JPS6263851A - Humidity detecting device - Google Patents

Abstract

PURPOSE:To detect humidity in the low temperature environment <='0' degree by receiving a temperature signal which is detected by a temperature detecting means, and varying a conducting area of a humidity sensing layer. CONSTITUTION:Plural electrodes 4c-6c are selected by switching switches 9, 10, and a conducting area of a humidity sensing layer 7 is varied. Also, the resistance variation of a thermistor 8 corresponding to the variation of an ambient temperature is supplied to a microcomputer through a AC/DC converting circuit 14 and an A/D converter 16. Next, the switches 9, 10 are switched in accordance with an ambient temperature. In such a way, even if a resistance coefficient of the humidity sensing layer 7 against the humidity variation of peripheral atmosphere is varied by a peripheral atmosphere temperature, the resistance can be corrected by varying a conducting area of the humidity sensing layer 7 in accordance with its variation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a humidity detection device that utilizes changes in electrical resistance due to changes in ambient atmospheric humidity. It is suitably used for detection.

[Conventional technology]

Conventionally, as a humidity sensing element that utilizes a change in electrical resistance due to a change in atmospheric humidity, an alkali metal oxide containing an alkali metal oxide between opposing electrodes has been used, for example, as disclosed in Japanese Patent Laid-Open No. 59-99701. A moisture-sensitive layer made of glass frit and tungsten oxide is formed, and the alkali metals contained in the alkali glass frit are ionized and eluted into the condensed water adsorbed to this moisture-sensitive layer depending on the humidity of the surrounding atmosphere. Humidity detection devices are known that can detect humidity by utilizing the decrease in electrical resistance.

[Problem that the invention seeks to solve]

However, in the humidity detection device described in the above publication,
Since it utilizes the elution and ionization of alkali metals from water vapor in the air into condensed water, in a low-temperature atmosphere below 0°C, the condensed water solidifies, inhibiting the elution of alkali metal ions, and completely dissolving the condensed water. Because the electrical resistance coefficient changes with respect to humidity changes compared to when it is in the liquid phase,
Humidity cannot be detected accurately at low temperatures below 0°C. All conventional humidity detection devices using this type of resistance change have had the problem of difficulty in detecting humidity at low temperatures below 0° C. due to the same cause.

[Means for solving problems]

Therefore, in order to solve the above-mentioned problems, the present invention has an electrode part composed of one electrode and a plurality of opposing other electrodes, and an electrode part formed between the electrode parts, which responds to changes in the humidity of the surrounding atmosphere. The circulation area of the humidity sensitive layer is changed by switching and connecting the plurality of other electrodes to a humidity sensing section whose resistance value changes depending on the temperature of the surrounding atmosphere, and a temperature sensing means that detects the temperature of the surrounding atmosphere. The humidity detecting device includes a switch means, and a control means for receiving a temperature signal detected by the temperature detecting means and generating a signal for switching and connecting the switch means.

[Effect]

According to the above means, even if the resistance coefficient of the humidity sensitive layer with respect to changes in the humidity of the surrounding atmosphere changes depending on the ambient temperature, the resistance can be corrected by changing the conductive area of the humidity sensitive layer according to the change. Even if the resistance coefficient changes at low temperatures, the humidity of the surrounding atmosphere can be detected regardless of the change.

〔Effect of the invention〕

Therefore, according to the present invention, it is possible to provide a humidity detection device that does not malfunction even at low temperatures.

〔Example〕

The present invention will be explained in detail below based on embodiments shown in the drawings. FIGS. 1(a) and 1(b) are a plan view and a sectional view showing the structure of the element section 1 of the humidity detecting device of the present invention, and 2 is a short shelf-shaped electrically insulating substrate made of glass or ceramics;
3.4 and 5.6 are for example A u + P on this substrate 2.
The electrode is formed by printing and applying a conductive or low-resistance paste in the form of a comb by screen printing or the like, which is a mixture of conductive powder such as t + Ru Oz and an organic binder, and then baking the electrode. And electrode 3 has 9 pieces, electrode 4.5 has 2 pieces,
The electrode 6 consists of four comb-shaped protrusions 3a, 4a, 5a, 6a and base parts 3b, 4b, 5b, 6b that connect them, and the width is 0.6fi at any location, and the width of the adjacent comb-shaped protrusions is 0.6fi. The spacing between parts is 1.8 cranes. Electrode 4 as shown in the figure
．． 5 and 6 are formed by alternately penetrating the comb-like protrusions into each other so as to face the electrodes 3; 7 are the comb-like protrusions 3a, 4a, and 5a of the electrodes formed oppositely penetrating each other;
A moisture sensitive layer was formed by baking to a thickness of about 20 μm across the top of 6a, and was formed by the following method. That is, sodium oxide (NazO) 7wt%, silica (S K Ox) 1
0ilit%, boron oxide (BzOs) 40i*t%
, alumina (Al2O2) 1wt%, zinc oxide 42-t
Lowt% of ethyl cellulose and 90-t% of α-terpineol were added to a mixture containing 70-t% of tungsten oxide (WOt) and 30i+t% of glass free z consisting of
A paste to which an organic binder consisting of the following was added was prepared.

Comb this paste into the tooth-like protrusions 3a, 4a, 5a, 6a.
The film was applied across the substrate 2 and the electrodes by screen printing or the like, and after drying, it was baked at 760° C. for about 10 minutes. Further, in order to further stabilize the moisture sensitivity characteristics of this device, the entire device was aged at 80° C. and relative humidity of 90% RH for 100 hours in an air atmosphere to transfer alkaline components to the surface as carbonates.

Further, 8 is a temperature detection thermistor adhesively fixed to the substrate 2 in the vicinity of the humidity sensitive layer 7, and 8a and 8h are connection electrodes.

Next, a control section connected to the humidity sensing element and generating an output signal according to the ambient humidity will be explained based on the electric circuit diagram shown in FIG. 2. Lead wires 4c, 5c6C are drawn out from the ends of the bases 4b, 5b, 6b of the electrodes 4, 5.6, of which the lead wires 5e, 6c are connected to the AC power supply via the relay switch 9.10, and the lead vA4C is connected directly to the AC power source. 11a, and the other end of the AC power supply 11a is grounded.

On the other hand, a lead wire 3c is drawn out from the end of the base portion 3b of the electrode 30 and is grounded via an AC/DC conversion circuit 12. Note that reference numeral 13 denotes an adjustment resistor interposed in parallel with this AC/DC conversion circuit 12. Further, one terminal 8a of the thermistor 8 is grounded via an AC power supply 11b, and the other terminal 8b is grounded via an AC/DC converter circuit 14 to detect a change in resistance of the thermistor 8 in response to a change in ambient temperature. Note that reference numeral 15 denotes an adjustment resistor interposed in parallel with this AC/DC conversion circuit 14. Voltage signals corresponding to the humidity and temperature detected by the AC/DC conversion circuits 13.14 are input to the microcomputer 18 via the A-D converters 16.17, and based on the comparison of these signals, the relay switch 9 .10 is configured to emit a signal that turns ON and OFF the energization to a relay coil (not shown). The micro convenience store 18 is also configured to output a signal representing the humidity of the surrounding atmosphere based on the relationship between the resistance change between the electrodes of the humidity sensing element 1 input in advance and the ambient humidity.

Next, the operation of the humidity sensor of the present invention having the above structure will be explained. Water vapor is adsorbed and condensed in the humidity sensitive layer 7 formed between the electrodes of the humidity sensitive element 1 depending on the humidity in the surrounding atmosphere. Na in the glass component dissolves into this condensed water and becomes sodium ions (Na), reducing the electrical resistance between the electrodes. Therefore, humidity can be detected by measuring the decrease in electrical resistance.

By the way, according to the experimental research conducted by the present inventors, the resistance at constant humidity between the electrode 3 and the electrode 4 of the element 1 (resistance with both relay switches 9 and 10 open in FIG. 2) is As shown by the broken line A in Figure 3, the temperature decreases and gradually increases until it reaches a certain temperature To below 0℃, and when it drops further from To, the rate of condensed water condensing increases and the resistance value suddenly becomes linear. begins to increase.

Therefore, in the present invention, by utilizing this property, when the temperature detected by the thermistor 8 of the element 1 is 10 or more, the relay switches 9 and 10 are opened by a signal from the microcomputer 18, and the electrodes 3 and 4 are connected to each other. A change in resistance between the two is detected. When the ambient temperature falls below T0, the resistance value increases rapidly, but when the temperature of the element detected by the thermistor 8 drops to 11°C (point (a) in Figure 3), a signal from the microcomputer 18 causes the relay to switch. 9 is closed and the resistance change between electrode 3 and electrodes 4 and 5 is detected. Therefore, at temperature T1, the resistance value changes from (a) to (b) by approximately 1.
/2. As the temperature further decreases, the resistance increases, and when it reaches T2, the signal from the microcomputer 18 opens the relay switch 9 and closes the relay switch 0, and the resistance change between the electrode 3 and the electrodes 4 and 6 is detected. . Therefore, at temperature T2, the resistance value changes from (c) to (
d), it decreases to about 2/3. As the temperature further decreases, the resistance increases, and when it reaches T, the relay switches 9 and 10 are closed by a signal from the microcomputer 18, and the change in resistance between the electrodes 3 and 4 is detected. Therefore, at temperature T, the resistance value decreases to about 3/4. When the temperature further decreases, the resistance value increases.

In this way, the temperature resistance characteristic at a constant humidity becomes sawtooth-like as shown by characteristic B in the figure below T0.

And the mountain of this serration [(a) and (c) in the figure.

(e)] and valleys [same (0), (d), (f)] are in the range of ±5% RH in terms of relative humidity from the straight line obtained by extrapolating the characteristic curves of 10 or more to T and below, It is within the permissible error range for rough humidity measurements.

However, it is also possible to further narrow this band and reduce the humidity deviation range, for example, by increasing the number of electrodes and switches so that more combinations of resistance values between electrodes can be selected. FIG. 4 is a flowchart illustrating the ON-OFF control method of the switch with respect to the voltage signals vI to ① from the thermistor 8 corresponding to the temperature T I''' T3.

Since the humidity detection device of the present invention can be used even at low temperatures, it can be used in all seasons for predicting dew condensation in automobiles, homes, and other industries.

Among these, it is very effective when used as a defogger to remove fogging from windows when installed inside an automobile and combined with an air conditioning system, as shown in Figure 5. A system that operates reliably can be provided. In the system shown in FIG. 5, the moisture sensing element 1 of the present invention is mounted on the rear window, and the defogger 20. Microcomputer 18. A blower fan 21 and a control device 22 of an automobile air conditioner. It is composed of a combination lever 23 and the like. Its operation is as shown in the flowchart of FIG. 6. When the moisture sensing element 1 detects fogging of the rear window, the resistance of the sensor changes and this is detected by the microcomputer 18. Control device 22
The compressor 232, the damper of the air conditioner (not shown), and the blower fan 21. Activate the defogger 20 etc. to remove fog from the car window.

In the present invention, the shape of the electrode part is not limited to the above-mentioned embodiments, and can be modified in various ways.In addition to the comb-like shape, for example, parallel electrodes may be simply arranged facing each other.

In addition to Na, the alkaline components constituting the moisture sensitive layer are Li.

A salt containing an alkali metal such as K may be used, and the WOl which becomes the aggregate of the moisture sensitive layer 7 may be other ceramic materials such as magnesia, alumina, and cordierite.

Furthermore, the present invention is applicable not only to a moisture sensing element that utilizes the change in electrical resistance of a moisture sensitive layer depending on the degree of elution of alkali metals as in the above embodiments, but also to a moisture sensing element that utilizes the moisture adsorption phenomenon of metal semiconductors, etc. Applicable.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are a front view and a sectional view illustrating the configuration of a humidity sensing element section of a humidity detecting device of the present invention, and FIG. 2 is a configuration of a humidity detecting device of the present invention including this element section. 3 is a characteristic diagram illustrating the relationship between resistance of the element and temperature; FIG. 4 is a flowchart illustrating the operation of the humidity detection device; and FIG. FIG. 6 is a schematic diagram illustrating an application example of the humidity detection device of the present invention and a flowchart illustrating its operation. 3.4, 5.6... Electrode, 7... Moisture sensitive layer, 8...
Thermistor, 9.10... Selector switch, 18...
microcomputer.

Claims (1)

[Scope of Claims] An electrode part composed of one electrode and a plurality of opposing other electrodes, and a humidity sensing device formed between the electrode parts, the resistance value of which changes according to changes in the humidity of the surrounding atmosphere. a temperature detection means for detecting the temperature of the surrounding atmosphere; a switch means for changing the conduction area of the moisture sensitive layer by switching and connecting the other electrodes; and a temperature detection means for detecting the temperature detected by the temperature detection means. A humidity detection device comprising: control means for receiving a signal and generating a signal for switching and connecting the switch means.