JPS60246594A - High frequency heater having wireless temperature probe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a high-frequency heating device that detects the temperature of a heated object using a wireless temperature probe and automates cooking control.

``Prior art'' In conventional high-frequency heating equipment, as a heating control automation method, the temperature of the object to be heated, the humidity in the heating chamber, and the gas generated from the object to be heated are measured using a thermistor, humidity sensor, and gas sensor, respectively. There are devices that detect the temperature of the heated object. Some systems use an infrared sensor to measure the surface temperature of the heated object, detect the finish of the heated object, and perform automatic control.

These methods have good cooking operability because the sensing chamber is installed outside the heating chamber, away from the object to be heated, so that it is not affected by high frequencies.

Because the temperature, humidity, and gas in the atmosphere inside the heating chamber are detected, there may be slight variations in the finish.

Furthermore, it was difficult to control the heating of the object to be heated at an intermediate temperature. In the method using an infrared sensor, the detection area is narrow, and if the object to be heated is removed from that area, it cannot be detected, and there are drawbacks such as the placement position of the object to be heated and the shape of the container.

As a method to solve these problems, a glove equipped with a temperature sensor such as a thermistor is inserted into the heated object.

There is a method in which the temperature signal is taken out of the heating chamber by wire and heating control is performed. This method can accurately determine the internal temperature of the object to be heated, and it is possible to control the heating at the user's desired set temperature. However, since the probe is connected by wire to a control circuit outside the heating chamber, it is mechanically and electrically difficult to use it in combination with a turntable, which is effective in preventing uneven heating of the heated object. Ta. It was also inconvenient to use because it was wired.

``Problem to be solved by the invention'' The high-frequency heating device equipped with a probe is difficult to use.

``Means for Solving Problems'' The present invention comprises a wireless temperature probe composed of an LC resonant circuit consisting of a coil antenna and a temperature-sensing capacitor, and is connected to an object to be heated.

``Function'' The capacitance I value of the capacitor changes as the temperature of the heated object changes, and the resonant frequency of the probe changes.

The resonant frequency is then captured and the temperature of the heated object is detected. Therefore, a transmitting antenna is installed inside the heating chamber, and a signal swept over a certain frequency width is transmitted from the antenna.The point of the resonant frequency of the probe appears in the transmitted signal of the sweep. Detect.

"Example" An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of a high-frequency heating device using a wireless temperature probe. 1 is the main body of the high frequency heating device, and 2 is the control signal.

6 is a heating chamber, and 4 is a door. 5 is the object to be heated.

6 is a turntable. 7 is a wireless temperature globe (hereinafter abbreviated as probe), and 8 is a transmitting antenna. FIG. 2 shows a cross-sectional view of FIG. 9 is ter/
The motor that drives the table.

10 is a magnetro 7 that oscillates a high frequency. In FIGS. 1 and 2, the transmitting antenna 8 is provided in an upper part or a lower part so as not to interfere with the object to be heated 5 in the heating chamber 6. The transmitting antenna 8 is.

/- can also be used as a heater.

Next, we will discuss the principle of the glove system.

FIG. 3 is an equivalent circuit diagram for explaining the principle.

As shown in Figure 6, there are two coils, and a capacitor is connected to one coil to form an LC resonant circuit.

The inductance of each coil is Ll.

L(1+ Capacity of capacitor is CO+ Mutual inductance is MIO.

In such a circuit configuration, when a signal having a frequency component in a band including the resonant frequency fo of the LC resonant circuit is applied to the coil to which no capacitor is connected, the current I
, flows. When a current 11 flows through the coil, a current ■ appears in the secondary coil due to electromagnetic induction.

flows. Here, the current 1G is a signal current having a resonant frequency fo because the secondary side is a resonant circuit. When a current 1o having only the component of the resonant frequency fo flows through the secondary side, the primary side current 1. The frequency f in the frequency component of
. The area decreases as shown in FIG. 5(a). Therefore, the capacitance ic of the secondary side capacitor. If F0 is changed depending on the temperature, the resonant frequency fo changes. If this change is detected in the primary side transmission signal, the temperature can be detected. A block diagram of a system applying this principle is shown in the fourth section.
It is 'N'.

The outline of this/stem is that the loop antenna 8 is installed inside the heating chamber.
The probe 7 uses a capacitor as a temperature sensor and forms an LC resonant circuit with the coil antenna 25. It is. The temperature detection means is a probe 7 from a loop antenna 8.
The signal in the band including the resonant frequency io is transmitted intermittently or continuously. This signal is a signal swept from a certain frequency 11 at f2i. Glove 7 in heating chamber 2
If there is, the transmitted signal will be as shown in FIG. 5(a). Therefore, by capturing this resonance point, the temperature of the probe can be detected. There are many ways to capture the resonance point of a transmitted signal, but one method that goes beyond that is to create the signal shown in FIG. 5(C) by combining the original signal and the transmitted signal through a differential amplifier or the like. FIG. 5(b) shows the sweep start pulse and sweep completion pulse of the transmission signal. FIG. 5(C) is a pulse signal diagram at the resonance point of the globe as described above. Therefore, by measuring the time T between the start of transmission and the time at the resonance point, changes in the resonance point can be detected.

Next, we will discuss the capacitor, which is a temperature sensor. Generally, the capacitance C of a capacitor is expressed as a function of temperature as follows.

C= (1+A (T-To) l Co-□ (11
Here, A is the temperature coefficient, T is the measured temperature + TO is the reference temperature (20°C) + Ql is the capacitance value of the capacitor at the reference temperature of 20°C.

The resonant frequency fo of the grooved globe is given by the inductance of the coil antenna being L.

to fo−2π. (2) It is expressed as Therefore, if the inductance L is fixed, the resonant frequency fo changes in proportion to the reciprocal of the square root with respect to the temperature T, but in reality, if the capacitance Co of the capacitor is 220
pF, temperature coefficient A is -750pp, /day.

When the inductance L of the coil antenna is 1.0 μH, the relationship between temperature and resonance frequency is as shown in FIG. 6.

According to this characteristic 27, when the temperature T is 0 to 100° C., the resonance frequency changes almost linearly. However, as can be seen from equation (2), the resonant frequency f with respect to the temperature T.

is a quadratic curve, but because the temperature range used is narrow, it can be regarded as a straight line.

In the 7-stem diagram of FIG. 4, 17 is a transmitting circuit that uses a VCO or the like to generate a sweep signal, amplify it, and transmit it from the transmitting antenna 8. 18 is a circuit that captures the resonance point from the transmission signal shown in FIG. 5 (ω) and creates a pulse waveform, and is connected to the microcomputer 20. is measured, and when the heated object 5 reaches the user's set temperature,
A signal is sent to the control circuit 19 of the magnetron 10 to stop the oscillation of the magnetron 1o. Reference numeral 21 denotes a display provided on the control panel 2, which displays temperature and the like.

Figure 22 indicates the key human power section of the control panel.

The user then sets the temperature.

Next, the structure of the glove 7 is shown in FIG. FIG. 7 is a sectional view of the temperature globe 7. Probe 7 is.

A temperature-sensing capacitor 30 for detecting temperature is enclosed within a protrusion 31 that is inserted into the object to be heated 5. In order to protect this capacitor 30 from the high frequency of the strong electric field in the heating chamber entering from the coil antenna 25, a band rejection filter is provided. As a band rejection filter,
A simple choke structure can be considered. In FIG. 7, two chokes 26 each having the length of a partition plate are connected in series within the choke.

A band rejection filter having a structure in which a coil 28 is connected between chokes 26 is provided. This is a great effect because the single frequency characteristic is wider than the attenuation characteristic of a single stage choke structure. However, there is no attenuating effect on radio waves near the signal frequency IQ MHz. Further, these chokes 26 are housed within a metal cylindrical conductor 29. Should there be a distance between the wires of the coil antenna 25 to prevent discharge due to high frequency waves of a strong electric field?

The structure is such that an insulating material 32 is sandwiched therebetween. Further, the entire coil antenna 25 is covered with a non-conductor material 33 to make it easier for the user to grip.

Further, since the prologue 7 has no electronic components except for the temperature-sensitive capacitor 30, it can be used without being affected by the ambient temperature of 200 to 250° C. during open cooking in the heating chamber.

"Effects of the Invention" As described above, according to the present invention, the wireless temperature probe consists of a coil antenna and a temperature-sensing capacitor, has a small number of parts, and does not require a power supply, so it can be made smaller and lighter. . The gloves do not contain any electronic components other than the temperature-sensing part.

Even if the glove is exposed to high temperatures, it will not be affected by it.

Therefore, high frequency heating using the same glove can be performed immediately after oven cooking. In addition, it is sufficient to provide only one loop antenna as a transmitting antenna in the heating chamber, and the structure inside the heating chamber is also simplified since it can also be used as a heater.

Therefore, the above features provide a high-frequency heating device that is easy to use.

[Brief explanation of drawings]

Figure 1 is an external view of a high-frequency heating device using a wireless temperature probe according to an embodiment of the present invention. Figure 2 is its cross-sectional view, Figure 6 is an equivalent circuit diagram explaining the same principle, and Figure 4 is the same system. Block diagram, Figure 5 (ω is the waveform diagram of the same transmission signal, Figure (b) is the sweep start/completion pulse waveform diagram, Figure 5 (C)
is a resonance point pulse waveform diagram. FIG. 6 is a characteristic diagram of the temperature and resonance frequency, and FIG. 7 is a cross-sectional structural diagram of the probe. 5. Object to be heated. 7...Wireless temperature probe. 8... Transmission antenna. 24...Relationship characteristics between temperature and resonance frequency. 25 Coil antenna. 26 Chalk. 30・Temperature sensing capacitor. Applicant: Hitachi Thermal Appliances Co., Ltd. Figure 1 Figure 2 Prisoner Figure 6 Fake T ("C1

Claims (1)

[Claims] A wireless temperature probe (7) comprising a resonant circuit with a temperature-sensing capacitor (30) and a coil antenna (c) for detecting the temperature of the object to be heated in the heating chamber is provided in contact with the object to be heated. 7) The frequency width that includes the resonant frequency corresponding to the temperature of the transmitting antenna (8) in the heating chamber is
A high-frequency heating device equipped with a wireless temperature probe, characterized in that it detects the temperature of a heated object by capturing the resonance point of the probe (7) that appears in the transmitted signal.