JPH0484748A - Humidity sensor - Google Patents

Abstract

PURPOSE:To obtain a sensor characterized high accuracy and quick response speed by setting the porosity of an insulating substrate at 15% or higher. CONSTITUTION:With respect to an insulating substrate 1 using a porous body having the porosity of 15% or more, water molecules tend to be adsorbed and desorbed. Even if ambient atmosphere is changed from high humidity to low humidity, the water molecules which are adsorbed in the insulating substrate are quickly desorbed from the substrate. Therefore, the amount of the re- adsorption of the water molecules in the insulating substrate with a moisture sensitive body 3 is less. Even if the water molecules are re-adsorbed into the moisture sensitive body 3, the molecules are quickly desorbed. Therefore, the hysteresis characteristic is remarkably improved. Since the insulating substrate 1 is porous, the adsorbing and desorbing properties of the water molecules become high even on the side where the moisture sensitive body 3 is in close contact with the insulating film. The effective surface area for the adsorption and the desorption becomes wide, and the response speed for the temperature change becomes quick.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a humidity sensor for detecting humidity.

[Prior Art] Humidity sensors currently in use are humidity sensors that capture and detect relative humidity as changes in impedance, including electrical resistance, or capacitance of a humidity sensing element applied between electrodes. It has high sensitivity, excellent stability, and
Since it is relatively easy to use, it is in high demand for near conditioners, humidifiers, dehumidifiers, and humidity measurement in industrial processes.

Such humidity sensors usually have a pair of opposing comb-shaped electrodes formed on an alumina or glass substrate using thin metal films such as gold, platinum, silver palladium, or silver, and a humidity sensing element is placed on these electrodes. A conductive ceramic powder mainly composed of zinc oxide is applied and fired, or a film of acrylic conductive polymer is formed on the electrode and cross-linked to change the relative humidity. In some cases, changes in relative humidity have been detected as changes in capacitance by forming a film of polyimide resin or the like on the electrodes.

[Problems to be Solved by the Invention] By the way, when a humidity sensor is left in a low-humidity atmosphere, the humidity is gradually increased to a high-humidity state, and then the high-humidity state returns to a low-humidity state. Even with regard to humidity, the output from the humidity sensor differs when going from low humidity to high humidity and when returning from high humidity to low humidity, and such characteristics are called hysteresis characteristics.

This hysteresis characteristic (hysteresis width) impairs the reproducibility of humidity measurement values and reduces measurement accuracy, so it must be kept as small as possible. However, in conventional humidity sensors with the structure described above, relative humidity The converted RH was usually 7%RH or higher, which was a problem.

Furthermore, the response time, which indicates the followability of the sensor output to changes in humidity, is 5.
It was slow at ~15 minutes, and an improvement was requested.

The present invention was proposed to solve the problems of the prior art as described above, and its purpose is to significantly improve hysteresis characteristics, achieve high measurement accuracy, and improve response speed to changes in humidity. The objective is to provide a fast and excellent humidity sensor.

[Means for Solving the Problems] A humidity sensor according to the present invention includes an insulating substrate, a pair of comb-shaped electrodes formed opposite to each other on one surface of the insulating substrate, and a humidity-sensitive sensor formed on the comb-shaped electrodes. The humidity sensor has external lead wires drawn out from each of the body and the comb-shaped electrode pair, and is characterized in that the insulating substrate has a porosity of 15% or more.

[Function] The function of the humidity sensor of the present invention having the above configuration will be explained below.

First, the occurrence of hysteresis characteristics in a humidity sensor is
This is due to the difference in adsorption of water molecules to the moisture sensitive element and separation of water molecules from the moisture sensitive element. This is further due to the fact that while adsorbing molecules, it is difficult to release adsorbed water molecules. That is, when the humidity sensor is left in a high humidity atmosphere and then placed in a low humidity atmosphere, the humidity sensor will
Since it is a thin film, it is easy for water molecules to separate, but on the other hand, water molecules adsorbed to the insulating substrate are difficult to separate, and the water molecules adsorbed to the insulating substrate move toward the moisture sensing element, causing moisture sensitivity. As the body adsorbs these water molecules again, the humidity sensor emits an output corresponding to a high humidity atmosphere, which is different from the actual low humidity atmosphere, which increases the hysteresis characteristic.

The present invention is based on such considerations, and aims to prevent re-adsorption of a moisture sensitive element and reduce hysteresis characteristics by increasing the ability of water molecules to separate from an insulating substrate.

That is, in the present invention in which a porous body with a porosity of 15% or more is used as an insulating substrate, water molecules are easily adsorbed and detached from the insulating substrate, and the surrounding atmosphere changes from a high humidity atmosphere to a low humidity atmosphere. Even when the atmosphere changes, the water molecules adsorbed to the insulating substrate quickly leave the insulating substrate, so the moisture sensitive element is less likely to re-adsorb water molecules on the insulating substrate, and even if they are re-adsorbed, Since it is quickly released, the hysteresis characteristics are significantly improved.

In addition, since the insulating substrate is porous, even on the side of the moisture sensitive element that is in close contact with the insulating substrate, the adsorption and desorption properties of water molecules are high, and the effective surface area for adsorption and desorption is widened, resulting in changes in humidity. There is also the advantage that the response speed to

[Example] An example (first example) according to the present invention will be described below.
This will be explained in detail with reference to the drawings.

First, as shown in Fig. 1, a metal paste such as gold, platinum, silver palladium, or silver is applied to a porous insulating substrate 1 made of alumina or magnesia and having a porosity of 15% to 20% and a thickness of 0.63 mm. A predetermined pattern of opposing comb-shaped electrode pairs was applied by screen printing, and then fired at 600 to 1200°C depending on the type of metal paste to form the comb-shaped electrode pair 2. Subsequently, on the surface of this comb-shaped electrode pair 20, a moisture sensitive material 3 whose main component is ZnCr2O4, which had been crushed in advance and kneaded into a slurry with an organic solvent, was printed using the same screen printing method as the electrodes.
Calcined at ~1000°C. Furthermore, external lead wires 4 were connected to each of the comb-shaped electrodes 2.

The operation of the humidity sensor of the first embodiment having the above configuration will be explained with reference to FIGS. 2 and 3.

FIG. 2 is a diagram showing the humidity resistance characteristics of the humidity sensor according to the first embodiment of the present invention and the conventional humidity sensor in terms of relative humidity. That is, as shown in FIG. 2, compared to the humidity-resistance characteristic curve C (L-H) when going from low humidity to high humidity, the humidity-resistance characteristic curve when returning from high humidity to low humidity in the conventional humidity sensor The curve Co has a large width and is located downward (H-L), whereas the humidity-resistance characteristic curve C1 (11) when returning from high humidity to low humidity in the first embodiment of the present invention is −
L) is much closer to curve C (L-11), and it is clear that the hysteresis characteristic of the first embodiment is significantly improved compared to the conventional one.

More specifically, the hysteresis width in the conventional humidity sensor was approximately 7%RH, whereas the hysteresis width in the first humidity sensor of the present invention
The hysteresis width in the humidity sensor of the example is approximately 3
%RH, which is significantly reduced.

FIG. 3 is a diagram showing the response speed characteristics of the humidity sensor of the first embodiment and the conventional humidity sensor. That is, as shown in FIG. 3, the response speed (characteristic curve Co) of the conventional humidity sensor changes when the sensor resistance increases (90% RH - 30% R
H) and when sensor resistance is reduced (30%RH-90%R
The response speed of the humidity sensor of the first embodiment (characteristic curve C+
) is much faster, approximately 3 minutes, both when the sensor resistance increases (90%RH - 30%RH) and when the sensor resistance decreases (30%RH → 90%RH). ing.

Next, a second embodiment of the present invention will be specifically described with reference to FIG. 1, similar to the first embodiment.

That is, as shown in FIG. 1, the porosity is 15% to 20%.
A predetermined pattern of opposing comb-shaped electrode pairs is formed on an alumina or magnesia porous insulating substrate 1 with a thickness of 0.63 mm by screen printing using a metal paste such as gold, platinum, silver palladium, or silver. Apply,
After this, 600 to 1200 depending on the type of metal paste.
C. to form a comb-shaped electrode pair 2. Next, on the surface of this comb-shaped electrode pair 2, a solution of a polymer prepared by adding a quaternary ammonium salt as a functional group to an acrylic polymer and a crosslinking agent diluted in a solvent is applied, and thermal crosslinking is carried out. After forming the moisture sensitive body 3, external lead wires 4 were connected to each of the comb-shaped electrodes 2.

The operation of the humidity sensor of the second embodiment having the above configuration will be explained with reference to FIGS. 4 and 5. In this case, FIG. 4 is a drawing corresponding to the above-mentioned FIG.
It is a figure which shows the humidity-resistance characteristic in relative humidity conversion of the humidity sensor of an Example, and a conventional humidity sensor. Similarly, the fifth
This figure corresponds to the above-mentioned FIG. 3, and is a diagram showing the response speed characteristics of the humidity sensor of the second embodiment and the conventional humidity sensor.

That is, as shown in FIG. 4, compared to the humidity-resistance characteristic curve C (L-11) when going from low humidity to high humidity, the humidity-resistance characteristic when returning from high humidity to low humidity in the conventional humidity sensor The curve Co has a large (11-L) width and is located downward, whereas the humidity-resistance characteristic curve C2 (when returning from high humidity to low humidity in the second embodiment of the invention) II-L) is much more similar to the curve C(L-
IO, and it is clear that the hysteresis characteristic is greatly improved compared to the conventional one, similar to the first embodiment described above.

Furthermore, as shown in Fig. 5, the response speed (characteristic curve Co) of the conventional humidity sensor changes when the sensor resistance increases (90% R
H→30%RH) and when sensor resistance is reduced (30%RH)
The response speed of the humidity sensor of the second embodiment was slow (about 5 minutes) in both cases (H-90% RH).
The characteristic curve C2) shows that when the sensor resistance increases (90% RH-
at 30%RH) and when sensor resistance is reduced (at 30%RH→
In both cases (at 90% RH), it takes about 2.5 minutes, which is significantly faster.

It should be noted that the present invention is not limited to the above embodiments, and the dimensions and shapes of the specifically used components, such as the insulating substrate, comb-shaped electrodes, moisture sensitive body, and lead wires, and the materials used may be changed as appropriate. Selectable.

[Effects of the Invention] As explained above, in the present invention, by making the insulating substrate have a porosity of 15% or more, water molecules can be easily adsorbed and detached from the insulating substrate; Since the effective surface area of the sensor is increased, it is possible to provide an excellent humidity sensor with significantly improved hysteresis characteristics, high measurement accuracy, and fast response speed to changes in humidity compared to conventional ones.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of the humidity sensor according to the present invention, and FIG. 2 is a comparison of humidity-resistance characteristics in terms of relative humidity between the humidity sensor of the first embodiment of the present invention and a conventional humidity sensor. FIG. 3 is a graph comparatively showing the response speed characteristics of the humidity sensor of the first embodiment according to the present invention and the conventional humidity sensor, and FIG.
A graph showing comparative humidity-resistance characteristics in terms of relative humidity between the humidity sensor of the embodiment and the conventional humidity sensor, and FIG. 5 shows the response speed characteristics of the humidity sensor of the second embodiment of the present invention and the conventional humidity sensor. This is a graph showing comparatively. DESCRIPTION OF SYMBOLS 1... Porous insulating substrate, 2... Comb-shaped electrode pair, 3...
...Moisture sensing element, 4...External lead wire.

Claims (1)

[Scope of Claims] An insulating substrate, a pair of comb-shaped electrodes formed opposite to each other on one surface of the insulating substrate, a moisture sensitive body formed on the comb-shaped electrodes, and each of the comb-shaped electrode pairs. A humidity sensor comprising an external lead wire drawn out, wherein the insulating substrate has a porosity of 15% or more.