JPH055530A - Heating and cooking device - Google Patents

Abstract

PURPOSE:To detect a variation of water vapor heated by a food and to enable a heating control to be carried out by a method wherein the first and second thermistors are fixed to an outer surface and an inner surface of a duct and outputs of amplifier circuits for these thermistors are compared with a predetermined voltage. CONSTITUTION:As vapor is started to generate from a food, a temperature of a thin metallic plate 12 and a temperature of the second thermistor 15 directly contacting with vapor are increased due to the fact that a heat energy in vapor is higher than a heat energy of a reference air in a closed spacing 20, resulting in that a resistance balance with the first thermistor 14 is destroyed and a rapid increasing of an output Vo is generated. Then, heat of the vapor is transmitted to the first thermistor 14 through the thin metallic plate 12 with a certain delay. At this time, vapor dew formed at the second thermistor 15 absorbs latent heat, the temperature is decreased, the resistance balance between the first and second thermistors is reversed and the output Vo is rapidly decreased. Accordingly, the output Vo is compared with a set level Ve, thereby a heating control for terminating a heating operation is enabled when the output Vo exceeds Ve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating cooker which detects changes in water vapor generated from foods during heating and controls heating.

[0002]

2. Description of the Related Art Conventionally, in this type of heating cooker,
When the ambient temperature of the sensor rises, the detection sensitivity decreases and the finish of the food varies, so in order to compensate for this, there is a separate temperature compensation element or a special steam outlet for the sensor. Known (for example, Japanese Patent Fairness 2
-154922).

[0003]

However, in such a conventional heating cooker, there is a problem that the structure around the sensor becomes complicated.

The present invention has been made in consideration of such circumstances, and provides a heating cooker capable of detecting the change of water vapor generated by food and controlling the heating with a relatively simple structure. To do.

[0005]

SUMMARY OF THE INVENTION According to the present invention, there is provided a heating cooker including a heating chamber for housing food and heating the casing, and an exhaust duct communicating from the heating chamber to the outside of the case. A metal plate that has an opening in a part of the wall surface, closes the opening, first and second thermistors fixed to the outer surface of the metal plate and the inner surface of the duct, and covers the first thermistor from the outside of the duct. A storage case for storing airtightly and a first and a second thermistor connected in parallel to form a parallel circuit
And a series circuit of the second resistance, a DC power supply for applying a voltage across the parallel circuit, and a voltage between the connection point of the first and second resistances and the connection point of the first and second thermistors An amplifier circuit for outputting and a control means for changing the degree of heating of the heating chamber when the output of the amplifier circuit reaches a predetermined voltage and correcting the predetermined voltage based on the terminal voltage of the first thermistor are provided. A characteristic heating cooker is provided.

The first and second thermistors preferably have a thermal time constant of 1 second or less and uniform temperature characteristics. Further, the amplifier circuit is preferably a combination of a DC operation amplifier and an AC amplifier.

[0007]

When the heating progresses and steam is generated from the food, the second thermistor contacts the steam and its temperature rises, and the heat of the steam is gradually transmitted to the first thermistor with a delay through the metal plate. As a result, the output of the amplifier circuit rises. Next, when the vapor is condensed on the second thermistor, the temperature of the second thermistor decreases, but the temperature of the first thermistor is maintained as it is, so that the output of the amplifier circuit rapidly decreases. Therefore, by comparing the output of the amplifier circuit with a predetermined voltage, it is possible to determine the state of steam generation from the food, and the heating control can be performed based on the state. Further, when the temperature in the vicinity of the first thermistor is rising, the temperature difference between the first and the second thermistors becomes small and the output of the amplifier circuit lowers. The predetermined voltage is detected and corrected.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. This does not limit the invention.

FIG. 1 is a transverse sectional view showing an embodiment of the present invention, in which 1 is a heating chamber, 2 is a turntable, 3 is food placed on the turntable 2, and 7 is an electromagnetic wave for heating. It is a magnetron. A fan 5 is provided in the electrical equipment chamber 4, and cooling air generated by the fan 5 cools the magnetron 7, and a part of the cooling air is introduced into the heating chamber 1 through an air supply port 8 on a side wall of the heating chamber 1. This cooling air is food 3
The generated steam is carried and discharged from the exhaust port 9 on the side wall opposite to the heating chamber 1. The exhaust containing the vapor is discharged to the outside through the exhaust duct 10 made of synthetic resin. 1
Reference numeral 1 is a steam sensor attached to the side wall of the exhaust duct 10, and 6 is a case of a heating cooker.

2 and 3 are a sectional view and a front view showing the structure of the vapor sensor 11, and 12 is a thin metal plate provided so as to close the opening 13 of the side wall of the exhaust duct 10,
Reference numerals 14 and 15 denote first and second thermistors adhered to substantially the centers of both surfaces of the metal plate 12, and these thermistors have substantially uniform temperature characteristics and small thermal time constants (for example, 1
A second or less) Thermistor is used. 13a is an opening 13
A cylindrical portion provided along the edge of the, 16 is the first and second
The slits 18 provided in the tubular portion 13a for leading out the lead wires 17 of the thermistors 14 and 15 are the tubular portion 13
The cap 18 is a cap engaged with a, and the cap 18 holds the metal plate 12 by sandwiching the metal plate 12 between the end surface of the cap 18 and the convex portion 19 provided on the inner peripheral surface of the tubular portion 13a, and holds the first thermistor 14. A closed space 20 for storing is formed.

FIG. 4 is an electric circuit diagram showing a main part of a control circuit of the heating cooker. The first thermistor 14 and the second thermistor 1 provided on both sides of the metal plate 12 of the steam sensor 11 are shown.
The first series circuit of No. 5 and the second series circuit of two resistors R1 and R2 are connected in parallel to form the bridge circuit 22, and the thermistors 14 and 15 are connected to each other via the current limiting resistor R3 so as not to self-heat. Is connected to a DC power supply (not shown). First and second thermistors 1 of bridge circuit 22
The voltage between the connection point A of Nos. 4, 15 and the connection point B of the two resistors R1, R2 is impedance-converted by the voltage hollow circuits 23, 24, and then amplified by the differential amplifier 25 about 10 times. Subsequently, the AC amplifier 26 amplifies the DC component by about 20 times in a form in which the DC component is removed, and is input as an output Vo to a microcomputer (hereinafter referred to as a microcomputer) 21.

On the other hand, the terminal voltage Vt of the first thermistor 14
Is also input to the microcomputer 21. The input ports a and b of the microcomputer 21 are A / D conversion ports. Reference numeral 27 is a diode for protecting the microcomputer input port to prevent the output Vo from becoming a negative level. Microcomputer 21
Receives the output Vo and the voltage Vt, determines the amount of steam generated by the food, and controls the output of the magnetron 7 correspondingly.

FIG. 5 is a graph showing changes in the output Vo and the voltage Vt with respect to the heating time. At the initial stage of heating, the ambient temperature of the steam sensor 11 increases as the supply air temperature and the heating chamber temperature increase due to the heat generation of the electric parts. However, since the temperature rise is relatively gradual, the first thermistor 1
Since there is almost no temperature difference between the No. 4 and the second thermistor 15, the output Vo hardly changes (however, slight vibration due to noise or the like exists).

When the heating further progresses and steam starts to be generated from the food (time T1), since the heat energy of the steam is larger than that of the reference air in the closed space 20, the temperature of the thin metal plate 12 and , The temperature of the second thermistor 15 that directly contacts the steam rises, and the first thermistor 1
The resistance balance with 4 is lost and the output Vo suddenly rises. Then, the heat of the steam is transmitted to the first thermistor 14 via the thin metal plate 12 with a slight delay. At this time, the vapor that has condensed on the second thermistor 15 absorbs latent heat from the second thermistor 15 to lower the temperature of the second thermistor 15, and the resistance balance between the second thermistor 15 and the first thermistor 14 is reversed and the output Vo Plunges.

Therefore, the output Vo is set to a predetermined set level (V
By comparing with e), heating control such as ending heating at time T2 when the output Vo exceeds the level Ve becomes possible. Since the output Vo increases as the temperature of the thermistor rises due to steam heat, the temperature change of the thermistor decreases and the output Vo also decreases when the ambient temperature of the sensor 11 increases due to continuous heating or the like.
Therefore, the correction of the set level Ve as shown in the following equation is performed in the microcomputer 21. Ve = Vc + (Vt−Vd) × α where Vc is a standard setting level, Vd is a standard thermistor voltage, and α is a proportional constant (a constant determined according to the characteristics of the sensor). That is, Ve is set to a large value because the Vt is large when the atmospheric temperature near the vapor sensor is low, and is set to a small value when the atmospheric temperature rises.

In this way, since the vapor sensor 11 detects the amount of heat of vapor by the thermistor, it has a high heat-resistant temperature and there are few restrictions on the mounting location even in a microwave oven with a heater, and the structure is simple, compact and cost-effective. You can Even if the ambient temperature near the steam sensor rises and the detection sensitivity decreases, the thermistor voltage, which is a component of the sensor, is monitored to compensate for the temperature change and the set level is corrected by the microcomputer. Since the heating is controlled, the finished state of the food is kept constant without variation.

Further, since the amplifier circuit is constructed by combining the differential amplifier circuit and the AC amplifier circuit, even if the thermistor has a difference in resistance value, an initial value adjusting circuit or the like is not required separately. Even if the resistance values of the two thermistors do not match due to the rise in the ambient temperature near the sensor, the DC component is cut off and an output corresponding to the steam heat is obtained, so the thermistor selection does not cost much and is stable. It is possible to realize the finish control of the processed food with a simple configuration.

[0018]

According to the present invention, there is provided a heating cooker capable of reliably detecting the finish of food and controlling heating with a simple structure.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a heating cooker according to an embodiment.

FIG. 2 is a cross-sectional view of a vapor sensor of an example.

FIG. 3 is a front view of the vapor sensor of the embodiment.

FIG. 4 is an electric circuit diagram of an example.

FIG. 5 is a graph showing a temporal change in sensor output due to heating in the example.

[Explanation of symbols]

 1 heating chamber 5 fan 7 magnetron 10 exhaust duct 11 vapor sensor 12 thin metal plate 14 first thermistor 15 second thermistor R1 first resistance R2 second resistance

Claims (1)

Claim: What is claimed is: 1. In a heating cooker including a heating chamber for housing and heating food in a case and having an exhaust duct communicating from the heating chamber to the outside of the case, the exhaust duct has a duct wall surface. A metal plate which has an opening in a part thereof and closes the opening, first and second thermistors fixed to surfaces of the metal plate outside the duct and inside the duct, respectively, and from the outside of the duct to the first.
A storage case that covers the thermistor and stores airtightly, a series circuit of first and second resistors connected in parallel to the series circuit of the first and second thermistors to form a parallel circuit, and both ends of the parallel circuit. DC power supply for applying voltage to
An amplifier circuit for amplifying and outputting a voltage between a connection point of the first and second resistors and a connection point of the first and second thermistors;
When the output of the amplifier circuit reaches a predetermined voltage, the degree of heating of the heating chamber is changed, and a control means for correcting the predetermined voltage based on the terminal voltage of the first thermistor is provided. ..