JPH0115815B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a moisture detection element that electrically senses the presence or absence of moisture by a change in impedance consisting of resistance and capacitance. Recently, in window glass for general architecture, aircraft, automobiles, etc., a heating circuit is formed on the window glass using a thin film of noble metal, a thin film of metal oxide, or a thin conductive wire, and a current is passed through this to heat the glass. It is known that there are windows that have an anti-fogging effect by increasing the temperature and evaporating moisture that has aggregated or is about to aggregate on the surface of the window glass. Generally, the above-mentioned anti-fog effect on window glass is automated, but in order to automate this, in conjunction with the heating circuit, the presence or absence of moisture on the glass surface can be sensed, and based on this, the heating circuit can be energized or shut off. A system is needed to do this. This system basically consists of a moisture detection element that senses the presence or absence of moisture on the glass surface, and a control circuit that controls energization and interruption of the heating circuit based on signals related to changes in the state of the moisture detection element. The performance of the device is highly dependent on the performance of the moisture sensing element. Conventional moisture detection elements include a moisture detection element (hereinafter referred to as A element) consisting of a pair of conductive wire electrodes placed on the glass surface facing each other with a narrow gap, and a moisture detection element (hereinafter referred to as A element) consisting of a pair of conductive wire electrodes placed on the glass surface facing each other with a narrow gap, and a moisture detection element (hereinafter referred to as A element) consisting of a pair of conductive wire electrodes placed on the glass surface facing each other with a narrow gap. There is a moisture detection element (hereinafter referred to as B element) which is made of a pair of opposing electrodes formed by the above method, and at least the space between them is coated with a compound containing a trace amount of charge carrier. The A element sends an interelectrode current that flows when moisture in the air adheres to the glass surface and a water droplet or a water layer is formed between the pair of conductive wire electrodes of the moisture detection element to the heating control circuit. The heating circuit is activated and electricity is applied to the heating resistance wire to heat the glass. By energizing the heating resistance wire, the temperature of the glass rises and a defogging effect is exerted.As a result, the water adhering to the glass surface evaporates, and the moisture present between the electrodes of the pair of conductive wires of the moisture detection element is removed. Eventually, the current flow between the electrodes of the moisture detection element is cut off, the heating circuit is cut off, and the current flow to the heating resistance wire is stopped. However, in the above A element, when moisture adheres, the inter-electrode resistance of the moisture detection element changes depending on the surface properties of the glass in the gap between the electrodes, the surrounding atmosphere, or the passage of time, and the resistance value between the electrodes and the amount of attached moisture change. It was difficult to find a correspondence between the two. For example, conductive compositions with high chemical stability, RuO ₂ , In ₂ O ₃ , SnO ₂ ,
Conductive metal oxides such as V ₂ O ₅ , or Au, Pd, Pt
Element A, which is equipped with electrodes made of conductive noble metals, etc., had the disadvantage that the resistance between the electrodes increased over time, causing the relay in the heating control circuit to become inoperable. The B element is a moisture detection element that has been improved to eliminate the drawbacks of the A element. When a certain amount of water droplets adhere between the electrodes of the moisture detection element, the B element elutes a very small amount of charge carriers that provide conductivity into the moisture and maintains an equilibrium state so that a resistance value within a certain range is obtained. _{Compounds that preserve the _ _}
The above-mentioned drawbacks are solved by applying a coating containing the above between the electrodes. However, both elements A and B have a common drawback in that the resistance between the electrodes changes depending on the temperature when moisture is attached. For example, the detected amount of element A is
Since the electrical resistance is due to the conductivity of the charge carriers of water ions H ⁺ and OH _- , the temperature dependence of the interelectrode resistance when water is attached is the equilibrium constant of ionic dissociation of water ions H ⁺ and OH ^- . Based on the interelectrode resistance when water is attached at 20℃, the amount of change is approximately 0.6 times when water is attached at 30℃, and the amount of change is approximately 0.6 times that when water is attached at 30℃. In the case of ice at -10°C, it increases by about 44 times. Similarly, the detected amount of the B element is the electrical resistance due to the conductivity of the charge carrier of the ions eluted in water, so the interelectrode resistance changes greatly depending on the temperature dependence of solubility, especially at temperatures below 0°C. Coating compounds containing trace-eluting charge carriers has no effect on freezing. Therefore, conventional moisture detection elements have the disadvantage that they do not detect icing under weather conditions of 0° C. or lower, which often occur in winter, and do not send a signal to a control circuit. As a moisture detection element that solves the above-mentioned drawbacks, the present applicant has developed a new moisture detection element (Japanese Patent Application No. 54-3730).
The present invention relates to an improvement thereof. The present invention forms a porous insulating film in which fine powder of a conductive substance is dispersed and mixed between two opposing electrodes, and changes the impedance between the electrodes when drying and when moisture is generated, thereby reducing the moisture content. To provide a moisture detection element which is configured to be able to detect the occurrence of icing, can be stably used for a long period of time with very little change in the impedance over time, and is further capable of sensing icing. An embodiment of the present invention will be described in detail below based on the accompanying drawings. The moisture detection element includes an electrode 2 having a terminal 1 at one end.
and an electrode 4 equipped with a terminal 3 are stacked together with a porous insulating film 5 interposed in which fine powder of a conductive substance is dispersed, and this three-layer structure is
It is constructed by forming it on the upper surface of a 0.4 mm alumina substrate 6. A method for forming the moisture detection element 7 will be explained. First, on the upper surface of the alumina substrate 6, a conductive paste mainly composed of powder of pyrochlore-type crystal metal oxide Bi ₂ Ru ₂ O ₇ with a diameter of 5 μ or less was printed in the pattern shape illustrated by screen printing, and the paste was heated at 850°C. at 10
It is baked for a minute to form a porous electrode 2 having dimensions of 3 mm x 12 mm and a thickness of 5 μm. On this electrode 2, 80 parts by volume of glass powder with a diameter of 5μ or less and 20 parts by volume of a metal oxide of pyrochlore type crystal are applied so as to cover at least the part facing another electrode 4 to be formed later.
A paste made of a powder mixture of Bi ₂ Ru ₂ O ₇ powder with a size of 5 μm or less is printed in the illustrated pattern shape by screen printing, and thoroughly dried at 150°C.
The above glass powder contains 30 parts by weight of SiO ₂ and 25 parts by weight.
BaO and 10 parts by weight Al ₂ O ₃ and 10 parts by weight Ti ₂ O ₃ and 10
Contains part by weight of ZnO as main component. Next, the conductive paste used to form the electrode 2 is printed into the illustrated pattern by screen printing, and the terminal portion of this potential electrode is electrically connected to the terminal portion of the electrode 4. A conductive paste containing silver as the main component was screen-printed into the illustrated pattern shape and baked at 800℃ for 10 minutes, thereby dispersing fine powder of the conductive material into the 30μ-thick insulating material. The mixed porous insulating film 5, the porous membrane electrode 4 having dimensions of 3 mm x 12 mm and thickness of 3 μm facing the electrode 2, and the terminals 1 and 3 are simultaneously formed. When the electrical characteristics of the moisture detection element 7 manufactured as described above are expressed in terms of impedance Z〓, it becomes Z〓=(1/R _w +j·2πC _s ) ⁻¹ (1). Here, R _w is the resistance component of the moisture detection element,
This is an amount given by the substantially porous insulating film 5, and the value of which can change as water enters the pores of the insulating film. C _s is the capacitance component between the electrodes 1 and 4 facing each other, and this is an amount that can change so that its value increases as moisture enters the pores of the insulation film, and the dielectric constant of water and ice is To detect. is the frequency of alternating current electricity applied to the moisture detection element. The resistance R _w , the capacitance C _s , and the impedance magnitude |Z〓| of the moisture detection element 7 are determined as shown in Table 1 by varying the measurement conditions of temperature and humidity.

[Table] 〓
(R _W ) and the absolute value of Z calculated using equation (1) from the capacitance (C _S ).
As is clear from Table 1, for example, if the impedance is higher than the standard value of 500KΩ at a temperature of 30°C and relative humidity of 95%, it is a dry state, and when it is lower than that, it is a wet state. If it is displayed as follows, the temperature is 10℃,
At 1°C, -10°C and -20°C, the relative humidity is 100
%, the impedance size is 7.8KΩ, 8.1KΩ, 180KΩ, 350KΩ at each temperature,
In particular, it is possible to reliably identify wet conditions even when freezing at temperatures below 0℃, and when the relative humidity is below 95%, 580KΩ, 650KΩ,
1200KΩ and 1200KΩ, and it can be reliably identified that it is in a dry state. Furthermore, this moisture detection element was tested by repeating dry and wet conditions 10,000 times as shown in Table 2.
In addition, when conducting a high temperature and high humidity energization test for 6 months, the change in impedance was limited to less than 5% and the decrease was less than 7%, respectively, and it was shown that the above dry and wet wires could withstand practical use. In the repeated test, a glass equipped with a resistance heating wire and a moisture detection element is inserted into the opening of a refrigerator with the surface on which the moisture detection element is attached facing outward, and the glass is cooled to cause moisture to condense. By activating the relay in this state, current was passed through the resistance heating wire to heat the glass and dry the moisture detection element, and these operations were automatically repeated. In addition, the high temperature and high humidity energization test was conducted at a temperature of 40℃ and a humidity of 95℃.
The test was carried out by applying AC3V to the moisture detection element in an atmosphere of ~100%. Furthermore, the test results show that the temperature is 30
This is the result of comparing the magnitude of impedance measured in an atmosphere of ℃ and 95% humidity with the initial value.

[Table] In the above embodiment, an alumina substrate was used as an insulating substrate, but a glass plate, a crystallized glass plate, a ceramic substrate, etc. can also be used as an insulating substrate. Further, the electrodes 2 and 4 are made of a conductive electrochemically stable substance such as metal oxide such as RuO ₂ , V ₂ O ₅ , Ti ₂ O ₃ or noble metal powder such as Au, Pd, Pt, etc., and glass frit. It can also be formed from a conductive paste made by sufficiently kneading a vehicle, a binder, and various other additives. The conductive substances contained in the porous insulating film 5 include RuO ₂ , V 2 O 5 , and V ₂ O ₅ instead of the metal oxide Bi ₂ Ru ₂ O ₇ .
It may be a metal oxide such as Ti ₂ O ₃ , a fine powder of a noble metal such as Au, Pd, Pt, etc., or a mixture of these fine powders, and the volume mixing ratio may be in the range of 5% to 40%. It is preferable to As is clear from the above description, according to the present invention,
The change in dielectric constant due to moisture impregnating the porous insulating film and the adhesion of a very small amount of moisture between the fine powders of the conductive material create a switch that creates electrical continuity between the fine powders of the conductive material. Since it utilizes the change in electrical resistance that acts like this, there is little change over time, there is little detection error due to the operating temperature, and it is possible to detect moisture even when the moisture freezes. Furthermore, since the moisture detection element according to the present invention is laminated on a substrate and has a pair of opposing electrodes with an insulating layer between them, the electrode Since the facing area of the insulating film can be increased and the distance between the electrodes can be reduced, a change in the capacitance of the insulating film can be detected as a large change, and a change in the electrical resistance can be detected as a large change. Furthermore, since the moisture detection element according to the present invention has an insulating film whose capacitance changes and resistance is covered with an electrode, the insulating film is less likely to be contaminated by dust, oil, etc., and electrical It exhibits various effects such as almost no change in characteristics.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a plan view of a moisture detection element, and FIG. 2 is a sectional view taken along the line 2--2 in FIG. In the drawings, 1 and 3 are terminals, 2 is an electrode, 4 is a porous electrode, 5 is an insulating film, and 6 is an alumina substrate.

Claims (1)

[Claims] 1. In a moisture detection element comprising an insulating substrate, an electrode formed on the insulating substrate, a porous insulating film formed on the electrode, and a porous membrane electrode formed on the insulating film, the insulating In the insulating material of the membrane
Contains at least one fine powder from the group consisting of conductive metal oxides such as Bi ₂ Ru ₂ O ₇ , RuO ₂ , V ₂ O ₅ , Ti ₂ O ₃ and noble metals such as Au, Pd, and Pt. Characteristic moisture detection element.