JPH06104080A - Microwave oven - Google Patents

Abstract

PURPOSE:To detect a disconnection in a microwave oven to stop heating, not only when a thermistor for detecting the burning of food is broken but also when the analog input terminal of a microcomputer is opened, and improve safety. CONSTITUTION:An analog input terminal 8 of a microcomputer 7 having an output transistor 14 also usable as an output terminal is used, and the analog input terminal 8 is switched from output state to input state before a fixed time from the time of temperature measurement, whereby the open of a signal line for connecting the analog input terminal 8 to a thermistor 5 which is the temperature detecting element of a combustion detecting means 12 is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave oven which detects combustion and ignition due to overheating of food and stops microwave heating.

[0002]

2. Description of the Related Art As a safety device for a microwave oven
As disclosed in JP-A-126589, there are some which stop microwave heating or have an alarm means.

A conventional microwave oven will be described below with reference to FIGS. As shown in FIG. 4, the microwave oscillated from the magnetron 1 as the microwave oscillating means is supplied into the heating chamber 3 in the main body 2 to heat the food 4.

On the other hand, outside the heating chamber 3, there is provided a thermistor 5 for detecting the heat of food when it is overheated and burned. The microwave oscillation of the magnetron 1 is stopped based on the temperature detection signal from the thermistor 5.

Further, FIG. 5 (a) shows an electric circuit diagram of the combustion detecting means. An intersection point where the thermistor 5 and the resistor 6 are connected in series is connected to an analog input terminal 8 of the microcomputer 7 to connect the thermistor 5 and the resistor 6. The other end is OV and 5 respectively
It is connected to the V power supply.

FIG. 5B is a diagram showing the relationship of the analog input terminal voltage with respect to the change in the thermistor temperature. In the analog input terminal voltage corresponding to a thermistor temperature of -10 ° C. or less, the disconnection detection region 9 of the thermistor 5 is set. In the voltage corresponding to the thermistor temperature of 110 ° C. or higher, the combustion detection region 10 of the food 4 is set.

The thermistor 5 is disconnected or the connector 11
If it comes off, the analog input terminal 8 is connected to the power supply of 5V through the resistor 6, and thus reaches the disconnection detection region 9 and the disconnection can be detected.

FIG. 6 is a block diagram showing the structure of the microwave oven. When the food 4 is overheated and burned, the signal from the thermistor 5 for detecting the heat is the combustion detecting means 12.
If the combustion level is judged to be combustible, the microcomputer 7 determines that the high voltage power source 1
3 is controlled and the microwave oscillation of the magnetron 1 is stopped.

[0009]

However, in such a configuration, the analog input terminal 8 of the microcomputer 7 is
When is opened, the input terminal voltage converges to a constant voltage determined by the internal resistance of the input terminal. Since the converged voltage value does not always come to the disconnection detection area 9 or the combustion detection area 10, the opening of the input terminal cannot be detected, and therefore even if food is burned, it cannot be detected and heating is not stopped. It was a composition.

An object of the present invention is to provide a highly safe microwave oven which has a function of detecting a disconnection and stopping heating even when an analog input terminal of a microcomputer is opened.

[0011]

In order to achieve the above-mentioned object, the present invention connects an analog input terminal with an output transistor which can also be used as an output terminal according to a program of a microcomputer, and starts from the time of temperature measurement. By switching the analog input terminal from the output state to the input state before a fixed time, it is configured to detect the opening of the signal line connecting the analog input terminal and the thermistor which is the temperature detecting element of the combustion detecting means. Is.

Further, a thermistor which is a temperature detecting element of the combustion detecting means has a resistor connected in series to it, and an intersection of the thermistor and the resistor is connected to an analog input terminal of a microcomputer, and the other end of the thermistor and the resistor is connected. Are respectively connected to the power source of the microcomputer, and the thermistor is arranged in parallel with the output transistor connected to the analog input terminal.

Further, a thermistor, which is a temperature detecting element of the combustion detecting means, has a resistor connected in series to it, the intersection of the thermistor and the resistor is connected to an analog input terminal of a microcomputer, and the other end of the thermistor and the resistor is connected. Are respectively connected to the power source of the microcomputer, and the resistor is arranged in parallel with the output transistor connected to the analog input terminal.

[0014]

According to the present invention, in the above-mentioned structure, when the temperature is measured by the thermistor whether or not the food is burned, the analog input terminal of the microcomputer is changed from the output state of low impedance to the high state at a certain time before the measurement time. The operation to switch to the input state, which is impedance, is being performed.

If the analog input terminal is open, the time required to charge the capacitance of the input terminal is sufficiently large because the input terminal has a high impedance, and the voltage at the analog input terminal is Change slowly. (Finally, it reaches a fixed value determined by the internal resistance of the input terminal.) When the analog input terminal is switched from the output state to the input state and the terminal voltage is measured after a certain time, when the thermistor is normally connected, Has a sufficiently low impedance, so the voltage value corresponding to the temperature information has been sufficiently reached, but when the analog input terminal is open, the terminal voltage in the almost output state is maintained for the above reason. .

When this voltage is detected, the heating of the food is stopped.

[0017]

【Example】

(Embodiment 1) A microwave oven according to a first embodiment of the present invention will be described below with reference to FIGS. 1 and 2. The same parts as those of the conventional example are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 (a) shows an electric circuit diagram of the combustion detecting means. Similar to the conventional example, the intersection point where the thermistor 5 and the resistor 6 are connected in series is connected to the analog input terminal 8 of the microcomputer 7. An output transistor 14 is connected in parallel with the analog input terminal 8 inside the microcomputer 7, and the thermistor 5 and the resistor 6 are connected so that the output transistor 14 and the thermistor 5 are connected in parallel.
The other end of each is connected to the OV and 5V (Vcc) power supplies, respectively.

FIG. 1 (b) shows a voltage waveform diagram of the analog input terminal 8, (1) is a voltage waveform diagram in a normal state, and (2) is an analog input at the open portion 15 in FIG. 1 (a). The voltage waveform diagram when the line connected to the terminal 8 is broken on the way is shown. Similar to the conventional example, the terminal voltage corresponding to the thermistor temperature of −10 ° C. or lower is set as the disconnection detection region 9, and the terminal voltage corresponding to the thermistor temperature of 110 ° C. or higher is set as the combustion detection region 10.

When the thermistor 5 is disconnected or the connector 11 is disconnected, the analog input terminal 8 has a resistor 6
Since it was connected to the power source of 5V via, the wire break detection area 9 was reached and the wire break detection was possible.

Next, the operation of the microwave oven will be described with reference to the flow chart of the program of the microcomputer 7 shown in FIG.

This flowchart is a combustion detection subroutine, and this routine is called from the main program when the temperature information of the thermistor 5 is input.

In step S1 of the combustion detection subroutine, the output transistor 14 is switched from on to off, and the analog input terminal 8 is released from the OV potential to bring it into a high impedance state. The symbol S1 in FIG. 1B indicates this point.

In step S2, the timer is activated and waits for a fixed time. This is because it takes time to charge the electrostatic capacitance 16 of the analog input terminal 8, and this is why the rising of the voltage waveform shown in FIG. 1B is smoothly curved. The symbol S2 in FIG. 1B indicates the point of time of waiting for this fixed time (1 msec in this embodiment).

In step S3, analog data is input. The symbol S3 in FIG. 1B indicates this point. The voltage V at this time is V = Vcc × Rs / (R + Rs). Here, Rs is the resistance value of the thermistor 5, R is the value of the resistor 6, and Vcc is the power supply voltage.

In step S4, the output transistor 14 is turned on from off to prepare for the next analog data input.

In step S5, the comparative analysis of the analog data is performed. That is, as in the case of FIG. 5B of the conventional example, the disconnection detection region 9 corresponding to the thermistor temperature of −10 ° C. or lower, or the thermistor temperature of 110.
It is compared whether or not the combustion detection region 10 corresponds to a temperature equal to or higher than ° C.

If it is in the above area, the process proceeds to step S6 to stop the microwave oscillation and return to the main routine. If not, it returns to the main routine.

Here, when the line connected to the analog input terminal 8 shown in the open portion 15 of FIG. 1 (a) is broken midway, its waveform is as shown in (2) of FIG. 1 (b). Since the impedance of the analog input terminal 8 is high, it takes a long time to charge the electrostatic capacitance 16 even after the step S2 is completed, and the process proceeds to step S6 to stay in the combustion detection region 10 at the time of step S3, and microwave oscillation is performed. To stop. That is, it is possible to detect disconnection and ensure safety. When the output transistor 14 remains off and the time further elapses, the voltage value is as shown by the dotted line in the figure.
Finally, the input internal resistances 17 and 1 of the analog input terminal 8
It converges to a voltage value determined by the voltage dividing resistance of 8.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3A shows a circuit of the combustion detecting means, and the other ends of the resistor 6 and the thermistor 5 are connected to the OV and 5V (Vcc) power sources so that the output transistor 14 and the resistor 6 are connected in parallel.

FIG. 3 (b) shows a voltage waveform diagram of the analog input terminal 8, (1) is a waveform in a normal state, and (2) is FIG.
The voltage waveform when the line connected to the analog input terminal 8 at the open portion 15 in (a) is broken on the way is shown. The disconnection detection area 9 and the combustion detection area 10 are opposite to those in FIG. 1, and depending on the characteristics of the thermistor 5, this allows the width of the disconnection detection area 9 on the OV side to be wider, so In some cases, even if the resistance values of the resistors 17 and 18 are small, the detection capability can be advantageously maintained.

[0032]

As is apparent from the above description, according to the microwave oven of the present invention, the temperature measurement is performed by using the analog input terminal having the output transistor which can be used as the output terminal by the program of the microcomputer. By switching the analog input terminal from the output state to the input state a certain time before the time when it is performed, the heating is stopped even if the analog input terminal of the microcomputer is opened and combustion detection becomes impossible other than the thermistor disconnection. Therefore, a more safe microwave oven can be provided.

[Brief description of drawings]

FIG. 1 (a) is an electric circuit diagram of combustion detecting means showing a first embodiment of a microwave oven of the present invention. (B) A waveform diagram of the analog input terminal voltage of the microwave oven.

FIG. 2 is a flowchart of a program of a microcomputer of the microwave oven.

FIG. 3 (a) is an electric circuit diagram of combustion detecting means showing a second embodiment of the microwave oven of the present invention. (B) A waveform diagram of the analog input terminal voltage of the microwave oven.

FIG. 4 is a sectional view showing an example of a conventional microwave oven.

FIG. 5A is an electric circuit diagram of a conventional combustion detecting means of a microwave oven. (B) The figure which shows the relationship of the analog input terminal voltage with respect to the change of the thermistor temperature of the same microwave oven.

FIG. 6 is a block diagram showing a configuration of a conventional microwave oven.

[Explanation of symbols]

 5 Thermistor 7 Microcomputer 8 Analog input terminal 12 Combustion detecting means 14 Output transistor 15 Opening point

Claims (3)

[Claims] 1. A microwave oscillating means for oscillating a microwave for heating food, a combustion detecting means for detecting combustion ignition due to overheating of the food, and a heating operation of the food based on the combustion detection. And a microcomputer for controlling the above, and the microcomputer has an analog input terminal capable of directly inputting an analog signal from the combustion detecting means, and the analog input terminal is also used as an output terminal by a program of the microcomputer. By connecting an output transistor capable of controlling the temperature, and by switching the analog input terminal from the output state to the input state at a certain time before the temperature measurement, the thermistor which is the temperature detecting element of the analog input terminal and the combustion detecting means. Characterized by the configuration that detects the opening of the signal line connecting to Microwave oven. 2. A thermistor, which is a temperature detecting element of combustion detecting means, has a resistor connected in series to it, and an intersection of the thermistor and the resistor is connected to an analog input terminal of a microcomputer, and the other end of the thermistor and the resistor is connected. Are connected to the power source of the microcomputer respectively,
The microwave oven according to claim 1, wherein the thermistor is arranged in parallel with an output transistor connected to the analog input terminal. 3. A thermistor, which is a temperature detecting element of the combustion detecting means, has a resistor connected in series to it, the intersection of the thermistor and the resistor is connected to an analog input terminal of a microcomputer, and the other end of the thermistor and the resistor is connected. Are connected to the power source of the microcomputer respectively,
The microwave oven according to claim 1, wherein the resistor is arranged in parallel with an output transistor connected to the analog input terminal.