JPS594838B2 - Constant temperature control method for microwave oven - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a D control method for constant temperature cooking in a microwave oven.

Normally, constant temperature control in a microwave oven detects the temperature of the food being cooked, compares this detected temperature with a preset temperature, and sets the cooking temperature by repeating the on and off states of a high-frequency oscillation circuit. It maintains approximately the same temperature.

In other words, the high frequency oscillation circuit turns off when the detected temperature rises above the set temperature, and turns on when it falls below the set temperature. Therefore, if there is noise superimposed on the input of the amplifier circuit or fluctuations in the power supply voltage to the amplifier circuit, the detected temperature output will be affected regardless of the actual temperature of the food being cooked. The level rises and falls in very short cycles after reaching the set temperature level, which causes the high frequency oscillation circuit to turn on and off frequently.
This results in shortening the life span 10 of the magnetron, which is a high frequency oscillation source.

On the other hand, when the detection output signal is passed through a delay means and the level of the detection output signal rises and falls in a very short period from the set level as described above, it is common practice to ignore such signal changes. This has been proposed as signal processing 15 technology (Japanese Utility Model Publication No. 49-57796).

When this technology is applied to a microwave oven, when the detected temperature output level falls below the set temperature level, the delay operation of the delay means is started, and after a certain delay time, the high frequency oscillation circuit is turned on. Therefore, even if the detected temperature output level rises and falls within the above delay time from the set temperature level in a short period, this will restart the above delay operation one after another, so that the high frequency oscillation circuit will eventually be affected. The ON operation is short period 1 of the detected temperature output level.
does not follow changes in the market. However, according to this, the high frequency oscillation circuit always turns on after a certain delay time from the point when the detected temperature output level falls below the set temperature level, even in normal conditions without noise etc.壬
There is a problem in that the temperature of the food to be cooked becomes much lower than the set value every 0 degrees, the temperature change width of the food to be cooked becomes larger, and the constant temperature cooking effect becomes weaker.

The present invention provides a constant temperature control method that eliminates the above-mentioned drawbacks, and the present invention will be described in detail below with reference to Examples. FIG. 1 shows a circuit according to an embodiment of the present invention, 1, 2
is a 100V commercial power supply terminal, 3 is a well-known high-frequency oscillation circuit including a high-voltage transformer 4, magnetron 5, etc., 6 is a bidirectional thyristor for connecting the high-frequency oscillation circuit 3 to power supply terminals 1 and 2 VC, and 7 is a terminal provided by the operator. It is an operable selection switch, and includes a common terminal 7a1, a first terminal 7b, and a second terminal 7c, and the common terminal 7a is connected to the gate of the bidirectional thyristor 6.

8, 9 and 10 are respectively known time signal generators;
An output control pulse generator and a timer signal generator.

The time signal generator 8 independently generates a time signal with a constant period T as shown in FIG. 2 AVC. Output control pulse generator 9
is composed of, for example, an astable multivibrator, which generates an output pulse with a constant period T as shown in FIG. can. The timer signal generator 10 outputs a pulse as shown in FIG. 2C for a time set manually by the operator. Reference numeral 11 denotes a first AND gate, which receives the outputs of the output control pulse generator 9 and timer signal generator 10 as inputs, and selects the selection switch 7.
The first terminal 7b provides a VC output.

The output control pulse generator 9, timer signal generator 10, and first AND gate 11 are provided for output control independent of cooking temperature, and their operations are as follows.

During such output control, the selection switch 7 selects the first terminal 7b.
Then, in the output control pulse generator 9, the pulse width of the pulse generated by the generator is set according to the desired output, and further, the desired cooking time is set in the timer signal generator 10. .

Therefore, since an alternating current voltage as shown in FIG. Then, the high frequency oscillation circuit 3 is repeatedly turned on and off. When the set time in the timer signal generation circuit 10 has elapsed, the output of the first AND gate 11 disappears, so the bidirectional thyristor 6 is always turned off and the high frequency oscillation circuit 3 does not operate. Referring again to the configuration of FIG. 1, 12 is a temperature sensor such as a thermistor for detecting the temperature of the food, and the detector is placed, for example, in the tip of a temperature probe inserted into the food. .

Reference numeral 13 denotes temperature determining means, which comprises an amplifier circuit 14 and an AD converter 15, which are well known per se.

The amplifier circuit 14 amplifies the signal input from the temperature detector 12 to produce an amplified output as shown in FIG. 3 AVC, and the AD converter 15
compares the level of the analog signal output from the amplifier with a predetermined set value level (indicated by a dotted line in the figure), and generates a pulse output as shown in FIG. 3B only when the level is lower than the set value level. Reference numeral 16 denotes a setting means operable by an operator for setting the above-mentioned setting level in the AD converter 15, and is composed of, for example, a variable resistor.

17 is a time signal generator 8, a timer signal generator 10 and A
a second AND gate whose input is the output of the D converter 15;
8 is a NAND gate that inputs the output of the AD converter 15 and the output of the timer signal generator 10; 19 is a second AND gate 1;
7 is set by the output of the NAND gate 18, and the set output of the flip-flop (FIG. 3D) is set by the second output of the selection switch r.
It is connected to terminal 7c.

The temperature detector 12, temperature determination means 13, setting means 16
, second AND gate 11, NAND gate 18, flip-flop 19, etc. are provided for constant temperature control, which is a feature of the present invention.) Their operations are as follows.

For constant temperature control, the second terminal 7c of the selection switch 7 is selected, the temperature detector 12 is placed inside the food, the setting means 16 sets a desired temperature, and the timer signal generator 10VC sets the desired temperature. Cooking time is set.

Therefore, since the temperature of the food to be cooked is initially low, a continuous output is generated from the AD converter 15, the flip-flop 19 maintains the set state, and the bidirectional thyristor 6 continues to turn on, and the high frequency oscillation circuit 3 maintains the on state. .

The temperature of the food increases due to the continuous oscillation of high frequency waves, and when the predetermined set temperature is reached, the output of the AD converter 15 disappears as shown at time TlitC in FIG. 3, so the flip-flop 19 is set and the bidirectional thyristor 6 is turned off, and the high frequency oscillation circuit 3 is turned off. When the high frequency oscillation stops, the temperature of the food to be cooked will eventually begin to drop and become lower than the set temperature again.

Thereafter, at time T2 when the time signal (Fig. 3c) from the time signal generator 8 is generated, the flip-flop 19 is set again and high frequency oscillation resumes, and when the temperature of the food to be cooked becomes higher than the set temperature, the high frequency oscillation stops. do. However, in an abnormal state, around time T3, due to fluctuations in the power supply voltage to the amplifier circuit 14VC, noise superimposed on the input of the circuit, etc., the output level of the amplifier circuit becomes short near the set temperature level as shown in Figure 3A. AD converter 1 when it goes up and down periodically
The output of No. 5 also changes accordingly, as shown in FIG. 3B.

However, since the time signal is generated at predetermined intervals, AD
The probability that the logical product of the above-mentioned short period change of the converter 15 and the time signal will be established is very small, so during this period A
Even though the output of the D converter 15 is changing, no output is output from the second AND gate 17, and in the end, the fluctuations in the power supply voltage and changes due to noise are substantially eliminated, and the high frequency oscillation circuit 3 is prevented from turning on and off abnormally frequently, and shortening of the life of the magnetron 5 can be prevented. Thereafter, the high frequency oscillation circuit 3 is repeatedly turned on and off in the same way, and when the time set by the timer signal generator 10 has elapsed, the second AND gate 11 is closed, and the flip-flop 1 is closed by the output of the NAND gate 18.
9 is set, and the high frequency oscillation circuit 3 terminates its oscillation operation.

Incidentally, the period T of the above-mentioned time signal is usually about 25 seconds, and this period can be made shorter if necessary. It needs to be longer than seconds.

Further, in the above embodiment, the output control pulse generator 9, timer signal generator 10, counter 20, and other functions can be performed by a program-controlled microprocessor made of a semiconductor LSI, and the present invention also applies in such a case. It is inclusive. Further, in the above embodiment, the temperature determining means 13 is composed of the amplifier circuit 14 and the AD converter 15, but when the output of the temperature detector 12 is sufficiently large, the amplifier circuit 1
4 is omitted and the output of the temperature sensor 12 is directly connected to the AD converter 1.
5, and in this case also the AD converter 15
There is a risk that the level of the signal representing the detected temperature will similarly change near the set temperature level due to noise superimposed on the input signal to the converter 15, fluctuations in the power supply voltage to the converter 15, etc. However, it is clear that the present invention provides an equally effective preventive effect in such cases, and therefore the present invention encompasses such cases as well. As is clear from the above description, according to the present invention, the temperature of the food to be cooked is detected, and the detected temperature is compared with a predetermined set temperature, while the high frequency oscillation circuit is repeatedly turned on and off. temperature determination means for outputting a signal when the temperature of the cooked food becomes lower than the set temperature when the temperature of the cooked food is maintained almost at the set temperature; A time signal generating means for generating a time signal is provided, and the on-state of the high frequency oscillation circuit is started in the AND state of the output of the temperature determining means and the time signal, so that the detected temperature is expressed. Even if the signal level changes in short cycles up and down around the set temperature level due to noise, etc., the high frequency oscillation circuit will follow this.
Therefore, abnormally frequent switching on and off of the circuit is prevented, and shortening of the magnetron's lifespan can be prevented.

Furthermore, according to the present invention, since the time signal is generated independently of the output of the temperature determining means, when the temperature of the food to be cooked becomes lower than the set temperature, one of the time signals is generated.
The high-frequency oscillation circuit starts to turn on at almost random timing within the two occurrence intervals, and therefore, even in a normal state without noise, the temperature of the food to be cooked becomes lower than the set temperature, unlike in the prior art. When the high-frequency oscillation circuit is turned on after a certain delay time, that is, after the temperature of the food has always decreased by a certain value, the width of the temperature change of the food becomes smaller on average, and the temperature of the food becomes constant. Temperature cooking is done more effectively.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIGS. 2 and 3 are signal waveform diagrams for explaining the operation of the embodiment. 8...Time signal generator, 13...Temperature determination means.

Claims (1)

[Claims] 1 A control method for maintaining the temperature of food at approximately a predetermined set temperature by repeating on and off states of a high-frequency oscillation circuit, and outputs a signal when the temperature of the food becomes lower than the set temperature. and a time signal generating means that generates a time signal at a time interval greater than a predetermined minimum time interval, regardless of the output of the temperature determination means. A constant temperature control method for a microwave oven, characterized in that the on-state of the high frequency oscillation circuit is started in an AND state with the time signal.