JPS6188485A - High frequency heating device with 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] Industrial Application Field The present invention relates to a high-frequency heating device equipped with a wireless temperature blower that detects the temperature of an object to be heated with a wireless probe and automates cooking control. .

Conventional technology In conventional high-frequency heating equipment, as a heating control automation method, the temperature, humidity, or gas generated from the heated object is detected using a thermistor, humidity sensor, and gas sensor, respectively, and the temperature of the heated object is detected. Things are missing.

There is also a method that uses an infrared sensor to capture 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 sensor is installed outside the heating chamber, away from the object to be heated, so as not to be affected by the high frequency ring.

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

It was difficult to control heating at the intermediate temperature of the heated object in the trench. 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 installation position of the object to be heated and the shape of the container. As a method to solve these problems.

A probe equipped with a temperature sensor such as a thermistor is inserted into the heated object, and the temperature signal is taken out of the heating chamber by wire.
There is a method for controlling heating. This method can accurately determine the internal temperature of the object to be heated, and also allows heating to be controlled at the user's desired set temperature. Since the test probe is connected by wire to a control circuit outside the heating chamber, it is mechanically and electrically difficult to employ a turntable system that is effective in countering uneven heating of the heated object. Note that high-frequency heating devices using wired probes are well known without reference to literature.

The problem to be solved by the invention is that the probe is not easy to use because it is connected to the control circuit by wire.

The only way to solve the problem is to construct a wireless temperature probe with an LC resonant circuit consisting of a coil antenna and a temperature-sensing capacitor, bring it into contact with the object to be heated, fix the inductance L of the coil antenna, and set the inductance of the capacitor. The resonant frequency of the temperature probe is changed by changing the capacitance [direction] as the ambient temperature changes.

The resonant frequency is then captured to detect the temperature of the heated object. Therefore, a transmitting/receiving antenna is installed inside the heating chamber, and a signal swept over a fixed frequency width is transmitted from the transmitting antenna.

Also, the receiving antenna receives the transmitted signal, connects to the receiving circuit, captures the resonance point of the temperature probe, counts the time from the start of the sweep to the resonance point using a different oscillation frequency, and reads this number using a microcomputer to measure the temperature of the heated object. The temperature is detected, and the repetition period of the sweep signal and the period of the commercial power supply are synchronized, and the count number at the time of high frequency oscillation is not captured, or the high frequency j5. This is because the sweep signal is not sent during oscillation.

A sweep signal with a frequency between f1 and f is sent from the working transmitting antenna to L.
Transmitted through the temperature probe of the C resonant circuit.

The received signal of the receiving antenna has a high voltage at a frequency f tuned to the temperature probe. This peak value is extracted by a detection circuit, a pulse is generated at this point, and it is input to the counter circuit along with the sweep start pulse, and the period from the rise of the sweep start pulse signal to the rise of the resonance point pulse signal is counted and the temperature is displayed. Outputs control signals for the set quality. In addition, the rising edge of the sweep start pulse signal is synchronized with that of the commercial power supply, and a signal that performs one sweep is output in a half cycle during which high frequency oscillation is not performed, so that the measurement accuracy is improved by not capturing the count number during high frequency oscillation. .

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

FIG. 1 is an overall 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 panel.

6 is a heating chamber, and 4 is a door. 5 is an object to be heated, and 6 is a turntable. 7 is a wireless temperature probe, 8
is a transmitting antenna, and 9 is a receiving antenna. Figure 2 (d
FIG. 2 is a sectional view of FIG. 1; 10j is a motor that drives the turntable, and 11 is a magnetron that oscillates a high frequency. In FIGS. 1 and 2, the transmitting antenna 8 is installed in the upper or lower part of the object to be heated 5, and the wireless temperature probe 7 and the rupture heating are sandwiched between it and the receiving antenna 9. to be installed. Note that it is also possible to use a heater for both transmitting and receiving antennas. A simple system block diagram is shown in Figure 6.

The outline is that two loop antennas are provided, and the two loop antennas are electromagnetically coupled, and the coil antenna of the probe is electromagnetically coupled to these loop antennas, changing the resonant frequency of the wireless temperature probe to the temperature. ℃.

Then, the resonant frequency is detected and the same probe is used to detect the temperature of the heated object.

This will be explained in more detail below.

The wireless temperature probe 7 consists of an electric 1S coil antenna and a temperature sensing capacitor. j'jTj capacitor is provided at the tip of probe 7 + Sakura + 1Jt'i
Detects the internal temperature of I-5. Generally, the 8°C of a capacitor is expressed as a function of temperature as follows.

C=(1+A(T-T, month・C0-fil where A is temperature, coefficient of variation, T is measured temperature, T.(is reference source +1 (20
C, +d is the capacitance value of the capacitor at a reference temperature of 20°C. Still the resonant frequency f of the probe.

is expressed as follows, where L is the inductance of the coil antenna. Therefore, if the inductance L is fixed, the resonant frequency f is approximately proportional to the reciprocal of the square root of the capacitance C with respect to the temperature T. In fact, when the capacitance C0 of the capacitor is 220 pF, the temperature coefficient A is -750 ppm/deg, and the inductance L of the coil antenna is 1.0 μH, the relationship between temperature and resonance frequency is as shown in FIG. 4. From this characteristic, when the temperature T is 0 to 100°C, the resonance frequency f. changes almost linearly. However, as can be seen from equation (2), the resonance frequency f is a quadratic curve with respect to the temperature T, but since the temperature range used is narrow, it can be regarded as a straight line.

The signal shown in FIG. 5(a) generated in the transmitting circuit 12 is transmitted from the transmitting antenna 8 in the heating chamber. This signal is a signal swept from a certain frequency f1 to f. This frequency width is still the resonant frequency f of the probe. shall be included. The frequency f1 corresponds to the temperature T=0° C., and the frequency f1 corresponds to the temperature T=1oor:, VC. When the signal from the receiving antenna 9 is amplified, the received signal shown in FIG. 5(b) is obtained. The frequency f tuned to the probe 7 in this received signal. A resonant special order is obtained in which the voltage becomes significantly larger. In order to make this resonance noticeable, the Q of the circuit of the probe 7 is increased.

Next, a cross section of the wireless temperature probe 7 is shown in FIG.

The wireless temperature probe 7 has a temperature-sensing capacitor 19 sealed in a protrusion 20 that is inserted into the object to be heated 5 to protect it from the high frequency of the strong electric field in the heating chamber that enters from the coil antenna 21.

Provide a band rejection filter. As a band rejection filter, there is a choke structure 22 which has a simple structure and a large passing loss. This is composed of a metal cylindrical conductor, and the structure is a distance A23 from the entrance of the cavity to the back 1.
has a length of m at@ 1/4 of the free space wavelength of the microwave. The coil antenna 21 has a structure in which a distance is provided between the wires of the coil or a disconnection material 24 is sandwiched in order to prevent discharge due to high frequency waves of a strong electric field within the heating chamber. Further, the coil antenna portion is coated with a non-conductive material 25 to make it easier for the user to grip. Also, as shown in Figure 6, the wireless temperature probe 7 includes a temperature sensing capacitor 1.
Since there are no so-called electronic parts except for 9, the heating chamber 6 can be used without being affected even if the ambient temperature during oven cooking is 200 to 250°C.

Next, we will describe this wireless temperature probe system.

Figure 7 shows a block diagram of the system. 2 in Figure 7
6 is a choke structure that prevents microwaves inside the oven from leaking from the transmitting/receiving antenna. 27 is a transmitting amplifier, and 2B is a VCO circuit.

29 is a sawtooth wave generation circuit, and 30 is a reference pulse generator. 31 is a counter circuit, and 32 is a stable oscillation circuit using a crystal or the like. 33 is an amplifier circuit for amplifying the received signal, 64 is a detection circuit, and 35 is a circuit for detecting the peak value of the resonance point on the received signal.

36 is a waveform shaping circuit that generates a pulse at the peak value point. 67 is a microcomputer, and filter 8 displays temperature and time.

Next, the signal waveform of each block is shown in FIG. 3(a) shows the waveform of the reference pulse generator 0, and a sawtooth wave is generated by the generator circuit 29 based on this waveform. The waveform from the sawtooth wave generation circuit 29 is input to the vCO00 circuit to generate a swept signal. This signal is amplified by the amplification i2 circuit 27 and transmitted from the transmitting antenna 8.

The transmitted signal waveform is shown in (d). A signal obtained by amplifying the signal from the receiving antenna 9 by the amplifier circuit 63 is shown in (e). To capture the resonance point of this signal, remove the carrier wave.

Take out the envelope. This can be realized using a detection circuit. Next, a peak value detection circuit using a capacitor and a comparator is used to capture the peak value at the resonance point. When a peak value is detected, a pulse is generated at that point. This is the waveform of (f). Further, a reference pulse generator 60 generates a sweep start pulse signal (C). Therefore, the position of the resonance point can be found by counting the time from the start of the sweep to the resonance point using a signal with a stable high oscillation frequency. The sweep start pulse signal (C) and the resonance point pulse signal (f) are input to the counter circuit 31, which counts at the rise of the sweep start pulse signal and stops at the rise of the resonance point pulse signal. The frequency to be counted is stable.

The frequency shall be ioo times or more that of the reference pulse signal. In FIG. 8, the rising time of the waveform signal (g) is the time width to be counted. The counter value is read by the microcomputer 67, the temperature is determined from the relationship between the counter value and the temperature, and is displayed on the display 38. When the user's set temperature is reached, a signal is output to the control circuit 39 that controls the drive power source of the magnetron 11. I do things. Since the temperature data, that is, the temperature data, varies slightly from one individual to the next, a method that obtains measurement data by taking the distribution of data when the turntable 6 makes one revolution has good measurement accuracy.

Also, while the microwave is being emitted from the magnetron 11 (during the positive portion of the commercial power supply voltage).

The received signal (FIG. 8(e)) is affected by microwaves. Therefore, in order to solve this problem, we made the base/zeta pulse signal and the commercial power pulse signal the same, made one sweep in half the period of the reference pulse signal, and made a design so that the data when the microwave was oscillating was not read. I will do it. The signal waveform of this means is shown in FIG. In FIG. 9, (a) is a reference pulse signal, which is the same as the commercial power nox signal, and (b) is a sawtooth waveform, which sweeps once in a half cycle of the standard nox signal. <C) is the sweep start pulse signal, (f)
is a pulse signal at the resonance point of the received signal. (g) is the time width in which the counter operates, that is, the temperature data (magnetic)
The data on which ON11 is operating is not read by the microcomputer 37.

In addition, on the circuit, one half period of the commercial power pulse signal oscillated by the magnetron 11 may not be swept, but the other half period may be swept to read the temperature data. The signal waveform in that case is shown in Fig. 10. Ta.

In Fig. 10, (a) is the same as Fig. 9 (a), (b) is a signal waveform with a sawtooth wave formed in the half period when the magnetron 11 is not oscillating, and (C) is the sweep start pulse signal. ,(
f) is a resonance point pulse signal of the received signal. (g) is a signal for operating the counter. In this case, the counter data is read and processed.

By doing so, the accuracy of temperature measurement is further improved.

Effects of the Invention As described above, according to the present invention, the wireless temperature probe is composed of a coil antenna and a temperature-sensing capacitor, and does not require a power supply, making it easy to use.In particular, the number of counts during high frequency oscillation is Since no heat is taken in, it is possible to obtain a high-frequency heating device with high measurement accuracy.

[Brief explanation of drawings]

FIG. 1 is an overall perspective view of a high-frequency heating device using a wireless temperature probe according to an embodiment of the present invention, and FIG. 2 is a sectional view of FIG. 1. Figure 6 is a block diagram of the same fireless temperature probe system. Figure 4 is a characteristic diagram showing the relationship between the temperature and the resonant frequency of the temperature probe, Figure 5 (a) is a waveform diagram of the transmitted signal + Ff (b) is the received signal, and Figure 6 is a cross section of the temperature probe. figure,
Figure 7 is a block diagram of the practical temperature probe system, Figure 8 is a signal waveform diagram of each part of the block diagram in Figure 7,
FIG. 9 is a signal waveform diagram when the influence of the magnetron is eliminated, and FIG. 1S is a signal waveform diagram according to the embodiment of B et al. 7. Wireless temperature probe. 8...Transmission antenna. 9...Receiving antenna. 21...Coil antenna. 19...Temperature sensing capacitor. 37...Microcomputer. Applicant Hitachi Thermal Appliances Co., Ltd. Tsuji Figure 1 Figure 2 Temperature T ('c'1 Figure 4 Figure 5 Figure 6 Figure 84 Figure 9 Figure 10

Claims (1)

[Claims] A wireless temperature probe (7), which has a resonant circuit composed of a temperature-sensing capacitor (19) and a coil antenna (21) that detects the temperature of the object to be heated in the heating chamber, is inserted into the object to be heated. ) A sweep signal that includes a resonance frequency corresponding to the temperature of The time from the start of the sweep to the resonance point is counted using a different oscillation frequency, and the number of counts is calculated using a microcomputer (
37), the temperature of the heated object is detected, and the repetition period of the sweep signal is synchronized with the period of the commercial power supply, and the count number during high frequency oscillation is not captured, or the sweep signal is transmitted during high frequency oscillation. High frequency heating device with wireless temperature probe characterized by: