JP2546013B2 - Capacitive differential pressure detector - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

This invention is a diaphragm that is displaced according to a differential pressure,
It is a detector that measures the differential pressure based on the electrostatic capacitance formed between each of the fixed electrodes on each side of the fixed electrode. Regarding the detector. 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. 4 is a sectional view showing the structure of a conventional example. In FIG. 4, a pair of fixed electrodes 15, 2 are provided on each side of the diaphragm 10.
0 is installed. One fixed electrode 15 is composed of a first conductive plate 12 made of silicon and arranged opposite to the diaphragm 10, a cordierite insulating plate 13 bonded to the first conductive plate 12, and the insulating plate 13. It is composed of the second conductive plate 14 made of bonded silicon, and the first conductive plate 12 and the second conductive plate 14 are electrically connected via the conductor film 27. The fixed electrode 15 is provided with an annular support body that is joined to the insulating plate 13 with an annular groove 23 surrounding the first conductive plate 12 interposed therebetween.
21 is provided. The support 21 is bonded to the diaphragm 10 at the glass bonding portion 11 having a predetermined thickness. First conductive plate 12
The support 21 is electrically insulated from the support 21. The support
21 may be either an insulator or a conductor, but the same silicon as that of the first conductive plate 12 is selected for ease of manufacture and improvement of temperature characteristics. Further, the fixed electrode 15 has a diaphragm 10
A pressure guiding hole 25 for guiding the pressure P1 is formed in a gap 29 formed between The other fixed electrode 20 has the same structure. The fixed electrode 20 has a pressure P2 in a gap 30 formed between the fixed electrode 20 and the diaphragm 10.
A pressure guiding hole 26 for guiding the is opened. 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 pressure difference (P1 to P2). The capacitances Ca and Cb change according to this displacement, and the differential pressure can be measured based on this change. The conventional example shown in FIG. 4 receives each pressure P1, P2,
It is housed in a housing which is sealed by a seal diaphragm (not shown), and a non-compressible fluid for pressure transmission, such as silicone oil, is enclosed in this housing. That is, the gaps 29, 30 and the pressure guiding holes 25, 26 are filled with silicone oil.

[Problems to be Solved by the Invention]

In the conventional technique as described above, as will be described in detail below, the span characteristic and linearity of the differential pressure signal of the detector are affected by changes in the ambient temperature, in other words,
There is a problem that the temperature characteristics deteriorate. The span characteristic is a variation width of the capacitance with respect to a 100% variation width of the differential pressure, in other words, a displacement width of the diaphragm. Each fixed electrode is composed of a first and a second conductive plate made of silicon on both sides and an insulating plate made of cordierite in the middle.
Since it is a layered structure, it can be regarded as a kind of bimetal in which plate-shaped members having different thermal expansion coefficients are bonded together. When each fixed electrode is deformed by a change in ambient temperature, a radial stress is generated in the diaphragm made of silicon and fixed to each fixed electrode at the peripheral portion. The displacement of the diaphragm due to this stress becomes a factor that impedes the linearity of the differential pressure signal generated by the original displacement based on the differential pressure. The radial stress generated in the diaphragm due to the change in ambient temperature and the displacement of the diaphragm due to this stress will be described in detail below. In FIG. 1, the synthetic thermal expansion coefficient α of the conventional fixed electrodes 15 and 20 is α = K1 (A−K2 / B) (α1−α2) + α2 (1) where α1 and α2: cordierite ， The coefficient of thermal expansion of silicon, E1, E2: Young's modulus of the same, H1, H2: its thickness, H3: the thickness of each support. K1 and K2 are constants determined by E1, E2, H1 and H2, respectively, and A = (H1 + 2H3) / 2 and B = 1 / (H1 · E1). E1 = 8,000, E2 = 15,300 ^{(unit: kg / mm 2), α1} = 1.1, α
2 = 3.1 (unit: 10 ^-6 / ° C), and H1 = 0.5, H2 = 1.5, H
When 3 = 1.5 (unit: mm), α = 2.53 × 10 ⁻⁶ / ° C. Therefore, when the ambient temperature changes ΔT, the radial stress σ generated in the diaphragm is: σ = E · Δα · ΔT / (1-ν) (2) where E, ν: Young's modulus of the diaphragm, Poisson's ratio, Δα: difference in coefficient of thermal expansion between fixed electrode and diaphragm. The displacement W of the diaphragm when the differential pressure P acts under the stress σ in the radial direction is W = P / [K + (4H / R ² ) σ] (3) where H and R are respectively Diaphragm thickness, radius, K:
It is a constant determined by E, ν, H, and R. The displacement W is determined by the first element related to the material and size of the diaphragm and the second element related to the radial stress, as is apparent from the equation (3). In particular, in order to measure a minute differential pressure P with high sensitivity, it is necessary to reduce the thickness H, and at the same time, the stress σ becomes an inhibiting factor. FIG. 5 shows the characteristics with respect to the thermal stress σ of the value W / G when the thicknesses of the diaphragms for measuring 0.1 m water column and 3.2 m water column are 0.03 mm and 0.1 mm, respectively. The solid line is 0.1 m water column, the broken line is
Corresponds to 3.2m water column respectively. Here, G is the size of the gap between the diaphragm and the fixed electrode when the differential pressure is zero. For example, when the ambient temperature changes by ± 60 ° C (120 ° C range), the thermal stress σ changes from Equation (2) by 0.62 kg / m ² , and the value W / G changes by about 82% in the case of 0.1 m water column and by about 6% in the case of 3.2 m water column. An object of the present invention is to solve the above problems of the conventional technique and suppress the influence of temperature change on the span characteristic and linearity of the differential pressure signal, in other words, to improve the temperature characteristic. An object is to provide a capacitive differential pressure detector.

[Means for Solving the Problems]

In order to solve this problem, the electrostatic capacitance type differential pressure detector according to the present invention comprises a diaphragm that is displaced according to a differential pressure, and a fixed electrode that is provided on each side of the diaphragm and has pressure guiding holes. In the detector in which the differential pressure is measured based on the capacitance formed between the fixed electrodes, the fixed electrodes closely face the center surface of the diaphragm and have a coefficient of thermal expansion similar to that of the diaphragm. A first conductive plate; and an annular support that surrounds the outer peripheral surface of the first conductive plate and is joined to the peripheral surface of the diaphragm; the annular support and the first conductive plate. Of each insulating plate, which is respectively bonded to each surface on the side opposite to the diaphragm and has a common thickness and the same shape and size as each surface; and is commonly bonded to the other surface of each insulating plate, In the first conductive plate Similar was has a thermal expansion coefficient, and a second conductive plate which is connected thereto and electrically; comprises.

[Work]

Since the insulating plate has a structure in which it is divided into a central portion and an annular portion respectively corresponding to the first conductive plate and the support, each fixed electrode is equivalent to the insulating plate when viewed from the surface of thermal expansion. Is a three-layer structure in which conductive plates having the same coefficient of thermal expansion as those of the diaphragm and having the same area are joined to each side, with the middle being the middle.
Therefore, the composite thermal expansion coefficient of this three-layer structure can be approximated to that of the diaphragm by selecting the Young's modulus and thickness of each layer.

【Example】

An embodiment of the capacitance type differential pressure detector according to the present invention will be described with reference to FIG. 1 which is a sectional view thereof. In FIG. 1, this embodiment is different from the conventional example shown in FIG. 4 in the structure of the fixed electrode. That is, the left fixed electrode 15 in the conventional example becomes the fixed electrode 15A by dividing the insulating plate 13 into the central insulating plate 13a and the annular insulating plate 13b in the embodiment. In other words, the void 23 in the conventional example becomes the void 23A in the embodiment, and the insulating plate 13 in the conventional example is dug deeply to divide into two parts, the central insulating plate 13a and the annular insulating plate 13b. The same applies to the fixed electrode 20A on the right side in FIG. Therefore, each fixed electrode 15A, 20A is equivalent to a conductive plate having a coefficient of thermal expansion similar to that of the diaphragm on each side, as shown in FIG. It is a joined three-layer structure. Therefore, even when the conductive plate and the insulating plate have different thermal expansion coefficients, the thermal deformation due to the difference in the thermal expansion coefficient between the upper conductive plate and the insulating plate, that is, the bimetal effect, is caused by the lower conductive plate and the insulating plate. The composite thermal expansion coefficient of the three-layer structure can be approximated to that of the conductive plate, that is, the diaphragm, by offsetting the difference between the two, and Young's modulus and thickness of each layer. Now, in the three-layer structure in FIG. 2, assuming that the synthetic thermal expansion coefficient is β when the conductive plate is silicon and the insulating plate is cordierite, the formula β = α2 + (α1-α2) / (1 + G) G = 2H2 · E2 / H1 · E1 Other symbols are the same as above. Numerical calculation shows that β = 2.94 × 10 ⁻⁶ / ° C., which is close to the thermal expansion coefficient α2 of silicon. Now, FIG. 3 is a sectional view of a differential pressure detecting device incorporating the embodiment. In FIG. 3, 50 is the capacitance type differential pressure detector shown in FIG. This detector 50 has a bottomed cylindrical body 51.
It is housed in the inner chamber 52 and is coupled to the metal pipe 54 via the insulator 53. The 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 this silicone oil, the pressure acting on each seal diaphragm 58, 59 is transmitted to each side of the diaphragm of the detector 50.

【The invention's effect】

As described above, according to the present invention, the insulating plate has the structure in which the central portion and the annular portion corresponding to the first conductive plate and the support body are separated from each other. Equivalently viewed from the surface, it is a three-layer structure in which a conductive plate having a coefficient of thermal expansion similar to that of a diaphragm is joined to each side with an insulating plate in the middle, and Young's modulus of each layer,
The composite thermal expansion coefficient of this three-layer structure can be approximated to that of the diaphragm by selecting the thickness. Therefore, according to the present invention, it is possible to suppress the influence of the ambient temperature on the span characteristic and linearity of the differential pressure signal without increasing the overall configuration size even for minute differential pressure measurement, as compared with the prior art. And the temperature characteristics of the detector can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment according to the present invention, FIG. 2 is an equivalent structure diagram of a fixed electrode in the embodiment, FIG. 3 is a sectional view of a differential pressure detecting device incorporating the embodiment, and FIG. FIG. 5 is a cross-sectional view of an example, and FIG. 5 is a characteristic diagram of the measured diaphragm displacement with respect to thermal stress. Reference 10: Diaphragm, 11, 16: Glass joint, 13a, 13b, 18a, 18b: Insulation plate, 12, 14, 17, 19: Conductive plate, 15A, 20A: Fixed electrode, 21, 22: Support , 23A, 24A: annular groove, 25, 26: pressure guide hole, 27, 28: conductor film, 29, 30: void, 31, 32, 33: conductor, 50: detector.

Claims (1)

(57) [Claims] 1. The differential pressure is measured on the basis of an electrostatic capacity formed between a diaphragm that is displaced according to the differential pressure and a fixed electrode that is provided on each side of the diaphragm and has a pressure guide hole. In the detector, each of the fixed electrodes closely faces the center surface of the diaphragm and has a first conductive plate having a coefficient of thermal expansion similar to that of the diaphragm.
An annular support that surrounds the outer peripheral surface of the first conductive plate and is joined to the peripheral surface of the diaphragm; and the annular support and the first conductive plate are opposite to the diaphragm. And an insulating plate having a common thickness and having the same shape and dimensions as those of the respective surfaces; and a common bonding to the other surface of each insulating plate, which is similar to the first conductive plate. And a second conductive plate having a thermal expansion coefficient and electrically connected to the electrostatic conductive differential pressure detector.