JPH10170543A - Capacitance-type sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitance-type sensor, to which the influence of a parasitic capacitance is reduced as far as possible, and whose characteristic is linear. SOLUTION: A fixed electrode 5, which faces a moving electrode, is formed on one face of a circuit board 6. The fixed electrode 5 is derived to the side on the other face of the circuit board 6 via a through hole 10 for continuity. When the fixed electrode is derived, it is possible to prevent a parasitic capacitance from being generated even when the fixed electrode is faced undesirably with the moving electrode. In addition, a guard pattern 8 is connected to a grounding terminal 11 so that a parasitic capacitance is not generated in the part of the guard pattern 8 around the fixed electrode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type sensor suitable for detecting acceleration, vibration or pressure.

[0002]

2. Description of the Related Art FIG. 12 is a circuit diagram of a conventional capacitance type sensor. This sensor has a capacitance generation section 17 for generating a capacitance C by a fixed electrode and a movable electrode facing each other. And an oscillation circuit section 18 for outputting a change in the capacitance C between the two electrodes as a change in the oscillation frequency.
The oscillation circuit unit 18 has three inverters 19 to 21 and a resistance element R1.

[0003]

In such an electrostatic capacitance type sensor, for example, due to a conductive path for connecting both electrodes to the oscillation circuit section 18, parts opposing each other are generated, and the opposing parts are formed. As shown by a broken line in FIG.
The distance d between the fixed electrode and the movable electrode and the oscillation frequency f of the oscillation circuit section do not have a linear relationship, and the measurement accuracy is degraded.

In particular, in order to reduce the size of the sensor and improve the measurement accuracy, the deterioration of the measurement accuracy due to the parasitic capacitance cannot be ignored. The solid line in FIG.
The graph shows the characteristics of the distance d between electrodes and the oscillation frequency f when there is no parasitic capacitance.

[0005] The present invention has been made in view of the above points, and has as its object to provide a capacitive sensor in which the influence of parasitic capacitance is reduced as much as possible to improve linearity. I do.

[0006]

In order to achieve the above-mentioned object, the present invention is configured as follows.

That is, the capacitance type sensor according to the present invention comprises:
In a capacitance type sensor including a fixed electrode and a movable electrode opposed to each other, the fixed electrode is formed on one surface of a circuit board arranged to face the movable electrode, and the other of the other of the circuit board. It is drawn through the through hole for conduction to the surface side.

Further, a conductor pattern is formed around the fixed electrode on the circuit board, and the conductor pattern is connected to a ground.

Further, the movable electrode has an end connected to a conductor pattern for signal derivation formed on the one surface of the circuit board, and the conductor pattern is connected through a through hole for conduction. The circuit board is drawn out to the other surface side.

[0010] Further, on the other surface of the circuit board,
An oscillation circuit unit that oscillates at an oscillation frequency according to a change in capacitance between the two electrodes is mounted, and the fixed electrode and the movable electrode are respectively connected to the oscillation circuit unit via the through holes for conduction. Is what is done.

Further, the oscillation circuit section includes a series circuit of a plurality of inverters, and a resistance element having one end connected to each of an input section and an output section of the series circuit. The two electrodes are connected together with a correction resistance element between a connection portion of the two inverters.

According to the capacitive sensor of the present invention, the fixed electrode is formed on one surface of the circuit board opposed to the movable electrode, and the other surface of the circuit board is connected via the through hole for conduction. As in the conventional example, there is no need to form a conductor pattern on the peripheral portion of the fixed electrode and route it. This makes it possible to undesirably oppose a portion of the conductor pattern for routing between the movable electrode and the movable electrode. This prevents the occurrence of parasitic capacitance due to the occurrence of parasitic capacitance, and improves the linearity between the inter-electrode distance d of both electrodes and the oscillation frequency f of the oscillation circuit unit, resulting in a linear sensor characteristic. The measurement accuracy can be improved with a simple configuration.

In addition, since the conductor pattern formed by the same manufacturing process as that of the fixed electrode is left around the fixed electrode of the circuit board, the fixed electrode and the surrounding conductor pattern have the same shape. When the fixed electrode and the movable electrode face each other with a spacer interposed between the fixed electrode and the movable electrode on the plane, the gap between both electrodes can be set with high accuracy, and the surrounding conductor pattern is Since the conductive pattern is connected to the ground, no parasitic capacitance is generated even when the conductive pattern faces the movable electrode.

Further, the movable electrode has an end connected to a conductor pattern for signal derivation formed on one surface of the circuit board by soldering or the like, so that a conductive part formed on the part of the conductor pattern is formed. It can be easily pulled out to the other surface side of the circuit board via the through hole.

Further, on the other surface of the circuit board,
Since an oscillation circuit unit that oscillates at an oscillation frequency according to a change in capacitance between the two electrodes is mounted, the fixed electrode and the movable electrode are drawn out through the respective through holes for conduction, and It can be easily connected to the oscillation circuit section.

Further, since the correction resistance element is connected between the connection portion between the oscillation circuit section and both electrodes, the effect of the parasitic capacitance generated in a portion other than the electrode is corrected by the correction resistance element. Linear sensor characteristics can be obtained.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an external perspective view of a capacitance type sensor according to one embodiment of the present invention, FIG. 2 is an exploded perspective view thereof, and FIG. 3 is a sectional view of a main part thereof. It is.

The capacitance type sensor 1 of this embodiment is
It comprises a base member 2 made of insulating plastic or the like, a movable electrode 3 made of, for example, a thin plate of phosphor bronze, an insulating sheet-like spacer 4, and a circuit board 6 having a fixed electrode 5 formed on the back surface. And they are stacked.

A circular concave portion 2a for allowing displacement of the movable electrode 3 is formed in the center of the upper surface of the base member 2, and the movable electrode 3 is provided on both sides of the concave portion 2a.
A pair of protrusions 2b for projecting the spacer 4 and the circuit board 6 to be stacked and fixed by thermal caulking are provided. The fixing of the movable electrode 3, the spacer 4, and the circuit board 6 to the base member 2 is not limited to thermal caulking, but may be performed by screws or the like.

The movable electrode 3 is formed by, for example, etching or precision press. As shown in an enlarged view of FIG. 4, the movable electrode 3 has a substantially circular electrode movable portion 3a at the center. A slit 7 is formed in an outer peripheral portion of the electrode movable portion 3a, and an electrode support portion 3b which is continuous in a partial arc shape is formed by cutting. The electrode support portion 3b has a linear spring property. The electrode movable section 3a is configured to be displaced in proportion to the force acting on the sensor.

A pair of mounting holes 3c are formed outside the electrode support 3b at positions corresponding to the pair of projections 2b of the base member 2. Further, the movable electrode 3
The peripheral portion has a tongue-shaped signal deriving portion 3d extending in a bent manner, and is connected to the oscillation circuit portion via the signal deriving portion 3d as described later.

The spacer 4 is formed such that the insulation between the fixed electrode 5 and the movable electrode 3 is maintained and the electrodes 3 and 5 are opposed to each other with a certain gap.
A circular opening 4a is formed at the center of the movable electrode 3 so as not to hinder the displacement of the electrode movable portion 3a of the movable electrode 3. Outside the opening 4a, a pair of mounting holes 4b are formed at positions corresponding to the pair of convex portions 2b of the base member 2.

The back surface of the circuit board 6, that is, the movable electrode 3
As shown in FIG. 5, a circular fixed electrode 5 made of a conductor pattern such as a copper foil is formed at the center of the surface facing the A guard pattern 8 made of a pattern is formed, and a rectangular signal deriving pattern 9 made of a conductor pattern is formed at a corner of the movable electrode 3 corresponding to the tongue-shaped signal deriving portion 3d. Each pattern 5, 8,
9 are formed by the same manufacturing process.

The circular fixed electrode 5 has a substantially equal area at a position facing the circular electrode movable portion 3a of the movable electrode 3 when attached to the base member 2. Are formed over the position where the spacer 4 is sandwiched and the outside thereof.

In the capacitance type sensor 1 of this embodiment, when the conductive path for connecting the fixed electrode 5 and the movable electrode 3 to the oscillation circuit portion is undesirably formed, a facing portion is generated. To prevent the occurrence of parasitic capacitance,
It is configured as follows.

That is, the fixed electrode 5 facing the movable electrode 3 is a conductive through-hole 10 having a plated inner wall.
And is connected to the oscillation circuit section mounted on the front side of the circuit board 6 via a conductor pattern (not shown). Since the fixed electrode 5 is drawn out to the front surface side of the circuit board 6 through the conduction through hole 10 formed in the fixed electrode 5 in this manner, a portion of the wiring portion other than the fixed electrode facing the movable electrode 3 is undesired. Does not occur, thereby producing a parasitic capacitance, thereby improving the linearity of the characteristic of the distance d between the electrodes and the oscillation frequency f.

Guard pattern 8 on which spacers 4 are arranged
Is formed in the same manufacturing process as the fixed electrode 5 as described above, so that the surface of the guard pattern 8 and the surface of the fixed electrode 5 are on the same plane and the spacer 4 is interposed. In addition, the gap between the fixed electrode 5 and the movable electrode 3 can be set with higher accuracy than when the guard pattern 8 is omitted.

Although the guard pattern 8 is opposed to a portion of the movable electrode 3 other than the electrode movable portion 3a, the guard pattern 8 is provided at the periphery of the circuit board 6 as shown in FIG. The terminal 11 is connected to the terminal 11, thereby preventing generation of a parasitic capacitance. A power supply terminal 12 and a signal terminal 13 are provided side by side on the periphery of the circuit board 6.

In the signal leading pattern 9 for leading the movable electrode 3 to the front side of the circuit board 6, there is formed a conductive through-hole 14 whose inner wall is plated as shown in FIG. As shown in FIG. 6, the movable electrode 3 has a tongue-shaped signal deriving portion 3 d connected to a portion of the signal deriving pattern 9 of the circuit board 6 by the solder 15, thereby forming the movable electrode 3. Is drawn out to the front surface side of the circuit board 6 through the signal deriving unit 3d and the conduction through hole 14, and is connected to the oscillation circuit unit. As shown in FIG. 2, a pair of mounting holes 6a are formed on both sides of the circuit board 6 in the longitudinal direction (the left-right direction in FIG. 5) at positions corresponding to the pair of protrusions 2b of the base member 2. On the front side of the circuit board 6, an IC 16 and other electronic components constituting an oscillation circuit section are mounted.

The capacitance type sensor 1 having the above configuration
Is to output a change in capacitance between the movable electrode 3 and the fixed electrode 5 due to the displacement of the electrode movable section 3a as a change in oscillation frequency by the oscillation circuit section.

FIG. 7 is a circuit diagram of the capacitance type sensor 1 according to this embodiment. Parts corresponding to those of the conventional example shown in FIG. 12 are denoted by the same reference numerals.

The capacitance type sensor 1 includes a capacitance generation section 17 for generating a capacitance C by the movable electrode 3 and the fixed electrode 5, and a capacitance C between the electrodes 3 and 5.
Is provided as the above-described oscillation circuit section 18 which outputs a change in the oscillation frequency as a change in oscillation frequency. The oscillation circuit section 18 includes a series circuit including three inverters 19 to 21 and an input section and an output section of the series circuit. And a resistance element R1 to which one end is connected. The above configuration is the same as that of the conventional example of FIG.

In this embodiment, it is determined that the distance d between the electrodes 3 and 5 and the oscillation frequency f do not have a linear relationship due to the parasitic capacitance generated in portions other than the electrodes, for example, the parasitic capacitance of the IC. For improvement, a correction resistance element R2 is connected in series between one electrode of the capacitance generation unit 17 and the oscillation circuit unit 18.

FIG. 8 is a diagram showing the sensor characteristics when the value of the correction resistance element R2 is changed, and FIG. 9 is a diagram showing the change in linearity at that time. The dots correspond to the respective characteristics in FIG.

As is apparent from these figures, the resistance value of the correction resistance element R2 has an optimum value. By connecting the correction resistance element R2 having the optimum resistance value, the influence of the parasitic capacitance is obtained. It is possible to obtain a capacitance sensor having good linearity, which is expressed by correcting. The optimum resistance value of the correction resistance element R2 is experimentally determined, for example.

As described above, since the influence of the parasitic capacitance can be corrected, a high-precision sensor can be realized at a relatively low cost while reducing the size.

As another embodiment of the present invention, the correcting resistor R2 may be provided between the other electrode of the capacitance generating section 17 and the oscillation circuit section 18.

FIG. 10 is a configuration diagram when the capacitance type sensor 1 having the above configuration is used as a vibration sensor.

This vibration sensor is a capacitance type sensor 1
A counter 22 for counting the pulse output from the oscillation circuit section 18 of the capacitive sensor 1;
And a control unit 23 comprising a microcomputer that takes in a vibration waveform as digital data from the output of the microcomputer.

FIGS. 11A and 11B are diagrams showing a vibration waveform acting on the capacitance type sensor 1 and a vibration waveform taken into the control unit 23, respectively.

The control unit 23 takes in the output of the counter 22 at every sampling interval ts,
Is reset, whereby the vibration waveform can be captured. The frequency higher than the sampling frequency fs indicated by the reciprocal of the sampling interval ts is cut, but by setting the sampling frequency to about 50 Hz, it is possible to measure low-frequency vibration such as an earthquake. become.

By measuring the upper and lower peak intervals of the captured vibration waveform, the frequency of the vibration acting on the capacitance type sensor 1 can be grasped. By measuring the upper and lower peak values, The maximum acceleration acting on the capacitance type sensor 1 can be grasped.

In the above-described embodiment, the present invention is applied to the vibration sensor for detecting the vibration. However, the present invention is configured such that the movable electrode is displaced via a plunger or a bellows according to the pressure. Pressure can also be detected.

[0045]

As described above, according to the capacitance type sensor of the present invention, the fixed electrode is formed on one surface of the circuit board opposed to the movable electrode, and the fixed electrode is formed through the through hole for conduction. Since it is pulled out to the other surface side of the circuit board, there is no need to form a conductor pattern on the periphery of the fixed electrode and lead it around as in the conventional example. This prevents the occurrence of parasitic capacitance due to undesired opposing portions between the conductor pattern and the movable electrode, and improves the linearity between the distance between the electrodes and the oscillation frequency to improve measurement accuracy. Can be improved.

Further, since the conductor pattern formed by the same manufacturing process as that of the fixed electrode is left around the fixed electrode of the circuit board, the surface of the fixed electrode and the surface of the conductor pattern around the fixed electrode are left. When the fixed electrode and the movable electrode face each other with a spacer interposed in the conductor pattern around the fixed electrode, the gap between the two electrodes can be set with high accuracy. Since the pattern is connected to the ground, no parasitic capacitance occurs even when the conductor pattern and the movable electrode face each other.

Further, since the correction resistance element is connected between the connection between the oscillation circuit section and the two electrodes, the effect of the parasitic capacitance generated in a portion other than the electrodes is corrected to obtain a linear sensor characteristic. It is possible to improve the measurement accuracy while reducing the size with a relatively inexpensive configuration.

[Brief description of the drawings]

FIG. 1 is a perspective view of a capacitance type sensor according to one embodiment of the present invention.

FIG. 2 is an exploded perspective view of FIG.

FIG. 3 is a sectional view of a main part.

FIG. 4 is a view showing a movable electrode.

FIG. 5 is a diagram illustrating a back surface of the circuit board.

FIG. 6 is a diagram showing a connection state between a movable electrode and a circuit board.

FIG. 7 is a circuit diagram of a capacitance type sensor.

FIG. 8 is a diagram showing sensor characteristics when the resistance value of the correction resistance element is changed.

9 is a diagram showing the linearity of the sensor characteristics in FIG.

FIG. 10 is a configuration diagram of a vibration sensor using a capacitance type sensor.

FIG. 11 is a diagram showing a vibration waveform.

FIG. 12 is a circuit diagram of a conventional capacitive sensor.

FIG. 13 is a diagram showing an influence of a parasitic capacitance on sensor characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitance sensor 3 Movable electrode 4 Spacer 5 Fixed electrode 6 Circuit board 8 Guard pattern 11, 14 Conducting through-hole 17 Capacitance generation part 18 Oscillation circuit part 19-21 Inverter

Claims (5)

[Claims] 1. A capacitance-type sensor comprising a fixed electrode and a movable electrode facing each other, wherein the fixed electrode is formed on one surface of a circuit board arranged to face the movable electrode. An electrostatic capacitance type sensor which is drawn out to the other surface side of a circuit board through a through hole for conduction. 2. The capacitive sensor according to claim 1, wherein a conductor pattern is formed around the fixed electrode on the circuit board, and the conductor pattern is connected to a ground. 3. An end of the movable electrode is connected to a conductor pattern for signal derivation formed on the one surface of the circuit board, and the conductor pattern is connected via a through hole for conduction. 3. The capacitance type sensor according to claim 1, wherein the capacitance type sensor is drawn to the other surface side of the circuit board. 4. An oscillation circuit section oscillating at an oscillation frequency according to a change in capacitance between the two electrodes is mounted on the other surface of the circuit board, and the fixed electrode and the movable electrode are 4. The capacitance type sensor according to claim 3, wherein the capacitance type sensor is connected to the oscillation circuit section via each of the conduction through holes. 5. The oscillation circuit section includes a series circuit of a plurality of inverters, and a resistance element having one end connected to each of an input section and an output section of the series circuit. 5. The capacitance-type sensor according to claim 4, wherein the two electrodes are connected together with a correction resistance element between a connection portion of the two inverters.