JPH116816A - Detecting and driving method for carbon monoxide gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a detecting and driving method in which carbon monoxide gas can be detected with high accuracy irrespective of its concentration by a method wherein the temperature of a sensor is set to be low in a measurement for a low-concentration region and to be high in a measurement for a high-concentration region. SOLUTION: The temperature of a sensor is set at a temperature (usually about 300 deg.C) at which an ionic conductivity is generated in stabilized zirconia. When it is set at about 800 deg.C or higher, the stabilized zirconia is damaged, and the life of the sensor becomes short. As a result, the sensor is usually used at about 500 deg.C or lower. The temperature of the sensor is set at least at two stages, i.e., a high-temperature stage and a low-temperature stage. For example, about 400 to 500 deg.C is used as the high-temperature stage, and about 300 to 400 deg.C is used as the lower-temperature stage. Then, carbon monoxide gas in a low- concentration region is measured at the low-temperature stage, and the carbon monoxide gas in a high-concentration region is measured at the high-temperature stage. The interval of a temperature changeover is set at a time or higher in which the output of the sensor is stabilized, and it is usually set at about 5 to 10 seconds. When an especially quick changeover is required, an estimation logic means or the like is installed. By this method, the carbon monoxide gas can be measured with good accuracy even in a concentration of 500 ppm or higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide gas detection driving method using a solid electrolyte type carbon monoxide sensor as a detection unit.

[0002]

2. Description of the Related Art Various types of carbon monoxide gas concentration measuring devices are currently in practical use.
It is widely used in fields such as safety management. Among these, a semiconductor sensor and a contact combustion sensor can be used as sensors of a carbon monoxide gas concentration measurement device that detects incomplete combustion of combustion exhaust gas of a combustion device such as an internal combustion engine or a water heater. Can be Among them, the contact sensor is usually used because the semiconductor sensor has a drawback that accurate measurement cannot be performed if the oxygen concentration or the moisture content in the sample gas changes. However, the flue gas temperature generally fluctuates between 70 and 200 ° C. 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.

Here, in order to obtain more safety in a water heater, a sensor capable of detecting a low concentration (500 ppm or less) is required. However, a contact combustion type sensor has a characteristic in detecting at such a low concentration. There are difficulties. Therefore, in order to solve such a problem, the development of an incomplete combustion detection sensor for exhaust gas using a solid electrolyte (oxygen ion conductor) has been studied and put into practical use (Japanese Patent Publication No. 58-498).
No. 5 publication). FIG. 1 shows a sectional view of such a solid electrolyte type carbon monoxide sensor. In FIG. 1, the center is a cross-sectional view of the sensor, and the diagrams on both sides are principle explanatory diagrams for explaining the reaction near the sensor electrode.

In the figures, reference numerals 1a and 1b denote porous platinum electrodes,
2 is a combustible gas oxidation catalyst layer, 3 is stabilized zirconia having oxygen ion conductivity (hereinafter also referred to as “YSZ”),
Heated to a temperature (300 to 500 ° C.) optimum for the conductivity by a heater 5 via an alumina layer 4.

When such a sensor is placed in an atmosphere containing carbon monoxide gas, carbon monoxide in contact with the electrode 1a combines with oxygen adsorbed on the electrode 1a to form carbon dioxide. On the other hand, since the combustible gas oxidation catalyst layer 2 exists around the electrode 1b, carbon monoxide in the atmosphere is oxidized by the catalyst layer 2 to carbon dioxide and does not reach the electrode 1b. Depending on the presence or absence of such an oxidation reaction on the electrode surface, an electromotive force is generated between the electrodes 1a and 1b in accordance with the concentration of carbon monoxide in the atmosphere where the sensor is placed. By measuring this electromotive force, the concentration of carbon monoxide in the atmosphere can be detected.

In general, a very small amount of flammable gas such as hydrogen gas remains in the combustion exhaust gas, but the above-mentioned solid electrolyte type carbon monoxide sensor has sensitivity to hydrogen gas. Since the output of such a solid electrolyte type carbon monoxide sensor is a logarithmic function like a semiconductor sensor, the concentration can be measured accurately with a low concentration gas, but can be measured with a high concentration gas. There was a problem that the accuracy was low.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a solid oxide carbon monoxide sensor capable of accurately detecting not only a low concentration gas but also a high concentration gas as a detection unit. It is an object of the present invention to provide a carbon gas detection driving method.

[0008]

According to a first aspect of the present invention, there is provided a carbon monoxide gas detecting and driving method using a solid electrolyte type carbon monoxide sensor as a detecting unit. The temperature of the sensor is set to be low when measuring the low-density region and to be high when measuring the high-density region. According to a second aspect of the present invention, there is provided a carbon monoxide gas detection driving method using a solid electrolyte type carbon monoxide sensor as a detection unit. It has a configuration in which two-stage switching is performed, the low-concentration region is measured at a low temperature, and the high-concentration region is measured at a high temperature.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, it is necessary that the sensor temperature is equal to or higher than the temperature at which ionic conductivity occurs in stabilized zirconia. Generally, sufficient ion conductivity is obtained at 300 ° C. or higher. Further, it is desirable that the temperature is at most 800 ° C. or less. If the temperature exceeds 800 ° C., the stabilized zirconia may be damaged, and the life of the sensor is significantly shortened. It is generally said that if the temperature is 500 ° C. or less, there is almost no effect on stabilized zirconia. In the present invention, it is necessary to set the sensor temperature to at least two levels. Normally, two levels of high and low are sufficient, but if necessary, three or more steps such as three steps of high, medium and low may be finely switched.

When the temperature of the sensor is set at two levels, for example, a temperature between 400 ° C. and 500 ° C. is set to a high temperature,
A temperature lower than 0 ° C. may be a low temperature. In order to obtain a sufficient effect, it is desirable that the difference between these temperatures be 100 ° C. or more. Further, in order to enable good measurement, the sensor temperature is required to be stable with good reproducibility. In the present invention, the sensor temperature may be set to a high temperature in order to measure carbon monoxide gas in a high concentration region, and the sensor temperature may be set to a low temperature in order to measure carbon monoxide gas in a low concentration region. . However, for example, the sensor temperature is set alternately with high and low temperatures, the sensor output is examined, and when the concentration of carbon monoxide gas in the measurement target gas is determined to be in the high concentration region, the concentration is measured at the high temperature setting, Further, when it is determined that the density is in the low density area, the density may be measured at a low temperature setting.

In the latter case, it is necessary to set the temperature switching interval to a time longer than the time when the sensor output is substantially stabilized.
Less than 0 seconds, but especially when a quick switch is needed,
This is not the case when a guessing logic means is provided, or when particularly accurate values are required. Note that switching of the sensor temperature and determination of the measurement area as described above can be easily performed by using a microcomputer.

[0012]

Embodiments of the present invention will be described below. The sensor used as the detection unit is the solid electrolyte type carbon monoxide sensor shown in FIG. 1, and a top view thereof is shown in FIG. The electrodes 1a and 1b of the sensor and the connection terminals 6 provided at the corners of the sensor are connected by lead wires 7 made of platinum, respectively. This sensor is made of a phenolic base 8 as shown in FIG.
It is fixed to. Note that four conductive pins 9 in FIG.
Are shown, two of which are the sensor electrodes 1
a and 1b, and the other two are connected to a heater inside the sensor.

The response to a sample gas containing carbon monoxide was examined using this sensor as a detection unit. When the heater voltage applied to the sensor heater is set low (Lo) and the sensor temperature is set to 350 ° C., the sensor output for a sample gas containing 0 to 1000 ppm of carbon monoxide is shown in FIG. In this measurement, hydrogen was added so as to be half of the carbon monoxide concentration. This assumes that the concentration of carbon monoxide in the exhaust gas when using hydrocarbons as fuel is measured, and this ratio is selected as a model of carbon monoxide and hydrogen generated during incomplete combustion in this case. The same ratio is used in the measurement described below. As shown in FIG. 4, when the heater voltage is Lo, a highly sensitive measurement is possible when the concentration of carbon monoxide gas is in the range of 0 ppm to 500 ppm.
It can be seen that the sensitivity is low in the concentration range of 00 ppm.

On the other hand, when the heater voltage is set high (Hi) and the sensor temperature is set to 450 ° C., 0 to 3000 ppm
Fig. 5 shows the sensor output for the sample gas containing carbon monoxide.
It was shown to. FIG. 5 shows that when the heater voltage is set to Hi, measurement with high accuracy can be performed even in the range of more than 500 ppm.

Next, the response of this sensor will be described. FIG. 6 is a diagram showing the response to a sample gas containing 200 ppm of carbon monoxide when the heater voltage is Lo.
The result is obtained when the sensor is exposed to the sample gas when the elapsed time is 30 seconds in the figure. It can be seen from FIG. 6 that the sensor output is substantially stabilized 15 seconds after exposure, and stabilized 25 seconds after exposure.

On the other hand, FIG. 7 is a diagram showing the results of a similar study of the response to a sample gas containing 1000 ppm of carbon monoxide when the heater voltage is Hi. From the figure, it is understood that the sensor output is substantially stabilized 15 seconds after exposure and stabilized 25 seconds after exposure, as in the case where the heater voltage is set to Lo.

Further, a result when the sensor temperature is alternately switched between high and low two stages will be described. FIG. 8 is a diagram showing the result when the heater voltage is switched between Hi and Lo.
The sample gas used contained 1000 ppm of carbon monoxide, and the sensor was exposed to this gas when the elapsed time in the figure was 30 seconds. From FIG. 8, it can be seen that when the sensor temperature is alternately switched between high and low, the response of the sensor output is good, and the sensor temperature can be favorably followed by switching. From this result, when the sensor temperature is switched alternately between high and low, the relationship between the gas concentration and the sensor output in FIGS. 4 and 5 is used as a calibration curve, so that the measurement of carbon monoxide can be performed with high accuracy up to the high concentration region. Understand that it can be measured

FIG. 9 is a timing chart of the heater voltage when the sensor temperature is continuously switched between high and low. As shown in FIG.
By alternately setting o, the measurement of the concentration of carbon monoxide can be continuously performed with high accuracy over a wide range.

[0019]

According to the present invention, in the carbon monoxide gas concentration measurement using the solid electrolyte type carbon monoxide sensor, the measurement in the concentration region of 500 ppm or more, which has been conventionally difficult, can be accurately performed. In addition, by continuously switching the sensor temperature to at least two levels of high and low, continuous measurement can be performed while taking advantage of the above advantages.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a solid electrolyte type carbon monoxide sensor and an explanatory diagram of its principle.

FIG. 2 is a top view of a solid electrolyte type carbon monoxide sensor.

FIG. 3 is a diagram (perspective view) showing a state where the sensor is fixed to a base.
It is.

FIG. 4 is a diagram showing gas concentration characteristics for a mixed gas containing 200 ppm of carbon monoxide and 100 ppm of hydrogen when a heater voltage Lo (sensor temperature: low).

FIG. 5 is a diagram showing gas concentration characteristics for a mixed gas containing 1000 ppm of carbon monoxide and 500 ppm of hydrogen when a heater voltage Hi (sensor temperature: high).

FIG. 6 is a diagram showing the response of the sensor output to a mixed gas containing 200 ppm of carbon monoxide and 100 ppm of hydrogen when the heater voltage is Lo (sensor temperature: low).

FIG. 7 is a diagram showing the response of the sensor output to a mixed gas containing 1000 ppm of carbon monoxide and 500 ppm of hydrogen when the heater voltage is Hi (sensor temperature: high).

FIG. 8 is a diagram showing the response of the sensor output to 1000 ppm CO gas when the heater voltage is alternately switched between Hi and Lo.

FIG. 9 is a diagram showing a timing chart of a heater voltage when the sensor temperature is continuously switched between high and low.

[Explanation of symbols]

 1a, 1b Porous platinum electrode 2 Flammable gas oxidation catalyst layer 3 Stabilized zirconia 4 Alumina layer 5 Heater 6 Connection terminal part 7 Lead wire part 8 Base 9 Pin

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Total Mochizuki 23 Minamikashima, Futama-machi, Tenryu-shi, Shizuoka Prefecture Inside Yazaki Keiki Co., Ltd.

Claims (2)

[Claims] 1. A carbon monoxide gas detection driving method using a solid electrolyte type carbon monoxide sensor as a detection unit, wherein the temperature of the sensor is set low when measuring a low concentration region and high when measuring a high concentration region. Driving method for detecting carbon monoxide gas. 2. A method for detecting and driving carbon monoxide gas using a solid electrolyte type carbon monoxide sensor as a detection unit, wherein the temperature of the sensor is switched between high and low at least two stages, a low concentration region is measured at a low temperature, and a high concentration is measured at a high temperature. A method for detecting and driving carbon monoxide gas, comprising measuring a concentration region.