JP2003043155A - Moisture sensor and moisture detecting device using this sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To overcome a problem of being unable to detect liquid having a low specific dielectric constant. SOLUTION: In this moisture sensor, an insulating covering is arranged on the outer periphery of a conductor, a conductive shielding layer is arranged outside of it, a large number of through holes are formed for forming an air layer by taking air in the conductive shielding layer, and when moisture sticks to the conductive shielding layer, the specific dielectric constant of the air layer of the conductive shielding layer changes, and stray capacitance between the conductor and the conductive shielding layer changes so that moisture is detected from a change in the stray capacitance. This moisture detecting device has the moisture sensor and an oscillator for converting a change in the stray capacitance of the moisture sensor into a change in a frequency, and is constituted so that the conductor of the moisture sensor is connected to the oscillator, the conductive shielding layer of the moisture sensor is grounded, and a capacitor is arranged between the conductor of the moisture sensor and the oscillator.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to water leakage, overflow, oil leakage,
The present invention relates to a moisture sensor capable of detecting the presence or absence of liquid (moisture) such as rain and snow, and a moisture detecting device capable of determining the presence or absence of liquid, the amount of liquid, the type of liquid, etc. using the moisture sensor.

[0002]

2. Description of the Related Art There are various types of moisture sensors for detecting liquids such as water and oil, and moisture detecting devices capable of determining the presence / absence of liquid, the amount of liquid, the type of liquid, and the like. Moisture detectors are used to detect water leaks around water in condominiums, to detect rain leaks from the outside, and to detect the amount of rain for controlling the drive of wipers in automobiles.

As shown in FIG. 6, when _two flat electrodes T ₁ and T ₂ having an area S are arranged in parallel at a distance d, when the battery E is connected to the _two electrodes T ₁ and T _2. , And the positive and negative charges are equally distributed to both electrodes T ₁ and T ₂ . In this case, the electrostatic capacitance (stray capacitance) C _X of the parallel electrodes T ₁ and T ₂ is given by the following equation (1). Therefore, the stray capacitance of the parallel electrodes T ₁ and T ₂ is large when the distance d is small and the area is large.
It is also understood from the following equation (1) that the stray capacitance changes based on the difference in relative permittivity (ε _r ) of the object to be detected. C _X = ε _r ε ₀ S / d (1) where d: parallel plate spacing S: parallel plate area ε _r : relative permittivity of dielectric ε ₀ : permittivity of vacuum (natural constant )

Moisture can be detected by detecting the change in the stray capacitance of the equation (1). The present inventor has previously developed a moisture sensor utilizing this principle. The main ones are shown in FIGS. 7 and 8. In FIG. 7, two copper foils B are provided separately on a base material A having a sheet shape or a plate shape. In FIG. 8, two copper foils B are provided separately on a base material A having a sheet shape or a plate shape, and a cover lay J covers the copper foils B. In this case, the end portions of the base material A and the copper foil B are not covered with the cover lay J and are exposed to serve as the connection portion D. In both of the moisture sensors of FIGS. 7 and 8, when liquid adheres between the copper foils B, the relative permittivity between the copper foils B changes from the relative permittivity of air to the relative permittivity of the adhered liquid. Both copper foils B caused by
The liquid is detected by detecting the change in the floating capacitance between them.

As one of the conventional moisture detecting devices, there is one shown in FIG. This applies a test signal from the oscillator G to the sensor unit K, and changes the voltage between the sensor units K with the voltmeter V.
The water content is measured based on the measured amount and the amount of change is detected.

[0006]

Since the moisture sensor shown in FIGS. 7 and 8 has a relative permittivity ε _r of the base material A and the coverlay J of about 4, the liquid having a relative permittivity lower than that is not detected. It was possible. In order to increase the sensitivity of the moisture sensor, two conductors H are arranged in parallel as shown in FIG. 9, and when liquid enters or permeates between the conductors H, the relative permittivity between the conductors H becomes It is conceivable to detect the liquid from the change in the relative dielectric constant of the liquid to the relative dielectric constant of the liquid and the change in the stray capacitance between the conductors H that changes based on the change. But in this case, 2
It is necessary to keep the distance d between the conductors H of a sheet to be several tens to several hundreds of microns, and it is actually impossible to keep the distance. Further, in such a narrow space, the liquid does not easily infiltrate or permeate, which is not practical.

The moisture detection device of FIG. 5 requires a large dynamic range in the measurement range depending on the sensor section K, and therefore there is a limit to the measurement in some cases. In addition, the number of parts becomes large, and it requires skill to adjust them, and it is difficult to maintain the performance.

[0008]

As shown in FIG. 1, the moisture sensor of the present invention is provided with an insulating coating 2 on the outer side of a conductor 1, a conductive shield layer 4 on the outer side thereof, and an air barrier on the conductive shield layer 4. When a large number of through holes 3 forming a layer are formed and moisture adheres to the conductive shield layer 4, the relative dielectric constant of the air layer of the conductive shield layer 4 changes, and the conductor 1 and the conductive shield layer 4 are The floating capacitance between the two changes, and moisture is detected from the change in the floating capacitance. The conductor 1 has a linear shape, a sheet shape, or a film shape.

The moisture detecting device of the present invention comprises the moisture sensor 5 and an oscillator 6 for converting a change in stray capacitance of the moisture sensor 5 into a change in frequency. The conductor 1 of the moisture sensor 5 is connected to the oscillator 6. The conductive shield layer 4 of the moisture sensor 5 is grounded, and the capacitor C ₁ is provided between the conductor 1 of the moisture sensor 5 and the oscillator 6. A CMOS timer is used for the oscillator 6.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment of Moisture Sensor) An example of a first embodiment of the moisture sensor of the present invention will be described with reference to FIG. In this moisture sensor 5, the insulating coating 2 is provided on the outer periphery of the linear conductor 1, and the conductive shield layer 4 is provided outside the insulating coating 2. A large number of through holes 3 are provided in the conductive shield layer 4,
Air is taken into the through holes 3 to form an air layer. In this moisture sensor 5, when moisture adheres to the conductive shield layer 4 and enters the through hole 3, the relative dielectric constant of the air layer in the through hole 3 changes. Along with this change, the stray capacitance between the conductor 1 and the conductive shield layer 4 changes, and moisture can be detected from the change in the stray capacitance.

A copper wire can be used for the conductor 1.
The conductor 1 is preferably thick enough to obtain a certain surface area, for example, having a diameter of about 1.0 mm.

The insulating coating 2 is for insulating the conductor 1 and the conductive shield layer 4 from each other. The insulating coating 2 includes, for example,
Polyamideimide, Teflon (registered trademark), and similar insulating materials can be used. In order to increase the detection sensitivity, it is preferable to make the insulating coating 2 thin so that the distance between the conductor 1 and the conductive shielding layer 4 becomes as small as possible. The thickness of the insulating coating 2 can be, for example, tens to hundreds of microns.

For the conductive shield layer 4, a conductor having a large number of fine through holes 3 is used. Examples of the conductor having a large number of minute through holes 3 formed therein include a metal wire braided to form a stitch, and the stitch is formed as the through hole 3, or a thin conductor having a large number of fine through holes 3 formed therein. It is possible to use a metal sheet or film, or a sheet or film made of foam metal, porous metal, porous sintered metal, or the like. Moreover, it is also possible to use other materials. By providing the through hole 3 in the conductive shield layer 4, air is taken into the through hole 3 to form an air layer. Since the relative permittivity of air is ε _r = 1, the relative permittivity between the conductor 1 and the conductive shield layer 4 becomes closer to ε _r = 1.

(Second Embodiment of Moisture Sensor) An example of a second embodiment of the moisture sensor of the present invention will be described with reference to FIG. In this moisture sensor 5, a conductor 1 is provided on a base material 10, an insulating coating 2 is provided thereon, and a conductive shielding layer 4 is provided on the insulating coating 2. The base material 10 is made of an insulating material and is in the form of a flexible thin plate or sheet, and the conductor 1 is in the form of a sheet or film having a width narrower than that of the base material 10. The insulating coating 2 is made of the same insulating material as that of the first embodiment, and is applied thinly on the conductor 1 or by another method. The conductive shield layer 4 also has a large number of minute through holes 3 similar to that of the first embodiment, and air is taken into the through holes 3 to form an air layer. . This moisture sensor 5 has a structure in which the conductor 1 is provided with neither the insulating coating 2 nor the conductive shield layer 4 at the longitudinal end portion thereof.
Is left exposed to serve as the connection portion 11. In the case of this moisture sensor 5 as well, when moisture adheres to the conductive shield layer 4 and enters the through holes 3, the relative permittivity of the air layer in the through holes 3 changes, and with this change, the conductor 1 and the conductive layer 1 are electrically conductive. The stray capacitance between the moisture shielding layer 4 changes, and moisture can be detected from the change in the stray capacitance.

(Embodiment of Moisture Detector) An example of an embodiment of the moisture detector of the present invention will be described with reference to FIGS. 3 and 4. This moisture detecting device uses the moisture sensor 5 shown in FIGS. 1 and 2. As shown in FIG. 3, one end (conductive shield layer 4) of the moisture sensor 5 is grounded and the other end (conductor 1) is an oscillator. 6 is connected to the capacitor C ₁ which is connected to the + pole, and the change in the stray capacitance C _X of the moisture sensor 5 is sent to the oscillator 6, and the oscillator 6 oscillates signals of different frequencies based on the stray capacitance C _X , The signal is output from the output terminal of the oscillator 6.

A CMOS (Complementary Mean) is used for the oscillator 6.
tal Oxide Semiconductor) timer is suitable. Among CMOS, especially LMC555, TLC555
Etc. are suitable. The CMOS timer repeats charging and discharging, and in that cycle, the potential of the capacitor C is discharged to 1/3 Vdd and charged to 2/3 Vdd. The CMOS timer has the following features. Low power consumption. Large noise margin and resistant to noise. Wide operating power supply voltage range. High input impedance and capacitive. High integration is possible. The present invention utilizes the high input impedance among these features. The oscillation frequency F of the oscillator 6 of FIG. 3 using the CMOS timer is determined by the following equation. F = (ln2) / R ₁ · C ··· (2) where C = (C ₁ · C _X ) / (C ₁ + C _X ) R ₁ is the resistance in FIG.

The oscillator (CMOS) 6 has a DC power source E.
DC voltage is supplied from. DC power supply E is maximum 15
V is suitable. The CMOS timer repeats charging and discharging. In that cycle, the potential of the capacitor C is 1/3 Vdd
Discharge to 2 / 3Vdd and charge to 2 / 3Vdd.

The capacitor C ₁ connected between the moisture sensor 5 and the oscillator 6 blocks a direct current component and regulates the maximum applied voltage to the moisture sensor 5 (2/3 of the power supply voltage).
It is for. Without the capacitor C _{1, according} to the formula (2), the output becomes 0V when the input terminal is short-circuited, and it is impossible to distinguish whether the power supply is cut off or the input terminal is short-circuited (signal system disconnection). In the present invention, since the capacitor C ₁ is provided, the specified output signal can be obtained even if the input terminal is short-circuited. The capacitance of the capacitor C ₁ is the moisture sensor 5
About 10 to several 100 times the stray capacitance C _X (C ₁ > C _X ),
For example, about 1000 PF is suitable.

The electrically conductive shielding layer 4 (FIGS. 1 and 2) of the moisture sensor 5 shown in FIG. 3 is normally exposed in the air so that air can be taken into the through holes 3 and rain. Or
If there is water leakage, they will penetrate into the through hole 3. In this case, since the relative permittivity of moisture is different from the relative permittivity of air in the through holes 3, the stray capacitance C of the moisture sensor is
x changes, and the frequency oscillated from the oscillator 5 also changes. At this time, the frequency F _X (H _z ) oscillated from the oscillator 6
And the frequency F _air (H _z ) oscillated from the oscillator 6 before the infiltration of water is as follows. F _air > F _X or F _air >> F _X Therefore, it is possible to easily detect moisture by comparing both frequencies.

The moisture sensor in the moisture detecting device of the present invention is normally arranged horizontally to detect moisture, but if it is vertically arranged, the amount of moisture (depth of moisture) can also be detected.

[0021]

Since the moisture sensor of the present invention is provided with a large number of through holes in the conductive shield layer, air (ε _r = 1) is taken into the through holes to form an air layer, and the conductor and the conductive layer are electrically conductive. The relative permittivity with respect to the shield layer becomes closer to 1. Therefore, even if the liquid that comes into contact with or infiltrates the conductive shield layer is a liquid with a low dielectric constant such as gasoline or kerosene, the relative dielectric constant between the conductor and the conductive shield layer is The change can be surely made, and the stray capacitance between the conductor and the conductive shielding layer can be surely changed with the change, and the water can be surely detected from the change. Therefore, almost all liquids having a high relative permittivity to a low relative permittivity can be detected.

The relative dielectric constants of various liquids are as follows. Ethyl ether: ε _r = 4.3 Toluene: ε _r = 2.3 to 2.4 Gasoline: ε _r = 2.0 to 2.2 Kerosene: ε _r = 1.8

Since the moisture sensor of the present invention uses the moisture sensor, it has the same effect as the moisture sensor.
Further, since the oscillator for converting the change of the stray capacitance of the moisture sensor into the change of the frequency is provided and the capacitor is inserted between the moisture sensor and the oscillator, the following effects can be obtained. 1. The conventional moisture detector requires an oscillator system for measurement and a measurement (sensing) system. However, the moisture detector of the present invention has an oscillator system that also serves as a measurement system, and therefore the circuit configuration is simple. Become. 2. Since the change in capacitance due to the difference in relative permittivity is used, even if the moisture sensor is coated with a resin film or resin to protect the moisture sensor, the detection sensitivity is not affected and is the same as when it is not coated. The moisture can be detected with the sensitivity of. 3. The detection accuracy is high because it is hardly affected by the external environment such as temperature and humidity. 4. Since the electrostatic capacitance C _X of the moisture sensor changes by changing S (contact area of the moisture sensor) and d (interval between electrodes) in Expression (1), the detection sensitivity can be easily adjusted. 5. Since the CMOS timer is used for the oscillator, there are the following effects. 6. From the change in the oscillation frequency oscillated by the CMOS timer, the moisture detection by the moisture sensor can be confirmed. 7. Since the oscillation frequency from the CMOS timer has the following relationship, it is possible to detect the abnormality of the power supply, the disconnection of the sensor system, and the liquid (water leakage, liquid leakage) only by grasping the frequency oscillated from the CMOS timer. F _open ＞ F _set ＞ F _leakage ＞ F _short F _open ： Frequency value (H _z ) of the output signal when the input terminal is open F _set ： The output signal when the moisture sensor is set to the input terminal (in air atmosphere) frequency value (H _z) F _leakage: the frequency value of the output signal during fluid contact with the moisture sensor (H _z) F _short: the frequency value of the input terminal and the output signal during a short circuit (H
_z )

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an example of a moisture sensor of the present invention.

FIG. 2A is a perspective view of an end portion of an example of the moisture sensor of the present invention, and FIG. 2B is a front end view of the moisture sensor.

FIG. 3 is an explanatory diagram of an example of a moisture detector of the present invention.

FIG. 4 is a schematic diagram of an example of a moisture detector of the present invention.

FIG. 5 is an explanatory diagram of a conventional moisture detection device.

FIG. 6 is an explanatory diagram of stray capacitance between parallel plates.

FIG. 7A is a plan view of an example of a moisture sensor previously developed by the present inventor, and FIG. 7B is a front end view of the moisture sensor.

FIG. 8A is a plan view of another example of the moisture sensor previously developed by the present inventor, and FIG. 8B is a front end view of the moisture sensor.

FIG. 9 is an explanatory diagram of another example of the moisture sensor.

[Explanation of symbols]

1 Conductor 2 Insulation Coating 3 Through Hole 4 Conductive Shielding Layer 5 Moisture Sensor 6 Oscillator 10 Substrate 11 Connection C ₁ Capacitor C _X Connected to Oscillator Stray Capacitance of Moisture Sensor

Claims (4)

[Claims] 1. A large number of through holes which form an insulating layer (2) on the outside of the conductor (1) and a conductive shield layer (4) on the outside thereof, and form an air layer in the conductive shield layer (4). There is (3),
When moisture adheres to the conductive shield layer (4), the relative permittivity of the air layer of the conductive shield layer (4) changes, and the stray capacitance between the conductor (1) and the conductive shield layer (4) is reduced. A moisture sensor that changes and detects moisture from the change in the stray capacitance. 2. The moisture sensor according to claim 1, wherein the conductor (1) has a linear shape, a sheet shape, or a film shape. 3. A large number of through holes for forming an insulating layer (2) on the outside of the conductor (1) and a conductive shielding layer (4) on the outside thereof, and forming an air layer in the conductive shielding layer (4). There is (3),
When moisture adheres to the conductive shield layer (4), the relative permittivity of the air layer of the conductive shield layer (4) changes, and the stray capacitance between the conductor (1) and the conductive shield layer (4) is reduced. The moisture sensor (5) is provided with a moisture sensor (5) that changes and detects moisture from the change in the floating capacitance, and an oscillator (6) that converts the change in the floating capacitance of the moisture sensor (5) into a change in frequency. Is connected to the oscillator (6), the conductive shield layer (4) of the moisture sensor (5) is grounded, and between the conductor (1) of the moisture sensor (5) and the oscillator (6). A moisture detector characterized in that a condenser (C ₁ ) is provided. 4. A moisture detector according to claim 3, wherein the oscillator (6) is a CMOS timer.