JPH04147026A - Pressure sensor and gas flow meter using it - Google Patents

Abstract

PURPOSE:To enable noise to be eliminated efficiently by allowing length and capacity of a fluid introduction path reaching first and second surfaces of each pressure element to be equal from each nozzle through each pressure buffer room. CONSTITUTION:Length and capacity between both surfaces and entrance nozzles 29 and 30 are equal for each of two piezoelectric elements since both pressure buffer rooms 47 and 48 have the same capacity and length and capacity of fluid pressure introduction paths 37 and 38 and 39 and 40 are equal. Then, both surfaces of two piezoelectric elements face in the same direction and faces in a same direction are provided so that they are of the same polarization polarity. Also, the polarization polarity of each piezoelectric element is connected to each opposite surface through the paths 37 and 40 and paths 38 and 39 from the nozzle 29 and the buffer room 47 and the nozzle 30 and the buffer room 48, electric charge of the same size is generated at two piezoelectric elements according to sound pressure to be propagated and is subjected to differential treatment, thus enabling noise due to sound pressure to be eliminated automatically.

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, etc. to the output signal (hereinafter referred to as the SN ratio).
The present invention relates to a pressure sensor that uses a high-performance piezoelectric element and is optimal for use in a gas flowmeter, and a gas flowmeter 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 semiconductor diaphragm type. These are generally used to detect large pressures, and are often large, complex, or expensive. Furthermore, since the pressure to be detected is large, noise caused by disturbances such as vibrations is not usually considered. Therefore, it cannot be used in applications that require the detection of very small pressures, or even if it is used, the noise ratio will be high, making it difficult to detect with high accuracy.

For example, there are fluid flowmeters and Karman vortex flowmeters that detect the flow rate of fluid through pressure detection as preferable applications that can detect even minute pressures (for example, Japanese Patent Application Laid-Open No. 60-187814, Japanese Patent Application Laid-Open No. 57-54809). Publication No.). In addition, pressure sensors using film-like piezoelectric elements are known as pressure sensors that are optimal for use in these flowmeters and can detect even minute pressure fluctuations (for example, in JP-A-57
-54809). The above full-sized flowmeter is
As disclosed in JP-A-60-187814, in the flowmeter element part, the main stream of the fluid ejected from the ejection nozzle is made to alternately follow a pair of partition walls using the Coanda effect, and the flow is controlled. The pressure fluctuation that occurs during the change is detected by a pressure sensor, 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 is used to detect the pressure fluctuation that occurs when the fluid passes through the fluid, and the flow rate of the fluid is detected by the Karman vortex generation number corresponding to the flow rate.

It is desirable for a pressure sensor used in such a flowmeter to have high sensitivity, that is, to be able to detect weak pressure changes and pressure changes over a wide range of frequencies. The ratio 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. The vibration that becomes the noise component is applied to both the piezoelectric element for pressure detection and the piezoelectric element for noise component correction, so in principle, if the signal from the piezoelectric element for noise component correction is subtracted from the output signal from the piezoelectric element for pressure detection, This will eliminate noise caused by vibration.

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. The problem is that vibration and temperature are transmitted in different ways, making it impossible to remove noise components 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 is mechanically weak or has a structure that is exposed in the fluid flow path, foreign matter in the fluid can easily adhere to the piezoelectric element, and the piezoelectric element may be damaged or damaged during the manufacturing, handling, and implementation processes. The problem is that it tends to cause a decrease in sensitivity.

To address these problems, the applicant previously proposed a method in which two piezoelectric elements were placed side by side, and pressure was applied to each surface of each piezoelectric element from two inlet nozzles through fluid pressure introduction paths of the same volume. A pressure sensor in which the pressure is propagated and simultaneously detected in opposite phases by each piezoelectric element, and a gas flow meter using the pressure sensor have been proposed (Japanese Patent Application No. 1-89633).
issue).

With this proposal, it is possible to accurately correct not only noise caused by vibrations, but also noise such as temperature fluctuations and miscellaneous noise propagated throughout the fluid, resulting in a high signal-to-noise ratio and high sensitivity that can detect even minute pressure fluctuations. Moreover, we have obtained a pressure sensor with a simple structure and high reliability, and a highly accurate gas flow meter using the pressure sensor.

However, as a result of further investigation, it was found that in addition to the noise described above, there was also noise due to sound pressure propagating simultaneously from the two inlet nozzles. Furthermore, when measuring the frequency of fluctuating pressure of a fluid using a pressure sensor, if turbulent fluid enters from the inlet nozzle of the pressure sensor, noise caused by the pressure fluctuation may cause the frequency of the fluctuating pressure to be measured to vary. It was also found that there was a problem in that it sometimes became clearer.

The purpose of the present invention is to further improve the previously proposed pressure sensor, to accurately compensate for vibrations, temperature fluctuations, and noise propagated throughout the fluid, as well as noise due to sound pressure. Even if a state fluid is introduced,
It is an object of the present invention to provide a highly sensitive and reliable pressure sensor with an extremely high signal-to-noise ratio, which can effectively eliminate noise caused by the noise.

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, each inlet nozzle is communicated with a pressure buffer chamber having the same volume, and one pressure buffer chamber is connected to a first fluid pressure introduction path. The second surface of the other piezoelectric element, which has a polarization different from that of the first surface of the one piezoelectric element, is connected to the first surface of the one piezoelectric element through the fourth fluid pressure introduction path.
The other pressure buffer chamber is communicated with the second surface of the one piezoelectric element through a second fluid pressure introduction path, and the other pressure buffer chamber is communicated with the second surface of the one piezoelectric element through a third fluid pressure introduction path. The first fluid pressure introduction path and the second fluid pressure introduction path are substantially equal in length and volume, and the third fluid pressure introduction path and the second fluid pressure introduction path are connected to the first surface of the piezoelectric element. The length and volume are substantially equal to those of the fourth fluid pressure introduction path.

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 made of a ceramic piezoelectric body represented by lead zirconate titanate (PZT), a polymer piezoelectric body, or a composite piezoelectric body in which PZT powder is mixed into a polymer.

The polymeric piezoelectric material is composed of, for example, a copolymer of vinylidene fluoride and ethylene trifluoride. The film thickness is
10 to 100 μm from the viewpoint of sensitivity, strength, and ease of handling
It is preferable to choose from the range of . 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 desirable that each fluid pressure introduction path has a bent structure or a constricted structure so that the introduced fluid does not directly hit the piezoelectric element surface. The volume of the pressure buffer chamber is
It is preferable that the volume is larger than the volume of the fluid pressure introduction path connected to the pressure buffer chamber.

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 within the pressure detection section so that both surfaces face in the same direction, but they may be arranged in parallel or in series.

[Function] In the pressure sensor as described above, the pressure of a fluid taken out from a certain pressure outlet is transmitted to one of the inlet (nozzle, one pressure buffer chamber, first fluid pressure guide) path, the fourth The pressure of the same fluid is simultaneously introduced into the first surface of one piezoelectric element Q and the second surface of the other piezoelectric element through the fluid pressure introduction path of an inlet nozzle, a pressure buffer chamber, a second fluid pressure introduction path, a third
The fluid pressure is simultaneously introduced into the second surface of one piezoelectric element and the first surface of the other piezoelectric element through the fluid pressure introduction path, and spontaneous force is applied to the piezoelectric body due to the deformation of each piezoelectric element 9 caused by the differential pressure between the two surfaces. Polarization is generated, and the resulting potential difference between the two sides of the piezoelectric element is output by applying force to the electrode layer. Both piezoelectric elements are connected to an amplifier so that the sum of both outputs is calculated. The subtracted detection output is output without being amplified.

In the detection of this pressure sensor, regarding the removal of noise components, (a) it has a structure that simultaneously introduces fluid pressure to both sides of the piezoelectric element and detects the differential pressure, and (6) it has a substantially the same structure and the same atmosphere. In particular, the length and volume of the first fluid pressure introduction path and the second fluid pressure introduction path, as well as the third fluid pressure introduction path and the fourth fluid pressure introduction path, This is achieved by making the lengths and volumes of the paths the same, and (c) by providing pressure buffer chambers with the same volume between the fluid pressure introduction path leading to each piezoelectric element and each inlet nozzle. All kinds of noise components are precisely removed.

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 pressure to both sides of the piezoelectric element and to guide local pressure fluctuations corresponding to the measurement position from one path. Since the pressure fluctuations of the entire fluid are simultaneously transmitted to both sides of the two piezoelectric elements, the two piezoelectric elements deform in the same manner due to this fluctuation component, and the potential difference due to the pressure fluctuation of the entire fluid is canceled by the piezoelectric elements themselves. , a potential difference corresponding to the differential pressure component between the two surfaces and a signal having a frequency corresponding to the number of times the differential pressure occurs are generated. The same applies to temperature fluctuations in the entire fluid; temperature fluctuations are simultaneously transmitted to both sides of each piezoelectric element, so the two piezoelectric elements undergo the same deformation due to this fluctuation component, causing the piezoelectric elements themselves to undergo the same deformation. Noise components due to temperature fluctuations are automatically eliminated.

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 cause noise, while eliminating pressure fluctuation components due to fluid vibration or Karman vortex flowmeters. 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 the sum of the two, it is possible to obtain an output signal that has been removed from noise components caused by fluctuations in the entire fluid, with a sensitivity twice as high as in the case of a single piezoelectric element.

Further, noise components caused by vibrations of the pressure sensor and the flow meter as a whole 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, if both piezoelectric elements simultaneously detect the pressure to be measured with opposite phases to each other, or if vibration is applied to both piezoelectric elements, the vibration causes one piezoelectric element to deform in a direction that reduces the detected pressure. When a force is applied, a deforming force of the same magnitude and in the direction of increasing the detected pressure is always applied to the other piezoelectric element. The output from the pressure detection section is taken as the sum of the detection outputs of opposite phases of both piezoelectric elements, so the noise component accompanying the vibration is automatically eliminated, and only the pressure to be measured is detected. , as described above, is detected with twice the sensitivity.

Furthermore, the sound pressure propagating simultaneously from the two inlet nozzles may become noise during pressure detection, but the pressure sensor according to the present invention automatically eliminates this noise due to sound pressure.

Regarding noise caused by this sound pressure, firstly, one piezoelectric element will be explained. Sound pressure propagating simultaneously from two artificial nozzles can be so-called noise for the present invention, which detects fluctuating pressure as a differential pressure. In other words, when the phases of the sounds reaching the front and back surfaces of the piezoelectric element from the two inlet nozzles are shifted, a pressure difference is generated between the front and back sides of the piezoelectric element, resulting in noise due to the in-phase sound pressure. Therefore, by making equal the length and volume of the paths from the two inlet nozzles to the piezoelectric element for one piezoelectric element, it is possible to match the phases of sound reaching both sides of the piezoelectric element.

However, even if the phases of the sounds match, an electric charge is generated in the piezoelectric element because the piezoelectric element expands and contracts in the thickness direction due to the in-phase sound pressure. This also results in noise due to in-phase sound pressure.

In the present invention, the volumes of both pressure buffer chambers are equal, and the first and second pressure buffer chambers have the same volume.
The length and volume of the fluid pressure introduction paths are equal, and the third,
Since the length and volume of the fourth fluid pressure introduction path are equal, 2
For each piezoelectric element, the length and volume between its both sides and each inlet nozzle are equal. And 2
The piezoelectric elements are arranged so that both surfaces face the same direction and the faces in the same direction have the same polarization, and from one inlet nozzle and one pressure buffer chamber, the first and fourth piezoelectric elements The polarization polarity of each piezoelectric element is communicated with the opposite sides of each piezoelectric element through a fluid pressure introduction path, and each piezoelectric Since the polarization polarities of the elements are communicated with opposite surfaces, the propagating sound pressure generates charges of the same size in the two piezoelectric elements, which are processed differentially to reduce the sound pressure. noise is automatically removed.

Furthermore, in the present invention, the pressure introduced from each inlet nozzle is introduced into the pressure buffer chambers with the same volume, so even if the introduced fluid is in a turbulent flow state, the pressure introduced from each inlet nozzle becomes a buffer. Noise associated with turbulence is reduced. As a result, in the stage where the pressure is propagated from each pressure buffer chamber to each piezoelectric element via each fluid pressure introduction path, substantially;
Noise accompanying the turbulent flow state is effectively eliminated, and only the pressure (pressure fluctuation) to be measured is efficiently transmitted to the piezoelectric element. Therefore, even if the fluid measurement target position is in a turbulent flow state, highly accurate detection is possible.

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

1 to 3 show a pressure sensor according to an embodiment of the present invention, FIG. 4 shows the configuration of a piezoelectric element, and FIG. 5 shows a configuration of a pressure sensor according to an embodiment of the present invention, and FIG. Figure 6 shows an example of use in a Karman vortex flow meter.

In FIG. 1, reference numeral 1 designates the entire pressure sensor according to the present invention, and the pressure sensor 1 includes a pressure control section 4 for growing two piezoelectric elements 2.3, and a pressure control section 4 for growing two piezoelectric elements 2. It consists of an amplifier 5 which amplifies and outputs the sum. The two piezoelectric elements 2.3 are stretched in a planar and deformable manner. As shown in an enlarged view in FIG. 4, 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.
As described above, various piezoelectric materials may be used as the material of 7, but in this example, a polymeric piezoelectric material made of a copolymer of vinylidene fluoride and ethylene trifluoride was used. The appropriate thickness of the polymer piezoelectric film is 10 to 100 μm for a gas pressure sensor in terms of sensitivity, strength, and ease of handling.
In this example, the thickness was set to 15 μm. 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 section, etc., which will be described later, 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 thin metal or rubber diaphragm and treat it as a reinforced polymer piezoelectric film. .

The periphery of the piezoelectric element 2.3 is connected from both sides to the holders I2, I3 and 14 via the electrode layers 8.9 and 10.11.
It is held by I5. The piezoelectric elements 2.3 held by 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 polarization. Holder 12.1
3.14.15 is composed entirely or on its surface of a conductive material such as brass, and each electrode layer 8.9, l0111
The piezoelectric elements are electrically connected to each other 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 holders 12.13.14.15 are formed in substantially the same shape to improve the signal-to-noise ratio, and pressure chambers I6, I7, 18.19 are formed on both sides of the piezoelectric element 2.3. . Each holder 12.13.14, ]5 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 includes a substrate 28 for housing and holding the holders 12.13 and 4.15, a body 32, two inlet nozzles 29.30 for introducing fluid pressure, and a lid 3 formed
1 is surrounded. The substrate 28 and the lid 30 are bonded with adhesive to prevent leakage from the inside. The substrate 28 and the lid 31 may be made of an engineered plastic such as an epoxy resin or a polyacetal resin, which has good insulation properties and has a high mechanical strength, and in this embodiment, they are made of a phenol resin.

Each inlet nozzle 29, 30 is connected to a pressure buffer chamber 47, 48 having the same volume (A), and one pressure buffer chamber 47 has a communication passage 33, an antechamber 24, an aperture 20, a pressure chamber The first surface of the piezoelectric element 2 (the two communicate with each other via the
The surface of the other piezoelectric element 3 having a different polarization polarity (second
). One strain force connects these communication passages 3
The path from the communication path 36 to the pressure chamber 16 constitutes a first fluid pressure introduction path 37 in the present invention, and the path from the communication path 36 to the pressure chamber 19 constitutes a fourth fluid pressure introduction path 40. are doing. The other pressure buffer chamber 48 communicates with the other surface (first surface) of the piezoelectric element 3 via the communication path 35, the front chamber 26, the throttle 22, and the pressure chamber I8, and also communicates with the other surface (first surface) of the piezoelectric element 3 through the communication path 35, the front chamber 26, the throttle 22, and the pressure chamber I8. It communicates with the other surface (second surface) of the piezoelectric element 2 via the aperture 21 and the pressure chamber 17 . Therefore, the path from the communication path 35 to the pressure chamber 18 constitutes the third fluid pressure introduction path 39, and the path from the communication path 34 to the pressure chamber 17
The mace path constitutes a second fluid pressure introduction path 38.

The first fluid pressure introduction path 37 and the second fluid pressure introduction path 38 are arranged in such a way that the third fluid pressure introduction path 39 and the fourth fluid pressure introduction path 40 are equal in length and volume. are constructed such that their lengths and volumes are equal. In particular, in this embodiment, the first fluid pressure introduction path 37, the second fluid pressure introduction path 38, the third fluid pressure introduction path 39, and the fourth fluid pressure introduction path 40 are all configured to have the same length and volume. has been done. Furthermore, in this embodiment, for the two piezoelectric elements 2.3, each inlet nozzle 2.
9.30, the arrangement of each pressure buffer chamber 47.48, fluid pressure introduction path 37.39, and fluid pressure introduction path 38.40, and the internal structure of the pressure detection section are configured to be identically symmetrical.

In the device shown in FIG. 1, a small hole is made in the substrate 28 and each lead wire 41, 42, 43 is passed through it, and the lead wire 41 is connected to the holder 13 at one end by soldering or the like and connected to the amplifier 5.
It is connected to the. The Riet wire 42 connects the holder 12 and the holder 14. The Leet wire 43 is connected to the holder 15 at one end and to the amplifier 5 at the other end.

44 indicates a terminal for output from the amplifier 5.

The pressure detecting section 4 and the amplifier 5 are housed in a shielding case 45 made of metal or the like, which is a good electrical conductor, so as not to receive electromagnetic induction noise from a commercial power source. In addition, the case 45 is filled with an epoxy filler 46 to prevent noise generated by the working of wiring materials and electronic components.
The pressure sensor l is constructed by fixing them and leaving no extra gaps inside. From the viewpoint of noise removal, it is preferable to use a shielded wire for the output terminal 44.

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 flow meter.

FIG. 5 shows a configuration in which the pressure sensor 1 is applied to a full-width flowmeter, and 50 in the figure shows the flowmeter element portion of the full-wave flowmeter. The gas to be measured is passed through the flowmeter element section 50 in the direction of the arrow.

Reference numeral 51 denotes a flow path reduction section, from which a jet stream with an increased flow velocity is ejected from an ejection nozzle 52 at its tip. Due to the Coanda effect, the main stream of the jet flows along one of the wall surfaces of the pair of partition walls 54 and 55 constituting the enlarged flow path section 53, or the direction of the wall flow is changed and flows through the control nozzle 56 (or 57). is directed perpendicularly to the jet from the jet nozzle 52, and a force acts so that the jet from the jet nozzle 52 flows along the other partition wall. Since this is repeated, the gas flows alternately along the partition walls 54 and 55, and pressure fluctuations occur within the flow meter element 5o 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 and 60 are respectively connected to the inlet nozzles 29 and 30 of the pressure sensor 1 via pressure guiding tubes 61 and 62 of equal length.

When the flow is switched to the internal pressure outlet 59 inside the flowmeter element section 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,
Pressure guiding tube 61. Inlet nozzle 29, pressure buffer chamber 47
, is introduced into the first surface of the piezoelectric element 2 and the second surface of the piezoelectric element 3 via the first fluid pressure introduction path 37 and the fourth fluid pressure introduction path 40, and the pressure at the internal pressure outlet 60 ( P2) is the pressure guiding tube 62, the inlet nozzle 30, the pressure buffer chamber 48, the second fluid pressure introduction path 38, and the third
The fluid pressure is introduced into the other surface (second surface) of the piezoelectric element 2 and the other surface (first surface) of the piezoelectric element 3 through the fluid pressure introduction path 39 . The 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 44 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, so 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 from which the noise has been eliminated is taken out as the sum of the outputs from both piezoelectric elements 2.3, so in the case of -
It is extracted with twice the sensitivity, allowing extremely high-precision detection.

Further, when vibration is applied as a disturbance, the excitation 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 different from the same direction with respect to the direction in which the deformation is increased or decreased. Become.

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

In addition, regarding noise due to sound pressure, each pressure buffer chamber 47
．． 48 have the same volume, and the first fluid pressure introduction path 37, the second fluid pressure introduction path 38, the third fluid pressure introduction path 39, and the fourth fluid pressure introduction path 40, respectively, have lengths, Since the volumes are equal, each piezoelectric element 2.3 is simultaneously deformed by the same amount in opposite directions due to the propagated sound pressure. By summing the outputs of these noises, both noise outputs are differentially processed and eliminated. Therefore, noise caused by sound pressure is automatically eliminated, and pressure fluctuations in the object to be measured can be detected with extremely high accuracy.

Furthermore, in this embodiment, in order to further enhance this noise removal effect, four fluid pressure introduction paths 37.
The lengths and volumes of 38, 39, and 40 are all equal, and for the two piezoelectric elements 2.3, the inlet nozzle 29.3o, each pressure buffer chamber 47.48, and each fluid pressure introduction path The arrangement of the pressure sensor and the structure of the pressure detection section are configured to be isomorphic and symmetrical.

Furthermore, the pressure introduced into each inlet nozzle 29.3o is introduced into a pressure buffer chamber 47.48 of the same volume and from there as described above in each fluid pressure introduction path 37.38.39.
．． 40 respectively. Each pressure buffer chamber 47.4
Since the pressure buffer chambers 47.8 function as buffer chambers against fluctuating pressures, even if the introduced fluid is in a turbulent flow state, the pressure buffer chambers 47.
48, and is transmitted to each fluid pressure introduction path with noise due to turbulence substantially eliminated. Therefore, unnecessary noise components accompanying the turbulent flow state are not transmitted to each piezoelectric element 2.3, and only pressure as a necessary measurement target is efficiently transmitted, making it possible to perform highly accurate measurement.

FIG. 6 shows an example in which the pressure sensor according to the present invention is used in a Karman vortex flow meter.

In FIG. 6, 70 indicates a flowmeter element of the Karman vortex flowmeter, and 71 indicates a vortex generator. The fluid flowing in the direction of the arrow in the figure hits the vortex generator 71, thereby intermittently generating Karman vortices 72 in its wake. One internal pressure extraction lower 3 is provided in the portion through which this Karman vortex 72 passes, and the other internal pressure extraction lower 4 is provided on the inner wall surface of the flowmeter element section 70. Both internal pressure extraction lowers 3.74 are connected to the inlet nozzle 30.29 of the pressure sensor 1 via a pressure guiding tube 75.76. Other configurations are similar to those shown in FIGS. 5 and 1.

In such a Karman vortex flow meter, the number of Karman vortices generated per unit time changes in proportion to the flow rate of the fluid.
The flow rate is detected by measuring the number of passages of the Karman vortex in the internal pressure extraction lower portion 3.

Pressure fluctuations caused by passing through the Karman vortex are introduced to one side of both piezoelectric elements 2.3 via the internal pressure extraction lower 3, the pressure guiding tube 75, and the inlet nozzle 30, 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 the passage of the Karman vortex is detected with high precision, making it possible to measure the flow rate with high sensitivity and precision. Other operations are similar to those of the full-volume flowmeter described above.

Although the above explanation has been made regarding a full-volume flowmeter and a Karman vortex flowmeter, the pressure sensor according to the present invention can be applied to other flowmeters as long as pressure fluctuation detection is essential.

Regarding amplification in a pressure sensor, conventionally, in a pressure sensor using two piezoelectric elements, three amplifiers were used to perform impedance conversion and differential amplification. In the present invention, as shown in FIG. 7, by connecting the two piezoelectric elements 2 and 3 with their polarities facing each other, differential operation is performed by the piezoelectric elements, and impedance conversion is performed by one amplifier 5. and differential amplification. This will (a) reduce the number of amplifiers from three to one, (b) reduce the number of parts, (c) reduce noise due to unbalanced amplifier bias, and (d) consume power to operate the pressure sensor. Power decreases. In Fig. 7, 85.86 is the output terminal, 81
．． 82 is a resistor, 83 is an input resistor, and 84 is a capacitor. Two pressures! In order to correct the sensitivity of the element and the unbalance of the signal with respect to vibration, it is effective to insert a capacitor 84 having a value corresponding to the difference in sensitivity. In other words, put capacitor 84 on the side with higher sensitivity,
Adjust to the one with the lowest sensitivity. If the sensitivities are the same, the capacitor 84 is not necessary.

In addition, as shown in FIG. 8, in order to improve sensitivity, in an amplifier circuit that amplifies the potential due to pressure fluctuation obtained from the piezoelectric element 2.3, the input resistance part is not only the resistor 83 but also the resistor 83. Therefore, it is effective to insert two diodes 87 and 88 in series with their polarities opposite to each other. By doing this, the resistance value of the diode increases at low temperatures, and the sensitivity of the pressure sensor at low temperatures improves.

Note that 89.90 indicates an output terminal.

Furthermore, in the present invention, as shown in FIG. 9, in an amplifier circuit that amplifies the potential due to pressure fluctuations obtained from the piezoelectric element 2.3, the piezoelectric element 2.3 and the input resistor 91 are not grounded. You can also do that. In other words, if one side is grounded, the impedance may become unbalanced, but by creating a circuit like the one above, each element can be arranged symmetrically with respect to the ground, and the The balance is lost, and (a) the electrical noise due to the unbalance of the noheias decreases.
(b) The advantage of reducing impact noise can be obtained.

Note that 92.93.94.95.96. in FIG.
97 represents a resistor, and 98.99 represents an output terminal.

Furthermore, in the above-mentioned embodiment, the piezoelectric element 2.3 is formed by a single piezoelectric film 6 (7) and an electrode layer 8.9 laminated thereon.
(10, 11), as shown in Figure 10,
The piezoelectric element 100 is composed of substantially two membrane-like piezoelectric bodies 101 and 102 of a bimorph type and electrode layers 103.
104.105 can also be configured. By doing this, the piezoelectric film basically needs to be formed into a flat shape instead of a hemispherical or diaphragm shape, which makes processing and assembly easier, and improves manufacturing yield. .

Furthermore, regarding the Le Holter 12.13.14.15 that holds the piezoelectric element 2.3 from both sides,
) is preferably made of a material with the same coefficient of linear expansion. For example, if the piezoelectric film is made of a copolymer of vinylidene fluoride and ethylene trifluoride, it should be made of the exact same material, or a plastic with a linear expansion coefficient similar to that of this material, such as ABS resin. , polybutylene terephthalate, polypropylene, polyethylene, etc. are preferably used. In this way, the linear expansion coefficients of the membrane piezoelectric material and the holder are substantially equal, so that the shape and tension of the piezoelectric element do not change. Therefore, the temperature characteristics of the film-like piezoelectric body directly indicate the temperature characteristics of the piezoelectric sensor, and the temperature characteristics can be further improved.

[Effects of the Invention] As explained above, when using the pressure sensor of the present invention, one inlet nozzle is applied to one surface of two piezoelectric elements arranged so that the surfaces are in the same direction or have the same polarization. pressure from the other inlet nozzle is applied to the other side at the same time, and the pressure difference between the two sides is taken.
In addition to automatically eliminating noise components caused by temperature fluctuations, the detection accuracy is increased by 2 by summing the outputs of both piezoelectric elements.
Since the piezoelectric elements are doubled and the two piezoelectric elements are placed side by side under the same conditions, noise caused by vibration can be automatically eliminated. Furthermore, each piezoelectric element is configured so that the length and volume of the fluid pressure introduction path from each inlet nozzle to the first and second surfaces of each piezoelectric element via each pressure buffer chamber are equal. , it is possible to automatically and reliably eliminate noise caused by sound pressure propagated simultaneously from two inlet nozzles. Furthermore, even if the fluid introduced into each inlet nozzle is in a turbulent flow state, unnecessary pressure fluctuations are alleviated and eliminated by each pressure buffer chamber, and noise accompanying this can also be effectively eliminated.

Therefore, only the pressure fluctuation to be measured can be detected with extremely high accuracy. The maximum detectable zlz pressure fluctuation range is 0.0001 to 0.1 in HtO, which is extremely +
:, /I\ becomes smaller, and it is possible to make it even smaller.

Also, the SN ratio is 0.0001mm H20 and 20dBV
, 0.1 Fox H20 is very high at 60 dBV.

For this reason, it has become possible to detect minute pressure fluctuations in gases and liquids that could not be detected in the past without being affected by surrounding noise.Currently, the technology has a detection range of 0.1 mm.
It is difficult to measure pressure fluctuations as small as HtO by force or by using expensive equipment.
By the way, the product of the present invention can be configured into a small sensor of about 20 x 20 x 10+n, and can be easily used by incorporating it into not only full-radiic flowmeters and Karman vortex flowmeters, but also other instruments and parts of machines. It can be expected to be used in a wide range of fields.

In addition, since the mechanically weak piezoelectric element is exposed (no It's also long. 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 the drawing]

FIG. 1 is a sectional view of a pressure sensor according to an embodiment of the present invention, FIG. 2 is a partial vertical sectional view taken along the line ■-■ in FIG. 1, and FIG. Bottom view, Figure 4 is an enlarged partial sectional view of the piezoelectric element part of the pressure sensor shown in Figure 1, Figure 5 is a schematic configuration diagram when the pressure sensor shown in Figure 1 is used in a full-volume flow meter, Figure 6 is a schematic configuration diagram when the pressure sensor shown in FIG. 1 is used in a Karman vortex flow meter, FIG. 7 is a circuit diagram showing one example of details of the amplification circuit according to the present invention, and FIG. 8 is an amplification according to another example. FIG. 9 is an amplifier circuit diagram according to yet another example, and FIG. 10 is a vertical cross-sectional view of a bimorph piezoelectric element applicable to the present invention. ..... Pressure sensor 3 ..... Piezoelectric element ..... Pressure detection section ..... Amplifier 7 ..... Piezoelectric body 9.1O111 .....・ Electrode layer 13.14.15 ...... Holder 17.18
．． 19... Pressure chambers 21, 22.23
・・・・・・ Aperture 25.26.27 ・・・・・・
Front chamber... Substrate 30... Inlet nozzle... Lid... Body 34, 35, 36... Communication path...
・First fluid pressure introduction route...Second fluid pressure introduction route...Third fluid pressure introduction route・
... Fourth fluid pressure introduction path 42.43 ・
...Lead wire 44 ...Output terminal 45 ...Shield case 47.48
...... Pressure buffer chamber 50 ...... Flowmeter element section 51 of full-buoy flowmeter ...... Channel reduction section 52 .... Spout nozzle 54.55 ... ... Partition wall 56,57 ... Control nozzle 58 ...
... Target 59.60.73.74 ... Internal pressure outlet 61, 62.75.76 ... Pressure guiding tube 70 ... Flow rate of Karman vortex flowmeter Gauge element section 71 ... Vortex generator 72 ... Karman vortex 81, 82.83.9L 92.93.94.95.9
6.97... Resistor 84... Capacitor 85.86.89.90.98.99...
Output terminal 88... Diode... Bimorph type piezoelectric element, 102... Film piezoelectric material, 104.10
5 ...... Cleaning of the electrode layer drawings (no changes in content) Figure 1 Figure 4 Figure 2 Figure 3 First fluid pressure introduction route Figure 7 Figure 8 Figure 9 Figure 10 Procedural amendment (formality) Case presentation 1990 Patent Application No. 270987

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, each inlet nozzle is in communication with a pressure buffer chamber having the same volume, and one pressure buffer chamber is connected to a first pressure buffer chamber.
The other piezoelectric element is connected to the first surface of the one piezoelectric element through a fluid pressure introduction path, and the other piezoelectric element has a polarization different from that of the first surface of the one piezoelectric element through a fourth fluid pressure introduction path. The other pressure buffer chamber is communicated with the second surface of the one piezoelectric element via a second fluid pressure introduction path, and the other pressure buffer chamber is communicated with the second surface of the one piezoelectric element through a third fluid pressure introduction path. communicated with the first surface of the other piezoelectric element through the
The length and volume of the first fluid pressure introduction path and the second fluid pressure introduction path are substantially equal, and the lengths of the third fluid pressure introduction path and the fourth fluid pressure introduction path are substantially equal. and a pressure sensor having substantially equal volumes. 2. A gas flowmeter in which the two inlet nozzles of the pressure sensor according to claim 1 are connected to a flowmeter element that generates pressure fluctuations in accordance with the flow rate of gas flowing.