JPH0441944B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a capacitive humidity sensor that detects a change in relative humidity of air flowing between opposing electrodes as a change in interelectrode capacitance.

(Prior Art) Humidity sensors are generally classified into those using ceramics as a moisture-sensitive material and those using polymers. The following are typical ceramics whose electrical resistance changes as the relative humidity changes:

The first is a composite of acidic and basic ceramics, such as titanium oxide (TiO ₂ ).
and magnesium chromium spinel (MgCr ₂ O ₄ ). In general, water is adsorbed into the pores of a porous ceramic body, and when subjected to the action of acids, bases, etc., it dissociates into hydrogen ions H ⁺ and hydroxyl groups OH ^- , and current flows. It is explained that when the pores change, the amount of water adsorbed into the pores changes, resulting in a change in the amount of dissociated ions, which in turn changes the resistance. The second type is an oxide containing mobile lithium ions Li ⁺ , such as ZnO−
There is _Li2O - _{V2O5 - Cr2O3 .} This type is
A moisture-sensitive glass is formed uniformly around the grains made of ZnCr ₂ O ₄ spinel, and the amount of ions that contribute to electrical conduction changes depending on the amount of moisture adsorbed in multiple layers on this moisture-sensitive glass, changing the resistance. It is said to be a thing.

In any case, conventional humidity sensors have a structure in which a moisture-sensitive material is continuously disposed between a pair of electrodes, and the same is true for humidity sensors using polymers.

However, each humidity sensor having the above configuration cannot continuously apply a DC voltage due to its ionic conductivity. In addition, the applied voltage when detecting humidity is usually less than a few volts; if it is higher than this, Joule heat is generated and the temperature of the humidity sensing part increases, so the moisture adsorbed on the humidity sensing part of the humidity sensor is dissipated, and the actual humidity is A resistance value greater than the resistance value will be detected, making accurate humidity measurement impossible. Furthermore, they have various drawbacks, such as thermal breakdown if a large overvoltage is applied, and at the same time, polymer-type humidity sensors can be left in high-temperature, high-humidity environments for applications such as bathroom ventilation or wood drying. This may cause the polymer material that becomes the moisture sensitive part to deteriorate.
It was not suitable for industrial use because it was sensitive to high temperatures above ℃.

(Problems to be Solved by the Invention) As described above, ceramic humidity sensors and polymer type humidity sensors deteriorate when DC voltage is applied continuously, and the voltage that can be applied is only a few volts.
Due to the following, we had to be very careful when using it.

In the present invention, since there is a space between two opposing electrodes constituting a humidity sensor, the capacitance generated between the electrodes is C, the distance between the electrodes is d, the area of the opposing electrode is S, and the air This was done by focusing on the well-known relational expression C=εS/d that holds true between the dielectric constant and ε, and that as ε increases and d decreases, C increases. It is an object of the present invention to provide a capacitive humidity sensor having a novel configuration that has a wide voltage range and does not deteriorate even if DC voltage is mistakenly applied for a long time.

[Structure of the Invention] (Means for Solving the Problems) The capacitance type humidity sensor of the present invention includes a lower electrode formed on an alumina substrate by baking a lower electrode extension portion extending from a part of the periphery. , an upper electrode lead-out portion formed by baking independently from the lower electrode, a glass insulating support layer protruding from the lower electrode surface formed by baking at several places around the lower electrode, and a tip portion of the insulating support layer fixed to the A porous ceramic element body having an upper electrode baked only on the opposite side to the fixed face which are arranged to face each other, a connecting body connecting the upper electrode and the upper electrode lead-out part, and a connecting body connecting the lower electrode and the ceramic body. Outside air and ventilated air between the facing surfaces of the element
It is characterized by consisting of parts.

(Function) According to the capacitance type humidity sensor having the above configuration, the structure is such that a cavity through which outside air is ventilated is provided between the porous ceramic body with the upper electrode formed on the opposite surface of the lower electrode. , when the humidity is high, the sky is empty.
There are many water molecules in the area, which acts to increase the capacitance between the electrodes. In other words, as the amount of water molecules increases, the dielectric constant increases, and the electrical resistance of the ceramic body decreases, so the effect is essentially the same as if the distance between the electrodes became smaller, and the capacitance C in the previous relation becomes growing. Therefore, the capacity changes greatly with changes in humidity. Furthermore, since the electrodes are insulated by the space, overvoltage and DC voltage can be applied.

(Example) An example of the present invention will be described below with reference to the drawings. That is, as shown in FIG. 3, a lower electrode 3 is provided with a lower electrode lead-out portion 2 extending from a part of the periphery by printing and baking, for example, gold or platinum paste on an alumina substrate 1, and this lower electrode 3. The upper electrode lead-out portion 4 is formed independently from the above. Next, print glass paste at several places around the lower electrode 3.
Repeat baking several times in descending order of melting point,
Glass insulation support layer 5 protruding from the lower electrode surface
1 and 2 at the tip of this support layer 5.
As shown in the figure, a separately formed metal oxide powder containing, for example, zinc oxide or chromium oxide as the main component and additives such as lithium carbonate or vanadium oxide is press-molded, high-temperature sintered, and one side is formed. For example, a gold or platinum paste is printed and baked to fix the surface of the porous ceramic body 7 on which the upper electrode 6 is formed, opposite to the formation of the upper electrode 6, and between the surface of the lower electrode 3 and the facing surface of the porous ceramic body 7. An air space 8 that is ventilated with outside air is provided.

The fixing means is to place the porous ceramic body 7 after the final printing of the glass paste constituting the glass insulating support layer 5 and to bake the glass paste.

Thus, the upper electrode 6 and the upper electrode extension portion 4 formed on the alumina substrate 1 are made of gold, for example.
The connection is made with a connecting body 9 made of platinum wire, and then the lower electrode lead-out part 2 and the upper electrode lead-out part 4 are connected.
A lead wire 10 is attached to each of them.

According to the capacitive humidity sensor configured as described above, a cavity 8 that is vented to outside air is provided between the lower electrode 3 and the porous ceramic body 7 on which the upper electrode 6 is formed on the opposite surface. Because of this structure, when the humidity increases, the amount of water molecules existing in the cavity 8 increases, the dielectric constant between the lower electrode 3 and the upper electrode 6 increases, and more water is added to the porous ceramic body 7. The static between the lower electrode 3 and the upper electrode 6 is reduced by the same effect as the electric resistance is reduced by adsorption of molecules, that is, the distance between the lower electrode 3 and the upper electrode 6 is substantially reduced. Capacity increases. That is, due to the synergistic effect of the change in dielectric constant and the change in the distance between the electrodes, the capacitance changes greatly with respect to changes in humidity. This means that the capacitance changes greatly in response to changes in humidity, and even a slight change in humidity can be easily detected. Furthermore, the generation of Joule heat due to the application of overvoltage is negligible and does not impair humidity measurement accuracy, and there is no risk of thermal damage.

Furthermore, even if DC voltage is accidentally applied for a long time, the ceramic body 7 is arranged with a cavity 8 that is vented to outside air between the lower electrode 3 and the upper electrode 6. The movement of ions in the element body 7 is negligible compared to the conventional structure, and there is no deterioration.

Next, an experimental example of the present invention will be described. That is, the relationship between relative humidity and capacitance characteristics between Example A according to the present invention and Reference Example B in which no porous ceramic body was used and only a void was provided between a pair of electrode plates via an insulating support layer. As a result of the investigation, as shown in FIG. 6, it was found that, compared to Reference Example B, Example A had a larger capacity for the same relative humidity, good linearity, and high sensitivity. The electrode plates used as samples were made of gold using the electrode paste in Example A and the electrode plate in Reference Example B, and the capacitance was measured at 1 KHz.

In the above embodiment, the connection body 9 between the upper electrode 6 and the upper electrode lead-out part 4 was explained using a wire as an example, but as shown in FIG. 4, the upper electrode lead-out part formed on the alumina substrate 1 4 patterns are formed in contact with or close to one location of the glass insulating support layer 5 provided around the lower electrode 3,
As shown in FIG. 5, a connection body made of a conductor coated and baked through the side surface of the glass insulating support layer 5 that is in contact with or close to the upper electrode lead-out portion 4 and the side surface of the porous ceramic body 7 located on this side surface. It may be a structure connected by 9. Figures 4 and 5
In the figure, the same parts as in FIGS. 1 and 2 are denoted by the same reference numerals, and explanations thereof are omitted.

In addition, in the above embodiments, gold and platinum were used as electrode materials in consideration of rust resistance, but costs could be reduced by using a structure in which copper was baked and then nickel plated. I can contribute. Further, in the above embodiment, the alumina substrate 1 is square in shape and the porous ceramic body 7 including the lower electrode 3 and the upper electrode 6 is circular. However, the present invention is not limited to this. Needless to say.

[Effects of the Invention] According to the present invention, the dielectric constant between the electrodes increases in accordance with the height of the relative humidity, and the distance between the electrodes equivalently decreases, resulting in a large capacitance and a high sensitivity. It is possible to obtain a capacitive humidity sensor with good measurement accuracy and which does not deteriorate or break even when overvoltage or DC voltage is applied.

[Brief explanation of drawings]

1 to 3 relate to an embodiment of the present invention, and FIGS. 1 and 2 show a capacitance type humidity sensor, and FIG. 1 is a plan view, and FIG. 2 is a top view of FIG. cross section,
FIG. 3 is a plan view of the manufacturing process, FIGS. 4 and 5 relate to other embodiments, FIG. 4 is a plan view of the manufacturing process, and FIG. 5 is a cross-sectional view of the capacitive humidity sensor. FIG. 6 is a relative humidity-capacitance characteristic curve diagram. 1... Alumina substrate, 2... Lower electrode extraction part,
3... Lower electrode, 4... Upper electrode extraction part, 5...
Glass insulating support layer, 6... upper electrode, 7... porous ceramic body, 8... void, 9... connection body.

Claims (1)

[Claims] 1. A lower electrode formed by baking a lower electrode lead-out part connected to the alumina substrate, an upper electrode lead-out part formed by baking independently from this lower electrode, and the lower electrode formed by baking at several places around the lower electrode. A glass insulating support layer that protrudes from the surface, a porous ceramic body that is fixed to the tip of the insulating support layer and has an upper electrode formed by baking only on the opposite surface to the fixed surface that is disposed facing the surface, and the upper electrode and A capacitance type humidity sensor, comprising: a connecting body connected to the upper electrode lead-out portion; and a cavity ventilated with outside air is provided between the lower electrode and the facing surface of the ceramic body.