JPH06235671A - Pressure sensor - Google Patents

Abstract

PURPOSE:To improve power supply fluctuation characteristics while stabilizing sensitivity in measurement by providing a constant voltage circuit in a signal processing circuit and feeding power supply voltage also to a voltage comparator through a constant voltage regulator. CONSTITUTION:Output from an amplifying circuit section 53 is converted through a voltage comparator 55 having hysteresis into a pulse signal which is outputted through a level converter 59. The voltage comparator 55 has input hysteresis width which is determined by the output width of an element in the comparator 55 and corresponds with the voltage of a power supply 2. When the supply voltage is kept constant using a constant voltage circuit 51 and thereby the hysteresis width is kept constant, total sensitivity of the circuit 5 is kept constant and stabilized. Furthermore, fluctuation of power supply 2 due to high slew rate of the converter 59 and high amplitude operation is absorded by the circuit 51 and noise in the circuit 5 is suppressed. This constitution allows highly accurate detection only of pressure fluctuation and frequency of an object with stabilized sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a gas flow meter using a piezoelectric element, which can detect even minute pressure fluctuations and has a high ratio of noise due to vibration to an output signal (hereinafter referred to as SN ratio). And optimal pressure sensor.

[0002]

2. Description of the Related Art In a fluidic flowmeter, a Karman vortex flowmeter, etc., a pressure sensor is used as a means for detecting a fluid vibration having a frequency proportional to the flow rate (for example, Japanese Patent Laid-Open No. 60-187814). JP-A-57-
54809). The pressure sensor can detect the pressure fluctuation due to the fluid vibration, process the signal into a pulse of that frequency, and then know the flow rate of the fluid.

However, the above-mentioned pressure fluctuation is very small and cannot be measured by a general pressure sensor, or the SN ratio is low.
Highly accurate measurement is difficult. Further, although a piezoelectric element is known as a material of a sensor capable of measuring a minute pressure (Japanese Patent Laid-Open No. 57-54809, etc.), a method of correcting a noise component is insufficient, or the piezoelectric element is in fluid. Since they are arranged, there is a problem that foreign matter in the fluid adheres or collides.

In order to solve such a problem, the present applicant previously arranged two piezoelectric elements side by side, and from each of the two inlet nozzles to each surface of each piezoelectric element via a fluid pressure introduction path of the same volume. There has been proposed a pressure sensor in which each pressure is propagated and the pressure is simultaneously detected by each piezoelectric element in a reverse phase, and a gas flow meter using the pressure sensor (Japanese Patent Application No. Hei 1 (1999) -135242).
-89633). With this proposal, it is possible to accurately correct not only noise due to vibration but also noise such as temperature fluctuations and noises transmitted throughout the fluid, which has a high SN ratio and high sensitivity that can detect even weak pressure fluctuations. Moreover, a highly reliable pressure sensor having a simple structure and a highly accurate gas flowmeter using the pressure sensor were obtained.

[0005]

However, as a result of further studies, it was found that the above-mentioned pressure sensor proposed above has the following problems. For example, in a fluidic flowmeter, the frequency of fluid vibration is proportional to the flow rate,
The amplitude, that is, the fluctuating pressure is proportional to the square of the flow rate (frequency). When the flow rate increases, the pressure fluctuation (differential pressure) introduced into the piezoelectric element portion increases, but at the same time, the pressure fluctuation due to the noise component also increases. The previously proposed pressure sensor simply amplifies the output from the piezoelectric element to a measurable level, so if the flow rate is large as described above, it will be output as an amplifier because of the relationship with a certain power supply voltage. May be in a saturated state (capture state where the output does not exceed a certain value). At this time, if there is a large noise component, the noise component may be counted as the flow rate proportional frequency to be measured. That is, the SN ratio decreases, and the measurement accuracy deteriorates.

Therefore, the present applicant further improved the above-mentioned pressure sensor to correct vibrations, temperature fluctuations, noise propagated in the entire fluid, etc. by the sensor structure, and further, electrically. By performing signal processing, a highly sensitive and highly reliable pressure sensor having an extremely high SN ratio was provided (Japanese Patent Application No. 3-274874).

However, it was found that in the field where this sensor is actually used, the fluctuation of the power supply voltage is quite large, and the average voltage value of the power supply is not constant. It has been found that the fluctuation of the power supply voltage causes a malfunction, or the average voltage value of the power supply is not constant, so that the hysteresis width of the voltage comparator is changed and the apparent measurement sensitivity may be different.

Therefore, an object of the present invention is to improve the above-mentioned proposal (Japanese Patent Application No. 3-274874) electrically, more specifically, to improve the power supply, improve the power supply fluctuation characteristic, and perform measurement. The object is to stabilize the sensitivity and provide a highly sensitive and highly reliable pressure sensor having an extremely high SN ratio.

[0009]

According to the pressure sensor of the present invention for this purpose, two piezoelectric elements each having an electrode layer provided on both sides of a film-shaped piezoelectric body are sandwiched by two pairs of holders from both sides. And the two piezoelectric elements are arranged so as to face in the same direction and have the same polarization polarity in the same direction, and the pressure of the fluid is introduced into the pressure detection unit. Two inlet nozzles are provided, and one inlet nozzle communicates with the first surface of the one piezoelectric element via the first fluid pressure introducing passage and the other one through the fourth fluid pressure introducing passage. Of the other piezoelectric element having a polarization polarity different from that of the first surface of the other piezoelectric element, and the other inlet nozzle is connected to the second surface of the other piezoelectric element via the second fluid pressure introduction path. Through the third fluid pressure introduction path A pressure sensor in communication with the first surface of the other piezoelectric element, wherein the outputs from the two piezoelectric elements are sent to an amplifier circuit section of a signal processing circuit inside the pressure sensor, and the signal processing circuit It consists of one that has a constant voltage circuit inside.

In this pressure sensor, it is preferable that the piezoelectric element is stretched in a diaphragm shape or a hemispherical shape in order to deform the piezoelectric element more sensitively to a pressure change and to make the pressure sensor more sensitive. In order to obtain such a stretched state, it is preferable that the holding surface of the holder that holds the two piezoelectric elements is formed as an inclined surface or a curved surface having an arbitrary curvature.

This pressure sensor is an optimum pressure sensor for use in a gas flow meter including a fluidic flow meter and a Karman vortex flow meter, and the two inlet nozzles of the pressure sensor are two of the same area. It is connected to a flow meter element section that generates a pressure fluctuation according to the flow rate of the fluid that is circulated, through a gasket having a pressure hole.

In the present invention, the piezoelectric body used for the piezoelectric element is a ceramic piezoelectric body represented by lead zirconate titanate (PZT), a polymer piezoelectric body, or a polymer containing P.
It is composed of a composite piezoelectric material mixed with ZT powder. The polymeric piezoelectric body is made of, for example, a copolymer of vinylidene fluoride and ethylene trifluoride. The film thickness depends on sensitivity, strength,
It is preferable to select it in consideration of handleability. The film thickness can be easily and highly accurately controlled by a known film forming technique.

The electrode layers provided on both sides of the piezoelectric body are made of a material such as aluminum, copper, gold, nickel and palladium, and are formed on the surface of the piezoelectric body by a metallizing method such as vapor deposition, sputtering and plating. It is desirable that each fluid pressure introduction path has a bent structure or a throttle interposition structure so that the introduced fluid does not directly contact the piezoelectric element surface. Further, the polarization polarity of the piezoelectric element is given in the process of manufacturing the piezoelectric body, and a well-known method can be applied to this. The piezoelectric elements are arranged in the pressure detection unit so that both surfaces thereof face in the same direction, but they may be arranged in parallel or in series.

[0014]

In the pressure sensor as described above, the pressure of the fluid taken out from a certain pressure outlet is passed through one inlet nozzle, the first fluid pressure introducing path, and the fourth fluid pressure introducing path to the one side. Of the same fluid that is simultaneously introduced into the first surface of the piezoelectric element and the second surface of the other piezoelectric element and taken out from another pressure outlet,
Through the third fluid pressure introducing path and the second surface of the one piezoelectric element and the first piezoelectric element of the other piezoelectric element.
Are simultaneously introduced into the surface of the piezoelectric element, the amount of polarization changes due to the deformation of each piezoelectric element caused by the pressure difference between the both surfaces, and the potential difference between the two surfaces of the piezoelectric body caused thereby is output via the electrode layer. Both piezoelectric elements are connected to the amplifier circuit section so that the sum of both outputs is input.

In the detection by this pressure sensor,
(A) A structure in which fluid pressure is simultaneously introduced to both sides of the piezoelectric element and the differential pressure is detected, (b) Two piezoelectric elements are arranged side by side in the same atmosphere with substantially the same structure,
(C) Since the electrical signal processing is performed so that the SN ratio becomes high, the noise component is extremely accurately removed.

First, since the fluid pressure is simultaneously introduced to both surfaces of one piezoelectric element, the pressure fluctuations of the entire fluid can be obtained by connecting two inlet nozzles to different measurement positions for the same fluid to be measured. The noise component) can be simultaneously guided to both surfaces of the piezoelectric element, and local pressure fluctuation corresponding to the measurement position can be guided from one path. Since the pressure fluctuation of the entire fluid is simultaneously transmitted to both surfaces of the two piezoelectric elements, the fluctuation component causes the two piezoelectric elements to undergo the same deformation and the piezoelectric element itself erases the potential difference due to the pressure fluctuation of the entire fluid. A signal having a frequency corresponding to the potential difference corresponding to the differential pressure component between the two surfaces and the number of times of differential pressure generation is output. The same applies to temperature fluctuations of the entire fluid, and temperature fluctuations are simultaneously transmitted to both surfaces of each piezoelectric element, so the two piezoelectric elements undergo the same deformation due to this fluctuation component, and the piezoelectric elements themselves are deformed. Noise components due to temperature fluctuations are automatically deleted. Therefore, by connecting this pressure sensor to the flowmeter element part of a fluidics flowmeter or a Karman vortex flowmeter, the fluctuation component of the entire fluid, which may cause noise, is automatically deleted, while the pressure fluctuation component due to fluid vibration or Karman Only the pressure fluctuation component due to the vortex can be detected with high accuracy.

Since the pressures from the same path are introduced to the surfaces of the respective piezoelectric elements arranged so that their polarization polarities are the same, the directions of deformation of both piezoelectric elements are different. Since the phases are opposite to each other and output as the sum of the two, the output signal from which the noise component caused by the fluctuation of the entire fluid is removed can be obtained with high sensitivity.

As a method of connecting the two piezoelectric elements, the piezoelectric element side-by-side structure can be removed almost completely. The first surfaces or the second surfaces of the two piezoelectric elements are electrically connected to each other, and the output from the other surface of the two piezoelectric elements is amplified by the amplification circuit section. So-called parallel connection, in which two piezoelectric elements having different polarization polarities are electrically connected to each other, and the output from one of the piezoelectric element connection portions is connected to the amplification circuit portion. There is a connection. Since each of these piezoelectric elements is manufactured in exactly the same structure, the impedance of the former is one-fourth of that of the latter, while the output of the former is twice that of the latter. Which one is used depends on the magnitude of pressure to be measured and the circuit environment.

Further, in the pressure sensor of the present invention, even when the output of the pressure sensor is limited due to the relationship with the power supply voltage, that is, the output of the pressure detection unit is amplified. Even in such a case, electrical signal processing is performed so as to obtain a large SN ratio. As described above, the fluctuating pressure due to the fluid vibration (that is, the differential pressure between the two surfaces of the piezoelectric element) is proportional to the square of the flow rate (frequency), and when the flow rate increases, the differential pressure increases and at the same time the pressure fluctuation due to the noise component. Also grows. Therefore, when the output from the pressure detection unit is simply amplified and the amplified output is in a saturated state, if there is a large noise component close to the saturation value, the SN ratio decreases. In such a case, in the pressure sensor of the present invention, the pressure detection unit is connected to, for example, an amplifier circuit unit having a gain characteristic of 1 or 1 / square of the output frequency from the pressure detection unit, thereby reducing the flow rate. This gain characteristic is multiplied by the output from the pressure detection unit, which is approximately proportional to the square, and the output as the pressure sensor is controlled to an appropriate level, and the noise component is suppressed to a small level. As a result, only the flow rate proportional frequency that is the measurement target is efficiently counted, and the SN ratio is greatly improved.

Such signal processing may be performed on a region having a certain frequency or more, that is, a region having a certain flow rate or more, in which the output from the pressure detecting unit becomes large. When applied to a region of too low frequency, the output itself from the pressure detection unit is suppressed to a small value.

Then, the output from the amplifier circuit section enters a voltage comparator having a certain hysteresis and is converted into a pulse having a frequency corresponding to the pressure fluctuation. The output of this voltage comparator is the maximum output amplitude of the operational amplifier that constitutes it, which corresponds to the magnitude of the power supply voltage. Therefore, by adopting a structure in which the power supply voltage is also supplied to the voltage comparator via the constant voltage regulator, the sensitivity of measurement becomes constant regardless of the power supply voltage supplied, and by arranging the constant voltage regulator, The fluctuation of the power supply voltage and the fluctuation of the power supply inside the signal processing circuit caused by the driving of the level converter are also cut (absorbed), the power supply fluctuation characteristic is improved, and the reliability is further improved.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows a pressure sensor according to an embodiment of the present invention, and FIG. 15 shows an example in which the pressure sensor is used in a fluidic flow meter.

In FIG. 3, reference numeral 1 denotes the entire pressure sensor according to the present invention. The pressure sensor 1 includes a pressure detecting section 4 having two piezoelectric elements 2 and 3, and an electric signal processing circuit described later. 5 (FIG. 1). Two piezoelectric elements 2, 3
Is sandwiched by two pairs of holders 12, 13 and 14, 15 from both sides, and the central part is stretched so as to be deformable. As shown in an enlarged view in FIG. 4, the piezoelectric elements 2 and 3 are provided on both surfaces of the film-shaped piezoelectric bodies 6 and 7 made of a piezoelectric material, and are made of a metal such as aluminum, copper, gold, nickel, or palladium having good corrosion resistance. Electrode layers 8, 9 and 10, 11 consisting of
It is formed by plating or the like. The planar shape of the two piezoelectric elements 2 and 3 is circular in the present embodiment, but is not limited to this. Although various piezoelectric materials can be applied as the material of the piezoelectric bodies 6 and 7, in this embodiment, a polymer piezoelectric material made of a copolymer of vinylidene fluoride and ethylene trifluoride was used. The thickness of the piezoelectric polymer film is determined considering sensitivity, strength, and ease of handling.
In this embodiment, the thickness is 15 μm. However, the pressure sensor according to the present invention includes, of course, a liquid sensor, and the thickness of the polymer piezoelectric film and the structure such as an electrode portion described later may be appropriately selected according to the liquid to be measured. Although not shown, depending on the fluid to be measured and the magnitude of pressure fluctuation, it is possible to attach a polymer piezoelectric film to a thin metal or rubber diaphragm and treat it as a reinforced polymer piezoelectric film as a whole. .

The peripheral portions of the piezoelectric elements 2 and 3 are holders 12, 13 and 1 from both sides via electrode layers 8, 9 and 10, 11.
Held by 4, 15. The piezoelectric elements 2 and 3 held by the respective holders are arranged in parallel so that both surfaces thereof face in the same direction, and the surfaces in the same direction have the same polarization polarity. Holder 12, 1
3, 14, 15 are wholly or entirely formed of a conductor such as brass, and are electrically connected to the respective electrode layers 8, 9, 10, 11 to function as output terminals of the respective piezoelectric elements. The holders 12 and 13, 14 and 15 are insulated by the piezoelectric bodies 6 and 7.

This pair of two holders 12, 13 and 14, 15
Then, the piezoelectric elements 2 and 3 are sandwiched and stretched as shown in FIGS. Piezoelectric elements 2 and 3 having a circular planar shape
Is sandwiched by the holder at its peripheral portion, and the piezoelectric element sandwiching surfaces 12a 1, 13a and 14a 1, 15a of the holder are formed as inclined surfaces inclined in the same direction at the same angle θ. As the inclination angle θ, an angle of 7 °, which gives the maximum output from the test results of the inclination angle θ and the output of the pressure sensor, is adopted. However, this inclination angle may be appropriately determined depending on the material, thickness, rigidity, etc. of the piezoelectric elements 2 and 3 so that the output of the pressure sensor is maximized. The piezoelectric elements 2 and 3 are formed as a simple flat film, as shown in FIG. 5, before being assembled, that is, before being sandwiched between the holders 12, 13 or 14, 15. And slopes 12a, 13a and 14a, 15a
When sandwiched between both holders 12, 13 and 14, 15 having
As shown in FIG. 6, the peripheral edges of the piezoelectric elements 2 and 3 are inclined surfaces 12a.
, 13a and 14a, 15a are forcibly deformed, so that the piezoelectric elements 2, 3 as a whole have a diaphragm shape (the shape shown) or a hemispherical shape and are stretched in that state.

By using a piezoelectric element previously formed in a diaphragm shape or a hemispherical shape and carefully holding it between both holders, the shape can be maintained and the sensitivity can be maintained.

The shape of the sandwiching surface of the pair of holders 12, 13 and 14, 15 for sandwiching the piezoelectric elements 2 and 3 is not limited to the above-mentioned inclined surface, but may be any one of those shown in FIG. 8 (before sandwiching) and FIG. 9 (after sandwiching). ), Curved surfaces 12b, 13b and 14b with arbitrary curvature ρ
, 15b may be formed.

On both sides of the piezoelectric elements 2 and 3, pressure chambers 16 and
17, 18, 19 are formed. Each pressure chamber 16, 17, 18, 19
Respectively communicate with the corresponding front chambers 20, 21, 22, 23.

The piezoelectric elements 2 and 3 are pressed and sandwiched as shown in FIG. Although the illustrated example shows the piezoelectric element 2, the piezoelectric element 3 has a similar structure. The piezoelectric element 2 is sandwiched by the holders 12 and 13 from both sides, the lower holder 12 is supported via the spacer 24 and the electrode plate 25, and the electrode plate 25 has a square head (rotated). It is fixed via screws 26. Upper holder
13 is urged by a spring 28 via an electrode plate 27, and the urging force of the spring 28 is used to cause the piezoelectric element 2 to move to both holders 1
It is clamped by pressure between 2 and 13. The electrode plate 27 is fixed in position by a screw 29 having a square head, while having the degree of freedom in the pressure contact direction. The screw 29 is fixed to the lid 33 of the substrate 32 via an O-ring 49, a washer 30, and a nut 31 for preventing gas from leaking from the pressure detecting portion 4. A circuit board 35 is fixed to each screw 29 via a nut 34, and the electrical signal processing circuit 5 is mounted on the circuit board 35.
Is built in. 36 and 37 in FIG. 3 are the circuit 5
The power input terminals of the circuit 5 and the output terminals 38 of the circuit 5 are shown. The input / output terminals 36, 37 and 38 are the lid 46.
Extend through. When the two piezoelectric elements 2 and 3 are connected in series, one electrode plate 25, 25 or 27, 27 of the piezoelectric elements 2 and 3 is connected to the circuit board 35 via the screw 29 or the screw 26. The other electrode plate 27, electrically connected above
One of 27, 25 and 25 is connected to the electric signal processing circuit 5 as an input to the electric signal processing circuit 5, and the other is connected to an intermediate potential pole (described later) of the potentials supplied from the power source. Also, when connecting two piezoelectric elements in parallel,
One electrode plate 25 and the other electrode plate 27 of the piezoelectric elements 2 and 3 are connected to each other via screws 26 and 29 and a short-circuit plate 86, respectively, and via the screw 29, one of the connecting portions is an electrical signal. As an input to the processing circuit 5, the other side of the circuit 5 is connected to an intermediate potential pole (described later) supplied from a power source. In addition,
When two piezoelectric elements 2 and 3 are connected in series, one electrode plate 25 or 27 is widened so that the piezoelectric elements 2 and 3 can be commonly contacted with each other to eliminate screws and short-circuit on the circuit board 35. Sometimes I don't.

The pressure detector 4 includes holders 12, 13 and 14,
A substrate 32 for accommodating and holding 15 and a second fluid pressure introduction path 43
Of the substrate and a part of the fourth fluid pressure introduction path 45 are surrounded by a substrate lid 33 and a shield case 41 in which two inlet nozzles 39, 40 for introducing the fluid pressure are formed. . The shield case 41 and the substrate 32, the substrate 32 and the lid 33 thereof, and the shield case 41 and the lid 46 thereof are joined to each other via a deformed O-ring so as not to leak from the inside. The substrate 32 and its lid 33 may be made of engineering plastic such as epoxy resin or polyacetal resin having good insulation and high mechanical strength. In this embodiment, it is made of polybutylene terephthalate resin (PBT resin). ing.

One of the inlet nozzles 39 has a front chamber 20 and a pressure chamber 16
Via the communication passage 47, the front chamber 23, and the pressure chamber 19 to the surface of the other piezoelectric element 3 having a different polarization polarity (the second surface). ing. Therefore, the path from the front chamber 20 to the pressure chamber 16 constitutes the first fluid pressure introduction path 42 in the present invention, and the path from the communication passage 47 to the pressure chamber 19 is the fourth fluid pressure introduction path.
It comprises 45. The other inlet nozzle 40 communicates with the other surface (first surface) of the piezoelectric element 3 through the front chamber 22 and the pressure chamber 18, and also through the communication passage 48, the front chamber 21, and the pressure chamber 17. 2 communicates with the other surface (second surface). Therefore, the path from the front chamber 22 to the pressure chamber 18 constitutes the third fluid pressure introduction path 44, and the communication passage 48 to the pressure chamber
The path to 17 constitutes the second fluid pressure introduction path 43.

Further, in this embodiment, two piezoelectric elements 2,
3, the arrangement of the inlet nozzles 39, 40, the fluid pressure introduction paths 42, 44, and the fluid pressure introduction paths 43, 45 and the internal structure of the pressure detection unit 4 are configured substantially symmetrically.

The pressure detector 4 and the electric signal processing circuit 5
Are housed in a case 41 which also serves as a shield made of metal, which is an electrically good conductor, so that they are not subjected to electromagnetic induction noise from a commercial power source or the like. The negative electrode of the power source in the circuit and the case 41 are connected via screws, nuts and washers, which are not shown.

Next, the electrical signal processing circuit 5 incorporated on the circuit board 35 will be described with reference to FIGS. 1 and 2. The piezoelectric elements 2 and 3 can be connected in series or in parallel,
It becomes like FIG. 1 and FIG. 2, respectively. This circuit configuration will be described. However, the only difference between FIG. 1 and FIG. 2 is the difference in the method of connecting the piezoelectric elements 2 and 3, and hence only the description in FIG.

The battery power source 52 is a 3V lithium battery, V _DD
The positive pole side is connected to the terminal 50a, and the negative pole side is connected to the V _SS terminal 50b. The + pole side of the battery power source 52 is connected to the constant voltage circuit 51 from the V _DD terminal 50a through the power source protection circuit 54. Then, the amplifier circuit section 53, the voltage comparator 55, the midpoint power source I (5
7), as a positive power source for the midpoint power source II (58), a constant voltage circuit 5
Supplying an output of 1. On the other hand, the + power supply of the level converter 59 supplies the output of the power supply protection circuit 54 and is approximately the same voltage as the voltage supplied from the outside. The output of the midpoint power source I (57) is used as the intermediate potential pole of the amplifier circuit section 53, and
The output of I (58) is used as the mid-potential pole of voltage comparator 55.

The outputs from the piezoelectric elements 2 and 3 are input to the AC amplification circuit section 53 having a gain characteristic as shown in FIG. Lines A to F in FIG. 11 show examples obtained by changing the constant of the amplifier circuit section 53. The amplifier circuit section 53 itself has low power supply voltage characteristics and malfunctions due to small fluctuations thereof, so the circuit configuration is provided with the constant voltage circuit 51 that cuts (absorbs) fluctuations in power supply voltage fluctuations.

In this embodiment, the output from the amplifier circuit section 53 is sent to the voltage comparator 55 having hysteresis and processed into a pulse signal, which is output from the output terminal 56 through the level converter 59. Has become. As for the circuit to the voltage comparator 55, the output reaches the saturation point with a small input, as shown in FIG. Voltage comparator
As shown in FIGS. 14 and 15, 55 has an input width, which is sometimes called a hysteresis width. This is determined by the output amplitude of the element used in the voltage comparator 55, which is also the power supply voltage. It corresponds to. Therefore, by using the constant voltage circuit 51 as in the present invention, when the supplied power supply voltage is kept constant, this hysteresis width also becomes constant and the sensitivity of the circuit 5 as a whole becomes constant and stable. For the output from the output terminal 56, an output pulse having a large slew rate (rising speed, falling speed) of almost the same voltage as the supply voltage is required from the power supply side because of signal processing. For this reason, the level converter 59
Supplies the output of the power supply protection circuit 54 which provides a voltage approximately the same as the supply voltage. Then, the fluctuation of the power supply caused by driving the level converter 59 at high speed is absorbed by the constant voltage circuit 51 and does not become noise.

In this embodiment, the potential of one battery power source 52 is divided, and the intermediate potential is used for signal processing from the piezoelectric element. In the present invention, this is the amplifier circuit unit 53 and the voltage comparator.
Two circuits are provided in order to increase the isolation between the circuit and 55. The midpoint power source I (57) is used for the amplifier circuit section 53, and the midpoint power source II (58) is used for the voltage comparator 55. By doing so, only one battery is required, and the space for accommodating the power supply may be small, so that it is possible to downsize the entire flow meter equipped with the pressure sensor.

The operation of the pressure sensor 1 configured as described above will be described below together with the configuration and operation when the pressure sensor 1 is used in a fluidic gas flowmeter.

FIG. 16 shows a configuration in which the pressure sensor 1 is applied to a fluidic flow meter, and 60 in the figure shows a flow meter element portion in the fluidic flow meter. Gas to be measured is circulated through the flowmeter element unit 60 in the direction of the arrow. Reference numeral 61 is a flow path reducing portion, and a jet nozzle 62 at the tip thereof.
A jet with an increased flow velocity is jetted from. The main flow of the jet flows due to the Coanda effect along the wall surface of either one of the pair of partition walls 64 and 65 forming the flow path expanding portion 63,
The wall flow is redirected along the reflector blades 69 to control nozzles.
A force is applied from 66 (or 67) so as to be orthogonal to the jet flow from the jet nozzle 62, and the jet flow from the jet nozzle 62 flows along the other partition wall. Since this is repeated, the gas flows alternately along the partition walls 64 and 65, and a pressure fluctuation occurs in the flowmeter element unit 60 in response to this flow change. Since the frequency of the flow change is proportional to the gas flow rate, the flow rate can be measured by detecting the frequency of pressure fluctuation. Incidentally, 68 in the figure is a target for efficiently directing the jet flow to one of the partition walls,
70 is a guide plate for guiding the flow.

Internal pressure outlets 71 and 72 are provided in the flow meter element portion 60 as described above, and the internal pressure outlets 71 and 72 are gaskets.
Pressure sensor 1 through 73 (preferably rubber with chemical resistance)
Are connected to the inlet nozzles 39 and 40, respectively.

Inside the flowmeter element 60, the flow is the internal pressure outlet
When switching to the 71 side, the fluid pressure in the vicinity of the internal pressure outlet 71 becomes lower than in the vicinity of the internal pressure outlet 72, and conversely the flow becomes the internal pressure outlet.
When switched to the 72 side, the fluid pressure near the internal pressure outlet 72 becomes lower. The pressure (P1) at the internal pressure outlet 71 is the gasket 73, the inlet nozzle 39, and the first fluid pressure introduction path 42.
And the piezoelectric element 2 via the fourth fluid pressure introduction path 45.
The pressure (P2) at the internal pressure outlet 72, which is introduced to the first surface of the piezoelectric element 3 and the second surface of the piezoelectric element 3, the gasket 73, the inlet nozzle 40, the second fluid pressure introduction path 43, and the third fluid pressure. It 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 introduction path 44. The pressures P1 and P2 are alternately applied to the two piezoelectric elements 2 and 3, and the amount of polarization changes due to the deformation of the piezoelectric element due to the pressure variation,
As a result, a potential difference is generated on both sides of the piezoelectric body itself. The sum of the outputs of both piezoelectric elements 2 and 3 is sent to the electric circuit 5, processed, and taken out from the output terminal 56 as a pressure fluctuation detection signal.

In the above detection, the fluid pressure is simultaneously introduced to both surfaces of the piezoelectric element, and the differential pressure is detected by each piezoelectric element. Therefore, the noise component due to the pressure variation and temperature variation generated in the entire fluid is eliminated. Since they are added 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 erased in the piezoelectric element itself. 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 and 3, so that it can be taken out with high sensitivity and extremely highly accurate detection becomes possible.

When vibration is applied as a disturbance, the exciting force acts on both piezoelectric elements 2 and 3 simultaneously as a force in the same direction. Although the deformation directions of the piezoelectric elements 2 and 3 due to the introduction of the fluid pressure are opposite to each other, the deformation margins of the two piezoelectric elements due to the above-mentioned vibration force are the same in the directions of increasing and decreasing the deformation. Become. Therefore, the increase / decrease in the output due to this noise component is automatically erased at the stage of adding the outputs of both piezoelectric elements 2 and 3.

Regarding the noise due to the sound pressure, the piezoelectric elements 2 and 3 are simultaneously deformed by the same amount in the thickness direction due to the propagated sound pressure. Therefore, the increase / decrease in the output due to this noise component is automatically erased at the stage of adding the outputs of both piezoelectric elements 2 and 3. As a result, the noise due to the sound pressure is also automatically deleted, and the pressure fluctuation of the measurement target is detected with extremely high accuracy.

Further, in this embodiment, in order to further enhance the noise removing effect, the inlet nozzles 39 and 40, the arrangement of the fluid pressure introducing paths, and the structure of the pressure detecting portion are provided for the two piezoelectric elements 2 and 3. Are configured to have almost the same shape and symmetry.

Next, the electric signal processing will be described. The basic principle of the pressure sensor of the present invention is to measure the frequency of pressure fluctuations that occur in proportion to the flow rate, and to use it in a gas flow meter for highly accurate flow rate measurement. As shown in FIG. 10, the differential pressure (differential pressure detected on both sides of the piezoelectric element) due to the pressure fluctuation transmitted to the inlet nozzles 39, 40 of the pressure sensor 1 is approximately 2 times the frequency (flow rate). Proportional to the square. The output obtained by multiplying the output from the piezoelectric elements 2 and 3 corresponding to this differential pressure by the gain of the amplifier circuit section 53 becomes the output as the amplifier circuit section 53. If the output is simply amplified, the output of the amplifier circuit may be saturated in the large flow rate region. In such a state, the output of the frequency to be measured is not amplified above the saturation value, which is in the peak state, and eventually the noise component is unnecessarily amplified and the SN ratio deteriorates.
Therefore, in order to prevent the deterioration of the SN ratio, it is necessary to reduce the gain at the time of amplifying the output from the piezoelectric elements 2 and 3 in a region above a certain frequency (region above a certain flow rate). In the present invention, the amplification circuit section 53 is configured to have the gain characteristic as shown in FIG.

In reality, due to the design of the flow meter element, etc.,
The relationship between frequency and differential pressure (characteristic at a certain flow rate)
The characteristics shown in Fig. 12 or the characteristics shown in Fig. 13 may be obtained, but the gain characteristics shown in the examples of A to F in Fig. 11 can be given by changing the constants. You can, so there will be no problems.

In the pressure sensor 1 of this embodiment, the output from the amplifier circuit section 53 is output as a pulse signal by passing through the voltage comparator 55. The voltage comparator 55 has an input / output waveform as shown in FIG. 14 and has a hysteresis characteristic as shown in FIG. 15, but since there are threshold levels SH1 and SH2, noise components below this level are completely removed. it can. Further, when the input reaches one of the threshold levels SH1, the threshold level changes to the other level SH2, so that the overdrive amount instantaneously increases. As a result, the output rises faster. Therefore, a stable pulse can be obtained accurately even if some noise is superimposed. As a result, the pulse signal can be extracted more accurately. Furthermore, since the pulse is converted into a pulse having a large slew rate and an amplitude substantially the same as that of the supply voltage through the level converter, when connecting to a MOS type digital IC for signal processing, the rise time is fast and the flowmeter as a whole It also has the advantage that it consumes less power.

In this embodiment, the final output is a pulse, but the pressure sensor final output may be a voltage or current output proportional to the frequency. Also, the output can be displayed as a numerical value or the like, or can be a circuit that converts the intensity of light or sound, blinking of light, or pitch of sound.

A battery may be provided in the pressure sensor 1 in order to cope with the case where it is necessary to prevent the pressure sensor 1 from being affected by the quality of the power source or when it is difficult to supply the necessary power source. Although it is possible, if the constant voltage circuit 51 is provided inside as in the present invention, the sensitivity of the measurement becomes constant as described above, and even for a power supply with poor quality such as power supply voltage fluctuation. An accurate pressure sensor can be provided.
Further, in the above embodiment, the power consumption is 17 μA or less, so that the battery can be used for a long time without replacement.

Although the above description has been made on the fluidic flowmeter, the pressure sensor according to the present invention can be applied to the Karman vortex flowmeter and other flowmeters as long as pressure fluctuation detection is essential. is there.

[0053]

As described above, when the pressure sensor of the present invention is used, one of the two piezoelectric elements arranged so that the surfaces in the same direction have the same polarization polarity is connected to one of the inlet nozzles. The pressure from the other inlet nozzle is applied to the other surface at the same time, and the noise component due to pressure fluctuation and temperature fluctuation is automatically eliminated by taking the differential pressure between the two surfaces, and at the same time, Detection accuracy is improved by taking the sum of outputs, and since two piezoelectric elements are positively arranged side by side under the same condition, noise due to vibration can be automatically deleted. Further, the signal from the piezoelectric element is passed through the amplifier circuit section to obtain the output as the pressure sensor, so that the noise component can be removed electrically and the constant voltage circuit is provided inside the signal processing circuit. As a result, the variation characteristic with respect to the power supply voltage was significantly improved, and furthermore, the hysteresis width of the voltage comparator was constant regardless of the supply voltage, and therefore the measurement sensitivity was constant. In addition, the slew rate of the level converter is large, and the influence on the power supply caused by the large amplitude operation is also absorbed, the noise inside the circuit is also small, and the stable sensitivity makes only the pressure fluctuation of the measurement object and the frequency of the measurement object extremely high. It can be detected accurately.

The minimum detectable pressure fluctuation range is 0.001
It becomes as small as ~ 1 Pa, and can be made even smaller. Also, the SN ratio is 0.001 Pa, 20 dBV, 1
It is very high at 60 dBV in Pa. For this reason, it has become possible to detect minute pressure fluctuations of gas or liquid that could not be detected conventionally without being affected by ambient noise. With the technology up to the present, a minute pressure fluctuation of about 1 Pa is quite large, or measurement cannot be performed unless expensive equipment is used. However, the product of the present invention can be configured as an extremely small sensor, and can be easily configured by a fluidic flow meter or Kalman. It can be used not only in the vortex flowmeter but also in other instruments and a part of the machine, so that it can be expected to be used in a wide range of fields. Also,
Since the mechanically weak piezoelectric element is not exposed, foreign matter in the fluid does not adhere to it, and it does not cause damage or decrease in sensitivity during the process of manufacture, handling, and implementation, and thus has a long life. Furthermore, the structure is simple, and there are no parts that require high technology for manufacturing, so that it can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is an electrical signal processing circuit diagram in a pressure sensor according to an embodiment of the present invention.

FIG. 2 is an electrical signal processing circuit diagram in a pressure sensor according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view of a pressure sensor according to an embodiment of the present invention.

FIG. 4 is an enlarged partial sectional view of a piezoelectric element portion of the pressure sensor of FIG.

5 is an enlarged partial exploded cross-sectional view of the pressure sensor of FIG. 3 before attachment of a piezoelectric element.

6 is a vertical cross-sectional view after the piezoelectric element of FIG. 5 is attached.

7 is an enlarged exploded perspective view of a piezoelectric element holding portion in the pressure sensor of FIG.

8 is an enlarged partial exploded cross-sectional view of the pressure sensor of FIG. 3 before attachment of another piezoelectric element.

9 is a vertical cross-sectional view after the piezoelectric element of FIG. 8 is attached.

FIG. 10 is a diagram showing the relationship between the frequency of the pressure sensor and the differential pressure due to pressure fluctuations.

FIG. 11 is a relationship diagram between a frequency and a gain in the amplifier circuit section.

FIG. 12 is a diagram showing a relationship between a frequency and a differential pressure due to pressure fluctuation in a certain flow meter.

FIG. 13 is a relationship diagram between the frequency and the differential pressure due to pressure fluctuation in another flow meter.

FIG. 14 is an input / output characteristic diagram of a voltage comparator that outputs a pulse.

FIG. 15 is a characteristic diagram showing hysteresis in the voltage comparator.

16 is a schematic configuration diagram when the pressure sensor of FIG. 3 is used in a fluidic flow meter.

[Explanation of symbols]

 1 Pressure Sensor 2, 3 Piezoelectric Element 4 Pressure Detection Section 5 Electric Signal Processing Circuit 6, 7 Piezoelectric Body 8, 9, 10, 11 Electrode Layer 12, 13, 14, 15 Holder 16, 17, 18, 19 Pressure Chamber 20 , 21, 22, 23 Front chamber 32 Substrate 33 Lid 35 Circuit board 36, 37 Input terminal 38 Output terminal 39, 40 Inlet nozzle 41 Shield case 42 First fluid pressure introduction path 43 Second fluid pressure introduction path 44 Third Fluid pressure introduction route 45 Fourth fluid pressure introduction route 46 Lids 47, 48 Communication passage 49 O-ring 50 Power supply terminal 51 Constant voltage circuit 52 Power supply 53 Amplification circuit section 54 Power supply protection circuit 55 Voltage comparator 56 Output terminal 57 Middle Point power source I 58 Middle point power source II 59 Level converter 60 Flow meter element section 61 Flow path reduction section 62 Jet nozzle 63 Flow path expansion section 64, 65 Partition wall 66, 67 Control nozzle 68 Target 69 Reflector blade 70 Guide plate 71 , 72 Internal pressure outlet 73 Gasket 86 Short circuit plate

Claims (3)

[Claims] 1. A pressure detecting portion, comprising two piezoelectric elements each having an electrode layer provided on both sides of a film-shaped piezoelectric body, sandwiched between two pairs of holders from both sides, and provided with tension. The elements are arranged so as to face in the same direction and the surfaces in the same direction have the same polarization polarity, and the pressure detection unit is provided with two inlet nozzles for introducing the pressure of the fluid, and one inlet nozzle is the first nozzle. The other is connected to the first surface of one of the piezoelectric elements via the first fluid pressure introduction path and has a polarization polarity different from that of the first surface of the one piezoelectric element via the fourth fluid pressure introduction path. Of the piezoelectric element is communicated with the second surface of the piezoelectric element, and the other inlet nozzle is communicated with the second surface of the one piezoelectric element through the second fluid pressure introduction path, and the third fluid pressure introduction path is connected. Pressure sensor communicated with the first surface of the other piezoelectric element through the pressure sensor The output from the two piezoelectric elements is sent to an amplification circuit section of a signal processing circuit inside the pressure sensor, and a constant voltage circuit is provided inside the signal processing circuit. Sensor. 2. The pressure sensor according to claim 1, wherein the holding surface of the holder for holding the two piezoelectric elements is formed as an inclined surface. 3. The pressure sensor according to claim 1, wherein a holding surface of the holder for holding the two piezoelectric elements is formed into a curved surface having an arbitrary curvature.