Amplifier 6.7... ... Piezoelectric body 8.9.10.11 ... Electrode layer 12.13.14.15.79.80.81.82 ...
・Holder 16.17.18.19...Pressure chamber 20, 21.22.23...Aperture 24.25.26.27...Ante chamber 28... Substrate 29.30174.76...Inlet nozzle 31...
......Lid 32.35...Communication path 33.75...First fluid pressure introduction path 34.
78...Volume adjustment chamber 36.77...Second fluid pressure introduction path 37.
38.39.40.83.84.85・・・・・・・・・
...Lead wire■...Output terminal 42...Shield case 50...
......Flowmeter element section 51 of full-width flowmeter ......Flow path reduction section 52 ...
......Blowout nozzle 54.55...Partition wall 56.57...Control nozzle 58...Target 59.60.
93.94...Internal pressure outlet 61.62.95.96.
・・Pressure tube 90 ・・・Flowmeter element part 91 of Karman vortex flow meter ・・・Vortex generator 92 ・・・
・・・・・・Karman vortex W [

Claims (1)

[Scope of Claims] 1. A pressure detection unit having two piezoelectric elements that are configured by providing electrode layers on both sides of a film-like piezoelectric material and stretched in a planar manner;
an amplifier that amplifies the sum of the outputs of both piezoelectric elements, the two piezoelectric elements are arranged so that both surfaces face the same direction, and the faces in the same direction have the same polarization, and the pressure The detection unit is provided with two inlet nozzles that introduce fluid pressure, and one of the inlet nozzles connects one surface of one piezoelectric element to the other surface through the first fluid pressure introduction path. The inlet nozzle communicates with one surface of the other piezoelectric element, and the other inlet nozzle communicates with the other surface of the one piezoelectric element and the other surface of the other piezoelectric element via a second fluid pressure introduction path. and wherein a volume of the one inlet nozzle and the first fluid pressure introducing path and a volume of the other inlet nozzle and the second fluid pressure introducing path in the pressure detection section are substantially equal. sensor. 2. The pressure sensor according to claim 1, wherein the fluid is a gas. 3. A gas flowmeter in which the two inlet nozzles of the pressure sensor according to claim 2 are connected to a flowmeter element that generates pressure fluctuations in accordance with the flow rate of gas flowing through the flowmeter.