JPS6325244B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to heating devices such as microwave ovens, microwave ovens, gas ovens, etc.
The purpose is to perform automatic cooking control.

In conventional heating devices of this type, the heating state of the object to be heated is controlled by a timer. In this method, the heating time or heating temperature differs depending on the type or amount of the object to be heated, so it is necessary to set the heating conditions in advance according to each type, which is tedious, and if the settings are incorrect, the cooking will fail. There was a drawback that it was difficult to use. Recently, in order to overcome the above problems, attempts have been made to automatically control the heating state using temperature sensors and humidity sensors.

One of the methods using a temperature sensor was to install a temperature sensor at the exhaust port and detect the temperature of the object to be heated based on changes in the temperature of the atmosphere. However, with this method, it is difficult to obtain an accurate correlation between the temperature change at the exhaust port and the heating temperature of the object to be heated. Therefore, it has been developed to control the temperature by inserting a temperature sensor directly into the object to be heated, and this method has shown relatively good results when preparing objects to be heated, such as chunks of meat. However, during final heating, uneven heating occurs and it is difficult to judge the degree of browning. Also, temperature sensors cannot be inserted into many vegetables, cakes, etc., so it is not suitable for these. Furthermore, during use, residues and odors of the heated material remain, so cleaning must be performed first before reuse, which is troublesome.

Next, as a further improved automatically controlled heating method, a method was developed in which a humidity sensor was installed in the exhaust port to detect the cooking status of various foods to be heated. Compared to temperature sensors, this method allows food to be heated over a much wider range, and heating conditions can be controlled independently of the amount of food. In the humidity detection method, all foods contain more or less water, and heating evaporates water from the food, changing the humidity in the atmosphere.
This study focused on this humidity change.

However, although either the temperature sensor or the humidity sensor method provides almost satisfactory results for some food dishes, it is insufficient for grilled dishes such as fish, meat, and bread, and alcoholic dishes such as sake cans. It wasn't something.

By the way, when food is heated to such high temperatures that it reaches a baked state, it generates alcohol components, various hydrocarbons as smoke components, and organic gases such as oil vapor in addition to moisture and carbon dioxide gas. These organic gases can be detected, for example, by semiconductor gas sensors. However, currently commercially available semiconductor gas sensors detect reducing gases including organic gases, but cannot detect moisture in the atmosphere. Therefore, a gas sensor that only has the function of detecting organic gases or reducing gases cannot precisely control the cooking of food, which is an object to be heated, and has limited specifications. Further, these semiconductor gas sensors are made of n-type semiconductor material. In moisture detection, moisture adsorption to these n-type semiconductor materials is usually due to physical adsorption, and if moisture adsorption changes electrical conduction, then
Ionic conduction of water is dominant. Therefore, the electrical conductivity of these semiconductors should increase as the moisture content increases. On the other hand, when detecting reducing gases, the electrical conductivity of n-type semiconductors increases as the concentration of these gases increases, and this shows almost the same tendency as that due to moisture adsorption, and its separability is important from the point of view of electronic circuits. It's not good to look at.

The present invention aims to provide a heating device that solves many of the problems described above when controlling the heating state of objects to be heated, mainly foods.

That is, the heating device of the present invention uses a p-type semiconductor gas sensor to detect reducing gas components generated from the heated object by increasing the sensor resistance value.
It controls the heating state of the heated object by detecting the humidity decrease, and an example of a p-type semiconductor gas sensor is magnesium chromate spinel (MgCr ₂ O ₄ −
Using plate-shaped porcelain made of TiO ₂ )-based porous porcelain semiconductor,
Ruthenium oxide (RuO ₂ ) glaze electrodes are provided on both sides.

To explain the principle of this p-type semiconductor gas sensor, like many metal oxides, it is chemically inactive in a low temperature range, for example, below 200°C, and in this temperature range it does not interact with ionic water and physical adsorption. Let's do it. The surface of a metal oxide semiconductor becomes a type of electrolyte due to the physical adsorption of water, and its electrical conductivity changes depending on the amount of adsorption, mainly due to the conduction of proton ions. Humidity sensors utilize this change. This change is characterized by a decrease in electrical resistance as the relative humidity of the atmosphere increases.

On the other hand, this p-type semiconductor gas sensor becomes chemically active at high temperatures of 200°C or higher, and when exposed to an atmosphere containing reducing gases such as various hydrocarbon component gases, hydrogen gas, hydrogen sulfide gas, and alcohol gas. Due to chemisorption reactions on the semiconductor surface, the electrical resistance increases as the concentration of these reducing gases increases. It was also found that at high temperatures of 200°C or higher, water vapor gas undergoes almost no physical adsorption or chemical adsorption (in other words, water vapor gas is essentially a neutral gas).

By using a p-type semiconductor gas sensor exhibiting such characteristics, it is possible to extremely accurately control the heating state of objects to be heated, such as foods.
In other words, all foods contain water to some degree. Many of these foods are cooked in prosthene, with initial heating for preparation and final heating for baking or browning. In the initial preparation heating, the food is heated at a relatively low temperature, and in this case, it is preferable to detect a kind of boiling state inside the food by heating it. In other words, it detects moisture in the atmosphere, and although the temperature of the food rises due to heating, it remains below 100°C. By using the sensor as a humidity sensor to detect such changes in moisture in the atmosphere, the state of preparation can be controlled more uniformly. If you continue to heat the food, the moisture will partially disappear,
Combustion begins from the surface, and various hydrocarbons mainly evaporate. For example, if the above sensor is
When heated to a constant temperature and held at a constant temperature, chemical adsorption occurs with these reducing gases, and oxygen is removed from the surface of the p-type semiconductor gas sensor, resulting in a sudden increase in electrical resistance. In this way, the sensor can be operated as a gas sensor to detect gas changes in the atmosphere due to combustion gas from the surface of the object to be heated, and heating conditions such as baking or burnt area weight can be controlled more uniformly.

As described above, when a p-type semiconductor gas sensor is used, the change in electrical resistance for humidity detection is completely opposite to the change for reducing gas detection, so if a certain threshold level is determined, food can be detected with one sensor. The cooking state of the object to be heated can be extremely accurately controlled, and the circuit configuration is also extremely simple. It is compatible with the fully automated system products that are becoming mainstream today, such as heater-type ovens,
This will further advance the automation of cooking systems such as microwave ovens, microwave ovens with heaters, and various gas-fired ovens. From this point of view, it can be said that the heating device incorporating these p-type semiconductor gas sensors is completely revolutionary.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic diagram of a microwave oven equipped with a heater equipped with a p-type semiconductor gas sensor according to an embodiment of the present invention. The object to be heated 1 is placed in a saucer 2, and these are placed inside the heating chamber. In the upper part of the heating chamber 3, heating means such as a magnetron 4 and a heater 5 are provided. A p-type semiconductor gas sensor 7 is installed at the exhaust port 6. Reference numeral 8 denotes a control device for controlling the magnetron 4 and heater 5 using signals from the p-type semiconductor gas sensor 7. FIG. 2 shows the control device 8 in detail. FIG. 3 is a schematic diagram of the sensor. FIG. 4 shows the electrical resistance characteristics of the atmospheric gas sensors.

Next, the operation shown in FIG. 1 will be explained with reference to the schematic diagram of the sensor shown in FIG. 3, the control circuit block shown in FIG. 2, and the changes in the atmospheric gas concentration and electrical resistance of the p-type semiconductor gas sensor 7 shown in FIG.

First, raw fish is placed in the saucer 2 as the object to be heated 1. When the control device 8 is turned on, the magnetron 4 starts working and the preparation of the raw fish begins.The raw fish is heated by dielectric heating and reaches a kind of boiling state, and the heating is completed and the temperature at the exhaust port 6 rises (approx.
temperature (does not rise above 100℃), and humidity increases rapidly. A p-type semiconductor gas sensor 7 installed at the exhaust port 6 detects this rapid humidity change, amplifies it in an amplifier circuit 20, and a signal is applied to one end of a comparison circuit 21. A reference voltage 23 is applied to the other end of this comparison circuit 21. The multi-relay 22 is activated by the output of the comparison circuit 21 to stop the magnetron 4 and cause the heater 5 to generate heat. At this time, the heater 12 provided to the p-type semiconductor gas sensor 7 is also energized, and the sensor 7 is maintained at, for example, 400°C.

With this operating system, after controlling the heating state by detecting water vapor for preparation, the fish to be heated starts to be grilled by high-temperature radiant heating using a heater. The temperature in the heating chamber 3 rises from 200°C to 300°C due to radiant heat, and the oil component on the surface of the fish boils and gradually begins to burn.
At this time, the heating chamber 3 becomes deficient in oxygen, and oil components, carbon monoxide, etc. are generated. These gases are all reducing so-called organic gases, and are chemically adsorbed on the p-type semiconductor gas sensor 7 installed at the exhaust port 6, detecting the heating state of the fish to be heated, such as the state of burnt eyes, and amplifying the gas. The circuit 20 amplifies and the comparison circuit 2
A signal is applied to one end of 1. The output of this comparison circuit operates a multi-relay to stop the heater and complete heating.

In this way, in the low temperature heating region, the magnetron 4
The dielectric heating is used to prepare, for example, the above-mentioned fish dish, and at this time the p-type semiconductor gas sensor 7 is operated as a humidity sensor.
After that, in order to grill the fish, the fish is heated using radiation heating, and at the same time the p-type semiconductor gas sensor 7 is also heated to a constant temperature, e.g.
It maintains the temperature at 400℃ and detects the evaporation of oil components coming out of the fish and reducing organic gases such as carbon monoxide components, which are combustion gases, to automatically control the heating of the fish in an extremely precise manner. Furthermore, from an electrical circuit perspective, if the increase in electrical conductivity of the p-type semiconductor gas sensor 7 when detecting humidity is +, then the increase in electrical conductivity when detecting reducing organic gases due to chemical adsorption at high temperatures becomes -, which can be easily explained using the comparison circuit 21. The changes in both can be separated. This is p
This is because the n-type semiconductor gas sensor 7 is used, and with an n-type semiconductor, both humidity and organic gas detection are positive, making it difficult to separate them.

Next, as an example, heating of sake cans will be explained. Place the container containing sake into saucer 2. In this case, dielectric heating is preferable in terms of electric power. As the heating progresses, water vapor and alcohol vapor also come out to the exhaust port 6. At this time, if the p-type semiconductor sensor 7 is heated in advance and maintained at, for example, 400°C, it will not chemically adsorb water vapor but will chemically adsorb alcohol.
Its electrical conductivity changes. Since alcohol is also a reducing organic gas, the electrical conductivity decreases depending on its adsorption concentration. By detecting this degree of change, it is possible to control the sake can to a favorable heating temperature.

As described above, according to the heating device characterized in that the p-type semiconductor gas sensor 7 detects the gas component generated from the heated object by heating and controls the heating state of the heated object, the heated object can be heated very precisely. It is possible to control the heating of objects.
In particular, when heating food, water vapor coming from the heated object is detected at the initial stage of heating.
We perform so-called preheating control, then high-temperature heating, detecting burnt spots and gases containing odors.
The final heating state can be controlled uniformly.

Such a heating device can be widely applied to a microwave oven, an oven, a gas oven, or an oven using a combination of these heating methods, such as dielectric heating, a heater, or a radiant heating method using gas combustion.

Further, as the p-type semiconductor sensor 7, a metal oxide type sensor is preferable. In other words, with recent ceramic technology, metal oxide-based ceramics can be easily obtained, and they are quite stable, including heat resistance, and can be heated to over 600℃ even if they absorb oil or dust. These can then be easily removed and regenerated. In theory, thin film systems and thick film systems such as glazes that have been heat treated at high temperatures are also suitable, similar to ceramics. Among these metal oxides, those suitable for the p-type semiconductor gas sensor 7 of the present invention are p-type at high temperatures.
It is necessary to have semiconductor characteristics, and typical examples include MgCr ₂ O ₄ spinel, Cr ₂ O ₃ , NiO
Examples include. Among them, MgCrO ₄ spinel
At low temperatures below 200℃, it only affects humidity and increases electrical conductivity due to physical adsorption. That is, humidity-resistance characteristics can be obtained over the entire humidity range, and the response is quick. Furthermore, at temperatures above 200°C, surface particles become chemically active and chemically adsorb reducing gases, conversely reducing electrical conductivity. This chemisorption property exists up to a high temperature of 550°C, making it effective as a gas sensor. Moreover, this system has a melting point near 2000°C, has excellent heat resistance, and even if it deteriorates due to surface adsorption, it can be regenerated by heating and cleaning in air at 600°C or higher, so it has a long life. In addition, in FIG. ₃ , electrodes 11, 12, 13, 14, 1
5 is a lead wire connected to the electrode and pulled out. A sensor detection resistor is located between one of the lead wires 14 and 15 and both terminals of the lead wire 13. That is, it becomes a detection resistance of a P-type gas sensor. Further, since the Grace resistor is inserted between the leads 14 and 15, it is used as a heater for heating the element, and is activated by applying electricity to heat it when gas is detected.

FIG. 4 shows changes in electrical resistance due to water vapor concentration and changes in electrical resistance due to concentration of various reducing gases, such as alcohol, when the resistance of the p-type semiconductor gas sensor 7 is standardized to a constant level. Various hydrocarbons, oil components, odor components, hydrogen sulfide, carbon monoxide, etc. also show changes similar to those of alcohol.

As described above, the heating device according to the present invention can automatically control the heating state by controlling the heating means using a p-type semiconductor gas sensor, unlike heating using a conventional timer or heating only by temperature control. Further, the p-type semiconductor gas sensor is thermally stable, has quick response, and has good gas selectivity, and can perform very stable heating control.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of a microwave oven according to an embodiment of the present invention, Fig. 2 is a block diagram of a control device, and Fig. 3 is an example of a p-type semiconductor gas sensor. The top view of FIG. 4 is a gas resistance characteristic diagram of the p-type semiconductor gas sensor of FIG. 3. 1... object to be heated, 2... saucer, 3... heating chamber,
4... Magnetron, 5... Heater, 6... Exhaust port, 7... P-type semiconductor gas sensor, 8... Control device, 11... Electrode, 12... Heater, 13, 1
4, 15...Lead wire, 20...Amplifier, 21...
...Comparison circuit, 22...Multi relay, 23...Reference voltage.

Claims (1)

[Claims] 1. A first heating means that heats an object to be heated, a P-type semiconductor gas sensor that detects a gas component generated from the object to be heated, and a second heating means that selectively heats the gas sensor according to the gas component to be detected. A heating device comprising: a heating means; and an output control means for controlling the output of the first heating means by increasing or decreasing a sensor resistance value of the gas sensor.