JP3399688B2 - Pressure sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type pressure sensor for detecting the pressure of a fluid to be measured, and more particularly to a pressure sensor having improved pressure resistance.

[0002]

BACKGROUND ART Conventionally, a capacitance type pressure sensor has been used. FIG. 6 shows a conventional general pressure converting element 50 used in a capacitance type pressure sensor (Japanese Patent Publication No. 60-34687). The pressure converting element 50 is provided on a thick substrate 51, a thin diaphragm 52 arranged to face the substrate 51 at a predetermined interval, and on respective facing surfaces of the substrate 51 and the diaphragm 52. Electrode
It has 53 and 54. When pressure is applied to the diaphragm 52, the diaphragm 52 elastically deforms and the electrostatic capacitance C of the electrodes 53 and 54 changes according to the deformation amount of the diaphragm 52. Therefore, from the change of the electrostatic capacitance C, the diaphragm 52 is changed.
The pressure applied to is detected. That is, the electrostatic capacitance C formed by the electrodes 53 and 54 is represented by C = ε * A / d ..., Where the electrode area A, the permittivity of the interelectrode substance is ε, and the interelectrode distance is d. . Therefore, when pressure is applied to the diaphragm 52, the diaphragm 52 is deformed, and the distance d is displaced according to the pressure applied to the diaphragm 52.
The pressure applied to the diaphragm 52 can be detected based on

Here, as can be seen from the equation, the capacitance C
Is inversely proportional to the inter-electrode distance d, and even if the pressure input to the pressure conversion element 50 changes linearly, the change in the capacitance C output from the pressure conversion element 50 is non-uniform. It will be linear. If this non-linearity is significant, the correction circuit becomes complicated when the correction is performed by the correction circuit that performs linear approximation, and the cost of the pressure sensor 50 becomes expensive. The non-linearity of this output is determined by the inter-electrode distance d and the maximum displacement f of the inter-electrode distance, and is improved by bringing the value of f / d close to zero. In addition, when the inter-electrode distance d is small, the variation of the capacitance and the variation of the capacitance in the measurement range becomes large, and the adjustment circuit becomes complicated.
The cost of 50 is expensive. Therefore, the maximum displacement f of the inter-electrode distance is determined so that the measurement range is sufficiently secured, and the inter-electrode distance d is made sufficiently large with respect to this maximum displacement f, so that the output characteristic of the pressure conversion element 50 becomes linear. The correction circuits and adjustment circuits are kept close to each other so that they are not complicated. Generally, the inter-electrode distance d is 3 which is the maximum displacement f of the inter-electrode distance.
It is preferably doubled or more.

[0004]

However, when the distance d between the electrodes is increased, when the diaphragm 52 is applied with a pressure exceeding the measurement range, the diaphragm 52 contacts the substrate 51 as shown in FIG. Deformed and Daifuramu 52
The internal stress of the diaphragm becomes large and the diaphragm 52 cannot maintain its function. Therefore, in the conventional pressure conversion element 50,
There is a problem that the pressure resistance performance in the measurement cannot be made larger than the measurement range.

An object of the present invention is to provide a pressure sensor in which the linearity of the output is sufficiently ensured and the pressure resistance performance is sufficiently large compared to the measurement range.

[0006]

According to the present invention, a thick-walled substrate, a diaphragm arranged at a predetermined interval so as to face the substrate, and provided on surfaces of the substrate and the diaphragm that face each other. A pressure sensor for detecting a pressure applied to the diaphragm by a change in electrostatic capacitance between the electrodes, the substrate including a plurality of ring-shaped stoppers for restricting displacement of the diaphragm. different and Tomo height of the stopper, respectively
In addition, the diaphragm is a thin disk-shaped insulator.
And said that you are. In the above description, it is desirable that each of the stoppers is a ring-shaped convex portion provided coaxially with the substrate, and the height thereof is lower toward the inner side. Further, each of the stopper is preferably made of a dielectric material laminated to the upper side of the front Symbol electrodes.

[0007]

In the present invention as described above, since the displacement generated in the diaphragm is limited by the stopper, a large stress is not generated inside the diaphragm even if an excessive pressure is applied. Therefore, the distance between the electrodes should be increased. You can Therefore, the output linearity can be sufficiently ensured, and the function of the diaphragm is not impaired even if an excessive pressure is applied, so that a sufficiently large pressure resistance performance is secured as compared with the measurement range. To be achieved. At this time, if a ring-shaped protrusion is provided on the substrate and this protrusion is used as a stopper, the displacement of the diaphragm can be limited by this protrusion, and if the position and size of this protrusion are set appropriately, the electrode Does not increase the electrostatic capacitance C, that is, does not reduce the apparent inter-electrode distance d, so that sufficient measurement accuracy can be ensured. Further, if the height of the convex portion is made lower toward the inner side, the tip of each stopper is arranged at a position corresponding to the deformation range of the diaphragm, and the deformation of the diaphragm is sufficiently allowed for the pressure in the measurement range, Since the stopper reliably suppresses the displacement of the diaphragm against an excessive pressure, both a desired measurement range and sufficient pressure resistance performance are ensured.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2 show a pressure conversion element 1 of a pressure sensor according to this embodiment. The pressure conversion element 1 is built in a pressure sensor (not shown) and detects the pressure of the measurement fluid. The pressure conversion element 1 is provided with a disk-shaped diaphragm 10 and a substrate 20 made of ceramic or the like. The diaphragm 10 and the substrate 20 are bonded together with the tubular bonded body 2 sandwiched therebetween, and are arranged to face each other with a predetermined gap therebetween. The diaphragm 10 is a thin insulator that is deformed by the pressure of the measurement fluid. The diaphragm 10 is provided with a disk-shaped common electrode 11 that covers almost the entire surface facing the substrate 20. This common electrode 11
Is electrically connected to an external connection terminal 13 provided outside the substrate 20 through a through hole 12 penetrating the bonded body 2 and the substrate 20. The through hole 12 has an inner surface coated with a conductive substance.

The substrate 20 is a thick insulator made of ceramic or the like. On the substrate 20, a disc-shaped measuring electrode 21 and a ring-shaped reference electrode 22 are provided coaxially on the surface facing the diaphragm 10. Measuring electrode 21
Each of the reference electrodes 22 and the reference electrodes 22 are electrically connected to the external connection terminals 25 and 26 provided on the outside of the substrate 20, respectively, through through holes 23 and 24 that penetrate the substrate 20. The through holes 23 and 24 have inner surfaces coated with a conductive substance, like the through holes 12. Here, the common electrode 11 on the side of the diaphragm 10 and the measurement electrode 21 on the side of the substrate 20 constitute the electrostatic capacitance C ₁ , and the diaphragm 10
Side common electrode 11 and substrate 20 side reference electrode 22
Constitutes the electrostatic capacitance C ₂ . When pressure is applied to the diaphragm 10, the diaphragm 10 is deformed, so that the electrostatic capacitances C ₁ and C ₂ change according to the pressure applied to the diaphragm 10. Changes in the electrostatic capacitances C ₁ and C ₂ are converted by a correction circuit (not shown) and output as an electric signal proportional to the pressure.

A ring-shaped convex portion 27 made of a dielectric material such as glass is formed on the upper side of the measuring electrode 21. This convex part
On the outer side of 27, a ring-shaped convex portion 28 is formed straddling the outer peripheral edge of the measurement electrode 21 and the inner peripheral edge of the reference electrode 22. The height of the inner convex portion 27 is lower than that of the convex portion 28. Each of these protrusions 27, 28 is a diaphragm.
It is a ring-shaped stopper that limits the displacement of 10.

Next, the operation of the stopper of this embodiment will be described. When a pressure within the measurement range is applied to the diaphragm 10, as shown in FIG. 3A, the diaphragm 10 is deformed and the electrostatic capacitances C ₁ and C ₂ formed by the electrodes 11, 21 and 22 are changed, The pressure is detected from the changes in the electrostatic capacitances C ₁ and C ₂ . Here, since the pressure applied to the diaphragm 10 is within the measurement range, the diaphragm 10 is not deformed even if it is deformed.
No contact with 7, 28. When the pressure increases from this state and deviates from the measurement range, the diaphragm 10 is further deformed and comes into contact with the convex portions 27 and 28, as shown in FIG.
Due to the contact with the convex portions 27, 28, the deformation of the diaphragm 10 is suppressed. Therefore, the displacement of the diaphragm 10 is
It is smaller than the displacement of the diaphragm 52 (indicated by the chain double-dashed line in the figure) when there is no 7, 28. Diaphragm 10 of the same shape,
The smaller the deformation, the smaller the internal stress generated in 52. Therefore, in order to generate the same amount of stress, it is necessary to apply a larger pressure to the diaphragm 10 in contact with the convex portions 27 and 28 than to the diaphragm 52. . Then, when the pressure further increases, the diaphragm 10 is deformed so that the vicinity of the corners 27A, 28A of the protrusions 27, 28 is bent downward as shown in FIG. 3 (C). As a result, a bending moment M is generated in the portions of the diaphragm 10 near the corners 27A and 28A. This bending moment M acts in the direction opposite to the stress due to the pressure P applied to the diaphragm 10, and as a result, the stress generated inside the diaphragm 10 is reduced. Therefore,
By providing the stopper, the maximum pressure at which the function of the diaphragm 10 can be maintained is increased, and the pressure resistance performance of the pressure conversion element 1 is improved.

Next, the influence of the stopper of this embodiment on the measurement will be considered. FIG. 4 shows a schematic diagram for obtaining a change in capacitance due to displacement of the diaphragm 10. Here, C ₁ and the capacitance of the electrode 11 and the electrode 21, the capacitance of the electrode 11 and the electrode 22 and C _2, obtains the amount of change in each of the electrostatic capacitance C _1, C _2. In the figure, each of the electrode 11 and the electrodes 21 and 22 is divided into regions U to Z depending on the presence or absence of the protrusions 27 and 28. For example, area U
Is a region at the center of the pressure conversion element 1, and only an interelectrode substance such as air is interposed between the electrodes 11 and 21. The region V is a region where the convex portion 27 inside the pressure conversion element 1 is formed, and between the electrode 11 and the electrode 21,
The inter-electrode substance and the convex portion 27 are interposed. Here, the electrode 11 and the electrodes 21 and 22 are regarded as parallel plates of infinite length, and the electrostatic capacitance C _V of the region _V is obtained. The dielectric constant of the inter-electrode substance is ε ₁ , the dielectric constant of the convex portion 27 is ε ₂ , the distance between the electrodes 11 and 21 is S ₁ , the distance between the electrode 11 and the convex portion 27 is S ₂ , and the area of the counter electrode in the region V is A _V , the electrostatic capacitance due to only the interelectrode substance is C
_{Letting a} and the electrostatic capacitance C _b by only the convex portion 27, the electrostatic capacitances C _a and C _b are _Ca = ε ₁ * A _V / S ₂ C _b = ε ₂ * A _V / (S ₁ −S ₂ ) On the other hand, the electrostatic capacitance C _V is obtained by C _V = C _a * C _b / (C _a + C _b ). Here, since the convex portion 27 is a dielectric, ε ₁ <<
Since ε ₂ and C _a << C _b , C _V ≈C _a = ε ₁ * A _V / S ₂ is obtained.

Similarly, the electrostatic capacities of the other regions U and W to Z are obtained, and the electrostatic capacities of the regions U to X are added to obtain the electrostatic capacitance C.
While obtaining ₁ , the electrostatic capacitances of the regions Y and Z are added to obtain the electrostatic capacitance C ₂ . That is, the electrostatic capacitances C ₁ and C ₂ are expressed as follows. C ₁ = ε ₁ * A _U / S ₁ + ε ₁ * A _V / S ₂ + ε <sub>1
* A W / S 3 + ε</sub> 1 * A X / S 4 C 2 = ε 1 * A Y / S 4 + ε 1 * A Z / S 5 However, in each region U～Z, the area of the counter electrode A _U
To A _Z, the distance between the electrodes and S ₁ to S _5. Next, the differences δC ₁ and δC ₂ are calculated from the electrostatic capacitances C ₁ and C ₂ . In the measurement range, the electrode intervals S _{1 to} S _{5 in} the respective regions U to Z
ΔC ₁ = ε ₁ * A _U / (S ₁₁ −S ₁₀ ) + ε ₁ * A _V /, if each changes between the maximum value S _{10 to} S ₅₀ and the minimum value S _{11 to} S _51.
(S ₂₁ −S ₂₀ ) + ε ₁ * A _W / (S ₃₁ −S ₃₀ ) + ε ₁ *
A _X / (S ₄₁ −S ₄₀ ) δC ₂ = ε ₁ * A _Y / (S ₄₁ −S ₄₀ ) + ε ₁ * A _Z /
(S ₅₁ -S _50), where the area of the convex portions 27, 28 occupied by each region, the electrode 21,
Small enough compared to the area occupied by 22, A _U >> A _V , A _U
>> A _X , A _Z >> A _Y , so S ₂₀ , S ₂₁ , S ₄₀ , S
The effects of ₄₁ can be ignored. That is, even if the convex portions 27 and 28 are provided on the substrate 20 in order to suppress the excessive displacement of the diaphragm 10, the change in the measured capacitance is not substantially affected.

Next, the manufacturing procedure of the pressure conversion element 1 of this embodiment will be described. FIG. 5 shows a schematic sectional view of the pressure conversion element 1. In the figure, a substrate 20 is provided with a measurement electrode 21, a reference electrode 22 (not shown) and the like. On this substrate 20, the convex portion 27 and the convex portion 2
8 and the bonded body 2 are formed, and then the diaphragm 10 is bonded to manufacture the pressure conversion element 1. That is, the glass paste is printed at a predetermined position on the substrate 20 and then fired, so that the glass frit 271, having the same height,
281, 201 are formed. Here, the convex portion 27 is completed by the glass frit 271. Then the glass frit 281, 2
After printing glass paste on the upper side of 01 in the figure, fire it,
The glass frits 282 and 202 are formed to have the same height. Here, the convex portion 28 is completed by the glass frits 281, 282. Subsequently, a bonding glass paste is printed on the upper side of the glass frit 202 in the figure to form a bonding portion 203, and the diaphragm 10 is bonded at this bonding portion 203. After that, the pressure conversion element 1 is subjected to processes such as finishing, wiring, and adjustment of each part.
Is completed.

According to this embodiment as described above, the following effects can be obtained. That is, since the protrusions 27 and 28 that limit the displacement generated in the diaphragm 10 are provided and the displacement of the diaphragm 10 due to excessive pressure is limited by the protrusions 27 and 28, the distance between the electrode 11 and the electrodes 21 and 22 is reduced. Even if a certain electrode interval is increased, the diaphragm 10 will not be greatly deformed,
The function of the diaphragm 10 can be maintained even when a large pressure is applied. For this reason, the electrode interval can be expanded to ensure sufficient linearity of the output, and the pressure resistance performance can be made sufficiently large compared to the measurement range.

Further, the sectional areas of the convex portions 27, 28 provided on the substrate 20 are made sufficiently smaller than the areas of the electrodes 21, 22, and
Since the protrusions 27 and 28 are formed of a dielectric material such as glass, the protrusion 2
Even if 7, 28 is provided between the electrode 11 and the electrodes 21, 22 and the displacement of the diaphragm 10 is limited, the change in the capacitance measured directly does not substantially affect the measurement. It does not cause any problems such as loss of accuracy.

Further, the height of the convex portion 27 is made lower than that of the outer convex portion 28, and the contact position between the convex portions 27, 28 and the diaphragm 10 is gradually increased toward the central portion, so that the convex portions 27, 28 have the same height. Since the height corresponds to the displacement of the diaphragm 10, the diaphragm 10 is sufficiently displaced with respect to the pressure in the measurement range,
The displacement of diaphragm 10 is
28 is suppressed, and both a desired measurement range and sufficient pressure resistance performance can be secured.

In addition, the protrusions 27, 27
Since 28 and the like are formed, sufficient mass productivity can be secured for manufacturing the pressure conversion element 1, and good productivity can be imparted.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment, and various improvements and design changes can be made without departing from the gist of the present invention. It is possible. For example, the stopper is not limited to one provided on the substrate side, but may be one provided on the diaphragm side. Further, the stopper is not limited to a continuous body in which the convex portions are continuous in a ring shape, but may be an interrupted body in which a plurality of convex portions formed in an arc shape are discretely arranged in a ring shape and arranged in a plurality. Any shape may be used as long as it can be effectively limited. Further, the ring-shaped stopper is not limited to the one having two protrusions formed on the substrate, and may be one having three or more protrusions formed on the substrate. Further, the material of the stopper is not limited to glass, and other dielectrics or insulators may be used.

[0020]

As described above, according to the present invention, the linearity of the output can be sufficiently ensured, and the pressure resistance performance can be sufficiently increased as compared with the measurement range.

[Brief description of drawings]

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

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is a cross-sectional view showing how the diaphragm of the embodiment is deformed.

FIG. 4 is a schematic sectional view for explaining the influence of the stopper of the embodiment.

FIG. 5 is a schematic sectional view showing a main part of the embodiment.

FIG. 6 is a diagram corresponding to FIG. 1 showing a conventional example.

FIG. 7 is a cross-sectional view showing a state of deformation of the diaphragm of the conventional example.

[Explanation of symbols]

1 Pressure conversion element that constitutes pressure sensor 10 diaphragm 11 Common electrode 20 substrates 21 Measuring electrode 22 Reference electrode 27, 28 Convex part as stopper

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01L 9/00 305 G01L 19/06 102

Claims (3)

(57) [Claims] 1. A thick substrate, a diaphragm arranged to face the substrate at a predetermined distance, and electrodes provided on surfaces of the substrate and the diaphragm facing each other, respectively. A pressure sensor for detecting a pressure applied to the diaphragm by a change in capacitance between the electrodes, wherein a substrate is provided with a plurality of ring-shaped stoppers for limiting displacement of the diaphragm, and the heights of these stoppers are different from each other. In addition, the diaphragm is thin
A pressure sensor characterized by being a disc-shaped insulator . 2. The pressure sensor according to claim 1, wherein each of said stoppers is a ring-shaped convex portion provided coaxially with said substrate, and the height thereof is lowered toward the inner side. A pressure sensor characterized in that 3. A pressure sensor according to claim 1 or claim 2, wherein each of the stopper, the pressure sensor, characterized in that a dielectric laminated on the upper side of the front Symbol electrodes.