JPS5855633B2 - High frequency heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION As frozen foods have recently become popular, high-frequency heating devices have come to be frequently used to defrost them.

Defrosting frozen foods using high frequency waves has the advantage that the thawing time is shorter than that of general defrosting (for example, leaving the food in the air or thawing it under running water), and therefore there is less deterioration of the food.

However, considering the nature of high-frequency waves, when a part of the surface of a frozen food is thawed first, the dielectric constant of that part is tens of times higher than that of the unthawed part, so high-frequency energy is concentrated in the part that has been thawed. It has the disadvantage of overheating.

The following two methods are employed in general high-frequency heating devices to overcome this drawback.

For example, use a heating device with a maximum high frequency output of 600W to -15℃.
To explain the case of heating frozen food as an example, in the first example, as shown in Figure 1, a high frequency of 600W is turned on for 11 seconds, and then the following 1
This is an intermittent heating method that repeats the cycle of turning off for 2 seconds and attempting to equalize the temperature by heat conduction during this period.

The temperature changes in the surface temperature and internal temperature of the frozen food when this intermittent heating is performed are shown by solid lines in FIG. 2 a p b.

Note that the temperature change when continuously heated with a high frequency output of 600 W is shown by a broken line on the same diagram.

As is clear from the figure, when considering the time required to thaw the food to the inside (generally around 12 degrees Celsius is considered appropriate),
The thawing time T1 by intermittent heating is the thawing time T by continuous heating.

Although it is longer, the surface temperature is lower than in continuous heating, and the quality of the food deteriorates less.

However, even in the case of intermittent heating, when thawing a large piece of meat, it is inevitable that a part of the surface will become quite hot.

The second conventional example, as shown in Fig. 3, is a method in which the high-frequency output is reduced (200 W in the figure) and the temperature is diffused by heat transfer while heating. This approximates the state in which the off time is shortened, and the temperature changes are as shown in FIGS. 4a and 4b, giving almost the same results as in FIG. 2.

Further, the defrosting time T2 is also T2kiT.

Note that in both of the above examples, the thawing time is set using a timer, but since the thawing time varies depending on the initial temperature, moisture content, shape, etc. of the frozen food, this may cause undercooking or overcooking. It takes a great deal of skill to thaw food properly, and generally raising the temperature of food too much during thawing can have undesirable effects such as evaporation of moisture, oxidation, enzyme action, and bacterial growth.

Especially for meat and fish, it is necessary to keep the final thawing temperature below 5°C to avoid deteriorating the quality of the food.

The present invention eliminates the drawbacks of the conventional high-frequency heating apparatus described above, and provides a high-frequency heating apparatus that can automatically defrost food that meets the above-mentioned thawing requirements regardless of skill.

FIG. 5 shows the configuration of the heating chamber of the high-frequency heating device according to the present invention. In the figure, 1 is the heating chamber, 2 is a frozen food such as a meat loaf, and 3 is a saucer for the same.

A contact 4 detects the temperature of the food 2, and has a temperature sensing element (hereinafter referred to as a thermistor) 5 built therein.

6 is a contact holder, and a spring 7 presses the contact 4 onto the frozen food 2.

8 is a shielded wire that transmits the signal from the sensor 5 to a control circuit outside the heating chamber 1.

Next, the configuration and operation of the control circuit will be explained with reference to FIG.

First, a signal from the sensor 5 regarding the surface temperature of the frozen food 20 is sent to the temperature comparison circuit 9.

This temperature comparison circuit 9 is set to output an OFF signal when the food surface temperature becomes 5° C. or higher, and output an ON signal when the food surface temperature becomes 0° C. or lower.

This on/off signal passes through the amplifier circuit 10 and turns on/off the high frequency power supply operating circuit 110.

On the other hand, the off signal from the amplifier circuit 10 is clocked by the off signal clock circuit 12, and if this off time exceeds a predetermined time, high-frequency heating is terminated regardless of the signal from the thermistor 5. It is.

In other words, the decompression is completed.

Next, FIG. 7 shows the high-frequency heating time when the food is thawed using the circuit configuration described above, and FIGS. 8a and 8b show the progress of the surface temperature and internal temperature of the food.

As is clear from the figure, the frozen food at -15°C is heated at a high frequency of 600W for 1 second toN after the start of heating until the surface temperature reaches 5°C.

When the temperature reaches 5°C, the high frequency is turned off, and when the surface temperature reaches 0°C 1 second after EOFF due to heat transfer to the inside, it is turned on again and heating is continued for 2 seconds tON until the surface temperature reaches 5°C.

This on and off cycle is repeated until, for example, when the off time reaches ax, which is equal to the preset maximum freeze time t, defrosting ends.

This maximum freezing time tmax may be set so that the internal temperature will be between 12° C. and 0° C. at the end of thawing.

According to the heating operation described above, it is possible to heat the food at a maximum output of 600W until the surface temperature of the food reaches 5°C, which not only shortens the thawing time T compared to conventional methods, but also reduces the food surface temperature to 5°C. Defrosting takes place automatically without exceeding the limit and therefore without deteriorating the quality of the food.

In the above explanation, the high frequency output was explained as 600W, but it is also possible to switch to an appropriate output depending on the amount and type of food.

Further, as a method for determining the defrosting time T3, if the method using the off-time clock circuit described above is the first method, the following second and third methods may also be considered.

That is, the second method is a method in which heating is stopped when the surface temperature of the food reaches 5° C. a predetermined number of times (for example, three times) as shown in FIG.

This can be done by inserting an OFF number counting circuit in place of the OFF time counting circuit in FIG.

The third plan, as shown in FIG. 10, utilizes the fact that the surface temperature decreases more slowly with each heating cycle after the high-frequency heating is turned off.

In other words, this is a method of detecting the differential value of temperature change.

The decompression ends when the angle a3 becomes smaller than the predetermined angle a in FIG.

For this third plan, a temperature change differential value detection circuit may be inserted in place of the off-time clock circuit in FIG. 6.

As described above, according to the present invention, in a configuration in which high-frequency heating is stopped when the surface temperature of frozen food rises to about 5°C, and heating is restarted when the surface temperature of the frozen food drops to about 0°C, the heating The high-frequency heating is stopped when the number of stops reaches a predetermined number, so that for heavier frozen foods, the cycle at which the surface temperature reaches 5°C is shorter than for lighter weight items. It just gets longer.

Therefore, by simply repeating heating a predetermined number of times until the surface temperature reaches 5° C., very good thawing results can be achieved in a short time.

That is, by simply counting the number of times the food is heated, optimal thawing can be achieved without worrying about the weight of the food.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the thawing state using the conventional intermittent control method at an output of 600W, Figures 2a and b are diagrams showing the relationship between the surface temperature and internal temperature of frozen food under the same control method, and Figure 3 is the same. FIG. 4a is a diagram showing the decompression state using the continuous oscillation method at an output of 200 W. b is a diagram showing the relationship between the surface temperature and internal temperature of frozen food in the same thawing method, FIG. 5 is a cross-sectional view of the heating chamber in the high-frequency heating device of the present invention, and FIG. The block diagram shown in FIG. 7 is a diagram showing the output control state by the same device, and FIG. 8a is a diagram showing the output control state by the same device. b is a diagram showing the relationship between the surface temperature and internal temperature of the frozen food in the same control method, and FIGS. 9 and 10 are diagrams illustrating the thawing stop state in another embodiment of the present invention. 2...Frozen food, temperature comparison circuit, 11 12...-Stopping means. 5...Temperature sensing element, 9...-...-
・High frequency power supply operation circuit,

Claims (1)

[Claims] 1. A temperature sensing element that detects the surface temperature of frozen food, a temperature comparison circuit that intermittently controls high frequency oscillation based on the signal from this temperature sensing element, and a temperature comparison circuit that counts or detects the signal from this temperature comparison circuit to stop high frequency oscillation. and a stop means for stopping thawing, and the temperature comparison circuit stops high-frequency heating when the surface temperature of the frozen food rises to about 5°C, and restarts high-frequency heating when the surface temperature of the frozen food drops to about 0°C. The high-frequency heating device is configured such that the stopping means includes an off-counting circuit that stops high-frequency oscillation when the number of high-frequency heating stops reaches a predetermined number.