JPH0827315B2 - Microwave energy detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave energy detecting device using a microwave sensor suitable for detecting a heating condition or a finishing condition of an object to be heated in a microwave heating device such as a microwave oven. .

[0002]

2. Description of the Related Art Microwave ovens are equipped with various functions such as a function for thawing frozen food by microwave heating and a function for warming cold food. The microwave oven automatically controls the output of the magnetron that generates microwaves by detecting the heating status or finishing status of this type of food with a sensor.
Conventionally, there has been disclosed a microwave oven which detects the end of the thawing cycle by tracking the temperature change from the frozen state to the thawed state of food (Japanese Patent Laid-Open No. 64-50385). This microwave oven includes a detector that absorbs microwaves and generates heat, an element that measures the temperature thereof, and a calculation and control device that controls the operation of the microwave oven from the temperature. The detector is placed in the microwave oven in the vicinity of the product to be treated and the calculation and control device determines a curve representing the temperature rise of the detector as a function of time and calculates the value of the second derivative of this curve. It determines the end of the thawing cycle of the product and controls the operation of the microwave oven at the end of the thawing cycle where the value of the second derivative is less than a predetermined value.

Further, another microwave oven provided with a detector capable of detecting the end of each thawing operation with a constant sensitivity in a plurality of sequential thawing operations is disclosed (Japanese Patent Laid-Open No. 64-503).
84). This microwave oven also comprises a microwave detector, a temperature measuring element and a calculation and control device. In this microwave oven, the detector transmits microwaves, but includes a heat insulator that prevents heat generated by absorption of microwaves from being dissipated to the outside of the detector. The heat insulator reduces the heat exchange with the outside and increases the temperature rise, so that the detector can detect each thawing operation without reducing the sensitivity. Further, this detector has a large heat exchange area for the outside and a thin thickness. This facilitates heat exchange with the outside of the detector, resulting in a small thermal lag that rapidly restores its initial properties after each thawing operation.

[0004]

Problems to be Solved by the Invention JP-A-64-5038
In the microwave oven disclosed in Japanese Patent Publication No. 5, when the product shifts from the ice state to the water state, the product gradually absorbs more microwave energy and is gradually heated, and the energy absorbed by the detector gradually. Decrease to. Here, when measuring the slope (first derivative) of the curve showing the temperature rise of the detector as a function of time, when this slope decreases slightly and the absolute value of the second derivative becomes larger than a predetermined value. , The product in the microwave begins to thaw. When the gradient becomes gentle and the absolute value of the second derivative becomes smaller than the predetermined value, the product finishes thawing. The microwave oven determines the defrosting state from the change in the second derivative. However, according to this method of determining the defrosted state, it is only the change in the microwave energy absorbed by the detector that causes the change in the second derivative.

On the other hand, a substance to be heated, which generally has a heat capacity C,
For example, the temperature rise value θ after t hours when the microwave sensor receives the microwave energy E is expressed by the following equation (2) in a completely adiabatic state where there is no heat dissipation to the outside. This relationship is shown in FIG. Note that θ is the microphone
Micro from the temperature θ ₀ of before receiving the b wave energy E Namie
Temperature rise value up to temperature θ _t after receiving Nergi E for t hours
It is. θ = E · t / C (2) However, in the actual substance to be heated, the heat dissipation to the outside cannot be ignored when the microwave energy is received. In this case, if the substance to be heated has a heat dissipation constant δ, the energy E · dt received by this substance in a minute time dt
Is expressed by the following equation (3). E · dt = C · dθ + δ · θ · dt (3) where dθ is the temperature increased in a minute time, C · dθ is the thermal energy stored in the substance in a minute time, and δ · θ · dt is a minute time. Is the heat energy that is dissipated to the surroundings. From the equation (3), the temperature rise value θ is represented by the following equation (4) when the energy E is constant. This relationship is shown in FIG. θ = (E / δ) · {1-exp (−t / τ)} (4) However, τ is a thermal time constant and has a relationship of C = τ · δ. As is clear from FIGS. 9 and 10, the temperature rise value θ
As becomes larger, the difference between the equation (1) and the equation (2) increases.

From the above formula (4), Japanese Patent Laid-Open No. 64-50
When the first derivative (dθ / dt) and the second derivative (d ² θ / dt ² ) described in Japanese Patent No. 385 are obtained, the following equations (5) and (6) are obtained. These relationships are shown in FIGS. 11 and 12. dθ / dt = (E / δ / τ) · exp (−t / τ) (5) d ² θ / dt ² = (− E / δ / τ ² ) · exp (−t / τ) (6) Figure 12 and equation (6), the second derivative (d ² θ / dt ² ) is (−) in the range of time t from zero to infinity (0 to ∞).
E / δ / τ ² ) changes to 0,
Considering heat dissipation results in a change in the second derivative even if the energy does not change over time. This suggests that the method for determining the defrosting state of the microwave oven disclosed in JP-A-64-50385 is not accurate when the temperature rise value θ is large. That is, in the above microwave oven, the change of the second derivative is observed only by the change of the microwave energy absorbed by the detector, and the defrosting state is determined from the change of the second derivative. It is necessary to consider the heat dissipation of the sensor.

Further, the microwave oven disclosed in Japanese Patent Laid-Open No. 64-50384 uses a heat insulator as described above and employs a structure that easily dissipates heat. Thermal insulators reduce heat dissipation during microwave irradiation,
The structure that easily dissipates heat is intended to increase the heat dissipation while not being irradiated with microwaves to quickly return to the initial state, and prevent thermal destruction due to accumulated heat when repeatedly heated. However, it is contrary to the above, and it is impossible to satisfy each of them sufficiently. Furthermore, when considering heat dissipation to the outside of the detector, the amount of heat dissipated depends on the ambient temperature. That is, when the ambient temperature is high, the amount of heat radiated is small, and when it is low, it is large. For example, in a microwave oven, the detection error becomes large when the temperature of the heating chamber becomes high depending on the usage conditions.
The conventional single detector has a problem that the microwave energy cannot be accurately detected because the ambient temperature is uniformly captured.

It is an object of the present invention to provide a device that does not necessarily reduce the heat dissipation of a microwave sensor, and takes this heat dissipation into consideration and can accurately detect microwave energy without being affected by ambient temperature changes. To do.

[0009]

As shown in FIG. 1, in the present invention, a microwave sensor 10 and a temperature sensor 50 are installed side by side in a microwave heating chamber 17 . The microwave sensor 10 is a first radio wave absorber 1 that absorbs microwaves and generates heat.
2 and a first thermistor element 11 that detects the temperature of the absorber 12. The temperature sensor 50 is the first electromagnetic wave absorber 1
2, a radio wave reflector 55 having the same shape and size and the same heat capacity and reflecting microwaves, and a second thermistor element 51 having the same configuration as the first thermistor element 11 for detecting the temperature of the reflector 55. . This radio wave reflector 55 is designed to absorb the first radio wave.
The second radio wave absorber 52 having the same configuration as the collector 12 and the radio wave
The surface 52a of the absorber 52 that receives the microwave is
And a thin-film metal coating 53 that reflects light. Based on the detection outputs of the microwave sensor 10 and the temperature sensor 50, the calculation device 30 calculates the value of microwave energy as a function of time by the following equation (1). E = C · dθ / dt + δ · θ (1) However, E is microwave energy that the wave absorber has _{absorbed, θ = (θ t1 -θ 01} ) - A (θ _t2 -θ _02),
θ ₀₁ indicates that the radio wave absorber absorbs microwave energy E
Detection temperature of the first thermistor element before, theta _t1 is the
After the radio wave absorber has absorbed the microwave energy E for t hours
, The temperature detected by the first thermistor element , θ ₀₂ is the radio wave
The second before the absorber absorbs the microwave energy E
The temperature detected by the thermistor element, θ _t2, is _measured by the electromagnetic wave absorber.
The second sir after absorbing the microwave energy E for t hours
The detected temperature of the mister element , C is the heat capacity of the microwave sensor, and δ is the heat dissipation constant of the microwave sensor.

[0010]

In the calculation device 30, the relationship of the equation (1) and the respective values of the heat capacity C and the heat dissipation constant δ peculiar to the microwave sensor 10 are stored in advance. When microwaves arrive at the microwave sensor 10 and the temperature sensor 50, the metal coating material 53 reflects them at the temperature sensor 50, but the electromagnetic wave absorber 12
Absorbs this and generates heat. The thermistor element 51 that constitutes the temperature sensor 50 has an electric resistance value that changes depending on the temperature of the heating chamber due to radiant heat of the object to be heated. On the other hand, in the thermistor element 11 which constitutes the microwave sensor 10, the electric resistance value changes due to the heat generation corresponding to the microwave energy amount in addition to the temperature of the heating chamber. The calculation device 30 absorbs the first electromagnetic wave.
First thermist before body 12 absorbs microwave energy
From the detected temperature θ ₀₁ of the star element 11, the first electromagnetic wave absorber 12
First thermist after absorbing microwave energy for t hours
Temperature rise value to detect temperature theta _t1 of data elements 11 (θ _t1 -θ
₀₁ ), the first electromagnetic wave absorber 12 receives microwave energy.
Is the detected temperature θ ₀₂ of the second thermistor element 51 before absorption ?
The first radio wave absorber 12 absorbs microwave energy for t time.
Up to the detection temperature θ _t2 of the second thermistor element 51 after it is _stored
The temperature rise value (θ _t2 −θ ₀₂ ) is subtracted to obtain only the heat generation due to the absorption of microwave energy, and this θ = (θ _t1
Substituting −θ ₀₁ ) − (θ _t2 −θ ₀₂ ) into the equation (1),
The amount of microwave energy received by the object to be heated is accurately determined in consideration of the heat dissipation of the microwave sensor 10 and the ambient temperature change.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. As shown in FIG. 1, a door 14 is provided on the front surface of the microwave oven 13 so as to be openable and closable. The microwave sensor 10 and the temperature sensor 50 are arranged side by side on the ceiling of the heating chamber 17 of the microwave oven 13. Both sensors 10 and 50 are slits 15a formed in the frame 15 of the ceiling,
Both sensors 10 a and 15 b are fixed so as to face the heating chamber 17.
Leads 11c and 51c of 50 and 50 are provided at positions where microwaves from the magnetron 18, which will be described later, are not received.

Thermistor element 11 and thermistor element 5
Reference numeral 1 denotes a Melf (Metal Electrode Face) type element having a diameter of 1.35 mm and a thickness of 1.45 mm.
The temperature sensing parts 11a and 51a made of a sintered body of a metal oxide containing Co and Ni as main components are provided, and the terminal electrodes 1 at both ends thereof are provided.
It is made by soldering leads 11c and 51c to 1b and 51b. The resistance values of both thermistor elements 11 and 51 at 25 ° C. are 100 kΩ, and the B constants are 3965K. The radio wave absorbers 12 and 52 are sintered SiC bodies, each of which has a diameter of 12 mm and a thickness of 1 mm and has the same heat capacity. One surface 12a, 52a of the radio wave absorber 12, 52 is a microwave absorbing surface, and the temperature sensing portion 11 of the thermistor element 11 with lead is placed in the center of the other surface 12b, 52b.
a and 51a are adhered by the epoxy resins 10a and 50a. The temperature sensor 50 is further printed with Ag paste (Shoei Chemical Co., Ltd .: trade name H-5723) on the microwave receiving surface 52a of the radio wave absorber 52, baked at a maximum temperature of 800 ° C. for 10 minutes, and then the metal coating material 53. Got The metal coating material 53 may be formed by a thin film forming method such as another vapor deposition method or a sputtering method. The microwave sensor 10 including the thermistor element 11, the radio wave absorber 12 and the epoxy resin 10a has a heat dissipation constant δ of 6 mW / ° C. and a thermal time constant τ of 40 seconds. Further, the temperature sensor 5 including the thermistor element 51, the radio wave absorber 52, and the epoxy resin 50a.
The heat dissipation constant δ of 0 is also 6 mW / ° C, and its thermal time constant τ
Is also 40 seconds.

A magnetron 18 for generating a microwave of 2450 MHz is provided at the back of the heating chamber 17, and a blower fan 19 and a fan motor 20 are provided behind it. At the bottom of the heating chamber 17, there is provided a turntable 22 on which a container 21 is placed and which is rotated by a motor 23. An intake port 24 is provided near the fan motor 20, and an exhaust port 26 is provided at the ceiling of the heating chamber 17. The microwave oven 13 is provided with a controller 30 including a CPU and a memory. This memory stores the relationship of the above-mentioned equation (1) and the respective values of the heat dissipation constant δ and the thermal time constant τ of the microwave sensor 10 described above. The detection output of the microwave sensor 10 and the temperature sensor 50 is connected to the controller 30, the temperature rise value due to the heat generation of the wave absorber 12 (θ _t1 -θ ₀₁₎ and the temperature rise value due to the heat generation of the electric wave absorber 52 (theta _t2- θ ₀₂ ) is the thermistor elements 11 and 51
Is input to the controller 30. The control output of the controller 30 is connected to the magnetron 18 and the motors 20 and 23, respectively. Note that θ ₀₁ is the radio wave
Before the absorber 12 absorbs the microwave energy E
The temperature detected by the mister element 11, θ _t1, is measured by the electromagnetic wave absorber 12.
Thermistor element after absorbing the microwave energy E for t hours
The detected temperature of the child 11 , θ ₀₂ is the microwave of the radio wave absorber 12
Detected temperature of the thermistor element 51 before absorbing energy E
The angle, θ _t2, is that the microwave absorber 12 measures the microwave energy E by t.
The temperature detected by the thermistor element 51 after absorption for a time
It

Next, a microwave energy detection test was conducted using the microwave oven constructed as described above in a state where no object to be heated was placed on the turntable 22. A recording device 27 was connected to the controller 30 in order to check the amount of microwave energy applied to the heating chamber 17. <Test A> First, the microwave output was set to a state of a weak range corresponding to 200 W, and the heating chamber 17 was irradiated with microwaves from the magnetron 18 by the controller 30. For comparison, microwaves were similarly irradiated even when the temperature sensor was not connected to the controller 30. The energy amount calculated by the controller 30 was recorded by the recording device 27. The result is shown in FIG. When the temperature sensor 50 is not used, that is, when the temperature is not corrected, the amount of energy slightly increases with time, whereas when the temperature is corrected using the temperature sensor 50, the energy is increased regardless of the irradiation time. The amount was constant. <Test B> Next, the microwave output is 150 W, 200 W,
Switching to four stages of 250 W and 300 W, the energy amount calculated by the controller 30 for each was recorded by the recording device 27. The result is shown in FIG. As is clear from FIG. 3, when the temperature is corrected by the temperature sensor, even if the microwave output is changed and the irradiation time becomes long,
The amount of energy was constant. From these, it was found that the microwave energy can be detected more accurately by correcting the ambient temperature.

As the microwave sensor of the present invention, in addition to the examples shown in the above examples, those shown in FIGS. 4 to 8 to which the present applicant has applied for patents can be used.
Although not shown, the temperature sensor may be a temperature sensor having a metal coating formed on the surface of the microwave sensor that receives microwaves. In the microwave sensor 10 shown in FIG. 4, the temperature sensing portion 11a of the thermistor element 11 includes an organic substance 3 containing a radio wave absorber powder as a filler.
2 or coated with an inorganic substance. An application for this sensor was filed in Japanese Patent Application No. 3-244449. The microwave sensor 10 shown in FIG. 5 includes a metal encapsulation body 33 that is close to the thermistor element 11 and encloses the thermistor element 11 including its leads 11c, and a layer on the surface of the metal encapsulation body 33. The formed electromagnetic wave absorber 12 is provided. The thermistor element 11 is preferably fixed in the metal envelope 33 by a filler 36. An application for this sensor was filed in Japanese Patent Application No. 4-100348.

The microwave sensor 10 shown in FIG.
The radio wave absorber 12 has thermistor characteristics, and a pair of electrodes 42, 4 is provided on the surface of the radio wave absorber 12 that does not receive microwaves.
3 are provided at intervals. Leads 44 and 46 are connected to the electrodes 42 and 43, respectively, and the radio wave absorber 12 is attached to a cap-shaped attachment body 48 via a ceramic enclosure 47 that encloses the leads 44 and 46. An application for this sensor was filed in Japanese Patent Application No. 4-100349. The microwave sensor 10 shown in FIG.
Is close to the thermistor element 11 and the thermistor element 1
1 is encapsulated including its lead 11c. Radio wave absorber 1
2 is attached via a collar 54 made of metal. The thermistor element 11 is preferably fixed in the radio wave absorber 12 by a filling material 36. Japanese Patent Application No. 4-
Filed under No. 100350. In the microwave sensor 10 shown in FIG. 8, the front surface of the radio wave absorber 12 is a surface that receives microwaves, and the metal body 56 is provided on the back surface of the radio wave absorber 12 at a position that does not receive microwaves via the metal layer 58. The thermistor element 11 is joined and held by the metal body 56 and senses the temperature of the radio wave absorber 12 through the metal body 56. The leads 11c of the thermistor element 11 are covered with an insulating material. Regarding this sensor, Japanese Patent Application No. 4-16
Filed under 3582.

[0017]

As described above, according to the present invention, the relation of the equation (1), the heat dissipation constant δ of the microwave sensor and its thermal time constant τ are input to the calculation device in advance, and this δ Considering the heat dissipation of the microwave sensor with τ,
Since the microwave sensor is configured to detect the thermal energy associated with the absorption of microwaves, it is possible to accurately detect the amount of energy, and without providing the microwave sensor with a heat insulator that prevents heat dissipation as in the conventional case. I'm done. In particular, if the ambient temperature is corrected by the temperature sensor, the amount of energy can be detected more accurately. In addition, since the calculation device calculates the microwave energy over time,
If the output of the microwave source is controlled based on the change, the object to be heated can be appropriately processed into a desired defrosting state or heating state.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a microwave energy detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing changes in the amount of energy detected by a detection device when there is no object to be heated, with and without temperature correction.

FIG. 3 is a diagram showing changes in the amount of energy detected by the detection device when there is no object to be heated by changing the microwave output in four stages.

FIG. 4 is another sectional view of the microwave sensor.

FIG. 5 is another sectional view of the microwave sensor.

FIG. 6 is another sectional view of the microwave sensor.

FIG. 7 is another sectional view of the microwave sensor.

FIG. 8 is another sectional view of the microwave sensor.

FIG. 9 is a temperature change diagram when a substance receives microwave energy in an adiabatic state.

FIG. 10 is a temperature change diagram when a substance receives microwave energy in a state where heat is dissipated.

FIG. 11 is a diagram showing the first derivative of temperature with respect to time at this time.

FIG. 12 is a diagram showing a second derivative of temperature with respect to time at this time.

[Explanation of symbols]

 10 microwave sensor 11,51 thermistor element 11a, 51a temperature sensing part 11c, 51c lead 12,52 radio wave absorber 12a, 52a one side of radio wave absorber 12b, 52b other side of radio wave absorber 30 controller (calculator) ) 50 temperature sensor 53 metal coating 55 radio wave reflector

Claims (7)

[Claims] 1. A first radio wave absorber (12) installed in a microwave heating chamber (17) that absorbs microwaves to generate heat, and a first thermistor element (11) for detecting the temperature of the absorber (12). ) And a microwave sensor (10), the microwave heating chamber (17) in the microwave sensor (10)
And the temperature of the radio wave reflector (55), which has the same shape and size as the first radio wave absorber (12), has the same heat capacity and reflects microwaves, and the reflector (55). A temperature sensor (50) having the first thermistor element (11) and a second thermistor element (51) having the same configuration, and based on the detection outputs of the microwave sensor (10) and the temperature sensor (50). A microwave energy detecting device comprising: a calculating device (30) for calculating a value of microwave energy, wherein the radio wave reflector (55) is the same as the first radio wave absorber (12).
The second electromagnetic wave absorber (52) of the constitution and the electromagnetic wave absorber (52)
A thin film that reflects microwaves on the surface (52a) that receives the microwave
And a metal coating material (53) of (1) , wherein the calculation device (30) calculates the value of microwave energy as a function of time by the following formula (1). E = C · dθ / dt + δ · θ (1) However, E is microwave energy that the wave absorber has _{absorbed, θ = (θ t1 -θ 01} ) - A (θ _t2 -θ _02),
θ ₀₁ indicates that the radio wave absorber absorbs microwave energy E
Detection temperature of the first thermistor element before, theta _t1 is the
After the radio wave absorber has absorbed the microwave energy E for t hours
, The temperature detected by the first thermistor element , θ ₀₂ is the radio wave
The second before the absorber absorbs the microwave energy E
The temperature detected by the thermistor element, θ _t2, is _measured by the electromagnetic wave absorber.
The second sir after absorbing the microwave energy E for t hours
The detected temperature of the mister element , C is the heat capacity of the microwave sensor, and δ is the heat dissipation constant of the microwave sensor. 2. The microwave sensor (10) is a radio wave absorber (12).
Is formed in a flat plate shape having a larger area than at least the temperature sensing part (11a) of the thermistor element (11), and one surface (12a) of the radio wave absorber is a microwave absorbing surface, 2. The microwave energy detecting device according to claim 1, wherein the temperature sensing part (11a) is adhered to the other surface (12b) so that the thermistor element (11) does not receive microwaves. 3. The microwave sensor (10) is a thermistor element.
The temperature sensing part (11a) of (11) is covered with an organic substance (32) or an inorganic substance containing a radio wave absorber powder as a filler.
Microwave energy detection device as described. 4. The microwave sensor (10) is a thermistor element.
Connect the thermistor element (11) to its lead (1
The microwave according to claim 1, further comprising: a metal encapsulant (33) encapsulating the metal encapsulation (1c), and a radio wave absorber (12) formed in layers on the surface of the metal encapsulant (33). Energy detection device. 5. The microwave sensor (10) is a radio wave absorber (12).
2. The microwave energy detecting apparatus according to claim 1, wherein said microwave absorber has a thermistor characteristic, and a pair of electrodes (42, 43) are provided at intervals on a surface of said radio wave absorber (12) which does not receive microwaves. 6. The microwave sensor (10) is a radio wave absorber (12).
Is close to the thermistor element (11) and the thermistor element (1
The microwave energy detecting device according to claim 1, wherein the lead (11c) is encapsulated in (1). 7. The microwave sensor (10) is a radio wave absorber (12).
The surface of the electromagnetic wave absorber (1
The metal body (56) is bonded to the back surface of 2) at a position where it does not receive microwaves, the thermistor element (11) is held by the metal body (56), and the temperature of the radio wave absorber (12) is controlled by the metal body. (56)
The microwave energy detecting apparatus according to claim 1, wherein the microwave energy detecting apparatus detects the energy through a microwave.