JPS6141108B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects the temperature of an object to be heated using a detection means built into the tip of a temperature-sensitive probe provided independently in the microwave oven body, and responds to a signal output from this detection means. The present invention relates to an improved invention for a heat generation prevention device for a probe antenna in a temperature sensing device that controls the operation of a heating source through an operation control circuit provided in a microwave oven body by oscillating a detected temperature signal through a probe antenna.

Regarding such a temperature-sensing device, the applicant has already filed Japanese Patent Application No. 107087-1987 ``Temperature-sensing device for heating cooker'', Utility Application No. 140-582 ``Temperature-sensing device'' and Utility Application No. 140-140583. According to subsequent experiments and research, the probe antenna in such a temperature sensing device could be a loop antenna made of coiled copper wire, for example. It has been found that when this happens, the antenna is vulnerable to the effects of microwaves, resulting in abnormal heat generation of the loop antenna itself or discharge between adjacent copper wires of the loop antenna.

The present invention was invented in view of this problem, and aims to suppress self-heating or discharge of the loop antenna as much as possible by providing a temperature-sensitive probe with a means for reducing the influence of microwaves on the loop antenna. .

Hereinafter, one embodiment will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a microwave oven in which food is cooked using a temperature sensing device according to the present invention. While the food F is heated under the action of the magnetron 4 which is placed on the table 3 and whose operation is controlled by the magnetron control circuit 10, the temperature of the food F is measured by the temperature sensing device 5 according to the present invention.
At the same time as detecting this, it is converted into a radio wave P containing food temperature information and transmitted to a receiving antenna 9 provided in the oven 1.The receiving antenna 9 converts this radio wave P into a temperature signal and sends it to the magnetron control circuit 10. The magnetron 4 is controlled by the function of the circuit 10.

Such a configuration is based on the above-mentioned patent application No. 53-107087.
For the sake of convenience, further explanation will be omitted.

Now, the temperature sensing device 5 having a probe antenna made based on the device according to the present invention is as follows.
As shown in FIGS. 2 to 4, this consists of an insertion tube section 7 made of a small diameter metal tube with one end as a pointed end, and the other end of the insertion tube section 7 fitted into a fitting section 6a provided at one end. A handle tube section 6, a temperature sensing element 9 (an element such as a crystal oscillator whose resonance frequency changes depending on the ambient temperature) housed in one end of the insertion tube section 7, and a temperature detection element 9 disposed inside the handle tube section 6. A lead connects a circuit board 11 which is protected from microwaves by a cable damping device 10 formed in the handle tube 6, a circuit (not shown) provided on this circuit board, and the vibrator 9. The wire 12 is located outside the other end of the handle tube section 6, and one end passes through the handle tube section 6 and the yoke damping device 10 and is connected to the circuit of the circuit board 11, and the other end is connected to the handle tube section. 6 and a probe antenna 8 consisting of a loop antenna wound around a bobbin 15 made of synthetic resin. It consists of a metal protection piece 13 extending in the axial direction along the axial direction, and a heat-resistant protection film 14 that covers the entire outer periphery of the handle tube part 6, probe antenna 8, and metal protection piece 13 without shielding microwaves. has been done.

What should be noted here is that the temperature sensing device 5 of the present invention is provided with the metal protection piece 13 near and along the probe antenna 8 as described above, and the length of the probe antenna 8 is , the length is set to such a length that the impedance is such that a type of resonant circuit formed by the probe antenna 8 and the above-mentioned chiyoke damping device 10 does not resonate, and this feature was obtained from the following experiment.

〔experimental method〕

A certain temperature damping device 10 is installed on a turntable in a microwave oven with an output of 650W (watts), and a temperature sensing device with the following various conditions is placed on it, and in this state, the turntable is rotated and left unloaded for 1 minute. After operating (without food) and irradiating the temperature sensor with microwaves, measure the temperature of the probe antenna with a surface thermometer. The ambient temperature during measurement should be 20 to 22°C.

Experiment () As shown in Figures 5 and 6 a, a rod-shaped bobbin 15 is used.
We prepared several temperature-sensing devices with a structure of simply winding the probe antenna 8 around the probe antenna 8 with different winding lengths (actually, the dimensions were changed from 24 cm to 45 cm in 1 cm increments). When the temperature sensing device with the probe antenna 8 having different winding lengths was finally irradiated with microwaves in the oven 1 according to the above experimental method and its surface temperature was measured, Measurement results were obtained as shown in the characteristic line A in the graph (in which the temperature value of the antenna is shown and the winding length of the probe antenna is shown on the horizontal axis).

According to this experiment, as is clear from this characteristic line A, the winding length of the probe antenna 8 is approximately 24 cm.
At 30cm, 36cm, and 42cm, the lowest temperature was approximately 50℃.

Experiment () Hollow bobbin 15 as shown in Figures 5 and 6 b.
Similar to the above experiment (), several temperature sensing devices having a structure in which a probe antenna 8 is wound around the probe antenna 8 were prepared with different winding lengths, and they were finally placed in the oven 1 according to the above experimental method. When microwave irradiation was applied and the surface temperature was measured, measurement results as shown in characteristic line B in FIG. 8 were obtained.

According to this experiment, as is clear from the above characteristic line (b), the minimum temperature is approximately 60°C, which is higher than in the case of the above experiment (). 28cm, 34cm, 40cm
It came out when.

Experiment () The above experiment () was carried out using a temperature sensing device having a structure in which a probe antenna 8 was wound around a rod-shaped bobbin 15 and a metal protective piece 13 was provided on the handle tube 6 along the antenna 8 as shown in Fig. 7. Similarly, while preparing several probe antennas 8 with different winding lengths, they were finally irradiated with microwaves in the oven 1 according to the above experimental method and their surface temperatures were measured.
The measurement results shown in characteristic line C in the figure were obtained.

According to this experiment, as is clear from characteristic line C, the minimum temperature is considerably lower than in the above experiments () and (), and the winding length of the probe antenna 8 is approximately 28
cm, 34cm, and 40cm, the temperature was approximately 34℃.

As is clear from the above experiments () to (), regardless of the shape of the bobbin 15 and the presence or absence of the metal protection piece 13, the temperature of the probe antenna 8 becomes higher or lower every time the winding length of the probe antenna 8 changes by approximately 6 cm. Since this dimension of 6 cm corresponds to a half wavelength (λ/2) of the wavelength λ of the microwave, the winding length of the probe antenna 8 on which the microwave is easily or difficult to ride is determined for each half wavelength of the microwave. It was concluded that the difficult winding length is the length that does not cause the resonant circuit to resonate.

Furthermore, in addition to this conclusion, the above experiments have led to the conclusion that by providing the metal protection piece 13 along the probe antenna 8, the temperature rise of the probe antenna 8 can be suppressed. This is because the provision of the metal protection piece 13 reduces the influence of microwaves on the probe antenna 8 and prevents heat generation.

As mentioned above, the present invention reduces the influence of microwaves on the probe antenna by providing a metal protective piece at a certain distance near the probe antenna, so it has a simple structure and is reliable. In addition to reducing the current flowing through the probe antenna formed in the loop antenna, it is also possible to reduce the type of induction heating effect induced in the probe antenna. Discharge between the lines can be prevented, and self-heating of the probe antenna can be suppressed as much as possible.

Furthermore, in the present invention, the winding length of the probe antenna is determined in half-wavelength units of microwaves, and is set to a length that is not easily affected by microwaves (microwaves are difficult to ride). This is an excellent invention that can reduce the amount of current flowing inside the device and further ensure the above-mentioned effects.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the configuration of a microwave oven that employs a temperature sensing device formed using the device according to the present invention;
Fig. 2 is a schematic cross-sectional view of the configuration of a temperature-sensing device employing the device according to the present invention, Fig. 3 A and B are side views and main parts side views of the temperature-sensing device, and Fig. 4 is a schematic sectional view of the temperature-sensing device. A perspective view of the main parts, Fig. 5 and Fig. 6 a and b are diagrams showing the main parts of the temperature sensing device used in the experiment, and Fig. 7 shows the main parts of the temperature sensing device used in the experiment. 8 are diagrams showing the temperature characteristics of various probe antennas obtained through experiments or experiments. 5: Temperature sensing device, 8: Probe antenna, 13:
Metal protection piece.

Claims (1)

[Claims] 1. In a device that converts the food temperature detected by a temperature detection element into an appropriate electrical signal and transmits this electrical signal as a radio wave with a probe antenna consisting of a loop antenna, a metal protective device is installed at a certain distance near the probe antenna. A heat generation prevention device for a probe antenna in a temperature sensing device, which is constructed by installing a piece along the probe antenna to reduce the influence of microwaves on the probe antenna.