JPS6332233B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-frequency thawing machine, and more particularly to a high-frequency thawing machine having a thawing termination control function.

Conventionally, the most common methods for detecting the completion of defrosting in machines that use high-frequency dielectric heating to defrost frozen goods have been to insert a temperature detector such as a thermistor into the object to be thawed, or to simply set the defrosting time using a timer. Ta. However, in the former method,
Due to the temperature distribution inside the thawed product, it is difficult to judge the completion of thawing by measuring one or several points, and the latter method requires a lot of experience and requires a lot of experience, and there is a possibility of failure. It was a very sexual thing.

The present invention eliminates the above drawbacks and realizes a high-frequency thawing machine that automatically detects the end of thawing and stops dielectric heating. A detailed explanation will be given below.

FIG. 1 shows the configuration of a high-frequency decompressor according to the present invention, and FIG. 2 shows changes in high-frequency output over time of the high-frequency decompressor. Figure 3 shows the temperature and loss coefficient characteristics of the thawed product. FIG. 4 is a block diagram of one embodiment of a high frequency decompressor according to the present invention, and FIG. 5 is a block diagram showing another embodiment of the present invention.

In FIG. 1, opposing electrodes 2a and 2b are provided in a high frequency cavity 1, and high frequency electrolysis is applied from a high frequency power source 3 between the opposing electrodes 2a and 2b. An object to be thawed 4 is placed between opposing electrodes 2a and 2b with an insulating plate 5 interposed therebetween. The insulating plate 5 must support the object 4 to be thawed and at the same time provide electrical insulation, and must be made of a material with low high frequency loss.

Figure 2 shows the change in high frequency output over time when a nearly constant high frequency electric field is applied between the opposing electrodes 2a and 2b.
Two examples of thawing object B and small volume are shown.

For object A to be thawed, the high frequency output is low at the beginning of heating and gradually increases until it reaches the peak point P ₁
It shows the maximum value at , and gradually decreases. peak point
At time T ₁ when Q ₁ has decreased by a certain percentage from P ₁ , for example 80%, thawing has progressed considerably.

The high frequency output decreases to Q ₁ ' at time T ₁ ' until complete decompression, and a further time ΔT ₁ is required from time T ₁ .

In the case of the thawed object B, which has a small volume, the peak point P ₂ of the high frequency output occurs in a shorter time than the thawed object A, which has a large volume, and is at the point Q ₂ , which has decreased by a certain percentage from the peak point P ₂ . Time T ₂ is also early in time.
At time T ₂ when the high frequency output decreases to Q ₂ ,
The thawing has progressed considerably, but it will take △T ₂ time to completely thaw it. The high frequency output becomes Q ₂ ′, and decompression is completed in time T ₂ ′.

As mentioned above, the time T ₁ ' until the object to be thawed A is completely thawed is T ₁ +ΔT ₁ , and the time T ₂ ' until the object B is completely thawed is T ₂ +ΔT ₂ .

The relationship between the time △T ₁ and △T _{2 from the point T 1 , T 2 when the} thawing has progressed considerably until the complete thawing is △T ₁ > △T ₂
There is a difference between peak points P ₁ and P ₂ . The reason why the high frequency output to the thawed object changes as shown in Figure 2 is that the loss coefficient ε _r tan δ is small at subzero temperatures as shown in Figure 3.
This is because it reaches its maximum value near 0°C and decreases again as the temperature rises further.

Since the high frequency output is proportional to the frequency, the square of the electric field E, and the loss coefficient ε _r tan δ, the loss coefficient can be estimated from the high frequency output, and the internal average temperature of the object to be thawed can be estimated from the change thereof. Therefore, the present invention detects the maximum value of the high frequency output and a value that is reduced by some percentage from the maximum value, detects the defrosting state, and performs defrosting control.

FIG. 4 is a block diagram showing one embodiment of the present invention, in which a rectifier circuit 3 is connected to a low frequency AC power source 4.
Direct current power is applied to the high frequency generation circuit 31 via 0. The high frequency generation circuit 31 generates DC power from 10 to
Convert it to 100MHz high frequency power, counter electrode 2a,
A high voltage is applied between 2b and the object to be thawed 4 is heated. The output of the high frequency generation circuit 31 is controlled by a control circuit 32. The control circuit 32 includes an input current detection circuit 320, an information processing circuit 321, and a storage circuit 32.
2. Consists of an output control circuit 323.
The input current detection circuit 320 is a high frequency generation circuit 31
The input current is detected in order to indirectly detect the high frequency output of the Input current detection circuit 320
The output signal is sent from the information processing circuit 321 to the storage circuit 3.
Add to 22. An input current signal that changes with the defrosting time as shown in FIG. 2 is stored in the storage circuit 322.

The information processing circuit 321 compares and calculates the input current value from the input current detection circuit 320, which changes depending on the defrosting state, and the input current value stored in the storage circuit 322, and determines the peak value of the high frequency input during defrosting. That is, peak points P ₁ and P ₂ in FIG. 2 are determined.

The time from detecting the peak value to complete decompression (by adding △T ₁ and △T ₂ in Fig. 2 and applying a signal to the output control circuit 323,
Stop the output and finish decompression.

FIG. 5 shows another embodiment of the present invention, in which a controllable switch 33 is provided between the low frequency AC power source 4 and the rectifier circuit 30, and as in the embodiment of FIG. The memory circuit 322 detects the peak current value, and the information processing circuit 321 (or comparison calculation circuit) detects the peak current value and the point in time when the peak current has decreased by some percentage from the peak current value, and the timer circuit 322 detects the peak current value.
24, and after a certain period of time, the output control circuit 32
3 opens the switch 33. As described above, the control circuit 32 can be constructed relatively easily using a microcomputer, and the timer means can also be incorporated into the storage device. Therefore, if the input current is small, the heating time △T ₂ shown in Figure 2
If ΔT 1 in FIG. 2 can be made small and the input current is large, it is easy to control to lengthen ΔT ₁ in FIG. Note that the high frequency output is obtained by multiplying the input power of the high frequency generation circuit 31 by efficiency, and as the high frequency output increases, the input power also increases, and at the same time, the input current also increases. Of course, high frequency output current may also be detected.

The present invention is not limited to the above embodiments, and the same effect can be obtained even if a semiconductor switching element such as a thyristor is used in the rectifier circuit 30. Further, as a method of detecting the input current, it is possible to detect an electric signal according to the high frequency output by detecting a low frequency alternating current or by detecting a high frequency output current.

As described above, according to the present invention, in a high-frequency defrosting machine, it is possible to automatically detect the end of defrosting and stop the operation.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a high-frequency thawing machine according to an embodiment of the present invention, Figure 2 is a diagram showing changes in high-frequency output during high-frequency defrosting, and Figure 3 is a diagram showing the characteristics of the temperature and loss coefficient of the object to be thawed. 4 is a block diagram of the same high frequency decompressor, and FIG. 5 is a block diagram showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... High frequency cavity, 2a, 2b... Counter electrode, 3... High frequency power supply.

Claims (1)

[Claims] 1 Equipped with a high-frequency power source that performs dielectric heating using a high-frequency electric field, a detection means that detects a high-frequency output of this high-frequency power supply or an electric signal correlated to this high-frequency output, and a control circuit that determines a peak value signal from this detection means. , a high frequency defrosting machine in which the control circuit determines the end point of defrosting based on a peak value.