JPH01207644A - Humidity detector - Google Patents

Abstract

PURPOSE:To improve the measurement accuracy in a low temperature range by dispersing carbon particles in sol obtained by hydrolysis from silicon alkoxide, gelatinizing, drying, and sintering it and thus obtaining a humidity sensor and using the sensor after stabilization by a heat treatment. CONSTITUTION:Carbon particles are dispersed in the sol obtained by hydrolysis from silicon alkoxide Si(OR)4 (R: alkyl group) and this is gelatinized, dried, and sintered under a vacuum or in gaseous nitrogen, inert gas, etc., within a temperature range of 500-1,500 deg.C. The humidity sensor 3 which is thus obtained is stabilized in gas containing oxygen within a temperature range of 300-500 deg.C and installed in measurement environment. This sensor 3 is used as the feedback resistance of a logarithmic amplifying circuit 5 to constitute a detection amplifier 2 which varies in amplification factor with its electric resistance. A signal which has a constant amplitude and frequency is supplied to the input of this amplifier 2 from an oscillation circuit 1 and the output of the amplifier 2 is rectified 4, and logarithmic conversion 5 is performed to obtain an output signal proportional to variation in the humidity in the measurement environment.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a humidity detector that detects a change in relative humidity as a change in electrical resistance of a porous humidity sensor and outputs an analog signal proportional to the change in relative temperature. Regarding.

[Conventional technology] Conventionally, humidity sensors that detect changes in relative humidity as changes in the electrical characteristics of elements include electrolyte-based, organic material-based, metal-based, and metal oxide-based sensors, and currently in practical use. These include a condensation sensor with conductive powder mixed into a hygroscopic polymer resin, a humidity sensor with a conductive polymer, and a ZnCr20
4-LiZnVO4 ceramic humidity sensor x Ti
There are 0a-V206 series ceramic humidity sensors, etc. A dew condensation sensor made by mixing conductive powder into a hygroscopic polymer resin expands when the polymer resin absorbs moisture, increasing the distance between particles of the conductive powder and increasing the resistance value, which rapidly increases when the humidity reaches a certain level. This takes advantage of the property of causing a significant increase in resistance.

Conductive polymer membrane and ceramic humidity sensors utilize the property that the resistance value of the element decreases exponentially due to water adsorption.

[Problems to be Solved by the Invention] However, in the prior art, dew condensation sensors cannot measure humidity over a wide range, and polymer membrane humidity sensors cannot measure at temperatures above 60°C. Additionally, both the polymer membrane and ceramic humidity sensors have a drawback in that their accuracy deteriorates in low temperature ranges. Some ceramic humidity sensors have been used that require heating to several hundred degrees Celsius at regular intervals, but these sensors cannot be used in locations where flammable vapors or gases are present. Furthermore, both sensors deteriorate if used for long periods of time in high temperature and high humidity environments.

Therefore, the present invention aims to solve these problems.The purpose of the present invention is to provide a humidity detector that can be used for a long period of time in a high temperature and humid environment and that can perform highly accurate measurements over a wide range of humidity. It's there to provide.

[Means for Solving the Problems] (1) The humidity detector of the present invention uses a sensor made of a porous body in which conductive particles are dispersed in glass, in which (a) silicon alkoxide ( S i (OR)a,
Carbon particles are dispersed in a sol obtained by hydrolyzing R: alkyl group), the sol is gelled and dried, and sintered in a temperature range of 500°C to 1500°C in vacuum, nitrogen gas, or inert gas. , a humidity sensor subjected to heat treatment in the temperature range of 300° C. to 500° C. in the atmosphere or in a gas containing oxygen after sintering.

(b) A detection amplifier circuit having a configuration in which the humidity sensor is used as a feedback resistor, and the amplification factor changes according to a change in the resistance value of the humidity sensor.

(c) An oscillation circuit that serves as a signal source for the detection amplifier.

(d) A rectifier circuit that rectifies the output signal of the detection amplifier circuit and outputs a DC signal having a magnitude proportional to the change in relative temperature detected by the humidity sensor. (e) Logarithmically transforms the output signal of the rectifier circuit. It is characterized by being composed of a logarithmic amplification circuit.

By setting the sintering temperature of the humidity sensor to 500° C. or higher, the sintered body has high mechanical strength and is chemically stable. Further, since there is no advantage in sintering at a temperature higher than 1500°C, the sintering temperature is preferably 500°C to 1500°C. Regarding the temperature conditions for heat treatment after sintering, which will be shown in detail in later examples, by heat treatment after sintering, some of the carbon particles in the sintered body are burned out, resulting in a pore size distribution suitable for a temperature sensor. It becomes a structure with. Regarding the heat treatment temperature conditions, a comparative example will be shown in a later example when the heat treatment temperature conditions are not appropriate, but if the temperature is less than 300°C, the carbon particles will hardly be burned out and there is no effect, and if it exceeds 500°C, most of the carbon particles will be burned out. , 300 to 500°C is desirable.

[Function] The humidity sensor of the present invention uses a porous body in which carbon powder is dispersed in quartz glass as a humidity sensor in a measurement environment, and uses a temperature sensor as a feedback resistor of an inverting amplifier circuit to detect the humidity sensor. By configuring a detection amplifier whose amplification factor changes with changes in electrical resistance, applying a signal of constant amplitude and constant frequency from an oscillation circuit to the detection amplifier input, and rectifying and logarithmically converting the detection amplifier output, An output signal that changes proportionally to humidity changes is obtained.

[Example] The present invention will be explained in detail below based on the drawings.

FIG. 1 is a circuit diagram of a humidity detector according to the present invention, in which an oscillation circuit 1 outputs a signal with a constant amplitude and a constant frequency. The detection amplifier 2 is a circuit whose amplification factor changes according to a change in the resistance value of the humidity sensor 3. If the resistance value of the humidity sensor is Rs, the input/output amplification factor is -Rs/R1, and the amplitude of the output signal is equal to the relative humidity. Change with change. The rectifier circuit 4 is a circuit that converts alternating current into direct current, and outputs the average value of the absolute values of the output signals of the detection amplifiers. The logarithmic amplifier circuit 5 is a circuit that logarithmically transforms an input signal and outputs the result. The reference current of the logarithmic amplifier circuit is (VRI-VH2)/R2.

Next, a method for manufacturing a sample of the humidity sensor of the present invention will be explained.

(Production method example 1) Tetraethoxysilane (S i (OC2H3)4) 1
Add 33 ml of 0.02N hydrochloric acid to 0.00 ml and stir for 1 hour to hydrolyze the tetraethoxysilane to obtain a transparent and uniform sol. Carbon black 21 in this sol
．． Add 5 g and stir for 30 minutes to disperse the carbon black to obtain a black, uniform sol. This sol contains 0. When the pH value is set to 5 by dropping IN ammonia water, it becomes 1
It gelled after some time. After drying this gel at 60'C for 24 hours, it was placed in a sintering furnace, heated to 50,000 degrees under a vacuum degree of ITorr or less, and held at 500C for 1 hour. The obtained sintered body was heat-treated at 300° C. for 10 hours while flowing a mixed gas containing 50% oxygen and 50% nitrogen by volume. A sample of 5 mm x 5 mm x 1 mm was cut out from the sintered pair after heat treatment, adhered to an alumina substrate, and attached with electrodes.
A humidity sensor shown in Fig. 2 was manufactured. In Figure 2,
21 is a sintered body, 22 is an electrode, 23 is a lead wire, and 24 is a substrate. FIG. 3 is a diagram showing the humidity sensitivity characteristics of this humidity sensor.

(Production Example 2) A dried gel was produced in the same manner as Production Example 1 except that the amount of carbon black was changed to 10.8 g.

This dry gel was heated in a sintering furnace for 100 minutes while flowing nitrogen gas.
It was heated to 0°C and held at 1000°C for 5 hours. The obtained sintered body was heated to 400"C in the air and held at 400°C for 5 hours. A humidity sensor was manufactured from the sintered body after this heat treatment in the same manner as in Manufacturing Example 1. Figure 4 shows the humidity sensitivity characteristics of the temperature sensor.The humidity sensor was boiled in boiling water for 1 hour and then dried at 100°C for 1 hour. The characteristics were exhibited, and no deterioration was observed.

Next, a comparative example will be shown in which heat treatment was performed under heat treatment temperature conditions other than those described in the claims.

(Comparative Example 1) A humidity sensor was manufactured in the same manner as Manufacturing Example 2 except that the heat treatment temperature was 200°C. The moisture sensitivity characteristics are shown in FIG. The humidity sensor of this comparative example is considered to be impractical in both linearity and variation range.

(Comparative Example 2) A humidity sensor was manufactured in the same manner as Manufacturing Example 2 except that the heat treatment temperature was 600°C. The humidity sensor of this comparative example had extremely high resistance, and its temperature-sensitive characteristics could not be measured with a normal measuring device.

[Effects of the Invention] As described above, the humidity sensor of the present invention is produced by dispersing carbon particles in a sol obtained by hydrolyzing silicon alkoxide, gelling the sol, drying it, and sintering it. Since the resulting humidity sensor is used after being stabilized by heat treatment, it exhibits stable characteristics even when used for long periods of time in high-temperature environments, and due to the content of carbon particles (carbon black in the example) Since the temperature-sensing characteristics of the temperature sensor can be varied over a wide range, it is possible to perform measurements with high precision in low humidity regions, which have been difficult to measure in the past. Note that since the humidity sensor used in the present invention is extremely inexpensive, a temperature detector can be realized at a lower cost than when a conventional temperature sensor is used.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of the humidity detector of the present invention. Figure 2 is a structural diagram of the humidity sensor. Fig. 3.4 is a diagram of moisture sensitivity characteristics of the temperature sensor of the present invention. Figure 5 is a diagram of moisture sensitivity characteristics of a comparative example. that's all 21 great achievements Figure 2 Figure 5 -71jF Otsui Positive 1 (,Ω,) nM Mui Nao (,Ω,)

Claims (1)

[Claims] (1) In a humidity detector using a porous sensor with conductive particles dispersed in glass, (a) carbon is added to a sol obtained by hydrolyzing silicon alkoxide (Si(OR)_4, R: alkyl group). The particles are dispersed, the sol is gelled and dried, and sintered in a temperature range of 500°C to 1500°C in vacuum, nitrogen gas, or inert gas, and after sintering, the sol is dried in the atmosphere or in a gas containing oxygen. A humidity sensor that has been heat-treated in the temperature range of 300°C to 500°C. (b) A detection amplifier circuit having a configuration in which the temperature sensor is used as a feedback resistor, and the amplification factor changes according to a change in the resistance value of the temperature sensor. (c) An oscillation circuit that serves as a signal source for the detection amplifier. (d) A rectifier circuit that rectifies the output signal of the detection amplifier circuit and outputs a DC signal with a magnitude proportional to the change in relative humidity detected by the temperature sensor. (e) Logarithmically transforms the output signal of the rectifier circuit. A humidity detector comprising a logarithmic amplification circuit.