JPH09257822A - Current meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current meter which can be miniaturized easily, whose reliability is high, which is low-cost and which can be mass-produced. SOLUTION: A first electrode 4 is installed at a first board 1 and a second electrode 5 is installed at a second board 2 in such a way that they are faced via a gap. In addition, a measuring cavity 3 having a bottom part 3a which is formed to be a thin-film shape is formed around the second electrode 5, and the measuring cavity 3 is constituted in such a way that it can communicate with the outside via fluid communication passages 10a, 10b which are formed on the second board 2 and that, when it is placed in a steady flow, an electrode arrangement and installation part 9 in which the second electrode 5 is arranged and installed is displaced according to the difference between a pressure in the measuring cavity 3 and a pressure in a steady flow at the outside. Then, a flow velocity can be detected as a change in the capacitance value of a plate capacitor which is constituted of the first and second electrode 4, 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a velocity meter for measuring the velocity of a fluid such as gas or liquid, and more particularly to a velocity meter provided in a fluid passage and capable of being miniaturized.

[0002]

2. Description of the Related Art For example, in automobiles and air conditioners,
Fluid passages with very small cross-sections, and usually velocity sensing of fluids in locations where the instrument is not easily accessible, may be required. For example, specifically, the measurement of the flow rate of fuel in the fuel injection system of an automobile, the flow velocity of gas in an air-conditioning duct, the flow velocity with an extremely high time resolution in a wind tunnel experimental apparatus, and the like.

[0003]

Various types of velocity meters have been proposed, but they are small, highly reliable, inexpensive, and can be mass-produced by so-called micromachining technology. There is no one that satisfies the above condition, and such a velocity meter is desired.

The present invention has been made in view of the above circumstances, and provides a small-sized, highly reliable, low-priced velocity meter capable of mass production by so-called micromachining technology. Further, another object of the present invention is to provide a reliable current velocity meter, in which various so-called stresses that may occur during the manufacturing process or mounting of the velocity meter and the influence of fluid viscosity on measurement sensitivity are small. To do.

[0005]

A velocity meter according to the present invention comprises:
A flat plate-shaped first substrate made of an insulating member and a flat plate-shaped second substrate made of a semiconductor member are bonded to each other, and a first flat plate capacitor is formed between the first and second substrates.
And a second electrode are arranged to face each other with a gap, and the first electrode
A cavity having a thin-film bottom is formed in an annular shape around the second electrode, and the cavity is communicated to the outside through a fluid communication path formed between the first and second substrates. The capacitance change of the flat plate capacitor can be detected according to the pressure difference between the pressure in the cavity and the external pressure. In particular, it is preferable that the cavity be provided in a recess around the second electrode on the second substrate.

In such a structure, the fluid is also introduced into the cavity through the fluid communication passage, and when the velocity meter is arranged in the flow of a steady flow, the pressure inside the cavity and the pressure outside the cavity are increased. And a bottom portion of the cavity has a thin film shape, the portion where the second electrode is arranged is displaced according to this pressure difference. Since the pressure difference occurs according to the flow velocity, it is possible to detect the flow velocity as a change in the capacitance value of the flat plate capacitor composed of the first and second electrodes. In particular, the first and second
Since the formation of the first and second electrodes and the formation of cavities on the substrate can be performed easily, efficiently and accurately by so-called micromachining technology, it is easy to miniaturize,
It is possible to provide a velocity meter that can be mass-produced.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. The members, arrangements, and the like described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention. This anemometer is composed of two flat plates 1, 2
Is bonded to form a measurement cavity 3 filled with a fluid between the two substrates 1 and 2, and a flat plate capacitor C
Two electrodes 4 and 5 forming v are provided, and the flow velocity can be detected as the capacitance value of the plate capacitor Cv (see FIG. 1).

That is, the first substrate 1 is, for example, a flat plate made of an insulating member such as a heat-resistant glass material, and has a rectangular planar shape (FIGS. 1 and 2). reference). On one surface of the first substrate 1, that is, on the surface side facing the second substrate 2, a rectangular first electrode 4 formed of a conductive member such as aluminum is provided. (See FIGS. 1 and 2). In addition,
In the following description, for convenience, the surface on which the surface of the anemometer appears as shown in FIG. 2 is the XY plane, the X axis is the horizontal direction in the drawing and the Y axis is the vertical direction in the drawing. Further, as shown in FIG. 3, it is assumed that the Z axis is the vertical direction of the paper surface which is the thickness direction of the first and second substrates 1 and 2, and the Y axis is the horizontal direction of the paper surface.

A lead wire 6 is further extended from the first electrode 4. That is, the lead wire 6
Is extended from one corner of the first electrode 4 to one side of the first substrate 1 in the short axis direction along the longitudinal axis direction of the first substrate 1 (horizontal direction in FIG. 1). Further, it extends from here to the readout electrode 7 provided at one corner of the first substrate 1 along the side portion (see FIG. 1). It should be noted that both the extraction wiring 6 and the readout electrode 7 are manufactured at the same time when the first electrode 4 is manufactured, and the manufacturing method thereof is vapor deposition, etching treatment, etc., which is one of so-called micromachining techniques. Is preferably used.

On the other hand, the second substrate 2 made of a semiconductor member, for example, a silicon wafer, has an external shape and dimensions in the state of being bonded to the first substrate 1 as described above. 1 is substantially the same as the first substrate 1 except that a notch 8 is formed in a portion facing the read electrode 7 provided on the first substrate 1. However, the surface facing the first substrate 1 is The difference is that they are formed as described below.

That is, in the second substrate 2, a measurement cavity 3 having a substantially frame-like planar shape is formed on the side facing the first substrate 1 (see FIGS. 1 and 2). The measurement cavity 3 is formed by removing the thickness direction of the second substrate 2 made of a silicon wafer (vertical direction of the paper surface in FIG. 3) in a concave shape by, for example, an etching process, and the thickness of the bottom portion 3a ( The thickness in the vertical direction in FIG. 3) is formed in a thin film shape that can be displaced according to the pressure difference between the pressure inside the measurement cavity 3 and the external pressure, as will be described later.

The peripheral portion of the measurement cavity 3 is a joint surface to be joined to the first substrate 1. However, in the embodiment of the present invention, one side edge in the lateral axis direction. Since the fluid communication passages 10a and 10b are recessed in the joint surface as described later, the joint surface on the side where the fluid communication passages 10a and 10b are provided is larger than that on the other side. As described above, the measurement cavity 3 is provided so as to be deviated to one side in the longitudinal axis direction (the left-right direction on the paper surface in FIG. 2) (see FIG. 1).

Further, the second substrate 2 is provided with an electrode arrangement portion 9 formed in a so-called island shape so as to be surrounded by the measurement cavity 3 described above (see FIGS. 1 and 3). A second electrode 5 formed by, for example, vapor deposition of a conductive member is formed on the upper surface of the electrode placement portion 9, and the thickness including the second electrode 5 is formed on the first substrate 1. A minute gap is formed between the formed first electrode 4 and second electrode 5 (see FIG. 3). And
A so-called flat plate capacitor Cv is configured by the opposing arrangement of the first electrode 4 and the second electrode 5.

Further, in the second substrate 2, two fluid communication passages 10a and 10b are provided with appropriate intervals on the joint surface on one side of the second substrate 2 in the short axis direction (vertical direction of the paper in FIG. 2). The second substrate 2 is recessed along the longitudinal axis direction of the second substrate 2 (the left-right direction of the paper surface in FIG. 2) (see FIGS. 1 and 2). The two fluid communication passages 10a and 10b are for establishing communication between the measurement cavity 3 and the outside when the first and second substrates 1 and 2 are joined to each other.
b is provided such that a part of the lead-out wiring 6 formed on the first substrate 1 is located substantially at the center of the fluid communication path 10b in the width direction (vertical direction in the drawing of FIG. 2).

Furthermore, the one fluid communication passage 10b.
Near the end surface of the second substrate 2 of the fluid communication passage 10
Between the b and the notch 8, a lead wiring notch 11 is formed.
It is formed along the short axis direction of the second substrate 2 (see FIG. 1). Then, in a state where the first and second substrates 1 and 2 are joined to each other, among the lead wirings 6 arranged on the first substrate 1, the first wirings are arranged in the short axis direction of the first substrate 1. The part that has been cut is the second by the notch 11 for the lead wire.
The substrate 2 is separated from the substrate 2 to ensure a non-contact state.

The detection of the capacitance value of the plate capacitor Cv is performed by an external circuit (not shown). For this purpose, the wiring connection with the external circuit is performed by one of two wirings (not shown) from the external circuit. The other is connected to the readout electrode 6 at an appropriate position on the second substrate 2, respectively.

The anemometer having the above structure is preferably manufactured by using a so-called micromachining technique.
The plane dimensions (dimensions in the XY plane) of the first and second substrates 1 and 2 are about 2 × 2 mm.

Next, the principle of flow velocity measurement by the flow velocity meter according to the embodiment of the present invention having the above-mentioned configuration will be described with reference to FIGS. 4 and 5. First, the anemometer is positioned so that the fluid communication passages 10a and 10b are located on the upstream side of the fluid flow, in the approximate center in the radial direction of the passage 12 filled with a fluid as a measured object such as gas or liquid. Deploy. FIG. 4 schematically shows a state in which a velocity meter is arranged in the passage 12 through which the fluid moves, and in which the fluid velocity is zero.
It should be noted that the drawing is a cross-sectional view of the anemometer on the XZ plane, and is a cross-sectional view taken along the line BB of FIG. 2.

Under such a premise, the measurement cavity 3 is also filled with a fluid having a zero flow velocity, and there is no difference between the pressure outside the velocity meter and the pressure inside the measurement cavity 3. . Therefore, the first and second substrates 1,
The distance of 2 is maintained at a certain distance, and the bottom portion 3a of the measurement cavity 3 is also kept in a state where it does not particularly curve as compared with the case where it is substantially in the air (Fig. 4).

On the other hand, suppose that a steady flow having a certain flow velocity is generated, and in this steady flow, the velocity meter is arranged so that the inlet sides of the fluid communication passages 10a and 10b are located on the upstream side of the steady flow, as in the case described above. (See FIG. 5). In such a state, a stagnation point near the inlets of the fluid communication passages 10a and 10b of the anemometer (see a point marked with a circle in FIG. 5)
Assuming that the pressure at Ptot is Ptot, this stagnation point pressure Ptot will also be transmitted to the measurement cavity 3. On the outer surfaces of the first and second substrates 1 and 2, static pressure Pstat due to a steady flow is generated (see FIG. 5). The cross section of the anemometer shown in FIG. 5 is taken along the line BB of FIG. 2 as in FIG.

The pressure Ptot in the measurement cavity 3 and the first
The differential pressure Pdyn from the static pressure Pstat that acts on the outer surfaces of the second substrates 1 and 2 acts on the electrode placement portion 9. In other words, the stagnation pressure Ptot, the static pressure Pstat, and the differential pressure Pd.
Ptot = Pstat + Pdyn (hereinafter referred to as “Equation 1”) is established with yn. The bottom portion 3a around the electrode arrangement portion 9 is
As described above, since it has a thin film shape, the electrode disposing portion 9 has the first structure depending on the force acting on the electrode disposing portion 9.
Since the second substrate 1 and the second substrate 2 can be displaced in the thickness direction, that is, the Z-axis direction, the above-mentioned differential pressure Pdyn
Due to the occurrence of the above, the electrode arrangement portion 9 is displaced in the direction away from the first electrode 4 (see FIG. 5). For this reason,
The electrostatic capacitance between the first and second electrodes 4 and 5 changes according to the amount of displacement of the electrode arrangement portion 9, that is, the magnitude of the differential pressure Pdyn.

By the way, the Bernoulli's theorem holds in the inside and outside of the velocity meter placed in the steady flow. Therefore, regarding the pressure Ptot in the measurement cavity 3 of the anemometer and the static pressure Pstat at the location of the steady flow outside the anemometer based on Bernoulli's theorem, the velocity is assumed to be V
If f, the relational expression of Vf = α × (Ptot−Pstat) is derived.
Since it is yn, Vf = α × Pdyn (hereinafter referred to as “equation 2”). Here, α is a constant.

Therefore, since the differential pressure Pdyn is obtained as the capacitance value of the flat plate capacitor Cv formed by the first and second electrodes 4 and 5, as described above, the capacitance value and the differential pressure Pdyn are previously calculated. If the relationship is investigated, the differential pressure Pdyn can be obtained from the obtained capacity value, and the flow velocity Vf can be known by calculation based on the equation 2. Further, if the diameter or the cross-sectional area of the passage 12 in the radial direction is known, the fluid flow rate in the passage 12 per unit time can be obtained by calculating the product with the flow velocity Vf.

It should be noted that the relationship between the capacitance value of the flat plate capacitor Cv and the flow velocity Vf is investigated, and, for example, a conversion table or a conversion graph should be prepared in advance so that the flow velocity Vf can be immediately obtained from the capacitance value. For example, it is not necessary to calculate the flow velocity Vf each time based on the equation (2). Further, if an external circuit for displaying the flow velocity Vf is provided based on the obtained capacitance value,
The flow velocity Vf can be known directly.

In the anemometer having the above-mentioned structure, the amount of displacement of the electrode mounting portion 9 due to the pressure can change depending on the film thickness of the bottom portion 3a. Therefore, changing the film thickness of the bottom portion 3a means changing the so-called measurement sensitivity of this flowmeter, and by setting the film thickness of the bottom portion 3a, it is possible to obtain a flowmeter suitable for the desired use condition.

[0026]

As described above, according to the present invention,
A space into which a fluid flows is provided between a flat plate-shaped substrate made of a semiconductor member and a flat plate-shaped substrate made of an insulating member, and a flat plate capacitor whose interval is changed by the pressure of the fluid is formed between the two substrates. With such a configuration, it is possible to manufacture by so-called micromachining technology, so that it is possible to provide a low-cost and small-sized current meter that is easy to mass-produce. Also, due to the principle of operation, various so-called stresses that may occur during the manufacturing process and installation of this velocity meter and the influence on the measurement sensitivity of the viscosity of the fluid are extremely small, so a reliable velocity meter Will be provided.

Further. The anemometer according to the present invention is highly reliable and has a long life because there are no moving parts that cause continuous or intermittent friction. Furthermore, since the velocity meter according to the present invention has a configuration in which the number of moving parts is smaller and the amount of fluid flowing into the interior is smaller than that of the conventional one, particularly when the fluctuation period of the flow velocity is fast. It is suitable for measurement in.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a velocity meter according to an embodiment of the present invention.

FIG. 2 is a plan view of the velocity meter according to the embodiment of the present invention.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a schematic diagram for explaining the principle of flow velocity measurement by the flow velocity meter according to the embodiment of the present invention, in a state in which the flow velocity meter is arranged in a passage of zero flow velocity.

FIG. 5 is a schematic diagram for explaining the principle of flow velocity measurement by the flow velocity meter in the embodiment of the present invention, and is a schematic diagram in a state in which the flow velocity meter is arranged in the passage where a steady flow occurs.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... 1st board 2 ... 2nd board 3 ... Measurement cavity 3a ... Bottom part 4 ... 1st electrode 5 ... 2nd electrode 6 ... Lead-out wiring 7 ... Read-out electrode 9 ... Electrode arrangement part 10a, 10b ... Fluid Communication passage

Claims (2)

[Claims] 1. A flat plate-shaped first substrate made of an insulating member and a flat plate-shaped second substrate made of a semiconductor member are bonded to each other, and a flat plate capacitor is provided between the first and second substrates. A first electrode and a second electrode, which are arranged to face each other with a gap therebetween, and a cavity having a thin film-shaped bottom is formed in an annular shape around the first electrode and the second electrode; The plate is connected to the outside through a fluid communication passage formed between the first and second substrates, and the capacitance change of the plate capacitor can be detected according to the pressure difference between the pressure in the cavity and the outside pressure. A velocity meter characterized by being configured. 2. The velocity meter according to claim 1, wherein the cavity is formed in a recess around the second electrode on the second substrate.