JP2000304720A - Carbon monoxide sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make accurately detectable the concentration of carbon monoxide by bringing only a gas to be inspected through an anti-poisoning gas layer with a plurality of specific anti-poisoning gas material into contact with a solid-electrolyte sensor element. SOLUTION: The anti-poisoning gas layer 13 has at least one type out of granular silica gel, zirconia, ultra-stable zeolite, molecular sieve 5A, and powdered α-alumina. The layer is preferably as thick as 5-20 mm in the granular ultra-stable Y-type zeolite, 10 mm or longer in the granular silica gel, 10 mm or longer in the granular molecular sieve 5A, and 15 mm or longer in the granular zirconia. with a granular diameter of 50 mesh or larger and 2 mesh or less, a sufficient effect can be obtained, and the layer thickness is appropriately adjusted according to the effect and sensitivity. The layer is preferably as thick as 15 mm or longer and 20 mm or less in the case of the powered α-alumina. The anti-poisoning gas layer 13 is provided at the upper portion of a sensor cap 1, the upper and lower portions are covered with a mesh, and an anti- poisoning gas material is filled into the inside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte type carbon monoxide sensor.

[0002]

2. Description of the Related Art Various types of carbon monoxide sensors are currently in practical use, and they are widely used in fields such as process control and safety control. Among these, semiconductor sensors and contact combustion sensors can be used as carbon monoxide sensors that detect incomplete combustion of combustion exhaust gas from internal combustion engines and the like. Among them, the semiconductor sensor known in Japanese Utility Model Publication No. 2-20682 has a drawback that accurate measurement cannot be performed if the oxygen concentration or the moisture content in the sample gas changes. Therefore, a contact combustion sensor is usually used. ing. However, in general, in the case of combustion engine exhaust gas, the temperature of the combustion exhaust gas fluctuates between several tens to several hundred degrees Celsius due to the load fluctuation. In order to cope with such a change in the temperature of the sample gas, it is necessary to perform extremely strict temperature correction even in the contact combustion type sensor.

To solve the above-mentioned problems, an incomplete combustion detection sensor for exhaust gas using a solid electrolyte (oxygen ion conductor) has been developed (Japanese Patent Publication No. 58-4985, Japanese Patent Application Laid-Open No. Hei 7-4985). -306176).

However, there has been a problem that the measurement by such a sensor is hindered by a gas containing silicon or sulfur as a component. That is, an organic silicon-containing gas generated from a composition used as a putty in a building or a sulfur oxide gas due to sulfur contained in a fuel causes an obstacle to a measurement result of the carbon monoxide sensor. As a result, it is assumed that an unnecessary warning is given to give anxiety or cause damage to the user. Further, in the carbon monoxide sensor, when the measurement is repeated, there is a problem that a measurement value corresponding to the carbon monoxide concentration of the test gas may not be obtained.

[0005]

SUMMARY OF THE INVENTION A first object of the present invention is to eliminate an obstacle caused by a poisonous gas such as a sulfur oxide gas or a silicon-containing organic gas, and to accurately detect the concentration of carbon monoxide. It is an object to provide a carbon monoxide sensor.

A second object of the present invention is to obtain a measurement value corresponding to the concentration of carbon monoxide of a test gas even when the measurement is repeated by a carbon monoxide sensor, and to provide excellent long-term stability. It is an object of the present invention to provide a carbon monoxide sensor. It is to be.

[0007]

Means for Solving the Problems In order to achieve the first object among the above-mentioned objects, the present inventors have developed an anti-toxic gas layer made of activated carbon having a specific particle size and having a specific layer thickness. It has been found that the influence of the poisoning gas can be eliminated without substantially lowering the sensor sensitivity by providing the sensor around the sensor.

However, in such a toxic gas layer using activated carbon, an incomplete combustion detection sensor provided in a flue of a gas water heater or the like where the temperature of the test gas may be as high as nearly 200 ° C. It was found that there was a disadvantage that sufficient gas poisoning resistance could not be obtained when used. Further, when the temperature of the test gas changes remarkably, the durability of the toxic gas made of activated carbon may be remarkably deteriorated due to the thermal shock.

The present invention solves the problems of these techniques, eliminates the obstacles caused by poisonous gases such as sulfur oxide gas and silicon-containing organic gas, and enables accurate detection of carbon monoxide concentration. It is intended to obtain a carbon monoxide sensor which can be used at a high temperature and has a thermal shock resistance, and the present invention achieves the first object.
As described in the above, a carbon monoxide sensor having a solid electrolyte type sensor element, having a structure in which only the test gas that has passed through the anti-poisoning gas layer contacts the solid electrolyte type sensor element, and A carbon monoxide sensor in which the poisoning gas layer has at least one of granular silica gel, granular zirconia, granular ultra-stable Y-type zeolite, granular molecular sieve 5A, and powdered α-alumina. It is.

[0010] In order to achieve the second object of the above objects, the carbon monoxide of the present invention is a carbon monoxide sensor having a solid electrolyte type sensor element, A carbon monoxide sensor having a structure in which only a test gas that has passed through an output value stabilizing filter contacts an electrolyte type sensor element.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the first aspect of the present invention, the toxic gas layer having the above structure prevents the silicon-containing organic gas and the sulfur oxide gas in the test gas from affecting the sensor element. Removed.

Further, such a gas layer for preventing poisoning is composed of granular silica gel, zirconia, ultra-stable Y-type zeolite and molecular sieve 5A, and powdered α-alumina (collectively referred to as “poisoning-resistant gas material”). It is necessary that the toxic gas layer has at least one of the following: the other adsorbents achieve the object of the present invention, that is, eliminate the effects of toxic gases even in gas water heaters and the like. Can,
An accurate measurement cannot be made possible.

If the poisoning-resistant gas layer is made of granular ultra-stable Y-type zeolite (USY), sufficient poisoning gas resistance can be obtained even if the layer thickness is reduced to 5 mm.
However, care must be taken when the layer thickness is 20 mm or more, because the sensor sensitivity is low as in the case of other toxic gas materials.

Further, when granular silica gel is used as the material for the toxic gas layer, a higher toxic gas can be obtained although it is slightly lower than when ultrastable Y-type zeolite is used. In addition, silica gel needs to be granular,
When the powdered silica gel is used, the effect of the present invention cannot be obtained. When granular silica gel is used, the layer thickness of the gas layer to be poisoned is desirably 10 mm or more.

Similarly, when the gas layer is made of granular molecular sieve 5A, the layer thickness is 10 mm or more, and when it is made of granular zirconia, the layer thickness is 1 mm.
It is desirable that it is 5 mm or more.

In the case of using the particulate "poisoning-resistant gas material" as described above, the particle size is relatively little affected by the particle size. That is, a sufficient effect can be obtained in the range of 50 mesh or more and 2 mesh or less. The thickness of the toxic gas layer is appropriately adjusted within a range in which the toxic gas effect is obtained and the sensitivity to the test gas is not significantly affected.

On the other hand, when powdered α-alumina is used as the toxic gas material for the toxic gas layer, it is necessary to pay attention to the effect of the layer thickness on the sensitivity to the test gas, which must be 15 mm or more. It is preferably 20 mm or less. In order to obtain the effects of the present invention, α-alumina is necessary in order to obtain the effects of the present invention. However, since it is in a powder form, it is not very easy to handle. It is preferable to use granular ones. In the carbon monoxide sensor having an output value stabilizing filter according to the second aspect of the present invention, the output value stabilizing filter preferably has at least one of activated carbon, silica gel and ultra-stable Y-type zeolite. Output value stability, and a stable measurement value is always obtained even during repeated measurement.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Regarding the Shape of Sensor Used in the Embodiment) The shape of the sensor used in the embodiment of the present invention will be described below with reference to the drawings. FIG. 1A shows a model diagram of the carbon monoxide sensor used in the example, with the sensor cap partially cut away.

A sensor element 4 is provided inside the sensor cap 1, and the heater and signal leads of the sensor element 4 are connected to four pins 2, which penetrate the pedestal and extend outside the sensor. And can be connected to a power supply (not shown) and a detection circuit (not shown).

FIG. 1B shows an enlarged model diagram of the sensor element 4.
FIG. 1C shows a cross-sectional view of the model. YSZ in the figure
This is a solid electrolyte described as (symbol 6), in which an upper electrode 5 and a lower electrode 7 are arranged with stabilized zirconia having oxygen ion conductivity interposed therebetween. Below the lower electrode 7, a gas diffusion layer 8 is provided, which is formed by supporting an oxidation catalyst such as platinum or palladium on a porous material such as alumina. As described above, the lower electrode 7 is in contact with the test gas only through the gas diffusion layers 8. With such a structure, the carbon monoxide gas in the test gas is oxidized by the surrounding oxygen by the action of the oxidation catalyst of the gas diffusion layer 8, so that if the test gas contains a combustible gas, the lower electrode 7 and the concentration of oxygen in the test gas
, The concentration of oxygen in the test gas reaches a concentration difference, and as a result, a potential difference occurs between the electrodes 5 and 7. By detecting this potential difference, the concentration of combustible gas in the test gas can be measured.

In the figure, reference numeral 9 denotes an alumina insulating film, 10
Is a heater, 11 is an alumina substrate, and the heater 10
Keeps the temperature of the sensor element at a temperature suitable for the ion conduction of the stabilized zirconia (YSZ) 6. Both electrodes are connected to a sensor output lead wire 12 and are electrically connected to the pin 4 in FIG.

(Regarding Poisoning Prevention) A toxic poisoning gas layer 13 is provided above the sensor cap 13 of such a sensor, and only the poisoning gas which has passed through the toxic poisoning gas layer 13 is supplied to the sensor element. It has become. In this example, the poisoning-preventing gas layer 13 is covered with meshes at the top and bottom, and is filled with a powdery or granular poisoning-preventing gas material. As described above, this sensor has a structure in which only the test gas that has passed through the poisoning-preventing gas layer contacts the solid electrolyte sensor element.

Prior to the embodiment of the present invention, the influence of a silicon-containing organic gas or a sulfur oxide gas on a sensor element, which is a drawback of the prior art, will be described.

In FIG. 2, the sensor element is placed in a chamber having an inner volume of 50 l, and 4 g of a silicone-based sealing agent is heated in a hot plate maintained at 50 ° C. in this chamber to be poisoned with silicone gas. Shows the results of examining the sensitivity of the sensor element to carbon monoxide and hydrogen gas before and after performing the test for 24 hours.

After the sensor element is exposed to a silicon-containing organic gas, the sensitivity to carbon monoxide decreases and the sensitivity to hydrogen increases abnormally. In general, when carbon monoxide is contained in the combustion exhaust gas, hydrogen is often present at the same time, and if the sensor element exposed to the silicon-containing organic gas is subsequently used, accurate measurement of the carbon monoxide concentration becomes impossible. I understand. The poisoning conditions of the sensor element are based on the evaluation items of the Japan Gas Association.

FIG. 3 shows the influence of the sulfur oxide gas. In the figure, “Airbase” indicates the output when normal air is used as the test gas, and “CO 1000 ppm + H”.
"2500 ppm" indicates sensitivity to air in which 1000 ppm of carbon monoxide and 500 ppm of hydrogen are mixed,
“+ SOx” is 1000 ppm carbon monoxide and 500 hydrogen.
ppm, sulfur dioxide (SO ₂ ) as sulfur oxide
Shows the sensitivity when air to which 6 ppm was added was used as a test gas. It can be seen that the sensor output greatly changes due to the coexistence of such a small concentration of sulfur oxide, and therefore, accurate measurement cannot be performed. In the above description, 6 ppm was selected as a value higher than the SOx concentration of 2 to 3 ppm that is expected to be generated in the water heater depending on the conditions.

USY (Tosoh HSZ-330HUD,
Two types having layers (both having a thickness of 10 mm) made of a columnar shape having a diameter of about 1 mm and a length of 5 to 10 mm (hereinafter the same applies) or silica gel (small granules manufactured by Wako Pure Chemical Industries, the same applies hereinafter) as a toxic gas layer. The sensor was placed in a chamber having an inner volume of 50 l, and before and after the poisoning treatment with silicone gas generated by heating 4 g of a silicone-based sealing agent on a hot plate kept at 50 ° C. in this chamber for 24 hours. FIG. 4 shows the results of examining the sensor output for a mixed gas consisting of carbon monoxide, hydrogen and air. The measurement was performed on the assumption of combustion exhaust gas from a water heater.
It is performed under two conditions of 0 ° C. and 200 ° C. The numbers on the scale on the horizontal axis of the graph indicate the concentration of carbon monoxide in the test gas, and a hydrogen gas having a concentration half that of the carbon monoxide concentration is added to the test gas.

According to FIGS. 4A and 4B, in the case of a sensor having a layer made of USY or silica gel as a gas layer for preventing poisoning, the sensor output before and after poisoning is exactly the same level, and the influence of poisoning is obtained. It turns out that there is no.

In the case of a sensor having a layer made of activated carbon as an anti-poisoning gas layer, a result not affected by poisoning was obtained at the evaluation at 60 ° C., but the output at the evaluation at 200 ° C. was obtained. It was confirmed that the values were significantly different and could not be applied to actual measurement.

Further, when the carbon monoxide sensor is applied to a water heater, it is necessary to maintain the performance even when dew condensation occurs. Here, the results of examining the sensor output with respect to the mixed gas of carbon monoxide and hydrogen before and after the sensor was once subjected to dew condensation at 50 ° C. and RH 98% are shown in FIG.
Shown in The measurement was performed under two conditions of 60 ° C. and 200 ° C. assuming combustion exhaust gas from a water heater or the like.

FIGS. 5A and 6B show that in the case of a sensor having a layer made of USY or silica gel as a toxic gas layer, the sensor output before and after dew condensation hardly changes.

In addition to the granular USY and granular silica gel used above, the materials shown in Table 1 were used as the toxic gas material, and a 5 mm, 10 mm or 15 mm thick toxic gas layer was formed. Then, like the sensor in FIG.
Poisoned by silicon-containing organic gas, 10 before and after poisoning
The sensor output at 200 ° C. for a mixed gas produced by adding 00 ppm of carbon monoxide and 500 ppm of hydrogen to air was examined. The difference between the output value before poisoning and the output value after poisoning was The case where the output value was within 250 ppm or less was evaluated as ◎, the case where it was larger than 250 ppm and 500 ppm or less was evaluated as ○, and the case where it was larger than 500 ppm was evaluated as x. Table 2 shows the evaluation results.

[0033]

[Table 1]

[0034]

[Table 2]

From Table 2, it can be seen that granular silica gel, granular zirconia, granular super-stable Y-type zeolite (USY) and granular molecular sieve 5A, and granular α powder
-Alumina can provide sufficient gas-proof properties at high temperatures, especially when ultra-stable Y-type zeolite is used, a high effect can be obtained even when the layer thickness is as thin as 5 mm, and 10 mm
It can be seen that a very high effect can be obtained with the above.

When the above-mentioned sensor is applied to the flue of an actual water heater, a large temperature change from a temperature close to room temperature to a temperature around 200 ° C. is frequently repeated. Investigations on the effect of γ-granular silica gel, zirconia, ultra-stable Y-type zeolite (U
SY), molecular sieve 5A, and powdered α-
It was confirmed that a sensor using alumina as a poison-resistant gas layer can obtain sufficient durability.

Further, the granular silica gel used above,
Alternatively, for a sensor having an anti-poisoning gas layer with a layer thickness of 10 mm for each of the ultra-stable Y-type zeolites, as in FIG.
A sensor output for air to which 0 ppm has been added, and
6 ppm of sulfur dioxide as sulfur oxide in the system
The output of the sensor when added was examined, and it was confirmed that both of these sensors were not affected by sulfur dioxide and that accurate measurement was possible even in the presence of sulfur oxide.

(Carbon monoxide sensor having output value stabilizing filter) In the case of a carbon monoxide sensor according to the prior art, that is, a carbon monoxide sensor having no toxic gas layer, a phenomenon that can be called a reversal of the sensor sensitivity occurs. May have occurred.
An example will be described with reference to FIG.

FIG. 6 shows the result of a durability test using a conventional solid electrolyte type carbon monoxide sensor. In this test, measurement was performed for 35 seconds (ON) while the heater was constantly heated.
And repeating the non-measurement (OFF) for 15 seconds,
FIG. 7 shows the change over time of the sensor output when the sensor output is examined when the sensor is brought into contact with air to which carbon monoxide is added at various concentrations. 32000 times and 900 ON-OFF times
The relationship between the density and the sensor output is reversed at 00 times.
Although this example is a particularly extreme example, there may be a case where the correspondence between the concentration of carbon monoxide and the sensor output cannot be obtained. In addition, it is considered that 10,000 times of ON-OFF is equivalent to one year of use in a water heater application.
It is assumed that the service life of the water heater will be reached in 10,000 times.

On the other hand, FIG. 7 shows the results of the same repeated ON-OFF durability test performed with a sensor having the same structure as that of FIG. FIG. 7 (a) shows activated carbon (same as that used above; granular activated carbon S manufactured by Taihei Kagaku Sangyo (particle size: 9 to 50 mesh, irregular shaped granular crushed carbon))
FIG. 7B shows a USY (HSZ-330HU manufactured by Tosoh Corporation).
D, cylindrical shape with diameter of about 1mm and length of 5-10mm)
FIG. 7 (c) shows the results of a sensor using a silica gel (small granules manufactured by Wako Pure Chemical Industries, Ltd.) and having a layer manufactured to have a layer thickness of 10 mm as an output value stabilizing filter.

When the activated carbon shown in FIG. 7A is used as an output value stabilizing filter, the sensor output at the initial stage is slightly reduced, but in other cases, the output is stable and no conventional output value stabilizing filter is provided. The reversal phenomenon of the sensor output as observed in the result of the sensor according to the technology was not observed, and it was confirmed that the sensor had excellent long-term stability.

FIGS. 8 (a) to 8 (c) show the results of similarly examining the output for hydrogen in the sensors having these three types of output value stabilizing filters. It can be seen that, although the output at the time of the first measurement is slightly different from the output after that, an almost stable output is obtained for each sensor. In addition, similarly to FIGS. 7 and 8, in many experiments using different sensors, similarly stable results were obtained.

[0043]

According to the first aspect of the present invention, the carbon monoxide sensor according to the first aspect of the present invention eliminates obstacles caused by a sulfur oxide gas, silicon-containing organic gas or the like originating from putty and causing irreversible obstacles. It is an excellent carbon monoxide sensor that has sufficient durability and can accurately detect the concentration of carbon monoxide in a flue such as a water heater, making it easy to detect incomplete combustion and control combustion.・ Even a renovated house can be installed and measured from the beginning. In the carbon monoxide sensor according to the second aspect of the present invention, the output value stabilizing filter can always obtain a detected value corresponding to the detected gas concentration even during repeated measurement, and can perform accurate measurement. Becomes possible.

[Brief description of the drawings]

FIG. 1A is a model diagram of a solid oxide carbon monoxide sensor according to the present invention. (B) It is an enlarged model figure of a sensor element. (C) It is a model sectional view of a sensor element.

FIG. 2 is a view showing the influence of a silicon-containing organic gas in a sensor according to the related art.

FIG. 3 is a diagram showing the influence of a sulfur oxide gas in a sensor according to the related art.

FIG. 4 is a diagram showing the results of examining changes in sensor output before and after poisoning in order to examine poisoning gas resistance. (A) When USY is used (b) When silica gel is used

FIG. 5 is a diagram showing a result of examining a change in sensor output before and after dew condensation in order to examine dew condensation resistance. (A) When USY is used (b) When silica gel is used

FIG. 6 is a diagram for explaining a reversal phenomenon of sensor sensitivity in a sensor according to the related art.

FIG. 7 is a diagram showing a result of a durability test (indicating that a reversal phenomenon of sensor sensitivity does not occur) with a sensor having a filter made of activated carbon, USY, or silica gel as a toxic gas layer. (A) When activated carbon is used (b) When USY is used (c) When silica gel is used

FIG. 8 is a diagram showing the result when hydrogen gas is added to the test gas instead of carbon monoxide, similarly to FIG. 7; (A) When activated carbon is used (b) When USY is used (c) When silica gel is used

[Explanation of symbols]

Reference Signs List 1 sensor cap 2 pin 3 pedestal 4 sensor element 5 upper electrode 6 solid electrolyte layer made of YSZ (stabilized zirconia) 7 lower electrode 8 gas diffusion layer 9 alumina insulating layer 10 heater 11 alumina substrate 12 sensor output lead wire 13 Toxic gas layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Total Mochizuki 23 Minamikashima, Futamata-machi, Tenryu-shi, Shizuoka Inside Yazaki Keiki Co., Ltd. (72) Inventor Hiromasa Takashima 23 Minami-Kashima, Futama-machi, Tenryu-shi, Shizuoka 23 Terms (reference) 2G004 BB04 BC03 BC09 BD04 BE04 BF11 BF23 BG09 BH08 BJ02 BJ03 BL08

Claims (13)

[Claims] 1. A carbon monoxide sensor having a solid electrolyte type sensor element, wherein the carbon monoxide sensor has a structure in which only a test gas which has passed through a toxic gas layer is in contact with the solid electrolyte type sensor element. Carbon oxide sensor. 2. The method according to claim 1, wherein the toxic gas layer is granular silica gel, granular zirconia, granular ultra-stable Y zeolite,
The carbon monoxide sensor according to claim 1, wherein the carbon monoxide sensor has at least one of a granular molecular sieve 5A and a powdery α-alumina. 3. The carbon monoxide sensor according to claim 1, wherein the gas layer for preventing poisoning is made of ultra-stable Y-type zeolite. 4. The carbon monoxide sensor according to claim 3, wherein said ultra-stable Y-type zeolite is granular. 5. The carbon monoxide sensor according to claim 3, wherein the toxic gas layer is 5 mm or more. 6. The ultra-stable Y-type zeolite having a diameter of about 1 m.
The carbon monoxide sensor according to any one of claims 3 to 5, wherein the carbon monoxide sensor has a column shape of m and a length of 5 to 10 mm. 7. The carbon monoxide sensor according to claim 3, wherein the ultra-stable Y-type zeolite is in the form of a tablet. 8. The carbon monoxide sensor according to claim 2, wherein the poisoning gas layer is made of granular silica gel, and the layer thickness of the poisoning gas layer is 10 mm or more. 9. The carbon monoxide sensor according to claim 2, wherein the toxic gas layer is made of granular zirconia, and the thickness of the toxic gas layer is 15 mm or more. 10. The carbon monoxide according to claim 2, wherein the gas layer for preventing poisoning is composed of granular molecular sieves 5A, and the layer thickness of the gas layer for poisoning is 10 mm or more. Sensor. 11. The toxic gas layer comprises powdery α-alumina, and the toxic gas layer has a thickness of 15 μm.
The carbon monoxide sensor according to claim 2, wherein the diameter is not less than mm. 12. A carbon monoxide sensor having a solid electrolyte type sensor element, wherein the carbon monoxide sensor has a structure in which only a test gas that has passed through an output value stabilizing filter contacts the solid electrolyte type sensor element. Carbon oxide sensor. 13. The output value stabilizing filter is activated carbon,
The carbon monoxide sensor according to claim 12, comprising at least one of silica gel and ultra-stable Y-type zeolite.