JPH076937B2 - Capacitance type humidity sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a capacitance type humidity sensor that detects a change in relative humidity of air flowing between opposed electrodes as a change in inter-electrode capacitance.

(Prior Art) A humidity sensor is a ceramic humidity sensor whose humidity sensitive part is made of a ceramic material and detects relative humidity by a change in electric resistance or capacitance. Polymer type humidity sensors that detect relative humidity based on changes are roughly classified into two types. However, each of the humidity sensors has a structure in which a pair of electrodes are continuously connected by a moisture-sensitive material that serves as a moisture-sensitive portion of each.

However, each of the humidity sensors configured as described above cannot continuously apply a DC voltage because of ionic conductivity. In addition, the applied voltage when detecting humidity is usually several V or less. Above this, Joule heat is generated and the temperature of the humidity sensitive part rises, so the moisture adsorbed on the humidity sensitive part of the humidity sensor diverges and the actual humidity A resistance value larger than the resistance to is detected, and accurate humidity measurement cannot be performed. At the same time, it suffers from various drawbacks such as thermal destruction when a large overvoltage is applied, and at the same time, polymer type humidity sensors are exposed to high temperature and high humidity environments for applications such as bathroom ventilation or wood drying. It was not suitable for industrial use because the polymer material used as the moisture sensitive part deteriorates and it is vulnerable to high temperatures of 85 ° C or higher, for example.

(Problems to be Solved by the Invention) As described above, the ceramic humidity sensor and the polymer type humidity sensor are deteriorated when a DC voltage is continuously applied, and the applicable voltage is several V or less. I had to be very careful in doing this.

According to the present invention, the capacitance between two electrodes forming a humidity sensor due to the presence of a gap between the electrodes is C, the distance between the electrodes is d, the area of the counter electrode is S, and the permittivity of air is ε. And the well-known relational expression In C., the fact that C becomes larger as ε becomes larger and d becomes smaller, the applied voltage range is wide, and even if a DC voltage is mistakenly applied for a long period of time, no deterioration occurs. It is an object of the present invention to provide a capacitance type humidity sensor having a different structure.

[Structure of the Invention] (Means for Solving Problems) In the capacitance type humidity sensor of the present invention, a porous ceramic body is attached to at least one surface, and the surface of the body is used as a facing portion. It is characterized in that it is constituted by a pair of electrode plates which are integrated with each other through an insulating support in a state where a gap is provided between the gap and the outside air.

(Function) According to the capacitance type humidity sensor configured as described above, there is a gap between the electrodes for ventilating the outside air, and the porous ceramic element body fixed to the electrode is arranged in the gap. When the humidity is high, many water molecules are present between the electrodes, which increases the capacitance between the electrodes. That is, as the amount of water molecules increases, the dielectric constant increases,
In addition, since the electric resistance of the ceramic body is small, the same effect is obtained as the distance between the electrodes is substantially reduced, and the electrostatic capacitance C in the above relational expression is increased. Therefore, the capacity changes greatly with changes in humidity. Further, since the gaps between the electrodes are insulated from each other, it is possible to apply an overvoltage and a DC voltage.

(Examples) Details of the present invention will be described below with reference to the drawings. That is, as shown in FIG. 2, preferably considering rust resistance,
For example, gold, platinum, silver, nickel metal plate or gold, platinum,
Electrode plate 1 made of metal plate plated with silver, nickel, etc.
For example, a porous shellac element body 2 obtained by press-molding and high-temperature sintering a metal oxide powder containing zinc oxide, chromium oxide as a main component and lithium carbonate or vanadium oxide as an additive added to one surface of The porous ceramic element body 2 is adhered to the electrode plate 1 by adhesion through a conductive paste and baking, and then the ceramic element body 2 is adhered to the surface of the electrode plate 1 at four places around the electrode plate 1 as shown in FIG. , An insulating support 3 made of an insulating material such as ceramic or synthetic resin and having a thickness t ₂ larger than the thickness t _{1 of the} ceramic body 2 whose surface is coated with, for example, a water-repellent silicone material.
Are bonded via, for example, a water repellent silicone adhesive. Then, as shown in FIG. 1, an electrode plate 4 having the same structure as that of the electrode plate 1 is placed on the other end surface of the insulating support 3 and bonded and integrated with a water-repellent silicone adhesive as described above. The element body 2 is connected to the electrode plate 1 and the electrode plate 4
It is arranged with a void portion 5 provided therebetween, and the void portion 5 is configured to ventilate with the outside air. Reference numeral 6 in FIG. 1 denotes a lead terminal attached to the outside of the electrode plate 1 and the electrode plate 4.

According to the capacitance type humidity sensor configured as described above, the void portion 5 ventilated with the outside air exists between the electrode plate 1 and the electrode plate 4, and the porous ceramic body 2 is arranged. When the humidity is high due to the structure, the amount of water molecules existing in the voids 5 increases, the dielectric constant between the electrode plates 1 and 4 increases, and more water molecules are added to the porous ceramic body 1. As a result of the adsorption of the, the electrical resistance decreases, that is, the distance between the electrode plate 1 and the electrode plate 4 decreases substantially, and the electrostatic capacitance between the electrode plate 1 and the electrode plate 4 increases by the same action. That is, it has a characteristic that the electrostatic capacitance greatly changes with respect to the humidity change due to the synergistic effect of both the change of the dielectric constant and the change of the distance between the electrodes. This means that there is a large change in capacitance with respect to changes in humidity, and it is possible to easily detect even slight changes in humidity. Further, the electrode plate 1 and the electrode plate 4 are insulated from each other by the space 5, and the insulating support 3 interposed between the electrode plate 1 and the electrode plate 4 is made of a silicone-coated insulator, and the adhesive is also a silicone adhesive. Since it is used to repel water, the insulation between the electrode plate 1 and the electrode plate 4 is sufficiently maintained, the humidity measurement accuracy is not impaired, and the generation of Joule heat due to overvoltage application is negligible. However, there is no danger of thermal destruction. Further, even if a DC voltage is erroneously applied for a long time, the ceramic element body 2 will not
Since the air gap 5 is provided between the electrode plate 4 and the electrode plate 4 so as to ventilate the outside air, the movement of ions in the ceramic body 2 is negligible as compared with the conventional structure. It does not deteriorate.

Next, an experimental example of the present invention will be described. That is, as a result of investigating the relative humidity-capacitance relationship between Example A according to the present invention and Reference Example B in which only a void portion was provided between electrodes without using a porous ceramic body, the results are shown in FIG. In comparison with Reference Example B, Example A has a large capacity and good linearity with respect to the same relative humidity, and a large sensitivity is obtained.
The electrode plates used as samples were metal plates made of gold in both Example A and Reference Example B, and the capacitance was measured at 1 KHz.

In the above embodiment, the porous ceramic body 1 is attached to only one of the electrode plates 1, but the porous ceramic body is attached to both of the electrode plates 1 and 4 as shown in FIG. If the element body 1 is attached and the cavity 5 is provided between the ceramic element bodies 1, the sensitivity is further improved. In FIG. 4, the same parts as those in the above embodiment are designated by the same reference numerals and the description thereof is omitted. Also, in the above-mentioned embodiment, the insulating support structure has been described by exemplifying a structure in which a plurality of individually formed columnar members are interposed. However, as shown in FIG. 5, a ring-shaped structure matching the shape of the electrode plate is formed. Even if the ring-shaped insulating support 8 provided with the through hole 7 is used, the void portion and the outside air are ventilated through the through hole 7, and therefore the same effect can be obtained. Further, in the above-mentioned embodiment, the prismatic shape has been described as an example, but it goes without saying that it can be applied to other shapes such as a circular shape.

EFFECTS OF THE INVENTION According to the present invention, the dielectric constant between electrodes increases according to the height of relative humidity, and the distance between electrodes equivalently decreases,
As a result, it is possible to obtain a capacitance-type humidity sensor having a large capacitance and high sensitivity, and having no deterioration or destruction even when an overvoltage is applied or a DC voltage is applied.

[Brief description of drawings]

1 to 3 relate to an embodiment of the present invention, FIG. 1 is a front sectional view showing a capacitance type humidity sensor, FIG. 2 is a perspective view during manufacturing, and FIG. 3 is FIG. 2 is an enlarged perspective view showing an insulating support constituting FIG. 2, FIG. 4 is a front sectional view showing a capacitance type humidity sensor according to another embodiment of the present invention, and FIG. 5 is another embodiment of the present invention. FIG. 6 is a perspective view showing an insulating support according to an example.
The figure is a relative humidity-capacitance characteristic curve diagram. DESCRIPTION OF SYMBOLS 1 ... Electrode plate, 2 ... Porous ceramic body 3 ... Insulating support, 4 ... Electrode plate 5 ... Void, 7 ... Through hole 8 ... Insulating support

Claims (3)

[Claims] 1. A pair of electrode plates, which are integrated so as to face each other with an insulating support interposed therebetween, a porous ceramic body attached to at least one surface of the facing faces of the electrode plate, and a face facing the base body. An electrostatic capacitance type humidity sensor, characterized in that it is configured with a void portion provided between the voids and the outside air is ventilated. 2. The capacitance type humidity sensor according to claim 1, wherein the insulating support is columnar, and a plurality of insulating support members are provided around a pair of opposing electrode plates. 3. The capacitance type humidity sensor according to claim 1, wherein the insulating support is a ring-shaped insulating support having a through hole provided around the insulating support.