JP2016038220A - Capacitance sensor and electric device provided with the capacitance sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitance sensor capable of suppressing a malfunction due to noise. SOLUTION: The capacitance sensor (1) according to the present invention has a detection electrode (2), a dummy electrode (4) which is an electrode for detecting noise, and noise mixed from a detection electrode (2). It is provided with a calculation unit (6) that generates a calculation signal by calculating a signal including a signal including a first noise component based on the noise and a signal including a second noise component based on the noise mixed from the dummy electrode (4). [Selection diagram] Fig. 1

Description

  The present invention relates to a capacitance of a detection electrode or a capacitance sensor that detects a change in the capacitance, and more particularly to a capacitance sensor that uses an oscillation circuit and an electric device including the capacitance sensor.

  Conventionally, a capacitive proximity sensor that detects the approach of an object by detecting a change in capacitance is known. For example, Patent Literature 1 discloses a fluid detection sensor that detects the presence / absence, configuration, state change, and the like of a fluid using a capacitive proximity sensor.

In general, a capacitive proximity sensor includes a detection electrode and an oscillation circuit as a circuit for detecting a change in capacitance of the detection electrode. In the oscillation circuit, when an object approaches, the capacitance C _X of the detection electrode increases and the oscillation frequency f _OSC changes. The capacitive proximity sensor includes a determination circuit that determines whether or not the oscillation frequency f _OSC of the oscillation circuit has reached a predetermined reference value, and detects the approach of an object based on the determination result of the determination circuit. doing.

FIG. 22 is a circuit diagram showing a schematic configuration of a conventional capacitive proximity sensor. As shown in FIG. 22, the capacitive proximity sensor 201 includes a detection electrode 202, an oscillation circuit 203, and a determination circuit 207. In the illustrated example, the oscillation circuit 203 is a Wien bridge type oscillation circuit including an operational amplifier A, a capacitance element C ₂ , and resistance elements R ₁ , R ₂ , R _3, and R ₄ . The oscillation frequency f _OSC of the Wien bridge type oscillation circuit is expressed by the following equation (1).
f _OSC = (2π × (C _X × C ₂ × R ₁ × R ₂ ) ^1/2 ) ⁻¹ (1).

  In the present application, the symbol of the resistive element is also the resistance value of each resistive element, and the symbol of the capacitive element is also the capacitance of the capacitive element.

Therefore, when the capacitance C _X decreases, the oscillation frequency f _OSC increases. The oscillation circuit 103 outputs a signal having an oscillation frequency f _OSC that satisfies the above formula (1) to the determination circuit 207.

The oscillation circuit 203 oscillates under the condition that the positive feedback rate C ₂ × R ₂ / (C _X × R ₂ + C ₂ × R ₂ + C ₂ × R ₁ ) is negative at the oscillation frequency f _OSC . That is, the feedback rate R ₄ / (R ₃ + R ₄ ) or higher, which is expressed by the following equation (2).
R ₃ / R ₄ ≧ (C _X / C ₂ ) + (R ₁ / R ₂ ) (2).

The determination circuit 207 monitors the change in the oscillation frequency f _OSC of the signal from the oscillation circuit 203, converts it into a required signal according to the purpose, and outputs it. For example, the determination circuit 207 includes a period / voltage conversion circuit that converts the oscillation frequency f _OSC and the oscillation amplitude (output voltage) V _OSC into a DC voltage proportional to them, a comparator that compares the converted DC voltage with a predetermined reference value, When the direct current voltage is larger or smaller than a reference value, it is configured by an output circuit that issues a predetermined alarm or a control signal.

Japanese Patent Laid-Open No. 11-230815 (released on August 27, 1999)

  However, in the conventional capacitive proximity sensor 201, even if the oscillation circuit 203 does not satisfy the above formula (2), that is, the oscillation circuit 203 cannot oscillate, the noise mixed in the oscillation circuit 203 Due to the influence of disturbances such as (noise), a desired operation as a capacitance sensor may not be exhibited.

  The determination circuit 207 determines whether the oscillation circuit 203 is “oscillating” or “not oscillating” according to the frequency / amplitude voltage value of the output signal of the oscillation circuit 203. However, when noise is mixed from the detection electrode 202, the noise component is included in the output signal from the oscillation circuit 203, so that the determination circuit 207 should determine that the oscillation circuit 203 is “not oscillating”. As a result of the determination that the oscillation circuit 203 is “oscillating”, the capacitive proximity sensor 201 may malfunction.

  For example, when the capacitive proximity sensor 201 is used as a capacitive water level sensor or a human sensor, a sensitivity with a capacitance difference of about 1 pF is required. For this reason, the influence of the noise on the capacitive proximity sensor 201 is large.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a capacitance sensor that can suppress malfunction due to noise mixed from a detection electrode.

  In order to solve the above problems, a capacitance sensor according to an aspect of the present invention is a capacitance sensor that detects a capacitance between an object and a detection electrode or a change thereof, and the detection An oscillation circuit including a feedback circuit connected to the electrode; a noise electrode which is an electrode for detecting noise; a signal including a first noise component which is a signal component based on noise mixed from the detection electrode; and the noise A calculation unit that generates a calculation signal by calculating a signal composed of a second noise component that is a signal component based on noise mixed from the electrode, and detects the capacitance or a change thereof using the calculation signal. It is characterized by doing.

  In the above configuration, a signal including a first noise component that is a signal component based on noise mixed from the detection electrode and a signal including a second noise component that is a signal component based on noise mixed from the noise electrode are used. Arbitrary arithmetic processing can be performed in the arithmetic unit. Therefore, for example, when the processing unit subtracts the second noise component from the signal including the first noise component based on the noise mixed from the detection electrode, the first noise component based on the noise mixed from the detection electrode is reduced. The calculated calculation signal can be generated.

  Therefore, according to the above configuration, it is possible to detect the capacitance of the detection electrode or a change thereof using the calculation signal in which the first noise component is reduced, so that malfunction due to noise mixed from the detection electrode is prevented. An electrostatic capacity sensor that can be suppressed can be realized.

  According to one embodiment of the present invention, there is an effect that it is possible to provide a capacitance sensor that can suppress malfunction due to noise mixed from the detection electrode.

1 is a block diagram illustrating a schematic configuration of a capacitance sensor according to Embodiment 1. FIG. It is a circuit diagram which shows an example of the specific structure of the electrostatic capacitance sensor shown by FIG. It is a circuit diagram which shows the structure of the conventional electrostatic capacitance sensor which is not provided with a dummy electrode and an arithmetic circuit. It is a circuit diagram which shows the structure which connected the noise source to the electrostatic capacitance sensor shown by FIG. It is a circuit diagram which shows the structure which connected the noise source to the comparative example shown by FIG. It is a graph which shows the simulation result of the frequency response performed with respect to the electrostatic capacitance sensor shown by FIG. 4 and FIG. 6 is a block diagram illustrating a schematic configuration of a capacitance sensor according to Embodiment 2. FIG. It is a circuit diagram which shows an example of the specific structure of the electrostatic capacitance sensor shown by FIG. It is a circuit diagram which shows the structure which connected the noise source to the electrostatic capacitance sensor shown by FIG. It is a graph which shows the simulation result of the frequency response performed with respect to the electrostatic capacitance sensor shown by FIG. FIG. 6 is a block diagram illustrating a schematic configuration of a capacitance sensor according to a third embodiment. It is a circuit diagram which shows an example of the specific structure of the electrostatic capacitance sensor shown by FIG. It is a circuit diagram which shows another example of the specific structure of the electrostatic capacitance sensor shown by FIG. FIG. 12 is a circuit diagram showing still another example of the specific configuration of the capacitance sensor shown in FIG. 11. It is a circuit diagram which shows the structure which connected the noise source to the electrostatic capacitance sensor shown by FIG. It is a circuit diagram which shows the structure which connected the noise source to the electrostatic capacitance sensor shown by FIG. It is a circuit diagram which shows the structure which connected the noise source to the electrostatic capacitance sensor shown by FIG. It is a graph which shows the simulation result of the frequency response performed with respect to the electrostatic capacitance sensor shown in FIGS. It is a block diagram which shows schematic structure of the automatic water supply apparatus which concerns on Embodiment 4. FIG. (A) And (b) is a schematic diagram which shows the state in which the water level in a tank is more than predetermined level. (A) And (b) is a schematic diagram which shows the state in which the water level in a tank is less than a predetermined level. It is a circuit diagram which shows schematic structure of the conventional electrostatic capacitance type proximity sensor.

Embodiment 1
The embodiment of the present invention will be described below with reference to FIGS. The capacitance sensor according to the present invention detects the approach of an object (target object) by detecting the capacitance of the detection electrode or its change. For example, a water level sensor, a touch sensor, a proximity sensor, etc. Used for various sensors.

  FIG. 1 is a block diagram showing a schematic configuration of a capacitance sensor 1 according to the present embodiment. As shown in FIG. 1, the capacitance sensor 1 includes a detection electrode 2, a sensor circuit (oscillation circuit) 3, a dummy electrode (noise electrode) 4, a dummy circuit (processing circuit) 5, an arithmetic unit 6, and an evaluation circuit 7. It has.

  The detection electrode 2 is connected to the sensor circuit 3, and the dummy electrode 4 is connected to the dummy circuit 5. The output sides of the sensor circuit 3 and the dummy circuit 5 are connected to the calculation unit 6, and the output side of the calculation unit 6 is further connected to the evaluation circuit 7.

  The capacitance sensor 1 includes an input signal from the sensor circuit 3 including a noise component (first noise component) mixed from the detection electrode 2 and a noise component (second noise component) based on the noise mixed from the dummy electrode 4. By using a signal (arithmetic signal) generated by computing the input signal from the dummy circuit 5 consisting of the above in the computing unit 6, the malfunction due to the influence of conventional noise is suppressed.

Here, the transfer function from the detection electrode 2 to the output of the calculation unit 6 is H ₁ (s), the transfer function from the dummy electrode 4 to the output of the calculation unit 6 is H ₂ (s), and the detection electrode 2 and the dummy electrode 4 is given the same noise signal V _n . In this case, when the arithmetic unit 6 subtracts the input signal from the dummy circuit 5 from the input signal from the sensor circuit 3, the noise signal (noise component) included in the output signal of the arithmetic unit 6 is H ₁ (s) V. _n −H ₂ (s) V _n .

Therefore, for example, by setting the transfer function H ₁ (s) and the transfer function H ₂ (s) in the capacitance sensor 1 such that H ₁ (s) = H ₂ (s), the calculation unit 6 The noise signal H ₁ (s) V _n −H ₂ (s) V _n included in the output signal from the signal to the evaluation circuit 7 can be made zero, and the influence of noise can be suitably reduced.

Note that the transfer function H ₁ (s) and the transfer function H ₂ (s) do not necessarily have to be H ₁ (s) = H ₂ (s), and the transfer function H ₁ ( If s) and the transfer function H ₂ (s) are close to each other, it is possible to obtain an effect of reducing the influence of noise.

FIG. 1 conceptually shows the configuration of the present invention. Therefore, for example, if the transfer function H ₁ (s) and the transfer function H ₂ (s) can be set so that the influence of noise can be reduced without using the dummy circuit 5, the dummy circuit 5 is omitted. May be.

<Configuration of Capacitance Sensor 1a>
FIG. 2 is a circuit diagram showing an example of a specific configuration of the capacitance sensor 1 shown in FIG. As shown in FIG. 1, the capacitance sensor 1 a includes a detection electrode 2, a sensor circuit 3, a dummy electrode 4, an arithmetic circuit (arithmetic unit) 6 a, and an evaluation circuit 7.

(Detection electrode 2)
The detection electrode 2 is an electrode for detecting the approach of an object. Detecting electrode 2, depending on the approach of the object, the object and _the capacitance C _X is changed between the detecting electrode 2, the signal (current) sensor circuit 3 in response to changes in the capacitance C _X Is input.

(Sensor circuit 3)
The sensor circuit 3 is a Wien bridge type oscillation circuit including a differential amplifier OP1, a capacitance element C ₂ , and resistance elements R ₁ , R ₂ , R _3, and R ₄ . In the sensor circuit 3, a part of the feedback circuit is connected to the detection electrode 2, and among the signals amplified by the differential amplifier OP1, a signal in a predetermined frequency band is fed back to the differential amplifier OP1 with a predetermined feedback rate. . As a result, the sensor circuit 3 oscillates at the oscillation frequency f _OSC included in the predetermined frequency band.

The oscillation frequency f _OSC of the sensor circuit 3 is expressed by the following equation (1).
f _OSC = (2π × (C _X × C ₂ × R ₁ × R ₂ ) ^1/2 ) ⁻¹ (1).

Therefore, when the electrostatic capacitance C _X of the detection electrode 2 decreases as the object approaches, the oscillation frequency f _OSC of the sensor circuit 3 increases and enters an oscillation state. The sensor circuit 3 outputs a signal having an oscillation frequency f _OSC that satisfies the above expression (1) to the arithmetic circuit 6a.

Also, the condition for the sensor circuit 3 to oscillate is that the feedback rate C ₂ × R ₂ / (C _X × R ₂ + C ₂ × R ₂ + C ₂ × R ₁ ) of positive feedback is negative at the oscillation frequency f _OSC . That is, the feedback rate R ₄ / (R ₃ + R ₄ ) or higher, which is expressed by the following equation (2).
R ₃ / R ₄ ≧ (C _X / C ₂ ) + (R ₁ / R ₂ ) (2).

The sensor circuit 3 utilizes the property of the above formula (2), and if the capacitance value of the capacitance C _X of the detection electrode 2 that is the detection target is less than a predetermined value, the oscillation state and the electrostatic detection target. If the capacitance C _X is equal to or greater than a predetermined value, the oscillation is stopped.

(Dummy electrode 4)
The dummy electrode 4 is an electrode for detecting noise. The capacitance C _X of the dummy electrode 4 changes according to the amount of noise mixed from the dummy electrode 4. A signal (current) corresponding to the amount of noise mixed from the dummy electrode 4 is input from the dummy electrode 4 to the arithmetic circuit 6a.

In the capacitance sensor 1a, the transfer function H ₁ (s) from the detection electrode 2 to the output of the arithmetic circuit 6a and the transfer function from the dummy electrode 4 to the output of the arithmetic circuit 6a are used without using the dummy circuit 5. H ₂ (s) is set so that the influence of noise can be reduced. As described above, in the capacitance sensor 1a, the dummy circuit 5 may be omitted as appropriate.

(Calculation circuit 6a)
The arithmetic circuit 6 a is a circuit that calculates an input signal from the sensor circuit 3 including a noise component mixed from the detection electrode 2 and an input signal from the dummy electrode 4 based on the noise component mixed from the dummy electrode 4. Calculation circuit 6a is configured by a differential amplifier OP2, and a resistor _{R 1 · R 3 · R 4} .

  The signal from the sensor circuit 3 is input to the inverting input terminal (−) of the differential amplifier OP2, and the signal from the dummy electrode 4 is input to the non-inverting input terminal (+) of the differential amplifier OP2.

  In the arithmetic circuit 6a, the input signal from the dummy electrode 4 based on the noise mixed from the dummy electrode 4 is subtracted from the input signal from the sensor circuit 3. That is, the noise component included in the input signal from the sensor circuit 3 and the noise component from the dummy electrode 4 cancel each other. Thereby, in the arithmetic circuit 6a, a signal (arithmetic signal) in which a noise component mixed from the detection electrode 2 is reduced is generated. The arithmetic circuit 6 a outputs the generated signal to the evaluation circuit 7.

(Evaluation circuit 7)
The evaluation circuit 7 is a circuit that evaluates whether the sensor circuit 3 is in an oscillation state or an oscillation stop state based on a signal input from the arithmetic circuit 6a. If the input signal from the arithmetic circuit 6a is equal to or higher than a predetermined amplitude voltage at a predetermined frequency, the evaluation circuit 7 sends an “High” signal indicating that the sensor circuit 3 is in an oscillation state to an external device such as a control unit. Output to etc. On the other hand, if the input signal from the arithmetic circuit 6a is less than a predetermined amplitude voltage at a predetermined frequency, the evaluation circuit 7 sends a “Low” signal indicating that the sensor circuit 3 is in the oscillation stop state to the external device. Output to etc.

<Operation of Capacitance Sensor 1a>
Next, the operation of the capacitance sensor 1a will be described.

  FIG. 3 is a circuit diagram showing a configuration of a conventional capacitance sensor 101 that does not include the dummy electrode 4 and the arithmetic circuit 6a. This capacitance sensor 101 is a comparative example in which the dummy electrode 4 and the arithmetic circuit 6a are removed from the capacitance sensor 1a shown in FIG.

  As shown in FIG. 3, in the capacitance sensor 101, the detection electrode 2 is connected to the sensor circuit 3. The output side of the sensor circuit 3 is connected to the evaluation circuit 7.

  In the capacitance sensor 101, the evaluation circuit 7 evaluates the oscillation state of the sensor circuit 3 based on the input signal from the sensor circuit 3. Therefore, when noise is mixed from the detection electrode 2, the noise component is included in the input signal from the sensor circuit 3, so that the input signal changes. Therefore, in the capacitance sensor 101, the evaluation circuit 7 evaluates that the sensor circuit 3 is “oscillating” in the scene where the sensor circuit 3 should be evaluated as “not oscillating”. Malfunctions can occur.

  Therefore, in the capacitance sensor 1a, the dummy electrode 4 and the arithmetic circuit 6a are provided. In the arithmetic circuit 6a provided on the downstream side (downstream) side of the sensor circuit 3, a noise component included in the input signal from the sensor circuit 3; By canceling out the noise components from the dummy electrode 4, a signal in which the noise components included in the input signal from the sensor circuit 3 are reduced is generated, and the signal is output to the evaluation circuit 7. As a result, the evaluation circuit 7 can evaluate the oscillation state of the sensor circuit 3 based on the signal with the reduced noise component, and thus can suppress malfunctions due to the influence of noise as described above.

  In order to confirm the operation of the capacitance sensor 1a, a frequency response was simulated using the capacitance sensor 1a shown in FIG. 2 and the capacitance sensor 101 shown in FIG. .

In this simulation, each operation when noise is mixed through the detection electrode 2 when the capacitance C _X of the detection electrode 2 is greater than or equal to a predetermined value, that is, when the sensor circuit 3 is in an oscillation stop state. Was simulated.

FIG. 4 is a circuit diagram showing a configuration in which a noise source N is connected to the capacitance sensor 1a shown in FIG. As shown in FIG. 4, a common noise source N is connected to the detection electrode 2 and the dummy electrode 4 in the capacitance sensor 1a. C _n between the detection electrode 2 and the noise source N of the capacitance sensor 1 a indicates the capacitance between the detection electrode 2 and the noise source N. Similarly, C _n between the dummy electrode 4 of the capacitance sensor 1 a and the noise source N indicates the capacitance between the dummy electrode 4 and the noise source N.

In the electrostatic capacitance sensor 1a, mixed noise current I _n1 from the detection electrodes 2, noise current I _n2 is assumed that mixed from the dummy electrode 4 of the electrostatic capacitance sensor 1a. In the following, for convenience of explanation, it is assumed that I _n1 and I _n2 are DC currents.

First, consider _In1 . In the sensor circuit 3 of the capacitance sensor 1a, a voltage of I _n1 * R ₁ + V _cm is applied to the non-inverting input terminal (+) of the differential amplifier OP1. Here, since _In1 is a DC current, the influence of R ₂ and C ₂ is not considered. In this case, the output voltage Vosc of the sensor circuit 3 of the capacitance sensor 1 is

Than,

And given.

Next, In ₂ will be examined. In the arithmetic circuit 6a, a voltage of I _n2 * R ₁ + V _cm is applied to the non-inverting input terminal (+) of the differential amplifier OP2, thereby forming a non-inverting amplifier circuit. Its output voltage (output signal) _Vout is

From the above, the output voltage V _osc of the sensor circuit 3 described above is substituted,

It becomes.

In this equation (Equation 4), since the coefficients of I _n2 and −I _n1 match, the transfer function H ₁ (s) from the detection electrode 2 to the output of the arithmetic circuit 6a and the dummy electrode 4 to the arithmetic circuit 6a It shows that the transfer function H ₂ (s) up to the output has a relationship of H ₁ (s) = − H ₂ (s).

Here, if the detection electrode 2 and the dummy electrode 4 are designed so that I _n1 = I _n2 , a signal due to noise can be removed from the output voltage V _out of the arithmetic circuit 6 a, and the capacitance sensor 1 a Malfunction can be suppressed.

FIG. 5 is a circuit diagram showing a configuration in which a noise source N is connected to the capacitance sensor 101 shown in FIG. As shown in FIG. 5, in the capacitance sensor 101, a noise source N is connected to the detection electrode 2. C _n between the detection electrode 2 and the noise source N indicates a capacitance between the detection electrode 2 and the noise source N. In the electrostatic capacitance sensor 101, it is assumed that the detection electrode 2 noise current I _n are mixed.

  A frequency response simulation was performed on these capacitance sensor 1a and capacitance sensor 101 using Virtualo Spectre (registered trademark).

The capacitance C _X of the detection electrode 2 takes two states, and the first state is 6 pF and the second state is 7 pF. This assumes water detection conditions when the capacitance sensor 1a is applied to, for example, a water level sensor.

Note that ideal amplifiers were used as the differential amplifiers OP1 and OP2, and R ₁ = R ₂ = 1 MΩ, R ₃ = 470 kΩ, R ₄ = R = 100 kΩ, C ₂ = ₂ pF, and C _n = 1 pF. The two states of the capacitance C _X of the detection electrode 2 are 6 pF and 7 pF as described above, and the noise source N is a sine wave having a certain frequency and amplitude voltage.

For both the capacitance sensor 1a and the capacitance sensor 101, when the amplitude voltage of the noise source N is zero, the oscillation state is in the first state, the oscillation is stopped in the second state, and the sensor circuit 3 during oscillation is The oscillation frequency f _OSC was about 40 kHz, and normal operation when noise was not considered in both sensors was confirmed.

  Next, in the second state, AC analysis was performed in a frequency region from 1 kHz to 10 MHz with an AC amplitude voltage of 1 V of the noise source N.

  FIG. 6 is a graph showing a simulation result of frequency response performed on the capacitance sensor 1 a and the capacitance sensor 101. In FIG. 6, the horizontal axis indicates the frequency (Hz) of the noise source N, and the vertical axis indicates the output signal strength (dB) of the arithmetic circuit 6a of the capacitance sensor 1a and the sensor circuit 3 of the capacitance sensor 101. Show.

  As shown in FIG. 6, both the capacitance sensor 1a and the capacitance sensor 101 have a large output signal strength of a noise signal having a frequency near the oscillation frequency of the sensor circuit 3, and the most malfunctioning in the vicinity of this region. It turns out that it is easy to cause.

  Compared with the conventional capacitance sensor 101 that does not include the dummy electrode 4 and the arithmetic circuit 6a, the capacitance sensor 1a performs subtraction of the noise signal by the arithmetic circuit 6a located on the rear stage side of the sensor circuit 3. However, the output signal intensity was smaller. This is because in the capacitance sensor 1a, the noise component is subtracted from the input signal from the sensor circuit 3 in the arithmetic circuit 6a.

  Thus, the electrostatic capacitance sensor 1a can reduce the influence of noise and suppress malfunctions as compared with the electrostatic capacitance sensor 101 that does not include the dummy electrode 4 and the arithmetic circuit 6a.

  In the capacitance sensor 1a, a signal obtained by amplifying a noise component in the vicinity of the oscillation frequency represented by the above formula (1) in the sensor circuit 3 is input to the arithmetic circuit 6a. Therefore, when this signal is canceled by the noise component input from the dummy electrode 4 to the arithmetic circuit 6a, a frequency component (noise component) that cannot be canceled out can be generated. However, even in this case, as shown in FIG. 6, an effect of reducing the influence of noise can be obtained as compared with the capacitance sensor 101 not including the dummy electrode 4 and the arithmetic circuit 6a.

  In the present embodiment, the configuration in which the subtraction process is performed in the arithmetic circuit 6a has been described. However, any arithmetic process other than the subtraction process may be performed in the arithmetic circuit 6a as necessary.

[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIGS. For convenience of explanation, members having the same functions as those described in the embodiment are given the same reference numerals, and descriptions thereof are omitted.

  FIG. 7 is a block diagram showing a schematic configuration of the capacitance sensor 11 according to the present embodiment. The capacitance sensor 11 according to the present embodiment is configured to perform subtraction of the noise component mixed from the detection electrode 2 on the upstream side of the differential amplifier OP1 of the sensor circuit 13. That is, the capacitance sensor 11 receives the input signal from the detection electrode 2 including the noise component mixed from the detection electrode 2 and the input signal from the dummy circuit 5 based on the noise component mixed from the dummy electrode 4 in the calculation unit 6. The sensor circuit 13 is oscillated based on a signal (calculation signal) generated by the calculation.

  As shown in FIG. 7, the capacitance sensor 11 includes a detection electrode 2, a dummy electrode 4, a dummy circuit 15, a calculation unit 16, a sensor circuit 13, and an evaluation circuit 7.

  The detection electrode 2 is connected to the calculation unit 16, and the dummy electrode 4 is connected to the calculation unit 16 via the dummy circuit 15. The output side of the calculation unit 16 is connected to the sensor circuit 13, and the output side of the sensor circuit 13 is connected to the evaluation circuit 7.

In the capacitance sensor 11, the transfer function from the detection electrode 2 to the output of the calculation unit 16 is H ₁ (s), and the transfer function H ₂ (s) from the dummy electrode 4 to the output of the calculation unit 16 is H ₁ ( By setting so that s) = − H ₂ (s) or approximate to this, the influence of noise can be suitably reduced.

<Configuration of Capacitance Sensor 11a>
FIG. 8 is a circuit diagram showing an example of a specific configuration of the capacitance sensor 11 shown in FIG. As shown in FIG. 8, the capacitance sensor 11 a includes a detection electrode 2, a dummy electrode 4, a dummy circuit 15, a sensor circuit 13, and an evaluation circuit 7.

(Dummy circuit 15)
Dummy circuit 15 is a circuit comprised of a differential amplifier OP2, and a resistor _{R 1.} A part of the feedback circuit of the dummy circuit 15 is connected to the dummy electrode 4, and a signal from the dummy electrode 4 is input to the inverting input terminal (−) of the differential amplifier OP2.

(Sensor circuit 13)
The sensor circuit 13 is a Wien bridge type oscillation circuit including a differential amplifier OP1, a capacitance element C ₂ , and resistance elements R ₁ , R ₂ , R _3, and R ₄ . In the sensor circuit 13, the detection electrode 2 and the dummy circuit 15 are connected to a part of the feedback circuit, and the feedback circuit is connected to the non-inverting input terminal (+) of the differential amplifier OP1.

  In the capacitance sensor 11 a, the detection electrode 2 and the dummy circuit 15 are connected to a part of the feedback circuit of the sensor circuit 13, so that it is based on noise mixed in from the detection electrode 2 included in the input signal from the detection electrode 2. The noise component (first noise component) and the noise component based on the noise mixed from the dummy electrode 4 (second noise component) forming the input signal from the dummy circuit 15 cancel each other, and the input signal from the detection electrode 2 A signal (arithmetic signal) in which the noise component contained in the signal is reduced is generated. In other words, the capacitance sensor 11 a is configured such that the detection electrode 2 and the dummy circuit 15 are connected to a part of the feedback circuit of the sensor circuit 13 so that the upstream side of the sensor circuit 13 functions as the calculation unit 6. It is.

  Thereby, since it is not necessary to separately provide a calculation circuit for performing calculation, the configuration of the capacitance sensor 11a can be simplified. However, an independent arithmetic circuit may be provided and connected to the upstream side (upstream) of the sensor circuit 13.

<Operation of Capacitance Sensor 11a>
Next, the operation of the capacitance sensor 11a will be described.

  FIG. 9 is a circuit diagram showing a configuration in which a noise source N is connected to the capacitance sensor 11a shown in FIG.

As shown in FIG. 9, a common noise source N is connected to the detection electrode 2 and the dummy electrode 4 in the capacitance sensor 11a. C _n between the detection electrode 2 of the capacitance sensor 11 a and the noise source N indicates the capacitance between the detection electrode 2 and the noise source N. Similarly, C _n between the dummy electrode 4 and the noise source N of the capacitance sensor 11a indicates the capacitance between the dummy electrode 4 and the noise source N.

In the electrostatic capacitive sensor 11a, mixed noise current I _n1 from the detection electrodes 2, noise current I _n2 is assumed that mixed from the dummy electrode 4. In the following, for convenience of explanation, it is assumed that I _n1 and I _n2 are DC currents.

The output voltage (output signal) V _n of the dummy circuit 15 is

Given in.

The output voltage V _out of the sensor circuit 13 is

Than,

It becomes.

In this equation (Equation 7), since the coefficients of I _n1 and −I _n2 match, the transfer function H ₁ (s) from the detection electrode 2 to the output of the sensor circuit 13 and the output of the sensor circuit 13 from the dummy electrode 4 It is shown that the transfer function H ₂ (s) up to has a relationship of H ₁ (s) = − H ₂ (s).

Here, if the detection electrode 2 and the dummy electrode 4 are designed so that I _n1 = I _n2 , a noise-induced component can be removed from the output voltage V _out of the sensor circuit 13, and the capacitance sensor 11 a Malfunctions can be prevented.

  In order to confirm the operation of the capacitance sensor 11a, a frequency response was simulated using the capacitance sensor 11 shown in FIG. 9 under the same conditions as in the above embodiment.

If the amplitude voltage of the noise source N is zero, the normal operation of the electrostatic capacitance sensor 11 _(oscillating at C X = _6pF, oscillation stop at C X = 7 pF) was confirmed. The oscillation frequency f _OSC of the sensor circuit 13 at the time of oscillation was about 40 kHz.

  Next, in the second state, AC analysis was performed in a frequency region from 1 kHz to 10 MHz with an AC amplitude voltage of 1 V of the noise source N.

  FIG. 10 is a graph showing a simulation result of a frequency response performed on the capacitance sensor 11a. In FIG. 10, the horizontal axis indicates the frequency (Hz) of the noise source N, and the vertical axis indicates the output signal intensity (dB) of the sensor circuit 13 of the capacitance sensor 11a. FIG. 10 also shows a simulation result of frequency response performed on the capacitance sensor 101 shown in FIG. 3 as a comparative example.

  As shown in FIG. 10, the output signal intensity of the sensor circuit 13 of the capacitance sensor 11a increases in proportion to the frequency of the noise signal. However, the output signal is compared with the capacitance sensor 101 within the simulation range. The strength became very small. This is because, in the capacitance sensor 11a, a noise component is subtracted from the input signal to the differential amplifier OP1 of the sensor circuit 13.

  Thus, according to the electrostatic capacitance sensor 11a, compared with the conventional electrostatic capacitance sensor 101, the influence of noise can be reduced and malfunction can be suppressed.

[Embodiment 3]
The following will describe another embodiment of the present invention with reference to FIGS. For convenience of explanation, members having the same functions as those described in the embodiment are given the same reference numerals, and descriptions thereof are omitted.

  FIG. 11 is a block diagram illustrating a schematic configuration of the capacitance sensor 21 according to the present embodiment. The capacitance sensor 21 according to the present embodiment is configured to perform subtraction of the noise component mixed from the detection electrode 2 in the sensor circuit 23. That is, the capacitance sensor 21 is configured to cause the sensor circuit 23 to function as a calculation unit.

  As shown in FIG. 11, the capacitance sensor 21 includes a detection electrode 2, a dummy electrode 4, a dummy circuit 25, a sensor circuit 23, and an evaluation circuit 7.

  In the capacitance sensor 21, the detection electrode 2 is connected to the sensor circuit 23, and the dummy electrode 4 is connected to the sensor circuit 23 via the dummy circuit 25. The output side of the sensor circuit 23 is connected to the evaluation circuit 7.

In the capacitance sensor 21, the transfer function from the detection electrode 2 to the output of the sensor circuit 23 is H ₁ (s), the transfer function from the dummy electrode 4 to the output of the sensor circuit 23 is H ₂ (s), and H ₁ By setting (s) = − H ₂ (s) or approximating this, the influence of the noise component can be suitably reduced.

<Configuration of Capacitance Sensor 21a>
FIG. 12 is a circuit diagram showing an example of a specific configuration of the capacitance sensor 21 shown in FIG.

  As shown in FIG. 12, the capacitance sensor 21a includes a detection electrode 2, a dummy electrode 4, a dummy circuit 25a, a sensor circuit 23a, and an evaluation circuit 7. In the capacitance sensor 21a, the detection electrode 2 is connected to the sensor circuit 23a, and the dummy electrode 4 is connected to the sensor circuit 23a via the dummy circuit 25a. The output side of the sensor circuit 23 a is connected to the evaluation circuit 7.

(Dummy circuit 25a)
The dummy circuit 25a is a circuit configured by a differential amplifier OP2 and resistance elements R ₁ , R _3, and R ₄ . A signal from the dummy electrode 4 is input to the non-inverting input terminal (+) of the differential amplifier OP2, and is output from the output terminal of the differential amplifier OP2 to the sensor circuit 23a.

(Sensor circuit 23a)
Sensor circuit 23a, differential amplifier OP1, a Wien-bridge oscillator circuit constituted by the capacitance element _{C 2,} and a resistor _{R 1 · R 2 · R 3} · R 4. In the sensor circuit 23a, the signal from the detection electrode 2 is input to the non-inverting input terminal (first input terminal) (+) of the differential amplifier OP1. The signal from the dummy electrode 4 is input to the inverting input terminal (second input terminal) (−) of the differential amplifier OP1 through the dummy circuit 25a.

  In the capacitance sensor 21a, by including such a sensor circuit 23a, a noise component (first noise component) based on noise mixed in from the detection electrode 2 included in the input signal from the detection electrode 2, and a dummy circuit The noise component (second noise component) based on the noise mixed from the dummy electrode 4 that forms the input signal from 25a cancels each other in the sensor circuit 23a, thereby reducing the noise component included in the input signal from the detection electrode 2 The generated signal (calculation signal) is generated. In other words, the capacitance sensor 21 a is configured to cause the sensor circuit 23 a to function as the calculation unit 6.

<Configuration of Capacitance Sensor 21b>
FIG. 13 is a circuit diagram showing another example of the specific configuration of the capacitance sensor 21 shown in FIG.

  As illustrated in FIG. 13, the capacitance sensor 21 b includes a detection electrode 2, a dummy electrode 4, a dummy circuit 25 b, a sensor circuit 23 b, and an evaluation circuit 7. In the capacitance sensor 21b, the detection electrode 2 is connected to the sensor circuit 23b, and the dummy electrode 4 is connected to the sensor circuit 23b via the dummy circuit 25b. The output side of the sensor circuit 23b is connected to the evaluation circuit 7.

(Dummy circuit 25b)
Dummy circuit 25b is a circuit formed by the differential amplifier OP2, the capacitance element _{C 2,} and a resistor _{R 1 · R 2 · R 3} · R 4. The signal from the dummy electrode 4 is input to the non-inverting input terminal (+) of the differential amplifier OP2, and is output from the output terminal of the differential amplifier OP2 to the sensor circuit 23b.

  The configuration of the sensor circuit 23b is the same as the configuration of the sensor circuit 23a described above, and thus the description thereof is omitted.

<Configuration of Capacitance Sensor 21c>
FIG. 14 is a circuit diagram showing still another example of the specific configuration of the capacitance sensor 21 shown in FIG.

  As shown in FIG. 14, the capacitance sensor 21 c includes a detection electrode 2, a dummy electrode 4, a dummy circuit 25 c, a sensor circuit 23 c, and an evaluation circuit 7. In the capacitance sensor 21c, the detection electrode 2 is connected to the sensor circuit 23c, and the dummy electrode 4 is connected to the sensor circuit 23c via the dummy circuit 25c. The output side of the sensor circuit 23c is connected to the evaluation circuit 7.

(Dummy circuit 25c)
Dummy circuit 25c includes a differential amplifier OP2, a differential amplifier OP3, a circuit constituted by the capacitance element _{C 2,} and a resistor _{R 1 · R 2 · R 3} · R 3 · R 4. The signal from the dummy electrode 4 is input to the non-inverting input terminal (+) of the differential amplifier OP2, and after being input from the output terminal of the differential amplifier OP2 to the non-inverting input terminal (+) of the differential amplifier OP3, The signal is output from the output terminal of the differential amplifier OP3 to the sensor circuit 23c.

  Note that the configuration of the sensor circuit 23c is the same as the configuration of the sensor circuit 23a described above, and a description thereof will be omitted.

  According to the capacitance sensors 21a to 21c having such a configuration, the sensor circuits 23a to 23c, which are Wien-bridge type oscillation circuits, can function as an arithmetic unit according to the present invention.

<Operation of Capacitance Sensors 21a-21c>
Next, the operation of the capacitance sensors 21a to 21c will be described.

  15 is a circuit diagram showing a configuration in which the noise source N is connected to the capacitance sensor 21a shown in FIG. 12, and FIG. 16 is a circuit diagram in which the noise source N is connected to the capacitance sensor 21b shown in FIG. FIG. 17 is a circuit diagram showing a configuration in which a noise source N is connected to the capacitance sensor 21c shown in FIG.

As shown in FIGS. 15 to 17, a common noise source N is connected to the detection electrode 2 and the dummy electrode 4 in each of the capacitance sensors 21 a to 21 c. C _n between the detection electrode 2 and the noise source N indicates a capacitance between the detection electrode 2 and the noise source N. Similarly, C _n between the dummy electrode 4 and the noise source N indicates a capacitance between the dummy electrode 4 and the noise source N.

In the electrostatic capacitance sensor 21 a - 21 c, mixed noise current _{I n1} from the detection electrodes 2, noise current _{I n2} is assumed that mixed from the dummy electrode 4. In the following, for convenience of explanation, it is assumed that I _n1 and I _n2 are DC currents.

Here, the capacitance sensor 21a will be examined. The output voltage V _n of the dummy circuit 25a is

Than,

And given.

Next, the output voltage V _out of the sensor circuit 23a is

Thus, the output voltage V _n of the dummy circuit 25a is substituted,

It becomes.

In this equation (Equation 11), since the coefficients of I _n1 and −I _n2 match, the transfer function H ₁ (s) from the detection electrode 2 to the output of the sensor circuit 23 and the output of the sensor circuit 23a from the dummy electrode 4 It is shown that the transfer function H ₂ (s) up to has a relationship of H ₁ (s) = − H ₂ (s).

Here, if the detection electrode 2 and the dummy electrode 4 are designed so that I _n1 = I _n2 , a noise-induced component can be removed from the output voltage V _out of the sensor circuit 23 a, and the capacitance sensor 21 a Malfunctions can be prevented.

  In order to confirm the operation of these electrostatic capacity sensors 21a to 21c, the frequency response simulation is performed under the same conditions as in the above embodiment using the electrostatic capacity sensors 21a to 21c shown in FIGS. went.

If the amplitude voltage of the noise source N is zero, the normal operation of the electrostatic capacitance sensor 21 a - 21 c _(oscillating at C X = _6pF, oscillation stop at C X = 7 pF) was confirmed. The oscillation frequency f _OSC of each of the sensor circuits 23a to 23c at the time of oscillation was about 40 kHz.

  Next, in the second state, AC analysis was performed in a frequency region from 1 kHz to 10 MHz with an AC amplitude voltage of 1 V of the noise source N.

  FIG. 18 is a graph showing a simulation result of frequency response performed on the capacitance sensors 21a to 21c. In FIG. 18, the horizontal axis represents the frequency (Hz) of the noise source N, and the vertical axis represents the output signal strength (dB) of each of the sensor circuits 23a to 23c of the capacitance sensors 21a to 21c. FIG. 18 also shows a simulation result of a frequency response performed on the capacitance sensor 101 shown in FIG. 3 as a comparative example.

  As illustrated in FIG. 18, the output signal intensity of the sensor circuits 23 a to 23 c of the capacitance sensors 21 a to 21 c is smaller than that of the capacitance sensor 101. This is because in the capacitance sensors 21a to 21c, noise components are canceled and subtracted in the sensor circuits 23a to 23c.

In addition, when comparing the capacitance sensors 21a to 21c, the output signal intensity decreased in the order of the capacitance sensor 21a, the capacitance sensor 21b, and the capacitance sensor 21c. This is because the transfer function H ₂ (s) of the capacitance sensor 21c is set to be the closest to H ₁ (s) due to the difference in the configuration of the dummy circuits 25a to 25c. Therefore, it can be said that the capacitance sensor 21c has the greatest noise reduction effect.

  Thus, according to the capacitance sensors 21a to 21c, compared with the conventional capacitance sensor 101, the influence of noise can be reduced and malfunction can be suppressed.

When the noise is a direct current, the noise reduction effect by the dummy circuit 25a of the capacitance sensor 21a and the dummy circuit 25b of the capacitance sensor 21b does not change, but for high frequencies, R ₂ , C The effect of ₂ cannot be ignored. Therefore, a difference may occur in the transfer functions H ₁ (s) and H ₂ (s) in the capacitance sensor 21a.

  Further, since the dummy circuit 25c of the capacitance sensor 21c has a feedback configuration similar to the sensor circuit 23c, a noise reduction effect can be expected even when the gain of the differential amplifier OP2 is not sufficiently high.

[Embodiment 4]
The following will describe another embodiment of the present invention with reference to FIGS. In the present embodiment, an example of an electric device including the capacitance sensor according to the present invention will be described.

  For convenience of explanation, members having the same functions as those described in the embodiment are given the same reference numerals, and descriptions thereof are omitted.

<Configuration of automatic water supply device 30>
FIG. 19 is a block diagram illustrating a schematic configuration of the automatic water supply apparatus 30 according to the present embodiment. The automatic water supply device (electrical device) 30 automatically supplies water into the tank T when the water (object) in the tank T falls below a certain amount.

  As shown in FIG. 19, the automatic water supply apparatus 30 includes a capacitance sensor 31, a solenoid valve 37, a control unit 38, and a switching power supply 39.

(Capacitance sensor 31)
The electrostatic capacitance sensor 31 detects the water level in the tank T. The capacitance sensor 31 is attached to the tank T in which the detection electrode 2 and the dummy electrode 4 store water, and detects that the water level in the tank T has become a predetermined level or less.

  Specifically, in the capacitance sensor 31, a signal (calculation signal) obtained by subtracting a signal including a noise component input from the dummy electrode 4 from a signal including a noise component input from the sensor circuit 33 in the calculation unit 36. ) And output to the evaluation circuit 7. Thereby, the evaluation circuit 7 can detect the oscillation state of the sensor circuit 33 based on the signal in which the noise component mixed from the detection electrode 2 is reduced.

  In the evaluation circuit 7, the sensor circuit 33 evaluates the oscillation state based on the input signal from the calculation unit 36 and outputs the evaluation result to the control unit 38.

(Solenoid valve 37)
The electromagnetic valve 37 performs an opening / closing operation based on a control signal from the control unit 38. The electromagnetic valve 37 is attached to the water supply apparatus. For example, when the control signal from the control unit 38 indicates “open”, the water supply apparatus supplies water to the tank T by opening the electromagnetic valve 37.

(Control unit 38)
The control unit 38 controls the electromagnetic valve 32 according to the output of the capacitance sensor 31. Specifically, the control unit 38 controls the water supply to the tank T by opening the electromagnetic valve 32 when a signal indicating that the water level of the tank T is below a predetermined level is input from the capacitance sensor 31. To do.

(Switching power supply 39)
The switching power supply 39 obtains a DC voltage from an AC commercial power supply. The switching power supply 39 is connected to a commercial power supply, converts an AC voltage into a DC voltage, and supplies it to the capacitance sensor 31, the electromagnetic valve 37, and the control unit 38.

<Operation of Automatic Water Supply Device 30>
20A and 20B are schematic views showing a state where the water level in the tank T is equal to or higher than a predetermined level. FIGS. 21A and 21B show the water level in the tank T being a predetermined level. It is a schematic diagram which shows the state reduced to less than. 20A and 21A show the front of the tank T, and FIG. 20B and FIG. 21B show the side of the tank T.

As shown in FIGS. 20A and 20B, when the water level in the tank T is above the detection electrode 2 and the dummy electrode 4, the water W is regarded as a conductor, and the detection electrode 2 and the dummy electrode 4 Parallel plate capacitors each having a capacitance C _X are formed between the water W and the water W.

On the other hand, as shown in FIGS. 21A and 21B, when the water level in the tank T is below the detection electrode 2, the distance between the water W and the detection electrode 2 becomes long, so that the capacitance C _X becomes smaller. That is, the capacitance sensor 31 detects whether the water level is above or below the detection electrode 2 by measuring the capacitance C _X between the detection electrode 2 and the water W.

  When the capacitance sensor 31 detects that the water level is below the detection electrode 2, the control unit 38 controls the opening and closing of the electromagnetic valve 32 so that water is supplied from the water supply device to the tank T.

  Here, when a general AC commercial power supply is used to drive the automatic water supply apparatus 30, a desired DC voltage is often obtained by the switching power supply 39 or the like, but the process of conversion from the AC voltage to the DC voltage is performed. Causes high frequency noise.

  When this noise enters the detection electrode 2 through the water W, the capacitance sensor 31 may malfunction due to the influence of the noise.

  Therefore, in the capacitance sensor 31, the noise mixed from the detection electrode 2 is installed by subtracting the noise component mixed from the dummy electrode 4 from the signal including the noise component mixed from the detection electrode 2 by installing the dummy electrode 4. Has reduced the impact. Therefore, the malfunction due to the influence of noise can be suppressed by using the capacitance sensor 31 as a water level sensor.

  In the capacitance sensor 31, it is desirable that substantially the same amount of noise is mixed in the detection electrode 2 and the dummy electrode 4. That is, when noise is mixed through the object, the capacitance value between the detection electrode 2 and the object and the capacitance value between the dummy electrode 4 and the object are designed to be equal. It is desirable to arrange.

  In this embodiment, the detection electrodes 2 and the dummy electrodes 4 are arranged so as to be parallel to the water surface of the target water W, so that the respective capacitance values are equal.

  Further, in the present embodiment, an example in which the capacitance sensor according to the present invention is used as a water level sensor has been described. However, for example, a human sensor or a fluid that detects a capacitance formed between the detection electrode 2 and a human body. The present invention can be used as various sensors such as a detection sensor.

[Summary]
A capacitance sensor according to aspect 1 of the present invention is a capacitance sensor that detects a capacitance between an object (water W) and a detection electrode or a change thereof, and is connected to the detection electrode. An oscillation circuit including a feedback circuit (sensor circuits 3, 13, 23, 23a to 23c), a noise electrode (dummy electrode 4) as an electrode for detecting noise, and a signal based on noise mixed from the detection electrode An arithmetic unit (arithmetic circuit 6a) that generates an arithmetic signal by calculating a signal including a first noise component that is a component and a signal including a second noise component that is a signal component based on noise mixed from the noise electrode. And detecting the capacitance or a change thereof using the calculation signal.

  In the above configuration, a calculation is performed using a signal including a first noise component that is a signal component based on noise mixed from the detection electrode and a signal including a second noise component that is a signal component based on noise mixed from the noise electrode. Arbitrary arithmetic processing can be performed in the unit. Therefore, in the calculation unit, for example, when the process of subtracting the second noise component from the signal including the first noise component based on the noise mixed from the detection electrode is performed, the first noise component based on the noise mixed from the detection electrode is reduced. The operation signal can be generated.

  Therefore, according to the above configuration, since it becomes possible to detect the capacitance of the detection electrode or a change thereof using the calculation signal with the first noise component reduced, malfunction due to noise mixed from the detection electrode Can be realized.

  The capacitance sensor according to aspect 2 of the present invention is the capacitance sensor according to aspect 1, in which the arithmetic unit is connected to an output side of the oscillation circuit, and the arithmetic unit receives the first input from the oscillation circuit. A signal including one noise component and the second noise component input directly from the noise electrode or via a processing circuit (dummy circuits 5, 15, 25, 25a to 25c) for executing predetermined signal processing The structure which calculates a signal may be sufficient.

  In the above configuration, the calculation unit calculates a signal including the first noise component input from the oscillation circuit and a signal including the second noise component input directly from the noise electrode or via the processing circuit.

  Therefore, according to the above configuration, the arithmetic signal can be suitably generated in the arithmetic unit connected to the subsequent stage side of the oscillation circuit.

  In addition, the capacitive sensor according to aspect 3 of the present invention is the capacitive sensor according to aspect 1, in which the calculation unit is configured to directly input the signal including the first noise component input from the detection electrode and the noise electrode, or a predetermined value. The calculation signal generated by calculating the signal composed of the second noise component input through the processing circuit that executes the signal processing may be output to the oscillation circuit.

  In the above configuration, the calculation unit calculates a signal including the first noise component input from the detection electrode and a signal including the second noise component input directly from the noise electrode or via the processing circuit. The generated arithmetic signal is output to the oscillation circuit.

  Therefore, according to the above configuration, it is possible to suitably generate an arithmetic signal on the front stage side of the oscillation circuit and operate the oscillation circuit based on the arithmetic signal.

  The capacitance sensor according to aspect 4 of the present invention is the capacitance sensor according to aspect 3, in which the detection electrode and the noise electrode or the processing circuit are connected to a part of the feedback circuit included in the oscillation circuit. It may be a configuration.

  According to the above configuration, it is possible to generate an arithmetic signal using the feedback circuit included in the oscillation circuit, so that the oscillation circuit can function as an arithmetic unit. For this reason, it is not necessary to separately provide an independent arithmetic circuit or the like for performing computation, so that the configuration of the capacitance sensor can be simplified.

  In the capacitance sensor according to aspect 5 of the present invention, in the aspect 1, the oscillation circuit includes at least a first input terminal and a second input terminal, and the detection electrode is connected to the first input terminal. In addition, the operation signal may be generated in the oscillation circuit by connecting the noise electrode to the second input terminal via a processing circuit that executes predetermined signal processing.

  In the above configuration, the detection electrode is connected to the first input terminal of the oscillation circuit, and the noise electrode is connected to the second input terminal of the oscillation circuit via the processing circuit, thereby generating an arithmetic signal.

  Therefore, according to the above configuration, the oscillation circuit can function as an arithmetic unit. For this reason, it is not necessary to separately provide an independent arithmetic circuit or the like for performing computation, so that the configuration of the capacitance sensor can be simplified.

  Further, the capacitance sensor according to aspect 6 of the present invention is the structure according to any one of the above aspects 1 to 5, wherein the calculation unit subtracts the second noise component from the signal including the first noise component. May be.

  According to said structure, in a calculating part, the calculation signal which reduced the 1st noise component based on the noise mixed from the detection electrode can be produced | generated suitably.

  In addition, in the capacitance sensor according to Aspect 7 of the present invention, in any of Aspects 1 to 6, the detection electrode and the noise electrode are designed or arranged so that substantially the same amount of noise is mixed from each of them. It may be a configuration.

  In the above-described configuration, the first noise component amount mixed from the detection electrode and the second noise component amount mixed from the noise electrode can be made substantially to the same extent. Therefore, in the calculation unit, for example, when the process of subtracting the second noise component from the signal including the first noise component based on the noise mixed from the detection electrode, the first noise component and the second noise component cancel each other. Is possible.

  Therefore, according to said structure, the malfunctioning by the noise mixed from the detection electrode can be suppressed effectively.

  Moreover, the electric equipment (automatic water supply apparatus 30) which concerns on aspect 8 of this invention is equipped with the electrostatic capacitance sensor in any one of the said aspects 1-7, It is characterized by the above-mentioned.

  Therefore, according to said structure, the electric equipment which can suppress malfunctioning by the noise mixed from the detection electrode is realizable.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

[Supplement]
The present invention can also be expressed as follows. That is, the capacitance sensor according to the present invention is a capacitance sensor that detects the capacitance of the detection electrode or its change by the Wien bridge type oscillation circuit, and includes a second electrode different from the detection electrode. A signal including a calculation result between a noise signal mixed from the detection electrode and a noise signal mixed from the second electrode is obtained.

  In the capacitance sensor according to the present invention, the detection electrode is connected to a sensor circuit that detects capacitance or a change thereof, the sensor circuit is connected to an arithmetic circuit, and the second electrode is directly or oscillated. The calculation result may be obtained by connecting to the arithmetic circuit via a dummy circuit different from the circuit.

  Further, the capacitance sensor according to the present invention may be configured so that the signals mixed in the detection electrode and the second electrode cancel each other at the output of the arithmetic circuit. .

  In the capacitance sensor according to the present invention, the detection electrode is connected to an arithmetic circuit or a sensor circuit that detects capacitance or a change thereof, and the second electrode is connected directly or via a dummy circuit. The circuit may be connected to a sensor circuit that detects capacitance or a change thereof, and the calculation circuit may be connected to a sensor circuit that detects capacitance or a change thereof to obtain the calculation result.

  Further, the capacitance sensor according to the present invention may be configured so that the signals mixed in the detection electrode and the second electrode cancel each other at the output of the arithmetic circuit. .

  Further, the capacitance sensor according to the present invention may be configured such that the signals mixed in the detection electrode and the second electrode cancel each other by the output of the sensor circuit. .

  In the capacitance sensor according to the present invention, the detection electrode is connected to a sensor circuit that detects capacitance or a change thereof, the second electrode is connected to a dummy circuit, and the output signal of the dummy circuit is The structure which obtains the said calculation result by giving to a sensor circuit may be sufficient.

  Further, the capacitance sensor according to the present invention may be configured such that the signals mixed in the detection electrode and the second electrode cancel each other by the output of the sensor circuit. .

  The capacitance sensor according to the present invention may be configured such that the detection electrode and the second electrode are electrodes designed so that the same noise signal is mixed in each electrode.

  In addition, an electrical device according to the present invention is characterized by including the capacitance sensor according to the present invention.

  The present invention can be suitably used for various sensors such as a water level sensor, a touch sensor, and a proximity sensor.

DESCRIPTION OF SYMBOLS 1 Capacitance sensor 1a Capacitance sensor 2 Detection electrode 3 Sensor circuit (oscillation circuit)
4 dummy electrode (noise electrode)
5 Dummy circuit (processing circuit)
6 Arithmetic Unit 6a Arithmetic Circuit (Calculating Unit)
7 Evaluation Circuit 11 Capacitance Sensor 13 Sensor Circuit (Oscillation Circuit)
15 Dummy circuit (processing circuit)
16 Calculation Unit 21 Capacitance Sensors 21a to 21c Capacitance Sensor 23 Sensor Circuit (Oscillation Circuit)
23a-23c Sensor circuit (oscillation circuit)
25 Dummy circuit (processing circuit)
25a to 25c dummy circuit (processing circuit)
30 Automatic water supply equipment (electric equipment)
31 Capacitance sensor 37 Solenoid valve 38 Control unit 39 Switching power supply (noise source)
101 Capacitance sensor OP1 Differential amplifier OP2 Differential amplifier T Tank W Water (object)

Claims (5)

A capacitance sensor for detecting a capacitance between the object and the detection electrode or a change thereof;
An oscillation circuit including a feedback circuit connected to the detection electrode;
A noise electrode that is an electrode for detecting noise;
An arithmetic signal is obtained by calculating a signal including a first noise component which is a signal component based on noise mixed from the detection electrode and a signal including a second noise component which is a signal component based on noise mixed from the noise electrode. And an arithmetic unit for generating
An electrostatic capacity sensor that detects the electrostatic capacity or a change thereof using the arithmetic signal. The arithmetic unit is connected to the output side of the oscillation circuit,
The arithmetic unit includes a signal including the first noise component input from the oscillation circuit, and the second noise component input directly from the noise electrode or via a processing circuit that executes predetermined signal processing. The capacitance sensor according to claim 1, wherein the signal is calculated.   The calculation unit includes a signal including the first noise component input from the detection electrode, and the second noise component input directly from the noise electrode or via a processing circuit that executes predetermined signal processing. The capacitance sensor according to claim 1, wherein the calculation signal generated by calculating the signal is output to the oscillation circuit. The oscillation circuit has at least a first input terminal and a second input terminal,
The detection signal is connected to the first input terminal, and the noise electrode is connected to the second input terminal via a processing circuit that executes predetermined signal processing, whereby the arithmetic signal is generated in the oscillation circuit. The capacitance sensor according to claim 1, wherein:   An electric apparatus comprising the capacitance sensor according to any one of claims 1 to 4.

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