JP2655573B2 - Pressure sensor and gas flow meter using pressure sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pressure sensor using a polymer piezoelectric film, which is optimally used for a fluidic flow meter or a Karman vortex flow meter, and uses the pressure sensor. Gas flow meter.

[Prior Art] Fluidic flowmeters and Karman vortex flowmeters are known as flowmeters capable of accurately detecting the flow rate of a fluid, particularly a gas (for example, JP-A-57-110918, JP-A-57-110918).
58-169030, JP-A-60-187814). As disclosed in Japanese Patent Application Laid-Open No. 60-187814, a fluidic flow meter has a flow meter element section in which a main flow of a fluid ejected from an ejection nozzle alternately follows a pair of partition walls, and the fluid flows therethrough. The pressure fluctuation generated at the time of the change is detected by a pressure sensor, and the flow rate of the fluid is detected at a frequency of the pressure fluctuation corresponding to the flow rate. As described in Japanese Patent Application Laid-Open Nos. Sho 57-110918 and 58-169030, the Karman vortex flowmeter uses a vortex generator provided in the flow meter element to introduce Karman vortex into the flowing fluid. Intermittently occur,
A pressure variation generated when the Karman vortex passes is detected by a pressure sensor, and a flow rate of the fluid is detected by a Karman vortex generation number corresponding to the flow rate.

As a pressure sensor used in such a flow meter,
It is desirable that high sensitivity, that is, small pressure fluctuations and pressure fluctuations in a wide frequency range be detected, and that the structure be simple, inexpensive and easily manufactured.

As a typical example of a pressure sensor conventionally used in this type of flow meter, disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 57-110918, and further described in detail in "Nikkei Electronics, 1985," A pressure sensor using a diaphragm and a pressure sensor using a polymer piezoelectric film as disclosed in JP-A-58-169030 are known.

[Problems to be Solved by the Invention] However, a pressure sensor using a silicon diaphragm has the following problems.

That is, since the silicon chip itself is not a piezoelectric material, the silicon chip itself does not have a pressure detecting function, and a method of detecting a pressure change as a resistance change due to its strain requires a resistance change detection circuit such as a bridge circuit. In addition, since the silicon chip is close to a rigid body and there is a limit to an etching process for thinning the silicon chip, it is difficult to detect a slight pressure fluctuation. Therefore, there is a limit in improving the sensitivity, and the frequency range that can follow a change in pressure is narrow due to its structure.

In addition, it is difficult to control the thickness of the silicon diaphragm in manufacturing, and there is a problem that the sensitivity of the pressure sensor varies widely. Furthermore, temperature compensation is indispensable because it is a method of detecting a change in resistance that greatly changes with temperature, and since this temperature compensation circuit is usually integrated and manufactured,
Requires complex technology for manufacturing. In addition, large equipment is required for manufacturing.

Further, due to the manufacturing difficulties described above and the need for sensing and compensating circuits, silicon diaphragm type pressure sensors are usually quite expensive, especially those with high sensitivity.

In this pressure sensor using a polymer piezoelectric film,
Since the polymer piezoelectric film itself is a piezoelectric material, a potential difference generated from the polymer piezoelectric film itself can be directly output as a voltage signal, and sensitivity can be improved. In addition, the polymer piezoelectric film has high flexibility that can be easily deformed compared to the silicon chip,
In addition, since a thin film can be easily manufactured and its thickness can be controlled with high precision, it is possible to follow a high sensitivity and a wide pressure fluctuation frequency range.

However, a pressure sensor using a polymer piezoelectric film as disclosed in JP-A-58-169030 has the following problems.

That is, since the pressure detection method is such that the polymer piezoelectric film is directly inserted into the flow path of the fluid, the polymer piezoelectric film is easily damaged by the fluid and cannot withstand long-term use. Therefore, it is difficult to make a high-sensitivity pressure sensor by utilizing the characteristics of the polymer piezoelectric film.

In addition, since the pressure detecting section is configured by laminating the polymer piezoelectric film on a thin metal plate, the flexibility of the pressure detecting section is reduced as compared with the case of using only the polymer piezoelectric film, and the sensitivity to a weak pressure change is reduced. And it is difficult to follow pressure fluctuations at extremely low and high frequencies.

An object of the present invention is to provide a highly sensitive method capable of detecting a small pressure fluctuation and detecting a pressure fluctuation in a wide frequency range.
Another object of the present invention is to provide a pressure sensor which has a simple structure and is easy to manufacture, and which is suitable for practical use.

Another object of the present invention is to provide a high-precision gas flow meter using the high-sensitivity pressure sensor.

[Means for Solving the Problems] A pressure sensor according to the present invention, which meets the above object, comprises: (A) a polymer piezoelectric film stretched so as to be planar and deformable; and (B) both surfaces of the polymer piezoelectric film. (C) holding the periphery of the polymer piezoelectric film from both sides via the electrode layer, and providing the pressure of the fluid on both sides of the polymer piezoelectric film, respectively. A pressure chamber forming body surrounding a space located on both sides of the polymer piezoelectric film to form a pressure chamber to be formed; and (D) individually introducing pressure of a fluid into both the pressure chambers.
And (E) an amplifier for transmitting a potential difference between both surfaces of the polymer piezoelectric film caused by deformation of the polymer piezoelectric film through the two electrode layers, and amplifying and outputting the potential difference. (F) Further, the pressure guiding paths from each of the inlet nozzles to each of the corresponding pressure chambers are bent, and the respective flow passage volumes are equalized, so that the pressure guiding paths to both surfaces of the piezoelectric film are formed. The pressure propagation time is substantially equal.

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

This pressure sensor is an optimal pressure sensor used for 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 connected via two pressure guiding tubes and the like. , Which are connected to a flow meter element that generates pressure fluctuations in accordance with the flow rate of the flowing fluid. In the connection, the volumes of the two pressure guiding paths, that is, the paths from the inlet end of the pressure guiding tube to each pressure chamber and each surface of the polymer piezoelectric film are made equal.

In some cases, the two inlet nozzles of the pressure sensor are directly connected to the flow meter element to eliminate the pressure guiding tube.

The piezoelectric polymer film in the pressure sensor is made of, for example, a copolymer of polyvinylidene fluoride and ethylene trifluoride. The film thickness is preferably selected from the range of 10 to 100 μm from the viewpoint of sensitivity, strength and ease of handling. The film thickness can be easily and precisely controlled by a known film forming technique.

The electrode layers provided on both surfaces of the polymer piezoelectric film are made of a material such as aluminum, copper, gold, nickel, and palladium, and are formed on the surface of the polymer piezoelectric film by a metallizing method such as evaporation, sputtering, and plating. .

The pressure guiding path from each inlet nozzle to each corresponding pressure chamber has a bent structure so that the introduced fluid does not directly hit the polymer piezoelectric film surface.

Regarding the transmission of the potential difference between both surfaces of the polymer piezoelectric film to the amplifier, both electrode layers may be directly connected to the amplifier via a lead wire or the like, but a pressure chamber forming body connected to both electrode layers or It is structurally simpler to form the surface with a conductor and then connect it to the amplifier via a lead wire or the like.

[Operation] In the pressure sensor as described above, the pressure of the fluid is
Introduced separately into both pressure chambers via two inlet nozzles,
The polymer piezoelectric film is deformed by the pressure difference between both sides of the polymer piezoelectric film, and a charge is generated on the film surface by spontaneous polarization due to the deformation, and a potential difference is generated between both surfaces of the polymer piezoelectric film, and the potential difference is amplified through both electrode layers. And a voltage signal amplified by the amplifier is output.

Compared with a silicon diaphragm type pressure sensor, a signal is generated from the polymer piezoelectric film itself, so that a target output signal can be obtained only by the amplifier. Further, as compared with the structure disclosed in Japanese Patent Application Laid-Open No. 58-169030, the polymer piezoelectric film is not directly exposed to the flow passage of the pressure detecting fluid, so that a metal plate or the like for supporting the film is not required, and the high pressure is not required. By utilizing the flexibility of the molecular piezoelectric film substantially as it is, it is possible to increase the sensitivity and follow pressure fluctuations in a wide frequency range.

In addition, since fluid pressure is guided to both surfaces of one polymer piezoelectric film, two inlet nozzles are connected to different measurement positions for the same fluid to be measured. While simultaneously leading to both pressure chambers, a 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 polymer piezoelectric film, the deformation of the polymer piezoelectric film due to the high frequency fluctuation component is suppressed. Then, a signal having a potential difference corresponding to the differential pressure and a signal having a frequency corresponding to the number of occurrences of the differential pressure is output. Therefore, by connecting this pressure sensor to the flow meter element part of a fluidic flow meter or Karman vortex flow meter, while automatically eliminating high frequency fluctuation components of the entire fluid that may be noise,
High-precision detection of only pressure fluctuation components due to fluid vibration or pressure fluctuation components due to Karman vortices realizes a highly sensitive flow meter with a simple structure without complicated compensation circuits. .

Since the pressure guide paths are all bent, even if fine foreign matter is mixed in the introduced fluid, it adheres to and hits the piezoelectric film surface, or the jet directly hits the polymer piezoelectric film and causes Damage to the film and loss of sensitivity are prevented. Furthermore, since the flow passage volumes of the pressure guiding paths leading to the respective pressure chambers are made equal, noise due to the pressure propagation time difference and the pressure difference between both surfaces of the piezoelectric film is almost completely eliminated.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a pressure sensor according to an embodiment of the present invention,
FIG. 3 shows the structure of the polymer piezoelectric film, and FIG. 3 shows the structure of the sixth embodiment when this pressure sensor is used in a fluidic flow meter.
The figure shows an example of a case where the present invention is used for a Karman vortex flow meter.

In FIG. 1, reference numeral 1 denotes an entire pressure sensor according to the present invention, and the pressure sensor 1 has a polymer piezoelectric film 2 as shown enlarged in FIG. The polymer piezoelectric film 2 is stretched to be flat and deformable. In this embodiment, the polymer piezoelectric film 2 is made of a copolymer of polyvinylidene fluoride and ethylene trifluoride, but other polymer piezoelectric materials may be used. The thickness of the polymer piezoelectric film 2 is suitably 10 to 100 μm as a gas pressure sensor from the viewpoints of sensitivity, strength, and ease of handling, and is 15 μm in this embodiment.
However, the pressure sensor according to the present invention includes, of course, those for liquids, and the thickness of the polymer piezoelectric film and the structure of the electrode section and the like described below 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 the pressure fluctuation, it is also possible to attach a polymer piezoelectric film to a thin metal or rubber diaphragm and treat the whole as a reinforced polymer piezoelectric film. .

Ultra-thin electrode layers 3 and 4 are formed on both surfaces of the polymer piezoelectric film 2 by metallization such as vapor deposition, sputtering, and plating. As described above, the material of the electrode layers 3 and 4 is selected from aluminum, copper, gold, nickel, palladium and the like. The periphery of the polymer piezoelectric film 2 is sandwiched from both sides by holder electrodes 5 and 6 as pressure chamber forming members via electrode layers 3 and 4. Holder electrodes 5, 6
The electrode 5 is electrically connected to the electrode layer 3, and the electrode 6 is electrically connected to the electrode layer 4, respectively.
Both are insulated by the polymer piezoelectric film 2. The holder electrodes 5, 6 form pressure chambers 7, 8 on both sides of the polymer piezoelectric film 2, which surround the spaces located on both sides of the piezoelectric film 2 as shown in the figure, into which the pressure of the fluid is introduced. The pressure chambers 7 and 8 are formed as a fluid-filled type except for the portions of the throttles 9 and 10. The holder electrodes 5 and 6 holding the polymer piezoelectric film 2 are held by a body 11 made of a phenol resin, and communicate with the pressure chamber 7 via the throttle 9 on both sides of the holder electrodes 5 and 6 by the body 11. A front chamber 12 and a front chamber 13 communicating with the pressure chamber 8 via the throttle 10 are formed. As the material of the body 11, any other engineering plastic can be used as long as it is an insulator. In addition,
The diameter of the apertures 9 and 10 is suitably about 0.1 to 0.5 mm.

The front chambers 12 and 13 are individually connected to two inlet nozzles 16 and 17 via introduction paths 14 and 15, respectively. Inlet nozzle 1
In the present embodiment, the openings 6 and 17 are opened in the same direction, but the openings may be in any direction. However, introduction route 14,
The openings of the 15 into the front chambers 12 and 13 are not opposed to the diaphragms 9 and 10, but are shifted in position. That is, the pressure guiding path has a bent structure. In this embodiment, the volume of the fluid pressure introduction path from the inlet nozzle 16 to the pressure chamber 7 and the volume of the inlet nozzle
Each passage volume is set such that the volume of the fluid pressure introduction path from 17 to the pressure chamber 8 is equal.

Lead wires 18 and 19 are connected to the holder electrodes 5 and 6 by soldering or the like, respectively.
Connected to 20. The potential difference between both surfaces of the polymer piezoelectric film caused by the deformation of the polymer piezoelectric film 2 is transmitted to the amplifier 20 via the electrode layers 3 and 4, the holder electrodes 5 and 6, and the leads 18 and 19. The potential difference is amplified and output from the output terminal 21 as a voltage signal. The amplifier 20 is embedded in a resin 22, and the resin 22 and the entire body 11 are housed in a shield case 23. In this embodiment, the shield case 23 is manufactured by processing a brass plate, but may be formed by metallizing the surface of a resin case or by molding using a conductive resin.

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 fluid gas flow meter.

FIG. 3 shows a configuration in a case where the pressure sensor 1 is applied to a fluidic flow meter. In the drawing, reference numeral 30 denotes a flow meter element in the fluidic flow meter. The gas to be measured flows through the flow meter element section 30 in the direction of the arrow. 31
Is a flow channel reducing portion, and a jet having an increased flow velocity is jetted from the jet nozzle 32 at the tip thereof. The main stream of the jet is the channel expansion section
33 flows along one of the wall surfaces of the pair of partition walls 34 and 35, and a part of the wall flow is changed in direction and is orthogonal to the jet from the jet nozzle 32 from the control nozzle 36 (or 37). And a force acts so that the jet from the jet nozzle 32 flows along the other partition. Since this is repeated, the gas flows along the partition walls 34 and 35 alternately, and a pressure fluctuation occurs in the flow meter element unit 30 in accordance with the 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 the pressure fluctuation. Reference numeral 38 in the figure denotes a target for efficiently directing the jet to one of the partition walls.

Inside the flow meter element 30 as described above, the internal pressure outlets 39, 40
Is provided, and the internal pressure extraction pressure ports 39, 40 are provided with pressure guiding tubes 41,
It is connected to the inlet nozzles 16 and 17 of the pressure sensor 1 via 42, respectively. In the drawing, reference numeral 43 denotes the pressure sensor 1 described above.
2 schematically shows a pressure detecting section including the polymer piezoelectric film 2.

When the flow is switched to the internal pressure outlet 39 side inside the flow meter element unit 30, the fluid pressure near the internal pressure outlet 39 becomes the internal pressure outlet 40.
When the flow is switched to the internal pressure outlet 40 side, on the contrary, the fluid pressure near the internal pressure outlet 40 becomes higher. The periodic pressure fluctuation between the internal pressure outlets 39 and 40 is caused by the pressure guiding tube 41, the inlet nozzle 16, the introduction path 14, the front chamber 12, the throttle 9,
Pressure guiding path of pressure chamber 7, pressure guiding tube 42, inlet nozzle
17, the introduction path 15, the front chamber 13, the restrictor 10, and the pressure guiding path of the pressure chamber 8, are guided to both sides of the polymer piezoelectric film 2, respectively. Therefore, on both sides of the polymer piezoelectric film 2, a differential pressure having a magnitude relationship opposite to that of the polymer piezoelectric film 2 is alternately applied, and the polymer piezoelectric film 2 is alternately formed on the pressure chamber 7 side and the pressure chamber 8 side by the differential pressure. Deform. Due to the spontaneous polarization due to the deformation, a charge is generated on the surface of the polymer piezoelectric film 2, and an alternating potential difference is generated between both surfaces. The cycle of the change in the potential difference is the same as the cycle of the flow change in the flow meter element section 30 described above. This potential difference is amplified by the amplifier via the electrode layers 3 and 4, the holder electrodes 5 and 6, and the leads 18 and 19. It is transmitted to 20 and appropriately amplified and output as a voltage signal. If this voltage signal is sent to an appropriate signal processing circuit (not shown), and the number of pulses generated per unit time is measured by adjusting to an electric pulse train, a signal proportional to the gas flow rate in the flow meter element unit 30 can be obtained. The flow is measured. Further, the differential pressure at the internal pressure outlets 39 and 40 corresponds to the flow rate, and the magnitude of the differential pressure of the pressure introduced to both surfaces of the polymer piezoelectric film 2 is proportional to the deformation amount of the polymer piezoelectric film 2, Since the amount of deformation of the polymer piezoelectric film 2 and the magnitude of the voltage generated from the polymer piezoelectric film 2 due to the deformation are proportional, it is also possible to take out the output signal as an analog signal whose magnitude is proportional to the pressure.

The pressure sensor 1 holds the polymer piezoelectric film 2 in a state of having the pressure chambers 7 and 8 on both sides and in a state of being substantially confined in a container-like body. Since the polymer piezoelectric film 2 is prevented from directly acting on the polymer piezoelectric film 2, the polymer piezoelectric film 2 can be used without protection and a reinforcing plate, and the film thickness can be extremely thin as 10 to 100 μm. In this way, an output signal due to the deformation of the polymer piezoelectric film 2 can be obtained even by an extremely weak differential pressure. Therefore, even when applied to the above flowmeter, the detection sensitivity to pressure fluctuation is extremely high. A conventional pressure sensor comprising a silicon diaphragm using a piezoresistive effect as a detecting element can normally detect only a pressure fluctuation of about 0.2 mmH ₂ O even with a high-sensitivity type. mmH ₂ O
It becomes possible to detect a minute pressure fluctuation. Further, since only extremely thin electrode layers 3 and 4 are formed on both surfaces of the polymer piezoelectric film 2 by metallizing, the same flexibility of the piezoelectric film as in the case of only the polymer piezoelectric film 2 can be maintained. As described above, it is possible to detect a minute pressure fluctuation and follow a pressure fluctuation in a wide frequency range of about 0.1 Hz to several MHz.

Further, the thickness of the polymer piezoelectric film 2 can be controlled relatively easily and with high precision in its manufacture. By setting the film thickness with high accuracy, measurement accuracy is improved in addition to high sensitivity.

In addition, since the openings of the introduction passages 14 and 15 to the front chambers 12 and 13 are displaced without being opposed to the diaphragms 9 and 10, even if fine foreign matter is mixed in the introduced fluid, it is not affected. It is possible to prevent the piezoelectric film from being attached to or colliding with the surface of the piezoelectric film, or from directly hitting the polymer piezoelectric film 2 to damage the piezoelectric film or to lower the sensitivity.

In addition, since the fluid pressure is introduced to both surfaces of the polymer piezoelectric film 2, when the pressure sensor 1 is used in a flow meter as described above, the high frequency of the entire fluid introduced from the internal pressure outlets 39 and 40 is reduced. The pressure fluctuation component is applied equally to both surfaces of the polymer piezoelectric film 2 at the same time, and the polymer piezoelectric film 2 is not deformed by the high frequency pressure fluctuation component of the entire fluid which may be a noise in fluid flow rate measurement. Can be automatically eliminated.

In particular, since the pressure guiding paths from the inlet nozzles 16 and 17 to the pressure chambers 7 and 8 have the same volume, the pressure guiding tube 4
By adjusting the length of 1, 42, the pressure / propagation time from the internal pressure outlets 39, 40 to both surfaces of the polymer piezoelectric film 2 becomes equal, and the above-mentioned filtering effect is kept high. As shown in FIG. 4, this filtering effect is supplied from a pressurized air source 56 using a test pressure sensor 55 in which pressure chambers 52, 54 are formed by holder electrodes 51, 52 on both sides of a polymer piezoelectric film 50. The air is throttled by a throttle valve 57, and audible frequency noise generated by the throttle valve 57 is reduced from a small tank 58 to pressure guiding tubes 59 and 60, a pressure sensor.
The internal volume difference between the pressure guiding tubes 59 and 60 is measured by using a device that guides both sides of the polymer piezoelectric film 50 through both inlet nozzles 61 and 62 of 55 and measures an output voltage from an output terminal 64 through an amplifier 63. The audible frequency noise reduction effect was examined by changing. as a result,
As shown in FIG. 5, when the volume difference is adjusted within 20 mm ^{3 as} compared with the case where there is a volume difference between the pressure guiding tubes 59 and 60,
It was found that the noise could be almost completely eliminated. Therefore,
As described above, in the flow rate measurement shown in FIG. 3, by eliminating the volume difference between the two pressure guiding paths to both surfaces of the polymer piezoelectric film 2, noise generated in the entire fluid is almost completely eliminated. In addition, since the front chambers 12 and 13 and the throttles 9 and 10 in the pressure sensor 1 function as low-pass filters, external noise transmitted to the fluid to be measured and noise generated at the throttle portion of the piping system are efficiently eliminated. Thus, the ratio (SN ratio) between the flow meter output signal and the noise becomes extremely high.

Next, FIG. 6 shows an example in which the pressure sensor according to the present invention is used for a Karman vortex flowmeter.

6, reference numeral 70 denotes a flow meter element of the Karman vortex flow meter, and 71 denotes a vortex generator. The fluid flowing in the direction of the arrow in the figure hits the vortex generator 71, and generates a Karman vortex 72 intermittently in the subsequent flow.
One of the internal pressure outlets 73 is provided in the passage portion of the Karman vortex 72, and the other internal pressure outlet 74 is provided on the inner wall surface of the flow meter element 70. The two internal pressure outlets 73 and 74 are connected to the inlet nozzle 16 of the pressure sensor 1 through the pressure guiding tubes 75 and 76, respectively.
Connected to 17. Other configurations are the same as those shown in FIGS. 3 and 1.

In such a Karman vortex flowmeter, the number of Karman vortices generated per unit time changes in proportion to the flow rate of the fluid, and the flow rate is detected by measuring the number of Karman vortices passing through the internal pressure outlet 73. . The pressure fluctuation during the passage of the Karman vortex is introduced into one side of the polymer piezoelectric film 2 via the internal pressure outlet 73, the pressure guiding tube 75, and the inlet nozzle 16, and the internal pressure outlet 74, the pressure guiding tube 76, the inlet nozzle The pressure and the pressure fluctuation of the entire passing fluid are introduced to the other surface side of the piezoelectric polymer film 2 via 17. Therefore, by introducing pressure to both surfaces of the polymer piezoelectric film 2 and detecting the differential pressure, the pressure fluctuation (the high frequency noise) of the entire fluid is effectively eliminated, and the flexible polymer piezoelectric film 2 is used. Pressure fluctuation due to Karman vortex passage is detected with high accuracy, and high-sensitivity, high-precision flow measurement becomes possible. Other operations are the same as those of the above-described fluidic flow meter.

Although the above description has been made with respect to a fluidic flow meter and a Karman vortex flow meter, the pressure sensor according to the present invention can be applied to other flow meters as long as the pressure fluctuation detection is essential. Further, the pressure sensor according to the present invention can detect the differential pressure on both sides of the polymer piezoelectric film. For example, one of the inlet nozzles is opened to the atmosphere,
If the pressure of the fluid to be measured is guided to the other inlet nozzle, the gauge pressure with respect to the atmospheric pressure can be measured with high sensitivity. In addition, if one inlet nozzle is connected to a sealed container filled with a pre-calibrated fluid at a constant pressure and the pressure of the fluid to be measured is guided to the other inlet nozzle, the absolute value of the pressure can be accurately determined. It can also be used as a pressure sensor that can be detected by.

[Effects of the Invention] As described above, when using the pressure sensor of the present invention, pressure chambers are formed on both sides of the polymer piezoelectric film, and fluid pressures are individually applied from two inlet nozzles to both sides of the polymer piezoelectric film. To detect the differential pressure on both sides while maintaining the flexibility of the polymer piezoelectric film, so that it can detect small pressure fluctuations with high sensitivity and a wide frequency range from extremely low frequency to ultra-high frequency Up to pressure fluctuations. In signal processing, the potential difference generated from the polymer piezoelectric film itself can be output as an appropriate voltage signal only by amplifying it with an amplifier, so that the response speed is extremely fast and the structure is extremely simple, making it easy to manufacture. In addition, an inexpensive pressure sensor can be realized. In addition, since the pressure guiding paths are all bent, even if fine foreign matter is mixed in the introduced fluid, it adheres to and hits the piezoelectric film surface, or the jet directly hits the polymer piezoelectric film and causes Damage to the film and loss of sensitivity are prevented. Further, since the flow volume of the pressure guiding path leading to each pressure chamber is made equal, noise caused by the pressure propagation time difference and the pressure difference to both surfaces of the piezoelectric film can be almost completely eliminated.

In addition, by using the pressure sensor according to the present invention for a fluidic flow meter or a Karman vortex flow meter, high-sensitivity flow measurement can be performed from a low flow rate range to a high flow rate range, and a noise component is substantially eliminated. And high-accuracy flow measurement can be performed.

[Brief description of the drawings]

1 is a sectional view of a pressure sensor according to one embodiment of the present invention, FIG. 2 is an enlarged partial sectional view of a polymer piezoelectric film of the pressure sensor of FIG. 1, and FIG. 3 is a sectional view of the pressure sensor of FIG. FIG. 4 is a schematic diagram showing the configuration of a device for testing the filtering effect of a pressure sensor according to the present invention, and FIG. 5 shows the results of a test using the device shown in FIG. FIG. 6 is a diagram showing the relationship between the volume difference and the magnitude of noise. FIG. 6 is a schematic diagram showing the configuration when the pressure sensor of FIG. 1 is used in a Karman vortex flowmeter. 1, 55: Pressure sensor 2, 50: Polymer piezoelectric film 3, 4, ... Electrode layer 5, 6, 51, 52: Holder electrode as pressure air forming body 7, 8, 53, 54: Pressure Chamber 9, 10… Restrictor 11… Body 12, 13… Front chamber 14, 15… Introductory passage 16, 17, 61, 62… Inlet nozzle 18, 19… Lead wire 20, 63… Amplifier 21 , 64… Output terminal 23… Shield case 30… Flow meter element part of fluidic flow meter 31… Flow path reducing part 32… Jet nozzles 34, 35… Partition walls 36, 37… Control nozzle 38… … Target 39, 40, 73, 74… Internal pressure outlet 41, 42, 59, 60, 75, 76… Pressure guiding tube 43… Pressure detector 56… Compressed air source 57… Throttle valve 58… Compact Tank, 70: Flow meter element of Karman vortex flow meter 71: Vortex generator 72: Karman vortex

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-110918 (JP, A) JP-A-56-1333639 (JP, A) JP-A-57-147027 (JP, A) 35244 (JP, U) JP-B 52-10632 (JP, B2)

Claims (3)

(57) [Claims] (A) a polymer piezoelectric film stretched in a planar and deformable manner; (B) electrode layers respectively provided on both surfaces of the polymer piezoelectric film; and (C) the electrode layer. And a peripheral portion of the polymer piezoelectric film is held from both sides through the polymer piezoelectric film, and both sides of the polymer piezoelectric film are formed on both sides of the polymer piezoelectric film to form pressure chambers into which fluid pressure is introduced. A pressure chamber forming body surrounding a space located at a position (2); and (D) introducing a pressure of a fluid individually into the two pressure chambers.
And (E) an amplifier for transmitting a potential difference between both surfaces of the polymer piezoelectric film caused by deformation of the polymer piezoelectric film through the two electrode layers, and amplifying and outputting the potential difference. (F) Further, the pressure guiding paths from each of the inlet nozzles to each of the corresponding pressure chambers are bent, and the respective flow passage volumes are equalized, so that the pressure guiding paths to both surfaces of the piezoelectric film are formed. A pressure sensor wherein pressure propagation times are substantially equal. 2. The pressure sensor according to claim 1, wherein said fluid is a gas. 3. The gas flow meter according to claim 2, wherein said two inlet nozzles of the pressure sensor are connected to a flow meter element for generating a pressure fluctuation according to a flow rate of a gas to be circulated.