JPH0646339U - Piezoelectric pressure sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a piezoelectric pressure sensor with excellent chemical resistance and heat resistance. [Structure] A substrate 1 and a diaphragm 2 to which electronic parts are attached are attached in a case 8 via an outer frame 11 and an inner frame 12. The diaphragm 2 is a single ceramic piezoelectric element. The lower portion of the outer frame 11 has a lateral side bent inward in an L-shaped cross section, and a sharp end 11a is formed at the upper portion of the lateral side. A sharp end 12a is formed in the lower portion of the inner frame 12 so as to face the sharp end 11a, and both sharp ends 11a and 12a are formed.
The diaphragm 2 is sandwiched between them. Between the upper portion of the inner frame 12 and the substrate 1, a cushioning material such as an O-ring 6 that elastically presses the sharp end 12a of the inner frame 12 against the diaphragm 2 is inserted. The electrodes attached to both sides of the diaphragm 2 are electrically connected to the substrate 1.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a piezoelectric pressure sensor used for detecting a pressure change in a tank that stores a liquid or a gas, detecting a sound in a furnace, and the like.

[0002]

[Prior art]

 In order to detect pressure changes in tanks that store heavy oil and chemicals, as well as acoustics generated in combustion furnaces and turbine ducts, ceramic piezoelectric elements, which have high resistance to chemicals and heat, have been used in the past. I came.

FIG. 5 is a vertical cross-sectional view illustrating a pressure sensor using a conventional ceramic piezoelectric element, and the thickness is exaggerated for easy understanding. In FIG. 5, reference numeral 1 is a circular plastic substrate to which electronic parts are attached, and 2 is a diaphragm. The vibrating plate 2 is formed by attaching a ceramic piezoelectric element 5 to a circular metal thin plate 3 with an adhesive agent 4. The vibrating plate 2 sandwiches the peripheral edge of the metal thin plate 3 with two O-rings 6. The first frame 7 and the cylindrical second frame 9 between the lower end of the cylindrical case 8 and both ends 8a and 8b of the case 8 by caulking and bending them to connect the respective parts to each other and to press the piezoelectric type pressure. It constitutes a sensor. Reference numerals 10 and 10 are conducting wires for connecting the electrodes attached to both surfaces of the piezoelectric element 5 and the electronic components of the substrate 1. The vibrating plate support structure includes a structure for fixing the peripheral edge of the metal thin plate 3 (FIG. 6), a structure for supporting the peripheral edge of the metal thin plate 3 (FIG. 7), and a portion serving as a vibration node of the metal thin plate 3. There is a supporting structure (Fig. 8). The support structure of FIG. 5 is similar to that described above.

For example, in a fuel tank, there is a method of measuring the volume of gas in the tank based on the air pressure in the closed tank to know the remaining amount of fuel. By attaching it, the volume change of the air in the tank can be taken out as an electric signal via the piezoelectric element. The pressure enters the lower part of FIG. 5 with the case 8 open from the direction A and is applied to the diaphragm 2. The back pressure of the diaphragm is supplied from the hole provided in the substrate 1 or the hole provided in the first frame 7 and the case B Is discharged in the direction.

[0005]

[Problems to be solved by the device]

 Since the vibrating plate 2 is formed by adhering the ceramic piezoelectric element 5 to the thin metal plate 3, the adhesive may be corroded depending on the properties of the liquid or gas surrounding the sensor and the performance of the sensor may deteriorate. For example, epoxy resin-based adhesives containing epoxy resin as the main component and UV-curing anaerobic adhesives containing acrylic resin as the main component are often used as adhesives, but these are mixed with gasoline and alcohol. When it is immersed in a liquid called gasohol, it swells and softens, causing a decrease in adhesive strength and peeling of the joint surface. Further, it cannot be used under the condition that exceeds the heat resistance range of the adhesive, and further, the temperature characteristics of the diaphragm 2 are adversely affected by the difference in the thermal expansion coefficients of the thin metal plate 3, the adhesive 4, and the piezoelectric element 5. That is, since a general metal has a thermal expansion coefficient about 10 times larger than that of a piezoelectric ceramic, a diaphragm in which the piezoelectric ceramic is adhered to a metal plate at room temperature causes a warp due to a temperature change (heat hardening and bonding). When the temperature rises, it will warp at room temperature), which causes changes in vibration characteristics and sensitivity. The adhesive also softens and shrinks when the temperature rises, which reduces the performance of the diaphragm.

Therefore, stable performance cannot be maintained if the special environment such as chemicals or gas attacking the adhesive or the operating temperature range is widened.

[0007]

[Means for Solving the Problems]

 In this invention, a ceramic piezoelectric element is used alone as a vibrating plate, and the peripheral portion of the vibrating plate is sandwiched by the sharp edges of two frames to form a piezoelectric pressure sensor without using an adhesive. The use of an adhesive makes the sensor insensitive to rubbing and improves the heat resistance and chemical resistance of the sensor. Since the ceramic piezoelectric element, which has a relatively large resistance to bending, is sandwiched by the sharp ends as described above, the resistance to bending deformation is reduced, which is effective in increasing the sensitivity.

[0008]

[Function] Since the ceramic piezoelectric element is used as the vibration plate alone and no adhesive is used, the adhesive does not deteriorate or melt, and it attacks the adhesive, so that the conventional sensor cannot be used. It can also be used in gas. Further, the operating temperature range is widened, and the temperature characteristic does not deteriorate due to the difference in temperature coefficient among the ceramic piezoelectric element, the adhesive, and the metal plate as in the conventional case.

Further, since the peripheral portion of the diaphragm is sandwiched by the frame having the sharp end, the diaphragm can be easily deformed and the sensitivity is improved.

[0010]

【Example】

 FIG. 1 is a vertical sectional view showing a first embodiment of the present invention. The same parts as those of the conventional example shown in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted.

The substrate 1 to which the electronic components are attached is held by the end portions 8a and 8b bent inward of the case 8 via a cylindrical outer frame 11. The lower end portion of the frame 11 is formed in a ring shape having an L-shaped cross section, and forms an upward pointed sharp end 11a of a lateral side that protrudes inward. A circular diaphragm 2 formed of a single ceramic piezoelectric element having thin-film electrodes adhered on both sides is placed on the sharp end 11a. The inner frame 12 is fitted to the inner surface of the outer frame 11, and the lower end of the inner frame 12 is a sharp end 12a facing the sharp end 11a of the outer frame 11. The peripheral portion of the vibration plate 2 is sandwiched by 12a. An O-ring 6 (a cushioning material of another form, for example, a metal spring may be used) as a cushioning material is interposed between the inner frame 12 and the substrate 1 to press down the inner frame 12 to form the sharp edges 11a, The diaphragm 2 is elastically sandwiched between 12a. The position where the diaphragm is sandwiched must be determined in consideration of the matching of the piezoelectric ceramic with air and the mechanical strength. In this embodiment, the thickness of the piezoelectric element is 0. The outermost edge portion was sandwiched between the sharp edges 11a and 12a as much as possible, with a thickness of about 2 mm. This is a structure similar to the above-mentioned peripheral edge support. The position sandwiched by the sharp ends 11a and 12a does not have to be the nodal position.

As in the conventional structure shown in FIG. 5, when the peripheral portion of the diaphragm is relatively widely sandwiched by two O-rings, the diaphragm of the present invention composed of the ceramic piezoelectric element alone has a resistance against bending deformation. However, since it is sandwiched by the sharp ends in the first embodiment, the bending deformation during vibration is relatively free.

With this configuration, when the liquid pressure or the gas pressure is applied, the vibration plate 2 is deformed, and an electric signal having a magnitude corresponding to the liquid pressure or the like can be taken out through the substrate 1. In order to connect the electrodes of the vibration plate 2 of the piezoelectric element and the electronic components of the substrate 1, in addition to the conductor 10, the outer frame 11 and the case 8 are made of a conductive material, the outside (the lower side of FIG. 1). The electrode of (1) is conducted from the sharp end 11a to the substrate through the outer frame and the case, and in the case of the inner electrode (upper side of FIGS. 1 and 2), the inner frame 12 and the O-ring 6 are made of a conductive material. Can be conducted to. However, at this time, it is necessary to insulate the inner frame 12 from the outer frame 11.

FIG. 2 shows a second embodiment in which the frame 11 is divided into an upper portion 11b and a lower portion 11c. By lowering the height of the lower portion 11c in this way, it is possible to facilitate the processing for forming the sharp end 11a. Other structures, actions, effects, etc. are similar to those of the first embodiment.

FIG. 3 illustrates frequency characteristics of the pressure sensor according to the present invention. This pressure sensor uses a ceramic piezoelectric element having a diameter of 16 mm and a thickness of 0.2 mm, and has an output sensitivity of −70 dBv / 1 pa (0 dBv = 1 v) and a frequency band of 2 Hz to 1 kHz.

FIG. 4 shows the temperature characteristic of the output sensitivity in comparison with that of the conventional structure of FIG. 5, and shows the relative sensitivity when the sensitivity at 20 ° C. is 0 dB.

[0017]

[Effect of device]

 (1) Since the diaphragm is not used as a single ceramic piezoelectric element and no adhesive is used, the diaphragm will deteriorate or become unusable even if it is used in a liquid or gas that attacks the adhesive such as gasoline and alcohol. Never be. Although a cushioning material such as the O-ring 6 is used, chemical resistance and heat resistance can be maintained by selecting the material.

(2) Since no adhesive is used for the vibration plate, unlike the conventional structure, the temperature characteristics of the sensor are not adversely affected by the difference in the temperature coefficient of the metal thin plate, the ceramic piezoelectric element, the adhesive, etc. .

(3) The ceramic piezoelectric element has a high acoustic impedance and poor compatibility with air, but since the peripheral edge of the ceramic piezoelectric element is sandwiched by the sharp ends, the mechanical resistance at the time of vibration is small and bending deformation is not caused. Freedom and higher sensitivity levels.

(4) Since the fluctuation of the supporting stress of the ceramic piezoelectric element is absorbed by the buffer material such as the O-ring, the sensitivity change due to the temperature change can be reduced.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a first embodiment of a piezoelectric pressure sensor of the present invention.

FIG. 2 is a longitudinal sectional view showing a second embodiment in which a frame 11 is divided into two parts.

FIG. 3 is a diagram showing frequency characteristics of the example.

FIG. 4 is a diagram showing a temperature characteristic of output sensitivity of an example in comparison with a conventional one.

FIG. 5 is a vertical cross-sectional view showing a conventional example of a piezoelectric pressure sensor.

FIG. 6 is a schematic diagram showing a peripheral edge fixed support structure of the diaphragm.

FIG. 7 is a schematic view showing a peripheral edge support structure of a diaphragm.

FIG. 8 is a schematic diagram showing a nodal line position support structure of a diaphragm.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Vibration plate 3 Metal thin plate 4 Adhesive 5 Piezoelectric element 6 O-ring 7 First frame 8 Cases 8a, 8b Both ends 9 Second frame 10 Conductive wire 11 Outer frame 11a Sharp edge 11b Upper part 11c Lower part 12 Inner frame 12a Sharp end

Claims (1)

[Scope of utility model registration request] 1. An outer frame (11) is provided between both ends (8a) (8b) of a cylindrical case (8) bent inward.
(11b) (11c), a piezoelectric pressure sensor supporting a substrate (1) to which an electronic component is attached and a diaphragm (2) via an inner frame (12) and a cushioning material. ) Is a single ceramic piezoelectric element with electrodes attached on both sides, and an upward sharp edge (11a) is formed on the lower side of the outer frame on the side protruding inward with an L-shaped cross section. At the lower end of the frame (12) is a sharp end (12) facing the sharp end (11a) of the outer frame (11).
a), the diaphragm (2) is sandwiched between the sharp ends (11a) (12a), and the inner frame (12) and the substrate (1) are formed.
Between the inner frame (12) and the vibrating plate (2) is inserted between them and the electrodes of the vibrating plate (2) are electrically connected to the electronic components of the substrate (1). Sensor.