JPH0573041B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a humidity sensor, and more particularly to a humidity sensor that is attached to a simple hygrometer, a device that is used to control humidity at a constant level, or a humidity control device for a space. [Prior Art] Conventionally, efforts have been made to improve the working or living environment by mainly maintaining a constant humidity in a space, such as a room or a car. Additionally, there are some devices that do not operate correctly unless humidity is controlled, and these devices were also kept at a constant humidity level. For such humidity control, a humidity sensor is required to measure the humidity in the atmosphere. Conventionally, such humidity sensors have been made using ceramic materials or plastic materials. An example of such a humidity sensor is to place a hygroscopic metal oxide ceramic as a moisture-sensitive material between porous electrode plates, and by physically adsorbing moisture in the atmosphere to this ceramic, humidity can be measured. Measure the conductivity between both electrode plates by
It determined the humidity. [Problems to be Solved by the Invention] However, since such humidity sensors measure humidity by adsorbing moisture on the surface of the moisture-sensitive material, the moisture-sensitive material deteriorates due to long-term use and this deterioration occurs. There was a decrease in moisture sensitivity due to this. In addition, with humidity sensors using conventional moisture-sensitive materials, the resistance value in low humidity regions is extremely large at 1 to 10 MΩ or more, so it cannot be measured with a normal electrical detection circuit, and a special circuit must be created. Even so, the accuracy was poor. Furthermore, in order to measure humidity, moisture is adsorbed onto the moisture-sensitive material, so the next measurement cannot be made until the adsorbed moisture is gone, and in some cases a heater is required to remove the adsorbed moisture. There were cases. Therefore, the present invention not only can be used stably for a long period of time, but also enables continuous measurement in an extremely short period of time.It also significantly reduces the resistance value for measurement, making it difficult to detect with ordinary electrical detection circuits. The purpose is to provide a humidity sensor that enables [Means for Solving the Problems] and [Operation] In order to achieve the above-mentioned objects, the present invention is based on a NiO-based porous crystal with a wide pore distribution, and the surface of the fine particle crystal is We have developed a humidity sensor that uses water vapor in the atmosphere to detect changes in electrical resistance in the bulk direction of the ceramic, which occurs when water molecules adsorb or desorb to the surface of microparticle crystals, depending on the water vapor in the atmosphere. is converted into humidity. Specifically, the present invention uses 100 parts by weight of NiO, 10 to 20 parts by weight of _Li2CO3 , 5 to 20 parts by weight of _Sb2O3 , and 5 _to 20 parts by weight of _{Cu2O .} The mixture is sintered and crushed, and 6 to 16 parts by weight of Al ₂ O ₃ and 6 to 16 parts by weight of SiO ₂ are added to this.
It has dry and wet resistance and consists of a sintered body mainly consisting of 100% by weight. Such a humidity sensor can measure humidity based on a change in resistance value ranging from 1000 KΩ or less to several KΩ, and therefore humidity can be adequately measured using a commonly used electrical detection circuit. Furthermore, for example, even if the humidity changes from 50% to 95%, each resistance value changes in about 40 seconds, and even if it changes from 95% to 50%, it takes about 60 seconds, so it is extremely difficult to change the humidity. Measurements can be made quickly and in a short period of time even in harsh locations. [Example] The humidity sensor according to the present invention will be described below along with various characteristics and the like. First, a manufacturing method for an example of a humidity sensor according to the present invention will be explained. First, 5g of NiO, 0.75g of Cu ₂ O,
Add 1 g of Li ₂ CO ₃ and 0.75 g of Sb ₂ O ₃ and mix until uniform. Next, these materials were fired at 800℃ for 1 hour,
Then crush. For the weight of this total crushed material (Ai ₂ O ₃ )
After adding about 10% by weight of y(SiO ₂ )z and about 10% by weight of methylcellulose as a binder, water is added and kneaded to form a uniform paste. This paste-like material is then dried at 150°C for 3 hours, and after drying, it is ground into approximately 200 mesh pieces. This pulverized material is press-molded to a size of 5 mm in diameter and 0.3 mm in thickness, and then baked at 850°C for about 1 hour. A porous gold electrode or a porous ruthenium oxide electrode is coated or printed on the front and back surfaces of the disk-shaped moisture-sensitive element thus formed, and
It is completed by baking at ~850℃ for 5 to 10 minutes. The specifications of the humidity sensor formed in this way will be explained. Withstand voltage: AC.10V Operating voltage: AC.1V Operating frequency: 10 to 100kHz Operating range: 1 to 50℃, 20 to 95%RH Storage range: -30 to 80℃, 1 to 100%RH AC resistance value: Approx. 100kΩ, 25°C, 50%RH Response characteristics: Within 1 minute Temperature characteristics: B=3000, 1 to 50°C Next, various characteristics of this humidity sensor will be explained. Humidity-Resistance Characteristics and Their Temperature Variability As shown in FIG. 1, as the relative humidity increases, the sensor resistance value decreases exponentially. Furthermore, even if the humidity is the same, the resistance value changes depending on the temperature, so temperature compensation is necessary. Responsiveness As shown in Figure 2, the humidity ranges from 50%RH to 95%RH.
If it rises to %RH, it will take about 40 seconds, and vice versa, it will rise to 95
When decreasing from %RH to 50%RH, it takes about 60 seconds,
Since absorption or desorption occurs, the atmospheric humidity can be measured in about one minute. Voltage dependence When applied in the range of AC0.01 to 10V,
No voltage dependence of the element resistance value is observed. Reproducibility As shown in Figure 3, under normal atmosphere 20
Extremely stable in the range ~95%RH, ±
Can measure with accuracy within 3%RH. Moreover, this measurement accuracy has similar accuracy in the range of 1 to 50°C, which is a normal temperature atmosphere. Furthermore, in an environmental test conducted on this humidity sensor, the following results were obtained. High temperature storage After 500 hours of storage in an atmosphere with a temperature of 80±5°C, the fluctuation was within ±5%. Temperature Cycle As a result of a continuous test of 100 cycles in which one cycle was repeated at -25°C for 30 minutes, 20°C for 15 minutes, and 80°C for 30 minutes, the fluctuation was within ±3%. High humidity load life In an atmosphere with a temperature of 50℃ and humidity of 95%RH
As a result of applying AC3V as a load while leaving it for 500 hours, the fluctuation was within ±5%. Water Resistance When immersed in ion-exchanged water at 30°C for 2 hours and then air-dried, the variation was within ±3%. Tobacco smoke resistance After burning 10 cigarettes in a container with a volume of 4 liters, the variation was within ±3%. Malfunctions due to organic solvents No malfunctions could be detected even when applying solvent vapor (acetone, alcohol) or gas (propane, butane). Corrosion resistant gas _H2S is 3ppm, temperature is 40℃, humidity is 95%
As a result of being left in an RH atmosphere for 200 hours, the fluctuation was within ±5%. Formalin gas resistance No change was observed when the product was left in an atmosphere containing 1000 ppm formalin gas and a temperature of 25°C for 100 hours. 100% in an atmosphere with carbon tetrachloride gas CC1 of 200ppm and temperature of 25℃
I left it for a while, but there was no change. The above-mentioned humidity sensor is shown as Experimental Example 11, and 25% of the humidity sensor was produced using the same manufacturing method as this humidity sensor, but only with a different blending ratio.
Table 1 shows the results of measuring the resistance value at °C at humidity of 30%, 50%, 70%, and 90%.

[Table] In this table, Experimental Example 1 has a small resistance value and a small amount of change in resistance value, and cannot be used for practical purposes. Further, although Experimental Examples 2, 3, and 8 can be used in practice, the resistance value changes are small, and although they are practical, they are difficult to use. In Experimental Examples 6 and 7, on the contrary, because the resistance value was large,
The electrical detection circuit becomes complicated. Therefore, Examples 4, 5, 9, and 10 are examples of examples in which there is a change in resistance value, and the resistance value is relatively low and can be sufficiently measured. Furthermore, in the other experimental examples other than Experimental Example 1, although the values were different from those in Experimental Example 11 described above, they showed characteristics sufficient for practical use. In other words, based on these results, Experimental Example 1 and Experimental Examples 6 and 7 cannot be practically implemented, and the other experimental examples, Experimental Examples 4, 5, 9, 10,
It was concluded that it can be suitably used in Example 11, and that although it is difficult to use in Experimental Examples 2, 3, and 8, it is not impossible to use it. Therefore, experimental examples 2, 3, 4, 5, 8, 9, 10, 11
When examining the ratio of each compound shown in , the compound ratio is 100 parts by weight of NiO to 10 to 10 parts of Li ₂ CO ₃ .
20 parts by weight, 5 to 20 parts by weight of Sb ₂ O ₃ , 5 to 20 parts by weight of Cu ₂ O
20 parts by weight, 6 to 16 parts by weight of Al ₂ O ₃ , 6 to 16 parts by weight of SiO ₂
A value of parts by weight was obtained. [Effects of the Invention] As explained above, the present invention enables continuous measurement in an extremely short period of time, lowers the resistance value, enables detection with a normal electrical detection circuit, and improves durability and This greatly improves reliability.

[Brief explanation of the drawing]

The drawings show various characteristics of an experimental example of the present invention.
The figure shows the response characteristics, and FIG. 3 shows the reproducibility characteristics.

Claims (1)

[Claims] 1 100 parts by weight of NiO and 10 to 20 parts of Li ₂ CO ₃
Parts by weight, 5 to 20 parts by weight of Sb ₂ O ₃ , 5 to 20 parts by weight of Cu ₂ O
The weight parts were mixed and sintered and crushed, and 6 parts of Al ₂ O ₃ were added to this.
A humidity sensor characterized by having a dry-wet resistance made of a sintered body mainly composed of ~16 parts by weight and 6 to 16 parts by weight of _SiO2 .