JPH05264301A - Fluid vibration detecting device - Google Patents

Abstract

PURPOSE:To improve the S/N of output signals by preventing the generation of noise from a piezo-electric film even when external vibrations are applied to the film. CONSTITUTION:Since electrodes 22-24 are formed on both surfaces of a piezo-electric film 21 except its outer peripheral section sandwiched by compression between an upper and lower housings 15 and 27, any voltage generated across the sandwiched section of the film 21 is not collected to the electrodes 22-24 even when the inertial forces of the housings 15 and 27 press the sandwiched section against each other. Therefore, the output of noise caused by external vibrations can be reduced and the S/N of output signals can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid vibration detecting device used in a Karman vortex flowmeter, a fluidic flowmeter or the like for detecting the frequency of pressure vibration generated in a fluid to measure the flow rate.

[0002]

2. Description of the Related Art As a conventional fluid vibration detecting device, one disclosed in Japanese Patent Laid-Open No. 2-268230 is known.
This device is used in Karman vortex flowmeters, fluidic flowmeters, etc. to introduce a target fluid to a diaphragm part made of a film-shaped piezoelectric body, deform the diaphragm by pressure vibration of the fluid, and output a voltage according to the displacement. The frequency of the fluid pressure is detected from. The diaphragm used here is a piezoelectric film made of a polymer, and electrodes made of thin metal films are formed on the entire front and back surfaces of this piezoelectric film by sputtering, etc. The diaphragm is supported and sealed by abutting and adhering or pressing. As a result, pressure chambers are formed on both sides of the diaphragm.

[0003]

In the above-described conventional fluid vibration detecting device, since the electrode on the outer peripheral portion of the diaphragm is supported in a state of being in contact with the housing together with the piezoelectric film, the entire device is perpendicular to the diaphragm surface. When an external vibration is applied in any direction, an inertial force according to the mass of the housing is applied to the piezoelectric film via the support portion. As a result, the piezoelectric film expands and contracts according to the inertial force to generate a voltage. The voltage generated here becomes noise unlike the original pressure oscillation of the fluid. Regarding the noise generated in this way, even in the above-mentioned conventional device, it is possible to cancel the noise by combining two diaphragms whose operation directions are opposite to each other and taking the difference between the signals obtained from the respective diaphragms. I have to. However,
When the noise level is high or when the respective portions of the two diaphragms are subjected to uneven acceleration, there is a problem that the generated noise cannot be canceled completely and the SN ratio is deteriorated. The present invention has been made to solve the above problems, and an object of the present invention is to provide a highly sensitive fluid vibration detection device which suppresses the generation of noise caused by external vibration and improves the S / N ratio. To provide.

[0004]

In order to achieve the above object, according to the present invention, a concave portion is formed inside the outer peripheral portion of a diaphragm in which electrodes made of metal thin films are formed on both surfaces of a film-shaped piezoelectric body. A pair of housings sandwich and seal from both sides, and a recess inside the housing forms pressure introduction chambers on both sides of the diaphragm, and fluid pressures are introduced into both pressure introduction chambers, and the pressure difference between both fluids fluctuates. In the fluid vibration detection device that extracts the voltage signal generated in the piezoelectric body due to the displacement and bending of the diaphragm by the electrodes, electrodes are formed on both surfaces of the film-shaped piezoelectric body excluding the outer peripheral portion pressed by the housing. It is characterized by

[0005]

In the present invention, since no electrode is formed on the outer peripheral surface of the film-shaped piezoelectric body that is pressed by the housing, the inertial force generated in the housing by external vibration presses the film-shaped piezoelectric body of the diaphragm. Even if a voltage is generated in the film-shaped piezoelectric material in that portion, it is not output via the electrodes.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 is a sectional view taken along line XX shown in FIG. In FIGS. 1 and 2, 15
Are two congruent rectangular recesses 1 on the side of one surface 15a thereof.
6, 17 are formed side by side and communicate with the recesses 16, 17 on the side of the other surface 15b, respectively, and the fluid pressure P is applied to these recesses.
1 is a thick plate-shaped first housing provided with a first pressure guide port 8 and a second pressure guide port 9 for introducing P1 and P2. 18 is the pressure P
Reference numeral 1 denotes an O-ring that is fluid-tightly guided to the pressure guide port 8, and 19 is an O-ring that is fluid-tightly guided to the pressure guide port 9.

The diaphragm 20 is a single PVDF (poly
a piezoelectric film 21 made of vinylidene fluoride film, and a first thin metal film formed on one surface of the film 21 by a manufacturing method such as sputtering except for a portion of the surface that contacts the outer peripheral frame of the first housing 15. The electrode 22 and the second surface 23 of the piezoelectric film 21 are formed by the same method as that of the electrode 22 except for the two portions on the other surface which are in contact with the frame of the second housing 27. Third electrode 2
4, a resin-made protective film 25 adhered to cover the film 21 over the electrode 22, and a resin protective film 25 adhered to cover the film 21 over the electrodes 23 and 24. And a protective film 26.

The thick plate-shaped second housing 27 has one surface 2
7a has rectangular recesses 28 and 2 that are mirror-symmetrical to the recesses 16 and 17 with respect to the housing surface 15a.
9 is formed. In FIG. 1, the recesses 16 and 17
And the recesses 28 and 29 face inward, the recesses 16 and 28 face each other, and the recesses 17 and 29 face each other.
A portion of the housing 15 and the diaphragm 20 and a portion of the housing 27 and the diaphragm 20 which are in contact with each other in a state of sandwiching 0 are fluid-tightly bonded by an adhesive.

The seal member 30 is filled in the illustrated portion so that the space between the diaphragm 20 and the housings 15 and 27 and the atmosphere outside the housings 15 and 17 and the recess 1 are formed.
Ensure fluid tightness between 6, 17, 28 and 29. Further, in this case, the diaphragm 20 is adhesively fixed as described above between the housings 15 and 27 in a state in which a predetermined tension is applied in the left-right direction in FIG. 1 by means (not shown). In such a fixed state, as shown in FIG. 2, the frame body (not shown) is curved so as to be curved into a side wall of the cylinder.
5 is provided. Further, in this case, both electrodes 23 and 24 are provided on the piezoelectric film 21 so that the electrode 23 faces the recess 28 and the electrode 24 faces the recess 29.

The first communication hole 31 includes a through hole 32 provided in the portion 15c of the housing 15 between the recess 16 and the recess 17 as shown in the drawing, and a through hole 33 provided in the diaphragm 20.
And a through hole 34 provided as shown in the portion 27c of the housing 27 between the recess 28 and the recess 29, and the housings 15 and 27 and the diaphragm 20 are fixed as described above so that the recess 16 is formed. And diaphragm 2
The 11th chamber 35 formed by 0 and the 22nd chamber 36 formed by the recessed portion 29 and the dihauram 20 are communicated with each other.

The second communication hole 37 is a part 1 of the housing 15.
5c and a through hole 38 provided as shown by a dotted line and another through hole not shown different from the through hole 33 provided in the diaphragm 20 and a through hole provided at a portion 27c of the housing 27 as shown by a dotted line. The hole 17 and the recess 17
21st chamber 40 formed by the diaphragm 20 and the twelfth chamber 41 formed by the concave portion 28 and the diaphragm 20.
And communicate with. Each part of both through holes is configured so that the communication holes 31 and 37 do not communicate with each other.

The terminals 42a, 42b and 42c lead out the respective potentials of the electrodes 22, 23 and 24 to the upper surface 27b of the housing 27 as shown in FIG. The first conducting means 43 connects the terminal 42a to the ground potential 44, the second conducting means 45 connects the terminal 42b to the non-inverting input terminal 12b as the first input terminal of the differential amplifier 12, and the third conducting means 4
Reference numeral 6 connects the terminal 42c to the inverting input terminal 12c as the second input terminal of the differential amplifier 12. The voltage detecting means 47 is composed of the electrodes 22, 23, 24, the conducting means 43, 45, 46 and the differential amplifier 12, and the fluid vibration detecting device 48 is composed of the above-mentioned respective parts.

In the detection device 48, the terminals 42a to 42c penetrate the sealing material 30 and are fluid-tightly drawn out to the housing surface 27b as shown in FIG. It is a mounting hole provided in the housing 15 for attachment to a predetermined portion. Since each part of the detection device 48 is configured as described above, in this device 48, the housing parts 15c and 27c are
And the concave portion 16 and the concave portion 2 which are juxtaposed via a partition wall 60 composed of
The first chamber 61 composed of 8 and the second chamber 62 composed of the recess 17 and the recess 29 are fluid-divided into two halves by the piezoelectric film 21 to form the eleventh chamber 35, the twelfth chamber 41 and the twenty-first chamber 4 respectively.
0 and the 22nd chamber 36 are formed.

The detector 48 is constructed as described above, and the piezoelectric film 21 is polarized over the entire surface in the thickness direction with uniform strength and orientation. Thereby,
When pressures P1 and P2 are applied to the pressure guide ports 8 and 9, respectively, a first voltage E1 corresponding to P1 is generated between the electrodes 22 and 23, and at the same time, a second voltage E corresponding to P2 is applied between the electrodes 22 and 24.
Since 2 is generated, the output voltage 12a of the amplifier 12 becomes a voltage corresponding to the differential pressure (P1-P2) as in the detection device 1 described above. When an external vibration is applied to the piezoelectric film 21 in a vertical direction, an inertial force also acts on the piezoelectric film 21 and the second housing 27 mounted on the piezoelectric film 21, so that in the diaphragm 20 formed of the piezoelectric film 21, the second housing The portion bonded and supported by 27 expands and contracts due to the inertial force corresponding to the mass of the housing 27.

Since the weight of the housing 27 is larger than its own weight, the inertial force generated from this portion becomes very large, and the voltage generated by the piezoelectric effect is much larger than that generated by its own weight. It will be a large value. In this way
Even if a voltage is generated by the inertial force of the housing 27, it can be canceled in principle because the differential output of the two elements is actually taken, but if the noise output due to vibration becomes large, it cannot be canceled completely. The amount cannot be ignored. However, in this embodiment, since the portion of the piezoelectric film 21 to which an external force is applied is electrically insulated, even if an external force acts to generate a voltage at that portion, it does not appear as a noise output.

According to this embodiment, when the piezoelectric film 21 of the fluid vibration detecting device and the housings 15 and 27 are bonded,
Conventionally, the electrodes 22 to 24 provided on both surfaces of the piezoelectric film 21 are used instead of the electrodes 22 to 24 on the bonding surface between the piezoelectric film 21 and the housings 15 and 27, or the portion along the inner edge of the bonding surface. It is electrically insulated by removing and bonding. As a result, external vibration is applied in a direction perpendicular to the piezoelectric film 21, an inertial force corresponding to the mass of the piezoelectric film 21 acts on the housings 15 and 27, and even if a voltage is generated by the piezoelectric effect, the sensor No noise appears in the output. As a result, the fluid vibration pressure can be detected without lowering the S / N ratio.
Although the present invention is applied to the fluid vibration detection device having two diaphragms whose operating directions are opposite to each other, the embodiment can be similarly applied to a detection device having one diaphragm.

[0017]

As described above, according to the present invention, since no electrode is formed on the outer peripheral surface of the film-shaped piezoelectric body that is pressed by the housing, the inertial force generated in the housing due to external vibration is applied to the diaphragm. Even if a noise voltage is generated in the portion of the film-shaped piezoelectric body that supports the pressure, and a noise voltage is generated in that portion of the film-shaped piezoelectric body, it is not output via the electrode. As a result, the S / N ratio of the output signal is improved, and it becomes possible to measure the fluid pressure vibration with high accuracy.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment according to the present invention.

FIG. 2 is a sectional view taken along line XX in FIG.

[Explanation of symbols]

 12 Differential Amplifier 12a Output Voltage (Detection Signal) 12b First Input Terminal 12c Second Input Terminal 15 First Housing 16 Recess 17 Recess 20 Diaphragm 21 Piezoelectric Film 22 First Electrode 23 Second Electrode 24 Third Electrode 25 Protective Film 26 Protective film 27 Second housing 28 Recess 29 Recess 35 35 11th chamber 36 22nd chamber 40 21st chamber 41 12th chamber 43 1st conducting means 45 2nd conducting means 46 3rd conducting means 48 Fluid vibration detection device 61 1st chamber 62 Room 2

Claims (1)

[Claims] 1. A housing having a pair of housings having recesses formed inside the outer peripheral portion of a diaphragm having electrodes made of a metal thin film formed on both surfaces of a film-shaped piezoelectric body, as well as being pressed and sealed from both sides. Pressure introducing chambers are formed on both sides of the diaphragm by the inner recesses, and fluid pressures are introduced to both pressure introducing chambers, and the voltage signal generated in the piezoelectric body is generated due to displacement and bending of the diaphragm due to fluctuations in the differential pressure between both fluids. In a fluid vibration detecting device that is taken out through an electrode, the fluid vibration detecting device is characterized in that electrodes are formed on both surfaces of a film-shaped piezoelectric body excluding an outer peripheral portion pressed by a housing.