JPH051897B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a gas detection device that detects reducing gases other than hydrogen gas and hydrogen-containing compound gas, such as CO gas, with high selectivity.

(Prior art) Conventionally, gas detection devices for detecting reducing gases have been known to use a single sensor element whose electrical characteristics, such as resistance, change due to the adsorption of reducing gas molecules. However, in order to detect only a specific reducing gas, such as CO gas, multiple sensor elements with different operating temperatures are used because the gas selectivity changes depending on the operating temperature of the element. However, the detection outputs of these sensor elements are made to have selectivity to a specific gas.

(Problems to be Solved by the Invention) However, even if a plurality of sensor elements with different operating temperatures are combined, hydrogen and hydrogen-containing compound gas cannot be sufficiently compensated for. It has been difficult to improve the selectivity of a specific reducing gas to be detected, such as CO gas, which is interfered with by hydrogen compound gas.

(Means for Solving the Problems) The present invention has been made in view of such conventional problems, and is a method for detecting reducing gases other than hydrogen gas and hydrogen-containing compound gases with high selectivity. It has a layered structure of catalytic metals such as palladium Pd and solid compounds such as tungsten trioxide to produce hydrogen or hydrogen-containing compound gas (hereinafter referred to as "hydrogen/hydrogen-containing gas").
A sensor element with extremely high selectivity for hydrogen and hydrogen-containing compound gases, whose light absorption characteristics change upon contact with hydrogen-containing compound gases (referred to as "hydrogen-containing compound gas"), is used as a compensation element to achieve reduction that does not have conventional selectivity. By removing the influence of hydrogen and hydrogen-containing compound gas from the detection output of the gas sensor element, high selectivity is achieved in the detection of reducing gases other than hydrogen and hydrogen-containing compound gas.

(Embodiment) FIG. 1 is an explanatory diagram showing an embodiment of the present invention together with a detection circuit section.

First, the configuration will be described. Reference numeral 1 is a sensor element that detects a reducing gas, and has a function of changing light absorption characteristics with respect to hydrogen and hydrogen-containing compound gas. That is, the sensor element has a laminated structure of a catalytic metal semitransparent film 2 using palladium Pd, a chromic material film 3 using tungsten trioxide _WO3 , and a transparent conductive film 4 using ITO. Transparent film 2, chromic material film 3, and transparent conductive film 4
The manufacturing of the sensor element 1, which has a laminated structure, involves placing an ITO transparent conductive film 4 on a transparent substrate 5 made of glass.
is vapor-deposited to a predetermined thickness, then a chromic material film 3 made of WO ₃ is vapor-deposited to a predetermined thickness, and finally a catalytic metal translucent film 2 made of Pd is transparently deposited on the chromic material film 3. It is created by depositing it thinly enough to maintain the

When this sensor element 1 comes into contact with hydrogen gas or hydrogen-containing compound gas (NH ₃ , H ₂ S, etc.), its light absorption characteristics change as follows.

For example, when hydrogen gas comes into contact with the catalytic metal semitransparent film 2, hydrogen is adsorbed and dissociated to generate hydrogen atoms in the catalytic metal semitransparent film 2, and these hydrogen atoms form the chromic material film 3 as a solid compound. injected into the. The solid compound WO ₃ in the chromic material film 3 that has received the injection of protons H ⁺ by the catalytic metal semitransparent film 2 is reduced and its color center density changes. That is, when WO ₃ is used as the chromic material film 3, the light absorption increases due to a change in the color center density due to the injection of protons H ⁺ , and the degree of the increase becomes stronger as the dust concentration increases. Of course, once the hydrogen gas is gone, the protons H ⁺ injected into the solid compound WO ₃ escape again, reducing light absorption and returning to its original, more transparent state.

Such a light absorption phenomenon in the sensor element 1 is similar to contact with hydrogen-containing compound gases such as NH ₃ , H ₂ S, and SiH ₄ in addition to hydrogen gas.

On the other hand, the sensor element 1 is electrically connected between a catalytic metal semitransparent film 2 and a transparent conductive film 4 as electrodes formed on both sides of a chromic material film 3 in response to contact with a reducing gas containing hydrogen and hydrogen-containing compound gas. The characteristics, specifically the resistance value, change depending on the concentration of reducing gas,
Reducing gas containing hydrogen and hydrogen-containing compound gas can be electrically detected from this change in resistance value.

A light emitting element 6 as a light source is provided on one side of the sensor element 1 whose light absorption characteristics change upon contact with hydrogen/hydrogen-containing compound gas in order to optically detect changes in light absorption of the sensor element 1. Light emitting power supply 7
Detection light is incident on the sensor element 1 in response to light emission drive by the sensor element 1 . Further, on the opposite side of the sensor element 1, a light receiving element 8 is provided which receives the light transmitted through the sensor element 1 and converts it into an electric signal. It receives transmitted light that has been attenuated due to the change in the light absorption characteristics in step 3 and converts it into an electrical signal. The light-receiving current of the light-receiving element 8 is applied to a hydrogen/hydrogen-containing compound gas detection circuit 9, which detects the gas concentration of hydrogen gas and/or hydrogen-containing compound gas according to the attenuation of the transmitted light.

On the other hand, a power supply voltage for detecting the resistance value of the sensor element 1 is applied from a power supply 10 to the catalytic metal semitransparent film 2 and the transparent conductive film 4 of the sensor element 1 via the reducing gas detection circuit 11. Power supply 1
A detection current corresponding to the resistance value of the sensor element 1 is passed from zero to Accordingly, the gas concentration of reducing gases including hydrogen and hydrogen-containing compound gases is detected. Reference numeral 12 denotes a determination unit for detecting hydrogen/hydrogen-containing compound gas, such as CO gas, and determines the detected concentration of CO gas based on the detection outputs of the hydrogen/hydrogen-containing compound gas detection circuit 9 and the reducing gas detection circuit 10. to judge.

Next, the reducing gas detection operation according to the embodiment shown in FIG. 1 will be explained.

First, if the reducing gas that has come into contact with the sensor element 1 is a reducing gas containing hydrogen gas and CO gas, the light absorption of the chromic material film 3 in the sensor element 1 will change upon contact with the hydrogen gas, and the chromic material film 3 will change. Since WO ₃ is used as the material film 3, light absorption increases according to the gas concentration of hydrogen gas, and the transmitted light from the light emitting element 6 is transmitted to the sensor element 1.
The amount of transmitted light incident on the light-receiving hydrogen 8 is attenuated. Therefore, the hydrogen/hydrogen-containing compound detection circuit 9 detects the gas concentration of hydrogen gas from the decrease in the light reception signal by the light receiving element 8 and outputs it to the determination section 12 . On the other hand, the resistance value of the sensor element 1 changes due to contact with reducing gas including hydrogen gas and CO gas, and the sensor element 1 is
The gas concentration of the reducing gas consisting of hydrogen gas and CO gas is detected from the change in the detection current flowing through the sensor and outputted to the determination section 12 .

In the determination unit 12, the reducing gas detection circuit 1
Let the detected gas concentration in 1 be the total gas concentration,
The gas concentration of CO gas is determined by subtracting the gas concentration of hydrogen gas detected by the hydrogen/hydrogen-containing compound gas detection circuit 9 from this value. Of course, in the case of only hydrogen gas, the hydrogen/
Since the gas concentration detected by the hydrogen-containing compound gas detection circuit 9 and the gas concentration detected by the reducing gas detection circuit 11 substantially match, the determination unit 12 can determine that it is hydrogen gas. In addition, if there is only a reducing gas other than hydrogen/hydrogen-containing compound gas, such as CO gas, the detection output of the hydrogen/hydrogen-containing compound gas detection circuit 9 cannot be obtained. It can be easily determined that the gas is a reducing gas, such as CO gas.

FIG. 2 is an explanatory diagram showing another embodiment of the present invention together with a gas detection circuit.
The present invention is characterized in that an independent sensor element is used to detect reducing gas containing hydrogen-containing compound gas.

That is, the sensor element 1 and its optical system for detecting hydrogen and hydrogen-containing compound gas are the same as those in the embodiment shown in FIG. 1, but the sensor element 1 detects the total reducing gas including hydrogen and hydrogen-containing compound gas. Therefore, a new sensor element 13 is newly provided, a power supply voltage is applied via the reducing gas detection circuit 11 by the power supply 10, and the sensor element 13 is resistant to contact with reducing gases including hydrogen and hydrogen-containing compound gases. Since electrical characteristics such as resistance value change, the reducing gas detection circuit 11 detects the total reducing gas concentration based on the detected current corresponding to the change in resistance value, and the determination unit 12 detects the hydrogen concentration. - Compensation is made using the detection output of the hydrogen-containing compound gas detection circuit 9, and the gas concentration of a reducing gas other than hydrogen gas and/or hydrogen-containing compound gas is determined.

In the above embodiment, platinum Pt can be used in addition to palladium Pd as the catalytic metal semitransparent film 2 of the sensor element, and molybdenum trioxide MoO can be used as the solid compound forming the chromic material film 3. In addition to ₃ , titanium dioxide TiO ₂ , iridium hydroxide Ir(OH)n, vanadium pentoxide V ₂ O ₅
may also be used. Further, in the sensor element 1 shown in FIG. 2, the transparent conductive film 4 may not be provided.

(Effects of the Invention) As explained above, the present invention has a laminated structure of a catalyst metal such as palladium Pd and a solid compound such as tungsten trioxide, and has light absorption properties due to contact with hydrogen and hydrogen-containing compound gas. A sensor element that has extremely high selectivity for hydrogen gas and hydrogen-containing compound gases that change in hydrogen gas and hydrogen-containing compound gas is used as a compensation element, and hydrogen and hydrogen-containing compound gas By removing the influence of hydrogen, we have achieved high selectivity in detecting reducing gases other than hydrogen and hydrogen-containing compound gases, such as CO gas, so even if reducing gases include hydrogen gas and/or hydrogen-containing compound gas, By removing the influence of hydrogen gas and/or hydrogen-containing compound gas, gas detection can be performed with high selectivity for a specific reducing gas, such as CO gas.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention together with a detection circuit section, and FIG. 2 is an explanatory diagram showing another embodiment of the present invention. 1: Sensor element, 2: Catalytic metal semitransparent film, 3:
chromic material film, 4: transparent conductive film, 6: light emitting element, 7: power source for light emission, 8: light receiving element, 9: hydrogen.
Hydrogen-containing compound gas detection circuit, 10: Power supply, 11:
Reducing gas detection circuit, 12: judgment unit, 13: sensor element.

Claims (1)

[Scope of Claims] 1. A sensor element whose light absorption characteristics change depending on the concentration of only hydrogen or hydrogen-containing compound gas, and a sensor element whose light absorption characteristics change depending on the concentration of only hydrogen gas or hydrogen-containing compound gas, and a sensor element that changes the concentration of only hydrogen gas or hydrogen-containing compound gas from changes in the light absorption characteristics of the sensor element. A hydrogen/hydrogen-containing compound gas detection device, a sensor element whose electrical characteristics change depending on the concentration of a reducing gas containing hydrogen or a hydrogen-containing compound gas, and a sensor element whose electrical characteristics change depending on the concentration of a reducing gas containing hydrogen or a hydrogen-containing compound gas; A reducing gas detection device that detects the concentration of a reducing gas containing a hydrogen-containing compound gas; A gas detection device comprising: a determination unit that determines the concentration of a reducing gas other than hydrogen or hydrogen-containing compound gas by subtraction. 2 The sensor element whose light absorption characteristics change depending on the concentration of only hydrogen or hydrogen-containing compound gas is composed of a metal that adsorbs and dissociates hydrogen or hydrogen-containing compound gas, and a solid compound that is reduced by hydrogen atoms in the metal. Claim 1, wherein the hydrogen/hydrogen-containing compound gas detection device comprises a device that detects a change in the light absorption property of the solid compound due to reduction and converts it into an electrical signal. gas detection device.