JPH10153566A - Contact combustion type gas sensor and adjustment method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost, by setting the temperature of an element to a value to minimize effect of the change in the atmospheric temperature on the output of a sensor according to the kind of a gas to be inspected. SOLUTION: Platinum wire with the strand diameter of 25-50μm is formed into a coil shape with its diameter of about 0.5mm and in one of the two platinum wires thus obtained, a palladium alumina catalyst is molded into a sphere to cover the coil part thereof while in the other thereof, an alumina carrier alone is molded likewise. Then, both platinum wires are baked at 600 deg.C or higher to make a detector D and a comparator R, which forms a bridge circuit. A heater is provided to maintain a temperature necessary for a contact reaction. In the measurement, for example, when the gas to be detected is carbon monoxide, the temperature of the element needs be set in the range of 180-200 deg.C, and when it is a methane gas, the temperature thereof in the range of 330-370 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalytic combustion type gas sensor for detecting the concentration of a combustible gas in an atmosphere.

[0002]

2. Description of the Related Art A catalytic combustion type gas sensor detects the concentration of flammable gas such as carbon monoxide and hydrogen in the atmosphere. The principle is that a catalytic layer is provided around a conducting wire, and the flammable gas is burned by the catalyst. This is detected by a change in the electrical resistance of the conductive wire caused by the heat generated. In addition,
The sensor element is heated to efficiently perform combustion by the catalyst layer.

FIG. 6 shows the relationship between the element temperature and the sensor output. (The sensor output is a value obtained by converting a detection signal by an electric circuit into a voltage value. The same is true). This data was obtained using 0.3% oxygen gas and a mixed gas with isobutane, hydrogen or methane. As described above, it has been found that a stable output can be obtained with respect to many combustible gases at a sensor element temperature of 400 ° C. or higher. Such a catalytic combustion type gas sensor has high sensitivity and can be made compact, and is therefore widely used in gas detectors at home or in factories.

[0004]

However, the contact-combustion gas sensor excellent as described above is also required to be used as a gas sensor for a gas such as exhaust gas from a water heater or the like where the temperature changes rapidly. The influence of the change of the "ambient temperature" on the detected value has been a serious problem. That is, FIG. 7 shows a difference in output voltage between the case where the ambient temperature is 25 ° C. and the case where the ambient temperature is 200 ° C.
Thus, it can be seen that the difference in the ambient temperature has a great effect on the sensor output. Here, it was attempted to provide a temperature sensor separately or to check the change in the value of the current flowing through the conductor of the element of the catalytic combustion type gas sensor itself to detect the ambient temperature and correct the output value. It becomes complicated and costly. SUMMARY OF THE INVENTION It is an object of the present invention to provide a contact combustion type gas sensor which is hardly affected by an ambient temperature without taking special measures such as a temperature compensation circuit which causes a high cost.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a contact device in which the temperature of an element is set to a temperature at which the influence of a change in ambient temperature on the sensor output is reduced in accordance with the type of gas to be detected. It is a combustion type gas sensor. In other words, the present inventors have found that in the case of exhaust gas having a large temperature change such as a water heater exhaust gas, the sensitivity decreases due to a decrease in the number of molecules per unit volume due to the thermal expansion of the gas at a high temperature, as compared with a low temperature, that is, a decrease in the gas density. The present inventors have found that the above-described variations in measured values occur, and have focused on this change in gas density to arrive at the present invention.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, if the influence of the temperature change of the sensor installation atmosphere on the sensor output in the range of the element temperature of 25 ° C. or more and 200 ° C. or less is reduced, the water heater or the heater is used. It is preferable because it can be applied to the above. When the contact combustion type gas sensor of the present invention is applied to a water heater, a heating appliance, or the like, the sensor output at an ambient temperature of 200 ° C. is 100% higher than the sensor output at an ambient temperature of 25 ° C. , It is necessary to be 90% or more.

[0007] In the case of a catalytic combustion type gas sensor in which the gas to be detected is carbon monoxide gas, it is necessary to set the element temperature to 150 ° C or higher and 220 ° C or lower. In the case of a contact combustion type gas sensor in which the detection target gas is methane gas, it is necessary to set the element temperature to 330 ° C. or more and 370 ° C. or less. That is, in these sensors, if the temperature is lower than the lower limit temperature, the sensor output becomes too small and a sufficient S /
The N ratio cannot be secured, or a special electric circuit is required, resulting in an increase in cost. On the other hand, when the temperature is higher than the upper limit temperature, the temperature is affected by the ambient temperature, and the effect of the present invention cannot be obtained.

As described above, by adjusting the element temperature to a temperature according to the gas to be detected so as to reduce the influence of the change in the air temperature of the atmosphere in which the sensor is installed on the sensor output, it is possible to increase the cost of the temperature compensation circuit and the like. Without taking special measures, it is possible to obtain a contact combustion type gas sensor which is hardly affected by the ambient temperature.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below. First, a method of using the contact combustion type gas sensor will be briefly described with reference to FIG. A contact combustion type gas sensor is usually prepared by forming a platinum wire having an element wire diameter of 25 to 50 μm into a coil shape having a diameter of about 0.5 mm, and using a palladium alumina catalyst on one of them so as to cover the coil portion. After forming into a spherical shape and forming only the alumina carrier on the other side in the same manner, these are fired at 600 ° C. or higher to form a sensing element D and a comparative element R, respectively, and further form a bridge circuit as shown in FIG. Further, a heater (not shown) for maintaining the temperature required for the catalytic reaction is attached to use as a catalytic combustion type gas sensor.

[Example 1] Carbon monoxide gas sensor A contact combustion type gas sensor was manufactured using a sensor element formed using a platinum coil having a coil resistance of 2Ω and a platinum wire having a diameter of 40 µm. For this sensor, normal temperature (25
C.), the relationship between element temperature and sensor output when air mixed with 1000 ppm of carbon monoxide and 500 ppm of hydrogen was used as a sample gas. The results are shown in FIG.

Further, with respect to this sensor, the output voltage when the ambient temperature was 200 ° C. was similarly examined, and compared with the data at the normal temperature. The results are shown in FIG. FIG. 3 shows that the element temperature is hardly affected by a change in the ambient temperature when the element temperature is in the range of 150 ° C. or more and 220 ° C. or less. When the element temperature is within this range, the sensor output at an ambient temperature of 200 ° C. is 90% or more and 100% or less when the sensor output at an ambient temperature of 25 ° C. is 100%. , Measurement with a small error becomes possible.

A more detailed examination reveals that at least 180 ° C.
It was found that in the range of 0 ° C. or less, the change in the ambient temperature was extremely small and did not substantially affect the measured value. By setting the element temperature in the range of 150 ° C. to 220 ° C., preferably in the range of 180 ° C. to 200 ° C., the concentration of carbon monoxide can be measured without being affected by the ambient temperature. I understand.

[Example 2: Methane gas sensor] Diameter 50
Using a sensor element made in the same manner as in Example 1 using a platinum coil having a coil resistance of 1.5 Ω made of a platinum wire of μm,
A contact combustion gas sensor was fabricated. With respect to this sensor, the relationship between the element temperature and the sensor output when air mixed with 3000 ppm of methane gas at normal temperature (25 ° C.) was used as a sample gas was examined. FIG. 4 shows the results.

Further, with respect to this sensor, the output voltage when the ambient temperature was 200 ° C. was similarly examined, and compared with the data at the normal temperature. FIG. 5 shows the results. FIG. 5 shows that the element temperature is hardly affected by a change in the ambient temperature when the element temperature is in the range of 300 ° C. or more and 370 ° C. or less. However, when the element temperature is 300 ° C., the sensor output is too small, the S / N ratio is low, and the reliability of the measurement is low. Therefore, it is desirable to set the element temperature to 330 ° C. or higher.

When the element temperature is in the range of 330 ° C. or more and 370 ° C. or less, the sensor output at 200 ° C. ambient temperature is 100% when the sensor output at 25 ° C. ambient temperature is 100%. From 90% to 100% by weight, it can be seen that the measurement can be performed with a small error without being affected by the ambient temperature.

[0016]

The catalytic combustion type gas sensor of the present invention is an excellent catalytic combustion type gas sensor which does not require any special means such as a temperature compensation circuit which causes a high cost and is hardly affected by the ambient temperature. is there.

[Brief description of the drawings]

FIG. 1 is a model diagram showing a circuit of a catalytic combustion type gas sensor of the present invention.

FIG. 2 is a schematic view showing a catalytic combustion type carbon monoxide gas sensor according to the present invention.
It is a figure which shows the change of the sensor output with respect to the carbon monoxide sample gas obtained by mixing pm carbon monoxide with air.

FIG. 3 is a diagram comparing the data of FIG. 2 with the results of a carbon monoxide sample gas at an ambient temperature of 200 ° C.

FIG. 4 shows a change in sensor output with respect to a methane sample gas obtained by mixing 3000 ppm of methane with air at normal ambient temperature when the element temperature of the catalytic combustion type methane gas sensor according to the present invention is changed. FIG.

FIG. 5 is a diagram comparing the data of FIG. 4 with the results for a methane sample gas at an ambient temperature of 200 ° C.

FIG. 6 is a diagram illustrating a relationship between an element temperature and a sensor output.

FIG. 7 is a diagram showing the effect of the ambient temperature on the sensor output of a conventional catalytic combustion type gas sensor.

[Explanation of symbols]

 D Detection element R Comparison element

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[Procedure amendment]

[Submission date] July 1, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0003

[Correction method] Change

[Correction contents]

FIG. 6 shows the relationship between the element temperature and the sensor output. (The sensor output is a value obtained by converting a detection signal by an electric circuit into a voltage value. The same is true). This data is 0.3% meta
, Isobutane and hydrogen gas .
As described above, it has been found that a stable output can be obtained with respect to many combustible gases at a sensor element temperature of 400 ° C. or higher. In addition, such a contact combustion type gas sensor has high sensitivity and can be made compact,
It is widely used for gas detectors at home or in factories.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a model diagram showing a circuit of a catalytic combustion type gas sensor of the present invention.

FIG. 2 is a schematic view showing a catalytic combustion type carbon monoxide gas sensor according to the present invention.
It is a figure which shows the change of the sensor output with respect to the carbon monoxide sample gas obtained by mixing pm hydrogen with air.

FIG. 3 is a diagram comparing the data of FIG. 2 with the results of a carbon monoxide sample gas at an ambient temperature of 200 ° C.

FIG. 4 shows a change in sensor output with respect to a methane sample gas obtained by mixing 3000 ppm of methane with air at normal ambient temperature when the element temperature of the catalytic combustion type methane gas sensor according to the present invention is changed. FIG.

FIG. 5 is a diagram comparing the data of FIG. 4 with the results for a methane sample gas at an ambient temperature of 200 ° C.

FIG. 6 is a diagram illustrating a relationship between an element temperature and a sensor output.

FIG. 7 is a diagram showing the effect of the ambient temperature on the sensor output of a conventional catalytic combustion type gas sensor.

[Explanation of symbols] D detection element R comparison element

Claims (7)

[Claims] 1. A catalytic combustion type gas sensor wherein the element temperature is set to a temperature at which the influence of a change in ambient temperature on the sensor output is reduced according to the type of gas to be detected. 2. The catalytic combustion method according to claim 1, wherein an influence of a change in an ambient temperature in a range of 25 ° C. or more and 200 ° C. or less on the sensor output is reduced. Gas sensor. 3. The sensor output at an ambient temperature of 200 ° C. is 1 sensor output at an ambient temperature of 25 ° C.
A catalytic combustion type gas sensor characterized by being 90% or more and 100% or less when it is set to 00%. 4. A catalytic combustion type carbon monoxide gas sensor, wherein the element temperature is set to 150 ° C. or more and 220 ° C. or less. 5. The catalytic combustion type carbon monoxide gas sensor according to claim 4, wherein said element temperature is set at 180 ° C. or more and 200 ° C. or less. 6. A catalytic combustion type methane gas sensor characterized in that the element temperature is set between 330 ° C. and 370 ° C. 7. An element temperature according to a type of a gas to be detected.
A method for adjusting a contact combustion type gas sensor, wherein the temperature is adjusted to reduce the influence of a change in ambient temperature on a sensor output.