JP2595756B2 - Capacitive differential pressure detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a capacitance type differential pressure detector capable of obtaining a good linearity differential pressure signal even when a differential pressure is large and a dielectric constant in a gap is changed by pressure. This capacitance type differential pressure detector is used for gauge pressure or absolute pressure when one of the introduced pressures is atmospheric pressure or vacuum.

[Prior art]

FIG. 3 is a sectional view showing the structure of a conventional capacitance type differential pressure detector 50. A pair of fixed electrodes 15 and 20 are attached to each side of the diaphragm 10. The fixed electrode 15 is composed of a conductive plate 12 disposed to face the diaphragm 10 and the conductive plate 12.
An insulating plate 13 joined to the insulating plate 13 and a conductive plate 14 joined to the insulating plate 13. Further, the conductive plate 12 and the conductive plate 14 are electrically connected to each other via a conductive film 27 that covers the inner peripheral surface of the pressure guiding hole 25 formed therethrough. The fixed electrode 15 is provided with an annular support 21 separated by an annular groove 23 which is joined to the insulating plate 13 and surrounds the conductive plate 12, and this support 21 is bonded to the diaphragm 10 by a predetermined thickness glass bonding. The conductive plate 12 and the annular support 21 are electrically insulated from each other at the portion 11. The support 21 may be either an insulator or a conductor. Further, as described above, the fixed electrode 15 is provided with the pressure guiding hole 25 for guiding the pressure P1 to the gap 29 formed between the fixed electrode 15 and the diaphragm 10. The other fixed electrode 20 has the same configuration. An air gap 30 formed between the fixed electrode 20 and the diaphragm 10 is provided.
A pressure guiding hole 26 for guiding the pressure P2 is formed in the hole. A first capacitor is formed by the diaphragm 10 and the fixed electrode 15, and the capacitance Ca of this capacitor is taken out through each of the lead pins A and C. Similarly, a second capacitor is formed by the diaphragm 10 and the fixed electrode 20, and the capacitance Cb of this capacitor is determined by each of the lead pins B,
Retrieved via C. Now, when the pressures P1 and P2 act on the diaphragm 10,
The diaphragm 10 is displaced according to the differential pressure (P1 to P2),
Each capacitance Ca, Cb changes according to this displacement, and a differential pressure can be measured based on this change. The differential pressure detector 50 shown in FIG. 3 is housed in a housing sealed by a seal diaphragm that receives the pressures P1 and P2, as described later in detail. A fluid, such as silicone oil, is enclosed. That is, each gap 29, 30 and each pressure guiding hole 2
5, 26 will be filled with silicone oil. FIG. 4 is a sectional view of a differential pressure detecting device incorporating a conventional example. In FIG. 4, reference numeral 50 denotes the capacitance type differential pressure detector shown in FIG. The differential pressure detector 50 is housed in an inner chamber 52 of a bottomed cylindrical body 51 and is connected to a metal pipe 54 via an insulator 53. And this metal pipe 54
Is welded to the mounting plate 55, and the mounting plate 55 is further welded to the opening of the bottomed cylindrical body 51. Further, a cap 56 is welded to the opening of the bottomed cylindrical body 51. The cap 56 has a through-hole 57, and a seal diaphragm 58 is attached to form a pressure receiving chamber 61 therebetween. On the other hand, the bottom of the bottomed cylindrical body 51 also has a through hole 60, and a seal diaphragm 59 is attached to form a pressure receiving chamber 62 therebetween. A hermetic seal terminal 63 having lead pins A, B, and C is provided on the side wall of the bottomed cylindrical body 51. The space formed between the seal diaphragms 58 and 59, that is, the inner chamber 52, the through holes 57 and 60, and the pressure receiving chambers 61 and 62 is filled with an incompressible fluid such as silicone oil. Through the silicone oil, the pressures P1 and P2 acting on the seal diaphragms 58 and 59 are changed by the differential pressure detector 50.
Is transmitted to the diaphragm 10 (see FIG. 3). Now, in FIG. 3, P1 <P2, and when the pressure difference is not so large, only the diaphragm 10 is displaced to the left. Therefore, the dimension of one of the variable gaps 29 is G-Δ,
The dimension of the other variable gap 30 is G + Δ. Where G
Is the common dimension of the gaps 29 and 30 when there is no differential pressure, and Δ is the displacement of the diaphragm 10 when there is a differential pressure. Assuming that the area of each of the conductive plates 12 and 17 is A and the dielectric constant of each of the gaps 29 and 30 is ε, each of the capacitances C1 and C2 formed by the diaphragm 10 and each of the fixed electrodes 15 and 20 is C1 = Ε · A / (G−Δ) (2) C2 = ε · A / (G + Δ) (2) When each of the pair of capacitances C1, C2 changes differentially, a signal F proportional to the displacement Δ of the diaphragm 10, that is, the differential pressure is obtained by the following equation (3), as is well known. Can be. F = (C1−C2) / (C1 + C2) (3) = Δ / G

[Problems to be solved by the invention]

The conventional technology described above has the following problems. That is, when the differential pressure (= P2−P1) is very large, the differential pressure causes the fixed electrode 15 on the left side of the differential pressure detector 50 in FIG. 4 to be displaced so as to curve rightward convexly. Diaphragm 10 and each fixed electrode only by displacement
Each capacitance between 15, 20 changes. Here, the displacement due to the differential pressure of the fixed electrode 15 is Δe, and the capacitances C1e, C formed by the diaphragm 10 and the fixed electrodes 15, 20 when the displacement Δe and the displacement Δ are generated simultaneously.
2e is as follows: C1e = ε · A / (G−Δ−Δe) (4) C2e = C2 = ε · A / (G + Δ) (5) Since each of the capacitances C1e and C2e does not accurately change differentially, if the differential pressure signal calculated by the equation (3) is Fe, then Fe = (C1e−C2e) / (C1e + C2e) = (2Δ + Δe) ) / (2Δ−Δe) (6) As is apparent from the equation (6), when Δe is not negligible with respect to Δ, the differential pressure signal Fe is equal to the differential pressure (= P2−
It is not proportional to P1), in other words, the linearity is broken. In FIG. 3, the dielectric constant of the silicone oil in each of the gaps 29 and 30 slightly changes due to the difference between the pressures P1 and P2. Due to the change of the dielectric constant due to the pressure, the linearity of the differential pressure signal Fe obtained from the equation (6) with respect to the differential pressure is further broken. An object of the present invention is to solve the above problems of the prior art, and to obtain a good linearity differential pressure signal even when the differential pressure is large or when the dielectric constant in the air gap changes due to the pressure. To provide a capacitance type differential pressure detector.

[Means for Solving the Problems]

In order to solve this problem, a capacitance-type differential pressure detector according to the present invention includes: a fixed electrode having a pressure-guiding hole opposed to a first gap; A diaphragm as a movable electrode opposed through a gap; and a fixed substrate having a pressure guide hole facing the other side of the diaphragm and another gap through another gap, and applying one pressure to each of the fixed electrodes. While acting on one side of the diaphragm through the pressure guiding hole, simultaneously acting on the outer surface of the fixed electrode not facing the diaphragm and the outer surface of the fixed substrate, and applying the other pressure Is applied to the other side of the diaphragm through the pressure guiding hole of the fixed substrate, a first capacitance formed between the fixed electrodes via the first gap, and the second gap Through the diaphragm, The formed between the fixed electrode opposed to Les 2
The difference between the pressures is measured on the basis of the capacitance.

[Action]

Since each fixed electrode is not displaced by the differential pressure and only the diaphragm is displaced by the differential pressure, the differential pressure signal obtained based on the first and second capacitances has good linearity. . In addition, since the first and second capacitances have the same pressure in the respective gaps, there is no change in the dielectric constant in each gap.

【Example】

An embodiment of a capacitance type differential pressure detector according to the present invention will be described with reference to FIG. In FIG. 1, reference numerals 1 and 2 denote fixed electrodes, respectively, and their respective structures are the same. The fixed electrode 1 is disposed concentrically with each conductive plate 1a, 1b fixed to each side thereof via an insulating plate 1c and an annular groove 1e radially outside the conductive plate 1b. And an annular support 1d fixed to the plate 1c. Further, a pressure guiding hole 1f is formed so as to penetrate the center at a right angle, and a conductive film 1g is formed on the inner peripheral surface thereof.
Is coated. Each of the fixed electrodes 1 and 2 is connected to the left side surface of the support
And the periphery of the right side surface of the conductive plate 2a belonging to the conductive plate 1b.
Are bonded by a glass bonding portion 4a so as to form a gap 4 between the left side surface of the conductive plate 2a and the right side surface of the conductive plate 2a. In addition,
The gap 4 corresponds to a first gap in the invention. The diaphragm 10 has its left side and the fixed substrate 3 joined at the periphery by a glass joint 6a, and the periphery of its right side and the left side of the support 2d are also connected to the right side of the diaphragm 10 and the conductive plate. It is joined by the glass joining portion 5a so as to form a gap 5 between the right side surface of 2b. The fixed substrate 3 may be made of any material of an insulator and a conductor, but here, the same silicon as the diaphragm 10 is selected in consideration of ease of manufacture and temperature characteristics. Further, a pressure guiding hole 3f is formed in the center, and a gap 6 is formed between the pressure guiding hole 3f and the diaphragm 10. Here, the gap 5 corresponds to a second gap in the invention. The conductor 7a is provided between the outer peripheral surfaces of the diaphragm 10 and the support 2d,
A conductor 7b is provided on the outer peripheral surface of the conductive plate 1a, and a conductor 7c is provided between the outer peripheral surfaces of the conductive plate 2a and the support 1d.Each of the lead pins A, B, and C comes into contact with each of the above conductors. Provided. FIG. 2 is a sectional view of a differential pressure detecting device incorporating the above embodiment. In this figure, the difference between this differential pressure detecting device and the conventional differential pressure detecting device shown in FIG.
Are that the conventional bottomed cylindrical body 51 is replaced, the inner chamber 72 is replaced with the conventional inner chamber 52, and the through hole 73 is replaced with the conventional through hole 60. In short, this is related to the fact that the lateral dimension of the differential pressure detector 40 is larger than that of the conventional differential pressure detector 50 by the addition of the fixed substrate 3. The operation of this embodiment will be described mainly with reference to FIG. 1 and supplementarily with reference to FIG. In FIG. 1, it is assumed that the pressure P2 from the right side is much larger than the pressure P1 from the left side. Pressure P2 is simultaneously
As shown in FIG. 2, it also acts on the outer periphery of the differential pressure detector 40.
Accordingly, the pressure P2 acts on the left side surface of the fixed substrate 3 and the pressure P1 acts on the right side surface thereof, and the fixed substrate 3 is bent to the right by a pressure difference (= P2−P1). To be displaced. On the other hand, each of the fixed electrodes 1 and 2
Since the common pressure P2 acts on each side surface, there is no displacement. Then, the diaphragm 10 is displaced leftward by the differential pressure (= P2−P1). Now, the capacitance C1a formed between the fixed electrodes 1 and 2 via the gap 4 and the capacitance C2a formed between the diaphragm 10 and the fixed electrode 2 via the gap 5 are different from each other at the pressure P2. Assuming that the common permittivity of the air gaps 4 and 5 is E, C1a = E · A / G (7) C2a = E · A / (G + Δ) (8) where A is each conductive plate 1b , 2b, G is a common dimension of the spaces 4 and 5 when there is no differential pressure, and Δ is the displacement of the diaphragm 10 when there is a differential pressure. Therefore, when the differential pressure signal Fa is obtained by the following known equation (9), Fa = (C1a−C2a) / C1a (9) = Δ / G Thus, the differential pressure signal Fa is Δ, that is, It is proportional to pressure.
Note that the displacement of the fixed substrate 3 is not related to the differential pressure measurement.

【The invention's effect】

In the present invention, since each fixed electrode is not displaced by the differential pressure and only the diaphragm is displaced by the differential pressure, the differential pressure signal obtained based on the first and second capacitances is good. Since the first and second capacitances have a common pressure in their respective gaps,
There is no change in the dielectric constant at each gap. As a result, a good linear pressure difference signal can be obtained even when the differential pressure is large, and a good linear pressure difference signal can be obtained even when the dielectric constant in the gap changes due to the pressure. Since the structure is simple, there is an excellent effect that it can be easily manufactured and cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of an embodiment according to the present invention, FIG. 2 is a sectional view of a differential pressure detecting device incorporating this embodiment, FIG. 3 is a sectional view of a conventional example, and FIG. FIG. 4 is a cross-sectional view of a differential pressure detecting device in which is incorporated. Description of symbols 1,2: fixed electrode, 1a, 1b, 2a, 2b: conductive plate, 1c, 2c: insulating plate, 1d, 2d: support, 1e, 2e: groove, 1f, 2f, 3f: pressure guide hole 1g, 2g: conductor film, 3: fixed substrate, 4, 5, 6: void, 4a, 5a, 6a: glass joint, 7a, 7b, 7c: conductor, 10: diaphragm, 40: differential pressure detector.

Claims (1)

(57) [Claims] 1. A fixed electrode which has a pressure guiding hole opposed to each other via a first gap; a diaphragm as a movable electrode opposed to any one of the fixed electrodes via a second gap; and A fixed substrate opposed to the opposite side via another gap and having a pressure guiding hole; and applying one pressure to one side of the diaphragm through the pressure guiding hole of each of the fixed electrodes; An outer surface of the fixed electrode that does not face the diaphragm and an outer surface of the fixed substrate are simultaneously acted on, and the other pressure is applied to the other side of the diaphragm through a pressure guiding hole of the fixed substrate. When actuated, a first capacitance is formed between the fixed electrodes via the first gap, and the diaphragm is formed between the diaphragm and the fixed electrode facing the same via the second gap. Second capacitance Based on the electrostatic capacity type differential pressure detector, characterized in that said a structure difference between the pressure is measured.