JPS62126341A - Gas sensor - Google Patents

Abstract

PURPOSE:To obtain a gas sensor having good sensitivity, by applying catalysts different in gas selectivity to elements formed by separating an oxide semiconductor into a plurality of sections. CONSTITUTION:An oxide semiconductor (e.g., stannic oxide SnO2)2 is mounted on one surface of an alumina substrate 1 and a heater 3 for heating elements is mounted on the other surface thereof. The oxide semiconductor 2 is one separated into elements 2a, 2b and an electrode 4 is mounted to the element 2a and an electrode 5 to the element 2b and, further, a common electrode 6 is mounted on the elements 2a, 2b. A catalyst (e.g., Pt-Rh-AlO2)7 is applied to the elements 2a and a catalyst (e.g., W-Cu-AlO2)8 to the element 2b. A sensor element A is formed on the basis of the element 2a and the catalyst 7 and a sensor element B on the basis of the element 2b and the catalyst 8. The sensor element A is low in the sensitivity to alcoholic gas and the sensor element B contrarily has good sensitivity to alcoholic gas. The sensor elements A, B have almost equal sensitivities to gas other than alcoholic gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a sensor used in a cooking appliance such as a microwave oven.

[Technical long-awaited inventions and their problems]

In general, cooking devices such as microwave ovens are equipped with a gas sensor that detects gases that are present in food, and the type of food is automatically determined based on the output of this gas sensor, and the cooking method is optimized to suit the type of food. There is something I did.

In such microwave ovens, a gas sensor that has good selectivity (sensitivity) for alcohol-based gases is used to detect whether or not the gas that is being absorbed from the food is alcohol-based. I am trying to determine the type of.

However, the reality is that it cannot be said that the gas sensor reacts only to alcohol-based gases, and may also react to other gases such as carbon monoxide (Go). In this case, it goes without saying that an error will occur in determining the type of food, which will adversely affect the quality of the cooking.

[Purpose of the invention]

This invention was made in view of the above circumstances,
The purpose is to provide a gas sensor with good selectivity that reacts strongly only to a specific gas.

[Summary of the invention]

In this invention, an oxide semiconductor is separated into a plurality of elements, and each of these elements is coated with a catalyst having a different gas selectivity, thereby forming a plurality of sensor elements.

[Embodiments of the invention]

An embodiment of this invention will be described below with reference to the drawings.

As shown in FIGS. 1 and 2, one side of the alumina substrate 1 is made of an oxide semiconductor (for example, stannic oxide 5nO2).
) 2 and a heater 3 for heating the element on the other side. The oxide semiconductor 2 is divided into two elements 2 as a whole.
It is separated into elements a and 2b, and the voltage Vi4 is applied to element 2a.
An electrode 5 is attached to the element 2b, and a common electrode 6 is attached to the elements 2a and 2b. And element 2
A catalyst (for example, PC-Rh-AlO2) 7 is applied on the element 2b, and a catalyst (for example, W-C1l -A(l
o2) Apply 8. That is, the sensor element A is formed mainly by the element 2a and the catalyst 7, and the sensor element B is formed mainly by the element 2b and the catalyst IB.

When the gas sensor configured as described above is actually used, a unit circuit as shown in FIG. 3 is configured.

A constant DC voltage Vd is applied to sensor element A (between electrodes 4 and 6) via resistor 11, and sensor element B (between electrodes 5 and 6) is applied to sensor element B (between electrodes 5 and 6).
．． 6) through a resistor 12. Furthermore, a DC power source 13 is connected to the heater 3.

Then, the phase U connection point 3a of the sensor element Δ and the resistor 11
The difference vab between the voltage generated at the sensor cord B and the voltage generated at the interconnection point Sb of the sensor cord B and the resistor 12 is output.

Here, the characteristics of sensor elements A and B are shown in FIG.

Sensor element A is less sensitive to alcohol-based gases, and conversely sensor element B is less sensitive to alcohol-based gases!
If 1 degree is good. - Sensor probe A for gases other than alcohol-based gases such as carbon oxide.

B has almost the same sensitivity.

Therefore, when alcohol-based gas is dissipated from food during actual cooking in a microwave oven, the resistance of sensor element A remains almost constant, but the resistance of sensor element B increases as the amount of gas increases. This results in a significant decrease. Therefore, the difference vab between the voltage generated at the connection point 5a and the voltage generated at the connection point 3b increases greatly as the gas reservoir increases, as shown in FIG.

On the other hand, when non-alcoholic gases such as carbon monoxide are diffused from food, the resistance to the sensor element and the low flow through sensor element B are almost the same. Therefore, the difference Vab between the voltage generated at the connection point 3a and the voltage generated at the connection point sb takes a value close to zero.

Therefore, the control section of the microwave oven determines that the gas is alcohol-based if the level of the voltage signal vah is large.
The type of food is determined based on the determination result. Also,
If the level of the voltage signal Vab approaches zero, it is determined that the gas is not alcohol-based, and the type of food is determined based on the determination result.

In this way, it is possible to obtain a gas sensor with good selectivity that responds strongly only to a specific gas, such as alcohol, which allows for accurate discrimination of the type of food in the microwave oven, and for always cooking to a good quality. be able to. In particular, since the sensor elements A and B are formed in one package, the cost can be reduced compared to the case where two gas sensors are provided. Moreover,
In response to changes in ambient temperature and humidity, B
There is an initial point where the resistance changes in the same way and they mutually charge each other.

It should be noted that the overall shape is not limited to the above embodiment, and may be constructed using a cylindrical ceramic substrate 1', as shown in FIG. 6, for example. Also, although two sensor elements are formed, three or more sensor elements may be formed by using various catalysts. Furthermore, although the in-IR properties for alcohol-based gases have been improved, it is also possible to improve the selectivity for gases other than alcohol-based gases by combining catalysts.

〔Effect of the invention〕

As described above, according to the present invention, an oxide semiconductor is separated into reformed elements, and each of these elements is coated with a catalyst having a different gas selectivity. Since a VR sensor element is formed, a gas sensor with good selectivity that can respond strongly only to a specific gas can be obtained.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of one embodiment of this invention +91, Fig. 2
The figure is a cross-sectional view taken along the line X-X in Figure 1, viewed in the direction of the arrow;
Figure 1 shows the structure of the unit 71 to the circuit of the same example, Figure 4 shows the characteristics of each sensor element in the same example, and Figure 5 shows the state of the output in the same example. FIG. 6 is a diagram showing the configuration of a modified example of the same embodiment. 1... Alumina substrate, 2... Oxide semiconductor, 3...
- Heater, 7.8... Catalyst, A, B... Sensor element. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) Separating the oxide semiconductor into multiple elements and
A gas sensor characterized in that a plurality of sensor elements are formed by coating these elements with catalysts having different gas selectivity. (2) The gas sensor according to claim 1, wherein the oxide semiconductor is SnO_2. (3) The catalysts are platinum (Pt)-rhodium (Rh)-alumina (AlO_2)-based catalysts and tungsten (W)-based catalysts.
The gas sensor according to claim 1 or 2, characterized in that the gas sensor is of two types: a copper (Cu)-alumina (AlO_2)-based gas sensor.