JPH0523124U - Capacitance type humidity sensor - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if the dielectric material interposed between the two electrodes of the capacitance type humidity sensor expands and contracts due to adsorption and desorption of moisture, the electrode expands and contracts with the dielectric material and deteriorates. It is an object of the present invention to provide a capacitance-type humidity sensor capable of accurately and reliably detecting humidity on the basis of a change in capacitance of the dielectric substance. [Structure] A dielectric 3 made of a polymer substance whose permittivity changes in response to a change in humidity is interposed between two electrodes 2A and 2B, and the humidity changes due to a change in capacitance generated between the electrodes 2A and 2B. In the electrostatic capacitance type humidity sensor for detecting, the two electrodes 2A and 2B extending parallel to each other along the front surface 1a of the insulating substrate 1 are fixed to the surface 1a of the insulating substrate 1 and the electrodes 2A and 2B are also fixed to each other. The dielectric 3
Has been established.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention interposes a dielectric substance made of a polymer substance whose permittivity changes in response to a change in humidity between two electrodes, and detects the humidity by the change in the capacitance generated between the electrodes. Type humidity sensor.

[0002]

[Prior art]

 As shown in FIG. 4, the capacitance-type humidity sensor has a structure in which a lower thin-film electrode 42 is formed by vapor-depositing gold or the like on an insulating substrate 41 made of glass or the like, and then the dielectric constant changes in response to a change in humidity. By coating the moisture-sensitive resin film 43 made of a polymer substance, and further vapor-depositing the moisture-permeable upper thin-film electrode 44 on the resin coating 43 to form the resin film 43 as the lower thin-film electrode 42. It has a three-layer structure sandwiched by the upper thin film electrode 44.

Then, the water contained in the air permeates the upper thin film electrode 44 and is adsorbed to the resin film 43, or the water in the resin film 43 permeates the upper thin film electrode 44 and is desorbed. Since the dielectric constant of the resin film 43 changes and the capacitance between the lower thin film electrode 42 and the upper thin film electrode 44 changes accordingly, it is necessary to measure the relationship between humidity and capacitance in advance. For example, the humidity can be detected from the capacitance.

[0004]

[Problems to be solved by the device]

 However, since the upper thin film electrode 44 has to be formed extremely thin in order to have moisture permeability, the resin film 43 is deteriorated and torn during repeated expansion and contraction due to adsorption and desorption of water, which causes a failure. There was a problem that it was easy to wake up and lacked in durability. If the upper thin-film electrode 44 is formed thicker to improve durability, its moisture permeability will decrease and the response will be impaired. At the same time, it is a fatal drawback for the humidity sensor that humidity cannot be detected accurately. Cause

Therefore, according to the present invention, even if the dielectric material interposed between the two electrodes expands and contracts due to the adsorption and desorption of water, the electrodes are not affected by the influence, and the capacitance The challenge is to be able to detect humidity accurately and reliably in a short time based on changes in the temperature.

[0006]

[Means for Solving the Problems]

 In order to solve this problem, the present invention interposes a dielectric material, which is a polymer substance whose dielectric constant changes in response to changes in humidity, between two electrodes and reduces the capacitance generated between the electrodes. In a capacitance type humidity sensor that detects humidity by changes, two electrodes extending parallel to each other along the surface of the insulating substrate are fixed to the surface of the insulating substrate, and the intervening electrode It is characterized in that the dielectric is fixed.

[0007]

[Action]

 According to the present invention, the two electrodes for measuring the capacitance of the dielectric are fixed to the surface of the insulating substrate so as to extend parallel to each other along the surface. Even if the interveningly fixed dielectric expands and contracts due to the adsorption and desorption of moisture, the electrode itself will hardly expand and contract with the dielectric and be adversely affected. Moreover, since the dielectric is open to the atmosphere without providing an electrode or the like in a portion in contact with the atmosphere, water is actively absorbed and evaporated. Then, the capacitance is measured through the electrode, and the humidity is accurately detected based on the capacitance.

[0008]

【Example】

 Hereinafter, a specific description will be given based on an embodiment shown in the drawings. FIG. 1 is a perspective view showing a capacitance type humidity sensor according to the present invention. In the figure, reference numeral 1 denotes a supporting substrate (insulating substrate) made of an insulating material such as glass. Two electrodes 2A and 2B extending parallel to each other along the surface 1a are fixed to the surface 1a of the supporting substrate 1, respectively. At the same time, the electric conductor 3 interposed between the electrodes 2A and 2B is fixed, and the lead wires 5A and 5B are connected to the lands 4A and 4B of the electrodes 2A and 2B.

The electrodes 2A and 2B are made of, for example, a metal such as gold, rhodium, or chrome, and are formed in a comb shape by vapor deposition on the surface 1a of the supporting substrate 1, and are separated from each other by a gap having a predetermined width. The comb teeth are fixed in a meshed state in a distorted state, and lands 4A and 4B formed by vapor deposition of silver-palladium or the like are formed at the ends of the electrodes 2A and 2B. In this case, the capacitance determined by the gap width of each of the electrodes 2A and 2B, the total area of the facing surfaces, and the dielectric constant of the dielectric 3 at a relative humidity of 0% RH is the smallest electrostatic capacitance that can be detected electrically. The gap width and the total area are selected so as to be larger than the capacity.

The dielectric 3 has a dielectric constant that changes in response to a change in humidity, such as a cellulose-based polymer such as CAB (cellulose acetate butyrate) or CA (cellulose acetate) or a polyimide-based polymer. And is fixed on the surface 1a of the support substrate 1 so as to be interposed between the gaps formed between the electrodes 2A and 2B.

The support substrate 1 on which the electrodes 2A and 2B are formed is immersed in a solution of a polymer serving as the dielectric 3 so that the electrodes are not only interposed between the electrodes 2A and 2B but also the electrodes 2A and 2B. As shown in the sectional view of FIG. 2, except for the lands 4A and 4B, if the polymer is formed so as to cover the entire outer peripheral surface of the supporting substrate 1, a protective film for protecting the electrodes 2A and 2B is formed. Become.

The above is an example configuration of the present invention, and the following operation will be described. First, when the capacitance-type humidity sensor thus formed is placed in a predetermined humidity atmosphere, the surface of the dielectric 3 between the electrodes 2A and 2B that is in contact with the atmosphere is open. The active absorption of water and evaporation of the water causes the dielectric constant ε of the dielectric 3 to change in proportion to humidity. At this time, the gap width d between the electrodes 2A and 2B and the total facing area S are constant, and the capacitance C changes in proportion to the dielectric constant ε from C = ε (S / d). When the rate ε changes in proportion to humidity, the electrostatic capacity also changes in proportion to humidity as shown in FIG.

Therefore, if the relationship between humidity and electrostatic capacity is measured in advance and stored in a one-chip microcomputer or the like, the humidity can be detected from the measured electrostatic capacity. As means for measuring capacitance, use a bridge circuit, detect changes in the oscillation frequency that changes with capacitance, use an LCR meter for capacitance measurement, or apply any other means. You can

In this case, since the surface of the dielectric 3 is open to the atmosphere, moisture is actively adsorbed and desorbed without being disturbed by the electrodes 2A and 2B, and humidity can be detected accurately in a short time. In addition, it is not necessary to form the electrodes 2A and 2B to be extremely thin or to perform processing for imparting moisture permeability. Further, since the dielectric 3 is interposed between the electrodes 2A and 2B and fixed on the surface 1a of the support substrate 1, the change in the capacitance of the dielectric 3 is surely performed via the electrodes 2A and 2B. To be measured.

Moreover, the capacitance determined by the width of the gap between the electrodes 2A and 2B, the total area of the surfaces facing each other, and the dielectric constant of the dielectric 3 at the relative humidity of 0% RH is the smallest static capacitance that can be detected electrically. Since the capacitance is selected to be larger than the capacitance, the capacitance is not too small to interfere with the measurement. Furthermore, even if the dielectric 3 expands or contracts due to adsorption / desorption of water, the electrodes 2A and 2B are not fixed on the dielectric 3 but are fixed on the surface of the support substrate 1. Therefore, the electrodes 2A and 2B themselves are not adversely affected by expansion and contraction with the dielectric 3 and deteriorate, and the durability is excellent. Further, if the protective film is formed so as to cover the electrodes 2A and 2B with the dielectric 3, it is possible to prevent the surface of the electrodes 2A and 2B from being scratched when the humidity sensor is attached to the measuring device. it can.

[0016]

[Effect of the device]

 As described above, according to the capacitance type humidity sensor of the present invention, two electrodes extending parallel to each other along the surface of the insulating substrate are fixed to the surface of the insulating substrate, and between the electrodes. Since the dielectric is fixed and fixed, the surface of the dielectric is exposed to the atmosphere, and water is actively adsorbed and desorbed without being disturbed by the electrode, so the electrode is made extremely thin. It has an excellent effect that humidity can be detected accurately in a short time without lowering the mechanical strength by forming or imparting moisture permeability. Also, even if the dielectric expands or contracts due to the absorption or evaporation of water, the electrode is not fixed on the dielectric but on the surface of the insulating substrate, so the electrode itself It has the effect of being excellent in durability without being adversely affected by expansion and contraction with the body and deterioration.

[Brief description of drawings]

FIG. 1 is a perspective view showing a capacitance type humidity sensor according to the present invention.

FIG. 2 is a sectional view showing another embodiment.

FIG. 3 is a graph showing the relationship between humidity and capacitance.

FIG. 4 is a perspective view showing a conventional capacitance type humidity sensor.

[Explanation of symbols]

 1 ... Support substrate (insulating substrate) 1a ... Substrate surface 2A, 2B ... Electrode 3 ... Dielectric 4A, 4B ... Land 5A, 5B ···Lead

Claims (1)

[Scope of utility model registration request] 1. A dielectric (3) made of a polymer substance whose dielectric constant changes in response to a change in humidity is provided with two electrodes (2A, 2A).
In a capacitance type humidity sensor which is interposed between B) and detects humidity by a change in the capacitance generated between the electrodes (2A, 2B), with respect to the surface (1a) of the insulating substrate (1),
Two electrodes (2A, 2B) extending parallel to each other along the surface (1a) are fixed, respectively, and the dielectric (3) interposed between the electrodes (2A, 2B) is fixed. A capacitance type humidity sensor characterized in that