JPH0435778Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electrostatic pressure sensor used in blood pressure monitors and the like.

[Prior art]

In an electrostatic pressure sensor, in order to interpret the magnitude of pressure as a change in capacitance and convert it accurately, the diaphragm must be displaced in direct proportion to the change in pressure, and two diaphragms must be used. It is necessary that the capacitance generated between the two electrodes changes functionally with respect to a change in the distance between the two electrodes. The former condition concerns the performance of the diaphragm, while the latter condition concerns the structure of the electrostatic pressure sensor.

As shown in FIGS. 3 and 4, the structure of the conventional electrostatic pressure sensor is that a diaphragm fixing base 2 with an outer diameter of A is provided on the top surface of a circular frame 1. A diaphragm 3 having an outer diameter A is similarly provided on the upper surface. A movable electrode support rod 4 is provided at the center of the upper surface of the diaphragm 3, and a movable electrode 5 having an outer diameter B is provided on the movable electrode support rod 4 so that the center portion thereof is supported from below. ing.
The diaphragm 3 and the movable electrode 5 are electrically connected to each other via the movable electrode support rod 4. Further, above the movable electrode 5, a fixed electrode 6 with an outer diameter C is installed parallel to the movable electrode 5, and the capacitance generated between the two electrodes is
6b.

However, in the conventional structure described above, since outer diameter C>outer diameter A>outer diameter B, in addition to normal capacitance occurring between the movable electrode 5 and the fixed electrode 6, the diaphragm fixed base 2 Unnecessary capacitance is generated between the fixed electrode 6 and the fixed electrode 6. That is, the fixed electrode outer peripheral portion 6a where the fixed electrode 6 protrudes from the movable electrode 5
and a diaphragm fixed base outer peripheral part 2 where the diaphragm fixed base 2 protrudes from the movable electrode 5.
Unnecessary capacitance occurs in a virtual region surrounded by a and having a substantially trapezoidal cross section. This unnecessary capacitance is unrelated to the displacement of the movable electrode 5 and has a constant value. Therefore, when the inter-electrode distance between the movable electrode 5 and the fixed electrode 6 is large, the normal capacitance generated between the movable electrode 5 and the fixed electrode 6 is small, so that unnecessary capacitance with respect to the sensor signal is reduced. The impact will be greater. On the other hand, when the distance between the electrodes is small, the normal capacitance is large, so the influence of unnecessary capacitance on the senna signal is reduced. Therefore, during use, the sensor signal had to be corrected according to the distance between the electrodes. Further, since the distance between the electrodes described above varies during the assembly process, the influence of unnecessary capacitance also differs for each electrostatic pressure sensor. Therefore,
Correction for unnecessary capacitance has to be performed for each electrostatic pressure sensor.

[Purpose of invention]

The present invention was devised in consideration of the above-mentioned conventional problems, and aims to improve quality and reduce costs by minimizing the amount of unnecessary capacitance generated. The object of the present invention is to provide an electrostatic pressure sensor that can be obtained.

[Structure of the idea]

In the electrostatic pressure sensor of the present invention, a fixed electrode and a movable electrode are provided in a facing arrangement, and the movable electrode is supported by a diaphragm whose peripheral edge is fixed on a diaphragm fixed base, and each has a concentric circular shape. In the electrostatic pressure sensor, a movable electrode terminal is provided on the diaphragm fixing base, and the movable electrode is electrically connected to the movable electrode via the diaphragm and the diaphragm fixing base in sequence, and
The outer diameter of the fixed electrode is set so as to fit within a virtual cone formed by connecting the outer circumference of the movable electrode and the outer circumference of the diaphragm fixing base, and the fixed electrode is integrally molded and fixed radially from the outer circumference. This is characterized in that the amount of unnecessary capacitance generated between the diaphragm fixing base and the fixed electrode is reduced as much as possible by being supported by a fixed electrode support rod serving as an electrode terminal.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

In the electrostatic pressure sensor of the present invention, as shown in FIG. 1, an L-shaped connecting portion 10a is integrally formed on the lower surface of a circular frame 10, and an air introduction hole 10b is formed inside the L-shaped connecting portion 10a. . Near the outer periphery of the upper surface of the circular frame 10, there is an annular groove 13 having a concave cross section.
An O-ring 14 is provided in the annular groove 13 to seal a gap between a diaphragm fixing base 15 and a circular frame 10, which will be described later. Moreover, on the top surface of the circular frame 10,
A diaphragm fixing base 15 with an outer diameter A is provided, and the air introduction hole 1 is provided near the center of the base 15.
A through hole 15a communicating with 0b is formed.
From the outer periphery of this diaphragm fixing base 15,
The conductive movable electrode terminal 15b is connected to the circular frame 10.
It penetrates and protrudes downward. A diaphragm 16 having a corrugated cross section is provided on the upper surface of the diaphragm fixing base 15, and an air space surrounded by the diaphragm 16 and the diaphragm fixing base 15 communicates with the through hole 15a.
At the center of the upper surface of the diaphragm 16,
A movable electrode support rod 17 is provided, and a movable electrode 18 having an outer diameter B is provided on the movable electrode support rod 17 with its center portion supported from below. Above this movable electrode 18, a fixed electrode 19 having an outer diameter C is provided so as to be arranged in parallel and facing each other, and the fixed electrode 19, the movable electrode 18, the diaphragm 16, and the diaphragm fixed base 15 are Each has a circular outer circumferential shape and is provided concentrically. The outer diameter C of the fixed electrode 19 is set to a size that fits inside a virtual cone 20 formed by connecting the diaphragm fixed base 15 and the outer periphery of the movable electrode 18.

As shown in FIG. 2, three fixed electrode support rods 19a are integrally formed on the outer periphery of the fixed electrode 19 and extend radially. On the other hand, as shown in FIG. 1, a ring-shaped frame 11 is fixed to the outer periphery of the upper surface of the circular frame 10 with three screws 12. Electrode support rod 19
a... is supported and fixed. Fixed electrode terminals 19b are provided at the protruding ends of these fixed electrode support rods 19a, projecting downward, and their tips are
It is configured to pass through the ring-shaped frame 11 and the circular frame 10 and protrude from the lower surface of the circular frame 10.

In the above configuration, when the electrostatic pressure sensor is activated, when the pressure reaches a certain predetermined value, the fixed electrode 1
The distance between movable electrode 9 and movable electrode 18 becomes a constant value in balance with the pressure, and a capacitance is generated according to this distance. This capacitance is measured through the movable electrode terminal 15b and the fixed electrode terminal 19b.

Next, when pressurized air higher than the above pressure is introduced into the air space surrounded by the diaphragm 16 and the diaphragm fixing base 15 through the air introduction hole 10b, the diaphragm 16 is pushed up. As a result, the movable electrode 18 is pushed up via the movable electrode support rod 17, and the movable electrode 18
The distance between the fixed electrode 19 and the fixed electrode 19 becomes smaller than before the high voltage was applied, and the capacitance increases.

On the other hand, when the air in the air area surrounded by the diaphragm 16 and the diaphragm fixing base 15 is discharged through the air introduction hole 10b and the pressure becomes lower than the above pressure, the diaphragm 16 is pulled down. As a result, the movable electrode support rod 1
7, the movable electrode 18 is pulled down, the distance between the movable electrode 18 and the fixed electrode 19 becomes greater than before the voltage becomes low, and the capacitance decreases.

By measuring such increases and decreases in capacitance, changes in pressure can be detected. Further, in this embodiment, the portion where the fixed electrode 19 faces the diaphragm fixed base 15 is connected to the fixed electrode support rod 19.
Since only a... occurs, the generation of extra capacitance becomes negligible. That is, in this embodiment, the area where the diaphragm fixed base 15 and the fixed electrode 19 face becomes 0.4 cm ² from the conventional 7.3 cm ² , and as a result, the capacitance increases from 3 pF to 0.4 cm 2 .
It was extremely small at 0.2pF.

As described above, in the electrostatic pressure sensor of the above embodiment, the fixed electrode 19 is arranged so as to fit within the virtual cone 20 formed by connecting the outer periphery of the movable electrode 18 and the outer periphery of the diaphragm fixed base 15.
The outer diameter of the fixed electrode 19 is set, and the fixed electrode 19 is
Since it is supported by fixed electrode support rods 19a extending radially from its outer periphery,
The area outside the movable electrode 18 that directly faces the diaphragm fixed base 15 is only the above-mentioned fixed electrode support rod 19a, and as a result, the generation of extra capacitance is so small that it can be ignored. Become. Therefore, there is no need to correct the sensor signal according to the distance between the electrodes during use, and it is possible to correct the sensor signal for each individual electrostatic pressure sensor to compensate for variations in the distance between the electrodes during the assembly process. There will be no need for it. As a result, the quality of the sensor is significantly improved, high reliability is obtained, and the sensor can be manufactured at low cost.

[Effect of idea]

As described above, the electrostatic pressure sensor of the present invention has the following features:
A virtual cone is formed by providing a movable electrode terminal on the diaphragm fixing base with which the movable electrode is electrically connected through the diaphragm and the diaphragm fixing base sequentially, and connecting the outer periphery of the movable electrode and the outer periphery of the diaphragm fixing base. The outer diameter of the fixed electrode is set so as to fit within the fixed electrode, and the fixed electrode is supported by fixed electrode support rods that are integrally molded radially from the outer periphery and serve as fixed electrode terminals.

Therefore, the area outside the movable electrode that directly opposes the diaphragm fixed base is only the fixed electrode support rod, which minimizes the generation of excess capacitance to the extent that it can be ignored. can do. As a result, it is no longer necessary to correct the sensor signal according to the distance between the electrodes during use, or for each electrostatic pressure sensor to account for variations in the distance between the electrodes during the assembly process, thereby improving the quality of the sensor. This has the effect of improving reliability, achieving high reliability, and reducing costs.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing one embodiment of the present invention;
The figure is a plan view showing the fixed electrode used in the present invention.
Figure 3 is a cross-sectional view of a conventional electrostatic pressure sensor.
FIG. 4 is a plan view showing a conventional fixed electrode. 15 is a diaphragm fixed base, 15b is a movable electrode terminal, 16 is a diaphragm, 18 is a movable electrode, 19 is a fixed electrode, 19a is a fixed electrode support rod, and 19b is a fixed electrode terminal.

Claims (1)

[Claims for Utility Model Registration] A fixed electrode and a movable electrode are provided in a facing arrangement,
In an electrostatic pressure sensor in which the movable electrode is supported by a diaphragm whose periphery is fixed on a diaphragm fixing base, each forming a concentric circle, a diaphragm and a diaphragm fixing base are mounted on the diaphragm fixing base. Providing a movable electrode terminal with which the movable electrode is electrically connected through sequentially,
The outer diameter of the fixed electrode is set so as to fit within a virtual cone formed by connecting the outer circumference of the movable electrode and the outer circumference of the diaphragm fixed base, and the fixed electrode is integrally molded radially from the outer circumference. An electrostatic pressure sensor characterized in that the electrode is supported by a fixed electrode support rod that serves as a fixed electrode terminal.