JPH07243931A - Fine differential pressure sensor - Google Patents

Abstract

PURPOSE:To provide a high-accuracy, small-sized fine differential pressure sensor by providing a moving electrode formed at the center position of a diaphragm of which periphery section is fixed to a housing, a fixed electrode formed to face the moving electrode on the back face of a wiring board and the like. CONSTITUTION:A base plate 2 having an opening section 2a, a diaphragm 3, and a base plate carrier 4 are overlappingly fixed in, the periphery section in a housing 1 having a pressure guide port 1a at the bottom section. A circular moving electrode thin plate 5 made of a ceramic is connected at the center position of the diaphragm 3. A ceramic wiring board 6 is fixed to the carrier 4, and a fixed electrode constituted of an output electrode section and an earth electrode section is formed to face the moving electrode 5 on the back face side of the wiring board 6. When low pressure is normally guided into the pressure guide port 1a, the distance between the output electrode section and the earth electrode section is increased in response to the difference between the pressures applied to both faces of the diaphragm 3. The electrostatic capacity between the electrodes is reduced, the electrostatic capacity between the output electrode section and the earth electrode section is decreased, and the change is amplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine differential pressure sensor for detecting a fine differential pressure generated by a flow of a fluid, and in particular, it is suitable for detecting a flow rate of combustion air in a gas appliance or the like. The present invention relates to a differential pressure sensor.

[0002]

2. Description of the Related Art Conventionally, it has been known that when the combustion state of fuel changes in a gas water heater or the like, the amount of environmental pollutants such as nitrogen oxides and carbon monoxide changes. It is important to suppress the generation of environmental pollutants by controlling the mixing ratio of. However, since the required amount of fuel gas in the water heater changes depending on the amount of water used and the water temperature at each moment, the rotation speed of the blower fan for sending combustion air is automatically adjusted according to the amount of fuel gas supplied. Then, the method of realizing the optimal combustion state is considered.

However, since the air flow characteristic of such a blower fan generally varies widely, even if the drive power of the blower fan is constant, the air flow rate varies from device to device and the supply amount of fuel gas changes. Even if the motor drive power corresponding to the above is sent to the blower fan, it is not always possible to adjust the blown air amount so that the optimum combustion state is always obtained.

[0004]

Recently, however, it has been sought to reduce energy consumption and prevent environmental pollution, and to control the amount of environmental pollutants generated from gas water heaters and the like. There is a movement to do. Then, even if the supply amount of the fuel gas changes, there is a demand for a device that accurately controls the amount of combustion air so as to follow the change and obtain an optimum combustion state.

According to the present invention, even if a blower fan having uneven air volume characteristics is adopted in a gas water heater or the like, the combustion air is supplied in an amount capable of maintaining an optimum gas combustion state corresponding to the changing supply amount of the fuel gas. It is an object of the present invention to provide a minute differential pressure sensor for air flow detection, which is suitable for controlling a blower fan.

[0006]

A fine differential pressure sensor according to the present invention is a thin film formed on a diaphragm whose peripheral portion is fixed to a housing and a ceramic thin plate surface fixedly connected to the diaphragm at a central position. A movable electrode formed, a fixed electrode formed in parallel with the movable electrode on the back surface of the wiring substrate so as to face the movable electrode, and a circuit component provided on the surface of the wiring substrate. The fixed electrode is formed of an output electrode part insulated from each other and an annular ground electrode part surrounding the output electrode part, and the output electrode part and the ground electrode part are respectively formed by wirings penetrating the wiring board. It is characterized in that it is connected to the circuit component.

[0007]

In the fine differential pressure sensor of the present invention having such a configuration, the movable electrode is formed on a ceramic thin plate having high rigidity and lightness, and the electrostatic capacitance between the ground electrode and the movable electrode and the movable electrode are The capacitance between the fixed electrode and the fixed electrode is connected in series to detect the combined capacitance, and there is no lead wire from the movable electrode. Therefore, when the size of the entire sensor is reduced and the small diaphragm is made of a material with low rigidity suitable for detecting a slight differential pressure, the movable electrode is particularly lightweight and the resistance against displacement of the movable electrode is extremely small. Even if the mounting posture of the sensor is changed, the error in the electrostatic capacitance between the movable electrode and the fixed electrode is small, and the electrostatic capacitance changes with high accuracy according to the change in the slight differential pressure.

Further, when the circuit component in the fine differential pressure sensor of the present invention incorporates the output circuit and the temperature compensating circuit, the output already compensated for the influence of the ambient temperature can be obtained without increasing the size of the entire sensor. Moreover, the wiring when the sensor is incorporated into the device is simple and the assembling work is easy.

In addition, since the surface of the movable electrode or the fixed electrode in the sensor is covered with an insulating thin film, the electrode functions even if an abnormal pressure load or abnormal vibration is applied. Reliability is greatly improved without any damage.

[0010]

The fine differential pressure sensor of the present invention will be described in detail below with reference to the examples shown in the drawings. In the figure, a bottom plate 2 having an opening 2a, a diaphragm 3, and a substrate support 4 are fixed in an overlapping manner at their peripheral portions inside a housing 1 having a pressure introducing port 1a at the bottom. A circular movable electrode thin plate 5 made of ceramics is joined to the center position at the center position. The surface of the movable electrode thin plate 5 is plated with a metal such as a palladium alloy to form the movable electrode 5a. An insulating protective layer formed of a glass thin film is provided on the surface of the movable electrode 5a, and at the same time, it has a function of preventing corrosion.

A wiring board 6 made of ceramics is fixed to the substrate support 4, and a circular output electrode portion 6a and an output electrode portion 6a are formed on the back surface of the wiring substrate 6 so as to face the movable electrode 5a. A fixed electrode composed of a ring-shaped ground electrode portion 6b that surrounds is formed by metal plating such as copper, and the area of the output electrode portion 6a and the area of the ground electrode portion 6b are substantially equal. An output circuit component 6c for obtaining a signal output according to the electrostatic capacitance between the output electrode portion 6a and the ground electrode portion 6b, and a temperature compensation circuit component 6d are attached to the front surface side of the wiring board 6. .

Further, between the output electrode portion 6a and the output circuit component 6c and between the ground electrode portion 6b and the output circuit component 6c,
They are electrically connected to each other through wirings in through holes provided in the wiring board 6. In addition, this output electrode unit 6
An insulating protective layer formed of a glass thin film is provided on the surfaces of a and the ground electrode portion 6b, and also has the function of preventing corrosion as with the movable electrode 5a.

A lid 7 having a pressure introducing port 7a is attached to the opening of the housing 1 as described above, and a wiring board 6 is provided.
Also, a pressure chamber 8 for accommodating the movable electrode thin plate 5 together is formed. A connector 9 is connected to the output circuit component 6c by a conductor 10.

The fine differential pressure sensor of the present invention thus constructed normally introduces a low pressure into the pressure inlet 1a and a high pressure into the pressure inlet 6a. Then, since pressure is applied to the diaphragm 3 from above in the drawing, the distance between the output electrode portion 6a and the ground electrode portion 6b and the movable electrode 5a is increased in accordance with the pressure difference applied to both surfaces of the diaphragm 3, and these The capacitance between the electrodes is small. for that reason,
The capacitance between the output electrode portion 6a and the ground electrode portion 6b is greatly reduced, and the change is amplified.

Further, since the movable electrode thin plate 5 is made of ceramics, the weight is lighter than that of a metal plate, and even if the diaphragm 3 is made of a thin and flexible material, the output electrode portion 6a and the movable electrode are formed. It is easy to maintain parallelism with 5a. In addition, since the conductive wire to the outside is not connected to the movable electrode 5a and the force that suppresses the movement of the movable electrode 5a does not work, the difference in pressure applied to the diaphragm 3 can be accurately changed as it is. Can be taken out as.

The change in capacitance in the slight differential pressure sensor of the present invention is detected as a change in capacitance between the output electrode portion 6a and the ground electrode portion 6b and is immediately provided on the surface of the wiring board 6. It is input to the output circuit component 6c and processed by an arithmetic circuit which is a combination of an output circuit having a variable frequency oscillation circuit and a temperature compensation circuit, for example, and a detection output corresponding to a slight differential pressure is obtained.

The detection output thus obtained is input to a control device not shown in the drawing and compared with a standard air volume function value corresponding to the gas supply amount in advance, and when the detected air volume is small, the drive power of the blower fan is increased. On the contrary, when the detected air volume is large, on the contrary, a control output for reducing the drive power of the blower fan is sent out.
At this time, the blower fan is controlled so that the air flow rate detected by the slight differential pressure sensor of the present invention and the standard air flow rate function value match, and the air flow rate of the blower fan is automatically adjusted to be in the optimum range. You can Such a blower fan control device may be provided separately from the fine differential pressure sensor of the present invention, or may be incorporated in the fine differential pressure sensor.

[0018]

The fine differential pressure sensor of the present invention has high accuracy and high sensitivity, is easy to miniaturize, and accurately detects the fine differential pressure generated due to air flow and the like. Not only is there an advantage that the number of components is small and the assembly is easy. And again
It can be suitably used for optimizing the amount of combustion air supplied to a gas burner or the like, and can also be widely used for general fine pressure detection and control.

[Brief description of drawings]

FIG. 1 is a sectional view showing a structure of a differential pressure sensor of the present invention.

FIG. 2 is a front view (A) and a top view (B) of a movable electrode thin plate in a slight differential pressure sensor of the present invention.

FIG. 3 is a front view (A) and a bottom view (B) of a wiring substrate in the differential pressure sensor of the present invention.

[Explanation of symbols]

 1 Housing 1a Pressure Inlet 2 Bottom Plate 2a Opening 3 Diaphragm 4 Substrate Support 5 Movable Electrode Thin Plate 5a Movable Electrode 6 Wiring Board 6a Output Electrode 6b Grounding Electrode 6c Output Circuit Component 6d Temperature Compensation Circuit Component 7 Lid 7a Pressure Inlet Port 8 Pressure chamber 9 Connector 10 Conductor wire

Claims (5)

[Claims] 1. A diaphragm having a peripheral portion fixed to a housing, a movable electrode formed in a thin film on a ceramic thin plate surface fixedly connected to the diaphragm at a central position, and parallel to the movable electrode. An output in which a fixed electrode formed on the back surface of the provided wiring board so as to face the movable electrode and a circuit component provided on the surface of the wiring board are provided, and the fixed electrode is insulated from each other. It is characterized in that it is formed of an electrode portion and an annular ground electrode portion surrounding the output electrode portion, and that the output electrode portion and the ground electrode portion are connected to the circuit component by wirings penetrating the wiring substrate, respectively. Fine differential pressure sensor. 2. The fine differential pressure sensor according to claim 1, wherein the circuit component is a combination of an output circuit and a temperature compensation circuit. 3. The fine differential pressure sensor according to claim 1, wherein the movable electrode is circular, the output electrode portion is circular, and the ground electrode portion is circular. 4. The fine differential pressure sensor according to claim 1, wherein the area of the output electrode portion and the area of the ground electrode portion are formed substantially equal to each other. 5. The fine differential pressure sensor according to claim 1, wherein the surface of the movable electrode or the fixed electrode is covered with an insulating thin film.