JP2014139515A - Liquid detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid detection device capable of simplifying a detection structure while maintaining the detecting accuracy of the existence of liquid in accordance with the change of capacitance to a certain extent.SOLUTION: The liquid detection device includes: a first sensor part 10 for measuring capacitance between a first electrode 11 and a second electrode 12; a second sensor part 20 for measuring capacitance between a third electrode 21 and a fourth electrode 22; and a control part 30 for applying a drive signal to the first sensor part 10 and a second sensor part 20, and for processing output signals from the first sensor part 10 and the second sensor part 20. The first sensor part 10 is arranged in a first sensing region R1 for measuring the first sensing region R1, and the second sensor 20 is arranged in a second sensing region R2 for measuring the second sensing region R2. In this case, the control part 30 uses the output signal from the first sensor part 10 as a first reference signal, and processes the output signal from the second sensor part 20 on the basis of the first reference signal.

Description

  The present invention relates to a liquid detection device that detects the presence of a liquid by changing a capacitance.

  Conventionally, a water level sensor for detecting the water level in the tank has been used. The measurement method applied to the water level sensor includes a type using a mechanical float and a type that measures the water pressure using a pressure sensor. There was a problem with the complexity. Compared with these methods, the water level sensor that measures the capacitance between the pair of measuring electrodes is a simple structure and excellent in reliability.

  For example, in Patent Document 1, the dielectric constant of the atmosphere and the dielectric constant of the liquid that is the measurement object are acquired by the reference electrode, and based on these information and the capacitance between the measurement electrodes. A water level sensor for measuring is disclosed.

  FIG. 13 is an explanatory diagram illustrating a state in which water level measurement is performed using the water level sensor 100 of Patent Document 1. As shown in FIG. 13, the water level sensor 100 of Patent Document 1 includes a pair of measurement electrodes 111 and 112 arranged in a water tank, for example, to measure the water level, and measures the water level h with reference to θ0. As shown in FIG. 13, the water level sensor 100 is provided with a pair of upper reference electrodes 121 and 122 and a pair of lower reference electrodes 131 and 132 with respect to the pair of measurement electrodes 111 and 112. The water level can be measured with sufficient accuracy.

  The sensor that measures the capacitance can detect the presence of liquid by changing the capacitance, so it can detect the state in which the water in the aquarium is drained by installing it in the drain pipe connected to the aquarium. You can also. For example, in a washing machine with a drying function, a water level sensor that detects a water level in a washing tub and a water droplet detection sensor that detects a dry state are separately provided. As a water droplet detection sensor for detecting such a dry state, a liquid detection device that detects that the water flow has stopped and the inner surface of the drain pipe has been dried has been proposed.

  A liquid detection device that detects a dry state as a water drop detection sensor detects changes in capacitance between a state in which no water drop exists between a pair of measurement electrodes and a state in which a water drop exists between a pair of measurement electrodes. In order to detect, the measurement precision which can detect the slight capacity | capacitance change between this state is required. For this reason, it was necessary to improve the measurement accuracy by using a reference electrode in addition to the measurement electrode.

JP-A-11-311561

  However, the water level sensor and the water drop detection sensor have measurement electrodes arranged at different positions in the apparatus for different purposes, and it is necessary to prepare a reference electrode in addition to the measurement electrode. For this reason, the liquid detection apparatus which implement | achieves two functions of a water level sensor and a water droplet detection sensor had the problem that it will become a complicated detection structure.

  The present invention solves the above-described problem, and is a liquid detection device having a first sensing region and a second sensing region as measurement target areas, each having a measurement electrode, and the liquid is detected by a change in capacitance. It is an object of the present invention to provide a liquid detection device capable of simplifying the detection structure while maintaining the accuracy of detecting the presence to some extent.

  The present invention provides a first sensor unit for measuring the capacitance between the first electrode and the second electrode, and a second for measuring the capacitance between the third electrode and the fourth electrode. A sensor unit, connected to the first sensor unit and the second sensor unit, applies a drive signal to the first sensor unit and the second sensor unit, and from the first sensor unit and the second sensor unit A control unit for processing the output signal of the first sensing unit, wherein the first sensor unit is disposed in a first sensing region, measures the first sensing region, and When the second sensor unit is arranged in a second sensing region that is a different measurement target area, and the measurement of the second sensing region is performed, the control unit outputs an output from the first sensor unit as a first reference signal. Signal and using the first reference signal Characterized by processing the output signal from the second sensor unit based on.

  According to this configuration, when measuring the second sensing region, the output signal from the first sensor unit is used as the first reference signal, and the second sensor arranged in the second sensing region based on the first reference signal. The output signal from the unit is processed. By so doing, the first sensor unit that measures the first sensing region can also serve as the reference electrode of the second sensor unit, so there is no need to provide a separate reference electrode. Therefore, the detection structure can be simplified while maintaining the liquid detection accuracy to some extent.

  In the liquid detection device of the present invention, when the measurement of the first sensing region is performed, the control unit uses an output signal from the second sensor unit as a second reference signal, based on the second reference signal. An output signal from the first sensor unit is processed.

  According to this configuration, when measuring the first sensing region, the output signal from the second sensor unit is used as the second reference signal, and the output signal from the first sensor unit is processed based on the second reference signal. . In this case, the second sensor unit that measures the second sensing region can also be used as the reference electrode of the first sensor unit, so there is no need to provide a reference electrode separately. Therefore, the detection structure can be simplified while maintaining the liquid detection accuracy to some extent.

  In the liquid detection apparatus of the present invention, the control unit includes an output signal processing unit that processes an output signal, the output signal processing unit can add an offset signal, and the output signal processing unit includes the second signal processing unit. When measuring the sensing area, the offset is added to the difference signal between the output signal from the second sensor unit and the first reference signal, or the difference between the output signal from the second sensor unit and the first reference signal. The differential signal to which the signal is added is processed.

  The output signal from the first sensor unit processed by the control unit is a signal corresponding to the capacitance of the first sensor unit, and this capacitance is defined as the first capacitance. The output signal from the second sensor unit processed by the control unit is a signal corresponding to the capacitance of the second sensor unit, and this capacitance is defined as the second capacitance. The first capacitance includes capacitance due to wiring to the first sensor unit, and the second capacitance includes capacitance due to wiring to the second sensor unit. However, by processing the difference signal in the control unit, the increase in capacitance due to wiring can be ignored. Therefore, the dynamic range of detection can be expanded or the resolution can be increased, and highly accurate detection can be performed.

  In the liquid detection apparatus according to the aspect of the invention, the output signal processing unit may perform a measurement of the first sensing region, and a difference signal between the output signal from the first sensor unit and the second reference signal, or the first The differential signal obtained by adding the offset signal to the difference between the output signal from the sensor unit and the second reference signal is processed.

  The output signal from the first sensor unit processed by the control unit is a signal corresponding to the capacitance of the first sensor unit, and this capacitance is defined as the first capacitance. The output signal from the second sensor unit processed by the control unit is a signal corresponding to the capacitance of the second sensor unit, and this capacitance is defined as the second capacitance. The first capacitance includes capacitance due to wiring to the first sensor unit, and the second capacitance includes capacitance due to wiring to the second sensor unit. However, by processing the difference signal in the control unit, the increase in capacitance due to wiring can be ignored. Therefore, the dynamic range of detection can be expanded or the resolution can be increased, and highly accurate detection can be performed.

  In the liquid detection device of the present invention, the control unit applies a drive signal having a positive phase to the first sensor unit and applies a drive signal having a reverse phase to the second sensor unit, and the first sensor unit and Differential signal processing for adding output signals from the second sensor unit is performed.

  According to this configuration, since the difference signal is detected, only a small change in the first capacitance can be detected even when the change in the first capacitance is small. That is, since only the change in the first capacitance can be detected without providing a separate reference electrode for the first sensor unit, the liquid detection accuracy can be improved when the reference electrode is provided separately. Same level. Similarly, since only the change in the second capacitance can be detected without providing a separate reference electrode for the second sensor unit, the liquid detection accuracy can be improved when the separate reference electrode is provided. To the same extent.

  In the liquid detection device of the present invention, the first sensing area is a water tank, the measurement of the first sensing area is a measurement for detecting the water level of the water tank, and the second sensing area is connected to the water tank. The drainage pipe is characterized in that the measurement in the second sensing region is a measurement for detecting a dry state of the drainage pipe.

  According to this configuration, in the capacitance detection device that performs the measurement for detecting the water level and the measurement for detecting the dry state of the drain pipe, the detection structure can be simplified while maintaining a certain degree of accuracy.

  According to the present invention, when the first sensing region in which the first sensor unit is disposed is in the non-measurement period, the output signal from the first sensor unit is used as the first reference signal, and the first reference signal is used based on the first reference signal. Since the output signal from the 2nd sensor part arrange | positioned in 2 sensing area | regions is processed, it is not necessary to provide a reference electrode separately. Therefore, it is possible to provide a liquid detection device capable of simplifying the detection structure while maintaining the liquid detection accuracy to some extent.

It is a block diagram which shows the liquid detection apparatus of 1st Embodiment. It is explanatory drawing which shows the principle of an electrostatic capacitance sensor. It is explanatory drawing which has arrange | positioned the liquid detection apparatus of 1st Embodiment to the water tank and the drain pipe. It is a schematic diagram showing a drive signal, a waveform of an output signal, and a differential signal. It is a schematic diagram showing a drive signal, a waveform of an output signal, and a differential signal. It is a schematic diagram showing a drive signal, a waveform of an output signal, and a differential signal. It is a block diagram which shows the liquid detection apparatus of 2nd Embodiment. It is a schematic diagram showing a drive signal, a waveform of an output signal, and a differential signal. It is a schematic diagram showing a drive signal, a waveform of an output signal, and a differential signal. It is a schematic diagram showing a drive signal, a waveform of an output signal, and a differential signal. It is a schematic diagram which shows an output value. It is explanatory drawing which shows the modification which has arrange | positioned the liquid detection apparatus. It is explanatory drawing which shows the state which is measuring the water level using the conventional water level sensor.

[First Embodiment]
The liquid detection apparatus 1 in the first embodiment will be described below.

  FIG. 1 is a block diagram illustrating a liquid detection apparatus 1 according to the first embodiment. FIG. 2 is an explanatory diagram showing the principle of the capacitance sensor. FIG. 3 is an explanatory diagram in which the liquid detection device 1 according to the first embodiment is disposed in the water tank 51 and the drain pipe 52.

As shown in FIG. 1, the liquid detection apparatus 1 includes a first sensor unit 10 for detecting the liquid in the first sensing region R1, and a second sensor unit 20 for detecting the liquid in the second sensing region R2. And a control unit 30. The control unit 30 is connected to the first sensor unit 10 and the second sensor unit 20, applies a drive signal DS to the first sensor unit 10 and the second sensor unit 20, and outputs an output signal S from the first sensor unit 10. processing the output signal _{S 2} from the _first and second sensor unit 20. Output signals S ₁ from the first sensor unit 10 to be processed by the control unit 30 is a signal corresponding to the capacitance of the first sensor unit 10 and the electrostatic capacitance between the first capacitance C _1. The output signal S ₂ from the second sensor unit 20 to be processed by the control unit 30 is a signal corresponding to the capacitance of the second sensor unit 20, and the electrostatic capacitance and the second capacitance C _2.

The first sensor unit 10 is disposed in a state where the first electrode 11 and the second electrode 12 are electrically insulated, and a predetermined first electrostatic capacitance is provided between the first electrode 11 and the second electrode 12. capacity _{C 1} is generated. When a liquid is present in the first sensing region R1, the dielectric constant of the liquid is different from the dielectric constant of the space when no liquid is present. Therefore, by the liquid present in the first sensing area R1, are formed first capacitance C ₁ is changed is between the first electrode 11 and the second electrode 12. In principle, as shown in FIG. 2, a capacitance measuring circuit CC that measures the capacitance C between the two electrodes (E1, E2), and the measured capacitance value as an output format (voltage, current, or frequency). The output can be obtained via a signal conversion circuit SC that converts the signal into analog output or digital output format). Based on this principle, the control unit 30 shown in FIG. 1, the first capacitance C ₁ is measured, it is possible to detect the liquid in the first sensing region R1.

The second sensor unit 20 is disposed in a state where the third electrode 21 and the fourth electrode 22 are electrically insulated, and a predetermined second electrostatic capacitance is provided between the third electrode 21 and the fourth electrode 22. capacity _{C 2} is generated. When a liquid is present in the second sensing region R2, the dielectric constant of the liquid is different from the dielectric constant of the space when no liquid is present. Therefore, by the liquid present in the second sensing region R2, is formed a second capacitance C ₂ is changed is between the third electrode 21 and fourth electrode 22. The control unit 30 shown in FIG. 1, a second capacitance C ₂ is measured, it is possible to detect the liquid in the second sensing region R2.

The control unit 30 has a function corresponding to the capacitance measurement circuit CC and the signal conversion circuit SC of FIG. The control unit 30 is configured by an integrated circuit (IC) having a drive signal generation unit 31 and an output signal processing unit 35. The integrated circuit operates the drive signal generation unit 31, the output signal processing unit 35, and the like according to a command from a control circuit based on a program recorded in the memory. As shown in FIG. 1, the drive signal generator 31 is connected to the first electrode 11 of the first sensor unit 10 and the third electrode 21 of the second sensor unit 20. A drive signal DS is applied. The output signal processing unit 35 has output signal processing means 36 and is connected to the second electrode 12 of the first sensor unit 10 and the fourth electrode 22 of the second sensor unit 20. An output signal S ₁ of the first sensor unit 10 is input from the second electrode 12 to the output signal processing unit 36, and an output signal S ₂ of the second sensor unit 20 is input from the fourth electrode 22. The output signal processing means 36 outputs the output signal S ₁ and the output signal S ₂ after converting them into a desired output format.

  The liquid detection device 1 is disposed in a measurement target area having a first sensing region R1 and a second sensing region R2. As shown in FIG. 3, when the first sensing region R1 is a water tank 51 (for example, a washing tank), the amount of water present in the water tank 51 is determined by the first sensor unit 10 disposed on the side surface of the water tank 51. It can be detected as (water surface height). If the water tank 51 is an insulating material such as glass or synthetic resin, the first sensor unit 10 can be disposed on the outer wall of the water tank 51. When the second sensing region R2 is a drain pipe 52 (for example, a drain pipe of a dryer), it is possible to detect whether or not water is present in the drain pipe 52. For this reason, the 2nd sensor part 20 is arrange | positioned at the drain pipe 52 as shown in FIG. The first electrode 11 and the second electrode 12 of the first sensor unit 10 are connected to the control unit 30 by a first wiring 11a and a second wiring 12a, respectively. The 3rd electrode 21 and the 4th electrode 22 of the 2nd sensor part 20 are connected to control part 30 by the 3rd wiring 21a and the 4th wiring 22a, respectively.

First, it is assumed that no liquid exists in the water tank 51 which is the first sensing region R1. When drainage through the drainage pipe 52 flows from the upstream side of the second sensing region R2, water enters the drainage pipe 52. At this time, since the dielectric constant of water is larger than the dielectric constant of air, the second sensor unit 20 has a second capacitance larger than the _second capacitance C ₂ (0) in the absence of liquid (initial). it is a C _2. That is, C ₂ = ΔC ₂ + C ₂ (0). Here, ΔC ₂ is an increase in capacitance.

The water tank 51 which is the first sensing region R1 is assumed to have a water level of zero when drainage is completed. In addition, when there is no liquid in the first sensing region R1 (the water level in the water tank 51 is zero), the initial first capacitance C ₁ (0) of the first sensor unit 10 is set.

In the present embodiment, the initial first capacitance C ₁ (0) of the first sensor unit 10 and the initial second capacitance C ₂ (0) of the second sensor unit 20 are made equal. The electrode shape and electrode interval are set. Output signals S ₁ from the first sensor unit 10, an output signal S ₂ from the second sensor unit 20, is signal processed by the output signal processing unit 35 of the controller 30. At this time, the control unit 30, using the output signals S ₁ from the first sensor unit 10 as a first reference signal, based on the first reference signal, for processing the output signal S ₂ from the second sensor unit 20. That is, performs a process of subtracting the output signals S ₁ to the output signal S ₂ and the first reference signal to obtain an output X _{2. X 2 = S 2 -S 1 =} B 2 {C 2 -C 1)} is. B ₂ is, for example, a capacitance-voltage conversion coefficient (constant) in the capacitance measurement circuit.

When there is no liquid in the water tank 51 and the initial first capacitance C ₁ (0) of the first sensor unit 10, X ₂ = B ₂ {C ₂ −C ₁ (0)} = B ₂ { Since ΔC ₂ + C ₂ (0) −C ₁ (0)} = B ₂ × ΔC ₂ , it is possible to detect that water remains in the drain pipe 52 until X ₂ stably returns to zero. In this way, even if C ₂ (0) is larger than ΔC ₂ , it is possible to cancel a large value of C ₂ (0) and detect only a small change in ΔC ₂ . That is, even if a reference electrode for the second sensor unit 20 is not provided separately, C ₂ (0) can be canceled and only the change in ΔC ₂ can be detected. It can be maintained at the same level as when provided separately.

On the other hand, when no drainage flows through the drainage pipe 52 from the upstream side of the second sensing region R2, there is no water in the second sensing region R2. For this reason, the second sensor unit 20 has the second capacitance C ₂ (0) when no liquid is present.

Aquarium 51 is a first sensing region R1 before the water is the water level is zero, the first capacitance C ₁ of the first sensor unit 10, the first sensor portion 10 when the liquid is absent early The first capacitance C ₁ (0). When water storage in the water tank 51 is started with the drain valve 53 closed, the first sensor unit 10 starts to increase the _first capacitance C1 because the dielectric constant of water is larger than the dielectric constant of air. That is, if the water level is L, it can be detected by L = A {C ₁ -C ₁ (0)}. A is a proportional coefficient, and is a constant determined by the first sensor unit 10 and the water tank 51.

In the present embodiment, the initial first capacitance C ₁ (0) of the first sensor unit 10 and the initial second capacitance C ₂ (0) of the second sensor unit 20 are made equal. The electrode shape and electrode interval are set. Output signals S ₁ from the first sensor unit 10, an output signal S ₂ from the second sensor unit, is the signal processing by the output signal processing unit 35 of the controller 30. At this time, the control unit 30, using the output signal S ₂ from the second sensor unit 20 as a second reference signal, based on the second reference signal, processes the output signals S ₁ from the first sensor unit 10. That is, performs a process of subtracting the output signal S ₂ to the output signals S ₁ and the second reference signal to obtain an output X _{1. X 1 = S 1 -S 2 =} B 1 {C 1 -C 2 (0)} is. B ₁ is, for example, a capacitance-voltage conversion coefficient (constant) in the capacitance measurement circuit.

At this time, the water level L is detected as L = A {C ₁ −C ₁ (0)} = A {X ₁ / B ₁ + C ₂ (0) −C ₁ (0)} = A / B ₁ × X ₁ it can. A and B ₁ are constants. For example, if X ₁ is a voltage output, the water level can be read as a voltage value. In this way, even when C 1 ₍₀₎ change in C ₁ is small relative, it can detect only a small variation to cancel the C ₁ of large value _(0). That is, even if the reference electrode of the first sensor unit 10 is not provided separately, C ₁ (0) can be canceled and only the change in C ₁ can be detected, so that the liquid detection accuracy can be improved. Can be maintained at the same level as that provided separately.

  In addition, at the timing which measures either the water tank 51 which is the 1st sensing area | region R1, or the drain pipe 52 which is the 2nd sensing area | region R2, the state which the liquid does not exist in the other was assumed. The present embodiment is applied to a liquid detection device having such a relationship.

  Hereinafter, the effect by having set it as this embodiment is demonstrated.

Liquid detecting device 1 is arranged in the measurement target area having a first sensing region R1 and a second sensing region R2, when the measurement of the second sensing region R2, the output signals S ₁ from the first sensor unit 10 Used as the first reference signal. Then, based on the first reference signal, for processing the output signal S ₂ from the second sensor unit 20 disposed in the second sensing region R2. In this case, since the first sensor unit 10 that measures the first sensing region R1 also serves as the reference electrode of the second sensor unit 20, there is no need to provide a reference electrode separately. Therefore, the detection structure can be simplified while maintaining the liquid detection accuracy to some extent.

Further, when performing the measurement of the first sensing region R1, using the output signal S ₂ from the second sensor unit 20 as a second reference signal, based on the second reference signal, the output signals S ₁ from the first sensor unit 10 Process. In this case, since the second sensor unit 20 that measures the second sensing region R2 also serves as the reference electrode of the first sensor unit 10, there is no need to provide a reference electrode separately. Therefore, the detection structure can be simplified while maintaining the liquid detection accuracy to some extent.

  In addition, when 1st sensing area | region R1 is the drain pipe 52 and 2nd sensing area | region R2 is the water tank 51, the 1st sensor part 10 detects the dry state of the drain pipe 52, and the 2nd sensor part 20 is the water tank 51. Detect the water level. Even in this case, as described above, the detection structure can be simplified while maintaining the liquid detection accuracy to some extent.

In the above description, the capacitance that becomes the reference signal after measuring the _first capacitance C _{1 of} the first sensor unit 10 and the second capacitance C _{2 of} the second sensor unit 20 by the capacitance measurement circuit. However, a configuration may be adopted in which only the differential capacitance is output in the capacitance measurement circuit. Specifically, it is preferable to use differential signal processing described below.

<Differential signal processing>
The differential signal processing will be described with reference to FIGS.

4 is obtained by subtracting the voltage waveform of the drive signal DS applied from the driving signal generating means 32, and the waveform and the output signal S ₂ waveform of the output signals S ₁ at this time, the output signal S ₂ from the output signals S ₁ FIG. 6 is a schematic diagram illustrating a difference signal ΔS ₁ . If a rectangular voltage waveform is applied as the drive signal DS and the output signal processing means 36 of the output signal processing unit 35 is a current signal circuit, the output signal S ₁ and the output signal S ₂ are output from the capacitance between the respective electrodes and the output. The differential waveform depends on the input resistance viewed from the signal processing means 36. When the input resistances are equal and C ₁ and C ₂ are initial C ₁ (0), C ₂ (0), the differential signal ΔS ₁ is zero.

FIG. 5 shows the voltage waveform of the drive signal DS, the waveform of the output signal S _{1 and} the waveform of the output signal S ₂ when the _first capacitance C _{1 of} the first sensor unit 10 gradually increases, and the output FIG. 6 is a schematic diagram illustrating a differential signal ΔS ₁ obtained by subtracting an output signal S ₂ from a signal S ₁ . Since C ₁ gradually increases from the initial C ₁ (0), the output signal S ₁ increases. On the other hand, since C ₂ has no change in value from the initial C ₂ (0), the difference signal ΔS ₁ gradually increases from zero. The difference signal ΔS ₁ is converted into a predetermined output format and output from the output signal processing means 36.

FIG. 6 shows the voltage waveform of the drive signal DS and the waveform of the output signal S ₁ when the _second capacitance C _{2 of} the second sensor unit 20 gradually increases and then returns to C ₂ (0). and the waveform of the output signal S _2, the difference signal [Delta] S ₂ by subtracting the output signals S ₁ from the output signal S _2, which is a schematic diagram showing a. While C ₂ gradually increases from the initial C ₂ (0), the output signal S ₂ increases, and when C ₂ returns to C ₂ (0), the output signal S ₂ has an initial magnitude. Therefore, the difference signal ΔS ₂ gradually increases from zero and then returns to zero.

In the above description, the initial first capacitance C ₁ (0) of the first sensor unit 10 and the initial second capacitance C ₂ (0) of the second sensor unit 20 are made equal. It assumes a set state. More precisely, the output signal S ₂ from the output signal S ₁ and the second sensor unit 20 from the first sensor unit 10 to be processed by the control unit 30, the first wiring 11a as shown in FIG. 3, the second wiring This includes stray capacitance (wiring capacitance) in 12a, the third wiring 21a, and the fourth wiring 22a. In addition, shields can be provided on the first electrode 11, the second electrode 12, the third electrode 21, and the fourth electrode 22. Here, the shield can measure the electrostatic capacitance between the first electrode 11 and the second electrode 12 and is made of a conductive material such as a metal through an insulating material so as not to cause an external stray capacitance change. It's covered. Although the shield and the electrode are generated by providing the shield, the increase in capacitance is a capacitance that does not change. Therefore, an initial state including the shield capacitance and the wiring capacitance may be set. The first capacitance C ₁ includes the capacitance due to the first wiring 11 a and the second wiring 12 a to the first sensor unit 10, and the second capacitance C ₂ is the third wiring 21 a to the second sensor unit 20. In addition, the capacitance by the fourth wiring 22a is also included. However, when the difference signal is processed in the control unit 30, the increase in capacitance is canceled out, and the influence can be ignored. Therefore, the dynamic range of detection can be expanded or the resolution can be increased, and highly accurate detection can be performed.

Furthermore, the initial first capacitance C ₁ (0) of the first sensor unit 10 and the initial second capacitance C ₂ (0) of the second sensor unit 20 are affected by stray capacitance and the like. If they are not equal, the control unit 30 may add and adjust the offset capacity. For example, a variable capacitor may be disposed in the output signal processing means 36 of the control unit 30 to add an offset capacitance. An offset signal can be added by this offset capacity, and the output signal processing means 36 can also process the output signal by adding the offset signal.

When the measurement of the second sensing region, using the output signals S ₁ from the first sensor unit 10 as a first reference signal, based on the first reference signal and the offset signal, which is disposed in the second sensing region R2 No. 2 for processing an output signal _{S 2} from the sensor unit 20. Output signal processing means 36 the output signal processing unit 35, the difference between the output signal S ₂ from the second sensor part 20 and the output signals S ₁ from the first sensor unit 10 disposed in the second sensing region R2, The differential signal to which the offset signal is added is processed.

Further, when the measurement of the first sensing region, using the output signal S ₂ from the second sensor unit 20 as a second reference signal, based on the second reference signal and the offset signal, the output from the first sensor unit 10 to process the signal _{S 1.} Output signal processing means 36 the output signal processing unit 35, the difference between the output signals S ₁ from the output signal S ₂ and the first sensor portion 10 from the second sensor unit 20, a difference signal offset signal is added To process.

In this way, the control unit 30 can process the differential signal including the offset capacity. According to this configuration, the difference between the initial _first capacitance C ₁ (0) of the first sensor unit 10 and the initial second capacitance C ₂ (0) of the second sensor unit 20 is determined as the offset capacitance. Since the difference signal is detected by adjusting the signal, only a small change can be detected. Therefore, the dynamic range of detection can be expanded or the resolution can be increased, and highly accurate detection can be performed.

[Second Embodiment]
Below, the liquid detection apparatus 2 in 2nd Embodiment is demonstrated using FIGS. 7-12.

  FIG. 7 is a block diagram showing the liquid detection device 2 of the second embodiment. FIG. 8 is a schematic diagram for explaining the output of the liquid detection device 2. In addition, when it is the same structure as 1st Embodiment, the same code | symbol is attached | subjected.

As shown in FIG. 7, the liquid detection device 2 includes a first sensor unit 10 for detecting the liquid in the first sensing region R1, and a second sensor unit 20 for detecting the liquid in the second sensing region R2. And a control unit 40. The control unit 40 is connected to the first sensor unit 10 and the second sensor unit 20, and processes the output signal S ₁ from the first sensor unit 10 and the output signal S ₂ from the second sensor unit 20.

The first sensor unit 10 is disposed in a state where the first electrode 11 and the second electrode 12 are electrically insulated, and a predetermined first electrostatic capacitance is provided between the first electrode 11 and the second electrode 12. capacity _{C 1} is generated. When a liquid is present in the first sensing region R1, the dielectric constant of the liquid is different from the dielectric constant of the space when no liquid is present. Therefore, by the liquid present in the first sensing area R1, are formed first capacitance C ₁ is changed is between the first electrode 11 and the second electrode 12. The control unit 40 shown in FIG. 7, the first capacitance C ₁ is measured, it is possible to detect the liquid in the first sensing region R1.

The second sensor unit 20 is disposed in a state where the third electrode 21 and the fourth electrode 22 are electrically insulated, and a predetermined second electrostatic capacitance is provided between the third electrode 21 and the fourth electrode 22. capacity _{C 2} is generated. When a liquid is present in the second sensing region R2, the dielectric constant of the liquid is different from the dielectric constant of the space when no liquid is present. Therefore, by the liquid present in the second sensing region R2, is formed a second capacitance C ₂ is changed is between the third electrode 21 and fourth electrode 22. The control unit 40 shown in FIG. 7, a second capacitance C ₂ is measured, it is possible to detect the liquid in the second sensing region R2.

The control unit 40 is configured by an integrated circuit (IC) having a drive signal generation unit 41 and an output signal processing unit 45. The integrated circuit operates the drive signal generation unit 41, the output signal processing unit 45, and the like according to a command from a control circuit based on a program recorded in the memory. As shown in FIG. 7, the drive signal generator 41 applies the drive signal DS <b> 1 to the first electrode 11 of the first sensor unit 10 by the drive signal generator 42. In addition, the drive signal generation unit 41 applies the drive signal DS2 to the third electrode 21 of the second sensor unit 20 via the inverting means 43. For example, when the voltage waveform of the rectangular pulse is input, the inverting means 43 is a circuit that outputs a voltage waveform in which the rising and falling of the rectangular pulse are switched. The output signal processing unit 45 includes an output signal processing unit 46 and is connected to the second electrode 12 of the first sensor unit 10 and the fourth electrode 22 of the second sensor unit 20. The output signal S ₁ of the first sensor unit 10 is input from the second electrode 12 to the output signal processing means 46. Further, the output signal S ₂ of the second sensor unit 20 is input from the fourth electrode 22. Output signal processing means 46, an output signal S ₁ and the output signal S ₂ is converted into a desired output format and output.

  The liquid detection device 2 is arranged in a measurement target area having a first sensing region R1 and a second sensing region R2. As shown in FIG. 8, when the first sensing region R1 is a water tank 51 and the second sensing region R2 is a drain pipe 52 connected to the water tank 51, the first sensing region R1 is disposed on the side surface of the water tank 51 that is the first sensing region R1. The amount of water present in the water tank 51 can be detected as the water level (the height of the water surface) by the first sensor unit 10 that has been made. If the water tank 51 is an insulating material such as glass or synthetic resin, the first sensor unit 10 can be disposed on the outer wall of the water tank 51. The second sensor unit 20 is disposed in the drain pipe 52 downstream from the drain valve 53 from the water tank 51 and detects whether water is present in the second sensing region R2 (downstream from the drain valve 53). Can do. The first electrode 11 and the second electrode 12 of the first sensor unit 10 are connected to the control unit 40 by a first wiring 11a and a second wiring 12a, respectively. The 3rd electrode 21 and the 4th electrode 22 of the 2nd sensor part 20 are connected to control part 40 by the 3rd wiring 21a and the 4th wiring 22a, respectively.

The water tank 51 which is the first sensing region R1 is assumed to have a water level of zero when drainage is completed. In addition, the capacitance of the first sensor unit 10 when no liquid is present in the first sensing region R1 (the water level of the water tank 51 is zero) is the initial first capacitance C ₁ (0 of the first sensor unit 10). ). When water is started, the first sensor unit 10, the first capacitance C ₁ since the dielectric constant of water is greater than the dielectric constant of the air starts to increase.

On the other hand, when water is stored in the water tank 51 which is the first sensing region R1, the drain valve 53 is closed. At this time, there is no water on the downstream side of the drain valve 53 of the drain pipe 52 which is the second sensing region R2. For this reason, the capacitance of the second sensor unit 20 at this time is the second capacitance C ₂ (0) when no liquid is present.

When draining from the water tank 51 which is the first sensing region R1, the drain valve 53 is opened. During drainage, water is present downstream from the drain valve 53 of the drain pipe 52, which is the second sensing region R2. The electrostatic capacity of the second sensor unit 20 at this time is larger than the second electrostatic capacity C ₂ (0) when there is no liquid (initial) because the dielectric constant of water is larger than that of air. 2 is a capacitance _{C 2.} That is, C ₂ = ΔC ₂ + C ₂ (0). Here, ΔC ₂ is an increase in capacitance.

In the present embodiment, the drive signal generator 41 applies the drive signal DS <b> 2 to the third electrode 21 of the second sensor unit 20 via the inverting means 43. As a result, the drive signal generating unit 42 applies the drive signal DS1 having the normal phase to the first sensor unit 10, and the drive signal DS2 having the opposite phase is applied to the second sensor unit 20. Therefore, the output signal S ₂ also positive and negative from the second sensor unit 20 to the output signals S ₁ from the first sensor unit 10 is in an inverted. Therefore, by adding the output signals S ₁ from the first sensor unit 10 and the output signal S ₂ from the second sensor unit 20, the difference signal ΔS is obtained. Hereinafter, the differential signal processing at this time will be described.

Figure 9 is a voltage waveform of the drive signal DS1 to be applied from the driving signal generating means 42, and the voltage waveform of the drive signal DS2 via a reversing means 43, the output signals S ₁ of the waveform of this time, the output signal S ₂ a waveform, and the differential signal ΔS obtained by adding the output signals S ₁ and the output signal S _2, which is a schematic diagram showing a. Rectangular voltage waveform is applied as a drive signal DS1, DS2, if the current signal circuit output signal processing unit 46 of the output signal processing unit 45, an output signal S ₁ and the output signal S _2, the capacitance between the respective electrodes And the differential waveform depending on the input resistance viewed from the output signal processing means 46. When the input resistances are equal and C ₁ and C ₂ are initial C ₁ (0) and C ₂ (0), respectively, the difference signal ΔS is zero.

Figure 10 is a voltage waveform of the drive signals DS1, DS2, the output signals _{S 1} of a waveform when the first capacitance C1 of the first sensor unit 10 is increased gradually, the waveform of the output signal _{S 2} FIG. 6 is a schematic diagram showing a difference signal ΔS obtained by adding the output signal S ₁ and the output signal S ₂ . Since C ₁ gradually increases from the initial C ₁ (0), the output signal S ₁ increases. On the other hand, since C ₂ (0) does not change, the difference signal ΔS gradually increases from zero. Yes.

Figure 11 is a voltage waveform of the drive signals DS1, DS2, the output signals _{S 1} of a waveform when the first capacitance _{C 1} of the first sensor portion 10 is gradually reduced to _C 1 (0), the second The waveform of the output signal S ₂ when the _second capacitance C ₂ of the sensor unit 20 gradually increases and then returns to C ₂ (0) is added to the output signal S ₁ and the output signal S _2. FIG. 6 is a schematic diagram illustrating the difference signal ΔS.

The difference signal ΔS is converted into a predetermined output format and output from the output signal processing means 46. FIG. 12 is a schematic diagram when the difference signal ΔS is converted into an output value X. Start the water from time T ₁ to the water tank 51 shown in FIG. 8, to hold the full level until the time T _2. After flowing is drained into the drainage pipe 52 by opening the drain valve 53 at time T _2, and are returned to the initial state to the drain pipe 52 there is no water between the water tub 51 at time T _3. Of the initial state of the initial output value X _0, the output value X output signal S ₁ is gradually beginning to increase as shown in Figure 10 from the time T ₁ is increasing. As shown in FIG. 11, from time T ₂ , the output signal S ₁ decreases. On the other hand, when the output signal S ₂ increases once and then returns to the initial state, the output value X becomes smaller than the initial output value X _0. (if the initial output value X ₀ and zero, from a negative value) to converge to the same output as the initial output value X _0. In the present embodiment, when the output value X is larger than the initial output value X ₀ is a period for measuring the first sensing region R1, when the output value X is less than the initial output value X ₀ is measured a second sensing area R2 It corresponds to the period to do.

In the above description, the initial first capacitance C ₁ (0) of the first sensor unit 10 and the initial second capacitance C ₂ (0) of the second sensor unit 20 are made equal. It assumes a set state. More precisely, the output signal S ₂ from the output signal S ₁ and the second sensor unit 20 from the first sensor unit 10 to be processed by the controller 40, the first wiring 11a as shown in FIG. 8, the second wiring This includes stray capacitance (wiring capacitance) in 12a, the third wiring 21a, and the fourth wiring 22a. In addition, shields can be provided on the first electrode 11, the second electrode 12, the third electrode 21, and the fourth electrode 22. The shield can measure the electrostatic capacitance between the first electrode 11 and the second electrode 12, and is covered with a conductive material such as a metal via an insulating material so as not to cause an external stray capacitance change. It is. Although the capacitance between the shield and the electrode is generated by providing the shield, the increase in capacitance is a capacitance that does not change, so an initial state including the shield capacitance and wiring capacitance may be set.

Since the output signal processing means 46 detects the difference signal ΔS between the output signal S ₁ and the output signal S ₂ , even if the change amount of C ₁ is smaller than C ₁ (0). By canceling a large value C ₁ (0), only a small change can be detected. That is, even if the reference electrode of the first sensor unit 10 is not provided separately, C ₁ (0) can be canceled and only the change in C ₁ can be detected, so that the liquid detection accuracy can be improved. Can be maintained at the same level as that provided separately. Similarly, C ₂ (0) can be canceled and only the amount of change in C ₂ can be detected without providing a reference electrode for the second sensor unit 20 separately. It can be maintained at the same level as when the electrodes are provided separately.

Furthermore, the initial first capacitance C ₁ (0) of the first sensor unit 10 and the initial second capacitance C ₂ (0) of the second sensor unit 20 are affected by stray capacitance and the like. If they are not equal, the output signal processing means 46 of the control unit 40 may adjust by adding an offset capacity. For example, a variable capacitor may be disposed in the output signal processing means 46 to add an offset capacitance. An offset signal can be added by this offset capacity, and the output signal processing means 46 can also process the output signal by adding the offset signal.

In this way, the control unit 40 can process the differential signal including the offset capacity. According to this configuration, the difference between the initial _first capacitance C ₁ (0) of the first sensor unit 10 and the initial second capacitance C ₂ (0) of the second sensor unit 20 is determined as the offset capacitance. Since the difference signal is detected by adjusting the signal, only a small change can be detected. Therefore, the dynamic range of detection can be expanded or the resolution can be increased, and highly accurate detection can be performed.

In addition, when continuously monitoring the period from the state in which the water tank 51 that is the first sensing region R1 is stored until the water in the drain pipe 52 that is the second sensing region R2 flows out from the drainage, A transient period occurs in which both the _first capacitance C ₁ and the second capacitance C ₂ are changing. In such a case, the transition period may be a blanking period. Further, for example, if it is desired to check the water level during drainage, the output value X when the drain valve 53 is closed and the output value X is stabilized and stabilized is used as the water level measurement data. On the other hand, since the drainage pipe 52 dries after the output value X continues to fluctuate during drainage and the water level stabilizes at C ₁ = C ₁ (0) corresponding to zero, the second sensing region R2 is in this state. It is only necessary to measure when.

  Hereinafter, the effect by having set it as this embodiment is demonstrated.

Liquid detecting device 1 is arranged in the measurement target area having a first sensing region R1 and a second sensing region R2, when the measurement of the second sensing region, the output signals S ₁ from the first sensor part 10 first Used as one reference signal. Then, based on the first reference signal, for processing the output signal S ₂ from the second sensor unit 20 disposed in the second sensing region R2. In this case, since the first sensor unit 10 that measures the first sensing region R1 also serves as the reference electrode of the second sensor unit 20, there is no need to provide a reference electrode separately. Therefore, the detection structure can be simplified while maintaining the liquid detection accuracy to some extent.

Further, when the measurement of the first sensing region, using the output signal S ₂ from the second sensor unit 20 as a second reference signal, based on the second reference signal, the output signals S ₁ from the first sensor unit 10 To process. In this case, since the second sensor unit 20 that measures the second sensing region R2 also serves as the reference electrode of the first sensor unit 10, there is no need to provide a reference electrode separately. Therefore, the detection structure can be simplified while maintaining the liquid detection accuracy to some extent.

  In addition, when 1st sensing area | region R1 is the drain pipe 52 and 2nd sensing area | region R2 is the water tank 51, the 1st sensor part 10 detects the dry state of the drain pipe 52, and the 2nd sensor part 20 is the water tank 51. Detect the water level. Even in this case, as described above, the detection structure can be simplified while maintaining the liquid detection accuracy to some extent.

  As described above, the liquid detection devices according to the first and second embodiments of the present invention have been specifically described. However, the present invention is not limited to the above-described embodiments and does not depart from the gist. It is possible to implement with various modifications. For example, the present invention can be modified as follows, and these embodiments also belong to the technical scope of the present invention.

  (1) In 1st Embodiment or 2nd Embodiment, you may arrange | position so that the 1st sensor part 10 may contact. In this case, each of the first electrode 11 and the second electrode 12 may be covered with insulation so that the first electrode 11 and the second electrode 12 are kept electrically insulated. Similarly, the second sensor unit 20 may be disposed so as to come into contact with the liquid. In this case, each of the third electrode 21 and the fourth electrode 22 may be covered with an insulation so that the third electrode 21 and the fourth electrode 22 are maintained in an electrically insulated state. In these cases, the wiring connected to the first electrode 11, the second electrode 12, the third electrode 21, and the fourth electrode 22 is also covered with insulation as necessary. In this way, liquid detection is possible even in a measurement target area that is covered with a conductive material such as a metal container or metal pipe.

  (2) In this embodiment, the 1st electrode 11, the 2nd electrode 12, the 3rd electrode 21, and the 4th electrode 22 are not limited to flat form, A various shape is possible. For example, if the third electrode 21 and the fourth electrode are arranged in a comb-like shape, the electrode spacing is reduced and the opposing effective electrode width is increased to increase the initial capacitance, the electrode required to obtain the same capacitance value Since the area can be reduced, the second sensor unit 20 can be reduced in size. Further, the first electrode 11 and the second electrode 12 may be arranged so as to be parallel plates, and the liquid between the parallel plate electrodes may be detected.

  (3) In the present embodiment, either the first sensor unit 10 or the second sensor unit 20 may be a liquid detection device, and the other may be a combination of capacitance sensors other than liquid detection. . For example, if a capacitance sensor for confirming that the door of the dryer is closed is arranged so that the capacitance increases when the door is not closed, the drain pipe can be used when the door is closed. In the liquid detection device that detects the dry state of the liquid and the device that prevents erroneous operation when the door is open, the detection structure can be simplified while maintaining the liquid detection accuracy to some extent.

DESCRIPTION OF SYMBOLS 1, 2 Liquid detection apparatus 10 1st sensor part 11 1st electrode 11a 1st wiring 12 2nd electrode 12a 2nd wiring 20 2nd sensor part 21 3rd electrode 21a 3rd wiring 22 4th electrode 22a 4th wiring 30 40 Control unit 31, 41 Drive signal generation unit 32, 42 Drive signal generation unit 35, 45 Output signal processing unit 36, 46 Output signal processing unit 43 Inversion unit 51 Water tank 52 Drain pipe 53 Drain valve R1 First sensing region R2 Second Sensing area

Claims (6)

A first sensor unit for measuring the capacitance between the first electrode and the second electrode; a second sensor unit for measuring the capacitance between the third electrode and the fourth electrode; Connected to the first sensor unit and the second sensor unit, applies a drive signal to the first sensor unit and the second sensor unit, and outputs output signals from the first sensor unit and the second sensor unit. A liquid detection device including a control unit for processing,
The first sensor unit is disposed in a first sensing region, and measures the first sensing region;
When the second sensor unit is arranged in a second sensing region, which is a measurement target area different from the first sensing region, and the measurement of the second sensing region is performed, the control unit uses the first sensor signal as the first reference signal. An output signal from the second sensor unit is processed based on the first reference signal using an output signal from one sensor unit.   When measuring the first sensing region, the control unit uses an output signal from the second sensor unit as a second reference signal, and outputs an output signal from the first sensor unit based on the second reference signal. The liquid detection apparatus according to claim 1, wherein the liquid detection apparatus performs processing. The control unit has output signal processing means for processing an output signal, and the output signal processing means can add an offset signal;
The output signal processing means, when measuring the second sensing region, the difference signal between the output signal from the second sensor unit and the first reference signal, or the output signal from the second sensor unit and the The liquid detection apparatus according to claim 1, wherein the difference signal obtained by adding the offset signal to the difference from the first reference signal is processed.   The output signal processing means, when measuring the first sensing region, the difference signal between the output signal from the first sensor unit and the second reference signal, or the output signal from the first sensor unit and the The liquid detection apparatus according to claim 3, wherein the difference signal obtained by adding the offset signal to the difference from the second reference signal is processed.   The control unit applies a drive signal having a positive phase to the first sensor unit and a drive signal having a reverse phase to the second sensor unit, and outputs from the first sensor unit and the second sensor unit. 5. The liquid detection apparatus according to claim 1, wherein differential signal processing for adding signals is performed. The first sensing area is a water tank, the measurement of the first sensing area is a measurement for detecting a water level of the water tank, and the second sensing area is a drain pipe connected to the water tank, The liquid detection device according to claim 1, wherein the measurement in the second sensing region is a measurement for detecting a dry state of the drain pipe.