JPH05203520A - Capacitance type pressure sensor - Google Patents

Abstract

PURPOSE:To avoid dispersion in capacitance when compressing force is zero, to ensure linearity in pressure measurement and to improve pressure measuring accuracy without stray loss by detecting the change in capacitance with a capacitance-type pressure sensor, wherein a ring-shaped or arc-shaped electrode is arranged between the first substrate and the second substrate. CONSTITUTION:A third electrode 5 keeps an interval (d) between a first electrode 3 and a second electrode 4. The cross section of the electrode 5 is circular. The accuracy of the size is high along the entire length, and the interval (d) is kept in high accuracy and high quality. It is preferable that the size A is close to zero. The electrode 5 concentrates electric lines of force 22 generated between the electrodes 3 and 4 into a part between the edges of the electrodes 3 and 4 so as to prevent the leaking of the electric lines of force to the outside. Since the electrode 5 is provided through a lead wire 12, capacitance Cs for stray loss is eliminated. Therefore, the measuring accuracy is improved based on a capacitance Cx in reference detection. The linearity of pressure and the capacitance Cx is improved. The stray loss caused by the capacitance is inebitably eliminated, and the power consumption in the pressure measuring circuit becomes less.

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.

[0002]

2. Description of the Related Art Capacitance type pressure sensors are used, for example, to detect oil pressure or air pressure in general industrial equipment, vehicle equipment, or consumer equipment.

A conventional capacitance type pressure sensor is disclosed in Japanese Unexamined Patent Publication No.
The structure is as disclosed in Japanese Patent Laid-Open No. 3-265128. That is, the conventional electrostatic capacitance type pressure sensor has a highly rigid electrically insulating substrate in which a first substrate having an electrically insulating property, a first electrode formed on the inner surface of the first substrate, and a sealing material are sealed. And a second electrode provided on the surface of the second substrate facing the first electrode.

When pressure is applied to the first substrate, the distance between the first electrode and the second electrode changes due to the displacement of the first substrate due to the pressure. A change in capacitance between the first electrode and the second electrode due to the change in this distance is detected. In this case, the initial distance between the first electrode and the second electrode when no pressure is applied is the sealing material (glass frit) with a high melting point sphere or rectangular frit between the first substrate and the second substrate. It is secured by sealing with

[0005]

However, such a capacitance type pressure sensor has the following problems (A) to (C).

(A) It is difficult to seal the first electrode and the second electrode with a constant initial distance. For this reason, in the individual capacitance-type pressure sensors that are produced, variations occur in the capacitance at the initial stage, that is, when the pressure is zero.

(B) When measuring the capacitance between the first electrode and the second electrode, the lines of electric force when a voltage is applied between the first electrode and the second electrode are as shown in FIG. In addition to the direction perpendicular to the electrode and the second electrode, the end surface of the first electrode and the second electrode bends outward, resulting in a capacitance different from the calculated value due to fringing (electric force lines go out). .. Therefore, there is no linearity in the pressure measurement.

(C) Since the first and second electrically insulating substrates, which are the constituent members, are both dielectric materials,
Besides the capacitance between the electrode and the second electrode, there is the capacitance between the first substrate and the second substrate. This results in a dielectric loss (stray loss) due to the capacitance of the constituent members, resulting in poor pressure measurement accuracy.

According to the present invention, there is no variation in capacitance when the applied pressure is zero, linearity in pressure measurement is ensured, and there is no dielectric loss (stray loss), and the precision of pressure measurement is improved. An object is to provide a pressure sensor.

[0010]

According to the present invention, a first substrate (diaphragm 1 in the embodiment) and a second substrate (2) are provided, and the first substrate (1) and the second substrate (2) are spaced at a predetermined distance. A capacitive pressure sensor for detecting a change in electrostatic capacitance between a first substrate (1) and a second substrate (2), which are arranged apart from each other, and which occurs when pressure is applied to the first substrate (1). The gist of the present invention is a capacitance type pressure sensor in which a ring-shaped or arc-shaped electrode (5) is arranged between the second substrate (2) and the second substrate (2).

In the present invention, the ring-shaped electrode means not only a circular ring-shaped electrode but also a polygonal shape such as a triangle, a square, a rectangle, a rhombus, and a continuous or discontinuous ring-shaped electrode. Including. Further, the arc-shaped electrode includes not only a strict arc but also an electrode having an arbitrary shape close to the arc.

[0012]

The ring-shaped or arc-shaped electrode secures the electrical distance (initial distance) between the first substrate and the second substrate.

The ring-shaped or arc-shaped electrode is the first
It acts as a guard electrode for preventing the lines of electric force generated between the electrode and the second electrode from protruding to the outer periphery. Furthermore, the ring-shaped or arc-shaped electrode can be grounded easily, and the dielectric loss (stray loss) is eliminated.

[0014]

FIG. 1 shows a preferred embodiment of the capacitance type pressure sensor of the present invention.

The capacitance type pressure sensor has a first substrate 1, a second substrate 2, a first electrode 3, a second electrode 4, a third electrode 5 and a sealing material 6.

The first substrate 1 is typically a diaphragm and is made of an electrically insulating material such as a ceramic substrate of alumina, silicon or fused silica. The first substrate 1 is circular and can be displaced by applying pressure P from the outside. The second substrate 2 facing the first substrate 1
Are arranged. The second substrate 2 has a circular shape and is made of, for example, a material having a high rigidity such as alumina.
In this embodiment, the diameter of the second substrate 2 and the diameter of the first substrate 1 are the same.

A first electrode 3 is arranged on the inner surface of the first substrate 1. On the other hand, the second electrode 4 is arranged on the inner surface of the second substrate 2. Therefore, the first electrode 3 and the second electrode 4 face each other.

As shown in FIG. 2, the first electrode 3 has a circular shape and is arranged on the first substrate 1 in a concentric manner. First electrode 3
The extension connection 7 is formed in the radial direction. A lead wire 8 is connected to the extension connecting portion 7. The lead wire 8 passes through the sealing material 6 as shown in FIG. 1, and is led out downward through the through hole 9 of the substrate 8. A conductive paste is poured into the gap of the through hole 9. Thereby, the lead wire 8 is sealed to the second substrate 2, and the electrical connection between the lead wire 8 and the extension connection portion 7 is ensured.

As shown in FIG. 3, the second electrode 4 has a circular shape and is arranged concentrically with the second substrate 2. Second electrode 4
A lead wire 10 is connected to the. The lead wire 10 is
As shown in FIG. 1, it is led out downward through the through hole 11 of the second substrate 2. A conductive paste is poured into the gap of the through hole 11. As a result, the lead wire 10 is sealed to the second substrate 2, and the lead wire 10 and the second
The electrical connection of the electrode 4 is ensured.

The third electrode 5 has a ring shape as shown in FIGS. 1 and 3, and is arranged in a circular center around the second electrode 4. The third electrode 5 is connected to the lead wire 12. As shown in FIG. 1, the lead wire 12 is led out below the second substrate 2 via the through hole 13 of the second substrate 2. A conductive paste is poured into the gap of the through hole 13. As a result, the lead wire 1 is attached to the second substrate 2.
2 is sealed to ensure the electrical connection between the lead wire 12 and the third electrode 5.

The material of the third electrode 5 is preferably a metal, particularly a metal having carbon C, and any material having a large electrical resistance value ρ can be used. For example, the third electrode 5
Is made of steel or Cu, or commercially available Ni fine wire or C
It is u thin wire. The ring-shaped third electrode 5 has a cutout 20. As clearly shown in FIG. 1, the extension connection portion 7 of the first electrode 3 is passed through the cutout portion 20.

The first role of the third electrode 5 is to maintain the distance d, which is also called the initial distance between the first electrode 3 and the second electrode 4. The cross section of the third electrode 5 is circular,
The diameter corresponds to the distance d, and the dimensional accuracy is sufficiently high over the entire length. The third electrode 5 has such a wire-like and ring-like shape, and compared to the conventional ball or rectangular parallelepiped made of silica or the like, the accuracy of the shape of the third electrode 5 allows the first electrode 3 and the second electrode 4 to have the same accuracy. The distance d can be accurately maintained with high quality. Therefore, it is not necessary to modify the measurement circuit constant every time the capacitance type pressure sensor is manufactured.

The second role of the third electrode 5 is shown in FIG.
As shown in FIG. 10, the lines of electric force 22 generated between the first electrode 3 and the second electrode 4 are concentrated between the end faces of the first electrode 3 and the second electrode 4, and the electric force lines 22 are generated outside as in the conventional example of FIG. It is to prevent the lines of force from coming out. That is, the third electrode 5 in FIG. 1 plays a role of a guard electrode for the lines of electric force by grounding the lead wire 12. This prevents fringing and stray loss, and prevents the lines of electric force from protruding to the outside.

Moreover, the third electrode 5 is arranged on the inner peripheral side of the sealing material 6 which functions as the sealing portion of FIG. Sealing material 6
Is a shield material such as glass paste, and the third electrode 5 is integrally sealed by the sealing material 6. The sealing portion 6 is preferably formed by printing. As a result, the first substrate 1, the second substrate 2, and the third electrode 5 form a pressure chamber R configured as a pressure response region.

As described above, the third electrode 5 serves both to maintain the distance d between the first electrode 3 and the second electrode 4 and to serve as a guard electrode for the lines of electric force, that is, to improve the electrical characteristics.
The dimension A in FIG. 1 is preferably close to zero.

The dimensional accuracy of the third electrode 5 is, for example, 20 μm.
m ± 1 μm. With the conventional method of using beads such as balls and rectangular parallelepipeds, the dimensional accuracy of beads is 20 μm ± 5 μ.
Since it is m, the dimensional accuracy of the third electrode 5 is significantly improved.

FIG. 5 shows an equivalent circuit of the capacitance type pressure sensor of FIG. Cx is a reference detection capacitance between the first electrode 3 and the second electrode 4. When the first substrate 1 is pressed with the pressure P, the first substrate 1 is deformed, and the capacitance Cx between the first electrode 3 and the second electrode 4 is detected as the pressure by using air as a dielectric medium.

As seen from the first electrode 3 and the second electrode 4, in addition to the reference detection capacitance Cx, the dielectric materials of the insulating first substrate 1 and second substrate 2 and the sealing material 6 are used. Capacitance Cs
Are connected in parallel as shown in FIG. If the capacitance Cs is large, the reference detection capacitance C
The change in x is not detected well, and the first electrode 3 and the second electrode
It is conceivable that a stray loss (dielectric loss) occurs between the electrodes 4 due to the voltage applied from the measurement circuit, and the current consumption of the circuit also increases.

However, in the present invention, as described above, the third
Since the electrode 5 is grounded via the lead wire 12, the capacitance Cs corresponding to the stray loss is eliminated. Therefore, the measurement accuracy is improved based on the reference detection capacitance Cx, and the linearity between the pressure and the capacitance Cx is improved. Naturally, the stray loss (dielectric loss) caused by the capacitance Cs is eliminated, and the power consumption of the pressure measuring circuit can be reduced.

6 and 7 show another embodiment of the second substrate in the capacitance type pressure sensor of the present invention. In any of the embodiments, the same first substrate 1 and first electrode 3 of FIG. 2 can be used.

In the embodiment of FIG. 6, the second substrate 52, the second electrode 60 and the two arc-shaped third electrodes 62 are shown. The second substrate 52 is similar to the second substrate 2 of FIG. The second electrode 60 includes a circular portion 60a and an extension connecting portion 60b.
Consists of. The extension connecting portion 60b is connected to the lead wire 70.

The two third electrodes 62 are arc-shaped and have an angle of approximately 180 degrees, and a gap 72 is set between them. The two third electrodes 62 are ring-shaped as a whole. In one gap 72, the second electrode 60
The extension connection portion 60b of the above is passing through. Another gap 72
The extension connecting portion 7 of the first electrode 3 shown in FIG.

The embodiment shown in FIG. 7 has a second substrate 82, a second electrode 80, and third electrodes 90, 92. Second electrode 8
0 has a circular portion 80a and an extension connecting portion 80b. Another short arc-shaped third electrode 92 is arranged between the substantially ring-shaped third electrodes 90. The third electrode 90 is connected to the lead wire 96, and the third electrode 92 is connected to the lead wire 96 (not shown) as necessary. The extension connection portion 80b of the second electrode 80 is connected to the lead wire 98. Third
The extension connecting portion 7 of the first electrode 3 of FIG. 2 passes through the gap 100 between the electrodes 90 and 92. Gap 1 between the third electrodes 90 and 92
The extension connection portion 80b passes through 02.

FIG. 8 and FIG. 9 show another embodiment. The second electrode 140 is arranged on the inner surface of the second substrate 2, and the sealing material 6 is provided around the second electrode 140. The ring-shaped third electrode 130 is placed on the sealing material 6. The cross section of the third electrode 130 is rectangular. The third electrode 130 is a metal plate punched into a ring shape.

The present invention is not limited to the above embodiments.
For example, the cross-sectional shape of the third electrode is not limited to a circle, but may be an ellipse or a square. The third electrode may be a thin plate-shaped circular ring other than the metal wire, and the third electrode is preferably made of metal and processed with good dimensional accuracy. The third electrode may be continuously formed in a circular shape or the like other than the one having the gap as shown in FIG.

In the illustrated embodiment, the first substrate and the second substrate
Using an insulating substrate as the substrate, the first electrode is formed on the inner surface of the first substrate and the second electrode is formed on the inner surface of the second substrate. However, not limited to this, a conductive substrate such as silicon may be used as the first substrate and the second substrate instead of the insulating substrate. When the conductive first and second substrates are used in this manner, the first and second electrodes are omitted. When a ring-shaped electrode is provided between the conductive first substrate and the second substrate, no electrical contact is made between the electrode and the first substrate or the second substrate.

[0037]

According to the present invention, the initial distance (spacing) can be made constant by the ring-shaped or arc-shaped electrode,
Capacitance does not fluctuate when the applied pressure is zero.

Further, since there is a ring-shaped or arc-shaped electrode, it is possible to prevent the lines of electric force from bending outward when a voltage is applied, that is, fringing.
Pressure measurement accuracy It is possible to secure the linearity of pressure change and the linearity of capacitance change during pressure measurement. If you eliminate the fringing,
The detection capacitance Cx to be measured can be set to a value as designed.

Further, unlike the conventional one using the beads, according to the present invention, the ring-shaped or arc-shaped electrode can be easily grounded, so that there is no gap other than the reference capacitance for detection. Since the electrostatic capacity is lost, dielectric loss (stray loss) can be prevented. By eliminating the stray loss, the power consumption of the pressure measuring circuit can be reduced and the pressure measuring accuracy can be improved.

Further, according to the present invention, it is not necessary to dispose a large number of frit as in the prior art, and the productivity is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a preferred embodiment of a capacitance type pressure sensor of the present invention.

FIG. 2 is a diagram showing an inner surface of a first substrate in a preferred embodiment of the capacitance type pressure sensor of the present invention.

FIG. 3 is a diagram showing an inner surface of a second substrate in a preferred embodiment of the capacitance type pressure sensor of the present invention.

FIG. 4 is a diagram showing a distribution of lines of electric force in a preferred embodiment of the capacitance type pressure sensor of the present invention.

FIG. 5 is a diagram showing an equivalent circuit in a preferred embodiment of the capacitance type pressure sensor of the present invention.

FIG. 6 is a diagram showing an inner surface of a second substrate which is another embodiment of the capacitance type pressure sensor of the present invention.

FIG. 7 is a diagram showing an inner surface of a second substrate which is still another embodiment of the capacitance type pressure sensor of the present invention.

FIG. 8 is a diagram showing an inner surface of a second substrate which is still another embodiment of the capacitance type pressure sensor of the present invention.

9 is a sectional view taken along line XX of the embodiment shown in FIG.

FIG. 10 is a diagram showing a distribution of lines of electric force in a conventional electrostatic capacitance type pressure sensor.

[Explanation of symbols]

 1 1st board 2 2nd board 3 1st electrode 4 2nd electrode 5 3rd electrode 6 Sealing material 7 Extended connection part 8 Lead wire 10 Lead wire 12 Lead wire ◆

Claims (1)

[Claims] 1. A first substrate (1) and a second substrate (2), wherein the first substrate (1) and the second substrate (2) are arranged separated from each other by a predetermined distance, and are generated when pressure is applied. In a capacitance type pressure sensor for detecting a change in capacitance between a first substrate (1) and a second substrate (2), a ring shape is provided between the first substrate (1) and the second substrate (2). Alternatively, a capacitance type pressure sensor in which arc-shaped electrodes (5) are arranged.