JPS59221530A - Electronic range - Google Patents

Abstract

PURPOSE:To obtain uniformly heated and finished provisions by providing detection means for detecting the gradient of the output characteristic of an absolute humidity sensor and cleaning time setting means in the title electronic range. CONSTITUTION:A cleaning time CT is selectively set responsive to the zero balance output characteristic of the AH sensor 11. Thus, in a case where, for example, there are an AH sensor 11A in which the zero balance output is deviated by +5mV and an AH sensor 11B in which the zero balance output is deviated by -5mV, when the cleaning time of 1min has elapsed (S11), the initial values A20A and A20B are stored (S12) in a RAM22c. Then, a relay 24 to which a ''High'' signal for turning ON a transistor 23 is ouputted from a microcomputer 22, whereby commercial power is supplied to the magnetron 8, and the magnetron 8 begins its operation to oscillate (S13) a microwave.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a microwave oven that automatically controls heating in response to a detection signal from an absolute humidity sensor.

<Prior Art> First, a microwave oven equipped with an absolute humidity sensor will be briefly described.

FIG. 1 is a front view of the microwave oven, and FIG. 2 is a schematic cross-sectional view thereof.A menu selection key 3 and a heating start key 4 are provided on the operation panel 2 on the front of the microwave oven 1, and inside A heating chamber 7 is provided with a tray 6 at the bottom on which food 5 to be heated is placed, and the food 5 is cooked by microwaves emitted from a magnetron 8 provided at the top of the heating chamber 7. During heating, outside air is sent in by a fan 9, and oil smoke and water vapor from the food 5 are exhausted to the outside via an exhaust passage 10. Reference numeral 11 denotes an absolute humidity sensor (hereinafter referred to as "AH sensor") disposed in the exhaust passage IO, which detects the finish of the food 5. As shown in FIG. 3, the external structure of this AH sensor 11 is an open type in which air freely flows inside above the terminal block 12 which forms the attachment part to the exhaust passage 10 and fixes the four lead terminals. The sensor 13 and the sealed sensor 14 whose interior is isolated from the outside air are provided in contact with each other, and in order to equalize the heat of these two sensors IJI 4, this pair of sensors 13 is connected by a cylindrical heat equalizing tube 15 made of, for example, brass.
．． 14 are connected, and a wire mesh 16 is covered to protect a part of the sensor.

Figure 4 shows the open type sensor 13 and the closed type sensor 14.
It is a sectional view showing the internal structure of both sensors Is, 14.
Glass fist coated bare bead type thermistor +3a, +4. Using a, two thermistors with well-matched characteristics are selected. These bead type thermistors 13a and +4a each have a thin platinum wire 13b.
, +4b to the hermetic terminals L3c and +4c. And, in the open type sensor 13 mentioned above, there is a ventilation hole! The metal case 13e formed with the shape 3d is covered and welded at the joint to form a temperature detection element, while the sealed sensor 1
4 has the same structure as the open type sensor described above, but a metal case +4e without ventilation holes is attached, dry air is introduced therein, and the joints are welded to form a temperature compensating element.

Note that holes 15a are formed in the cylindrical heat soaking tube 15 at locations corresponding to the ventilation holes lad. The thermistor humidity sensor described above measures absolute humidity by utilizing the difference in thermal conductivity between humid air and dry air, and the principle of its measurement circuit is shown in FIG.

In the figure, R1 is a humidity detection element corresponding to the open type sensor 13 equipped with a ventilation hole +3d, and R2 is a temperature compensation element corresponding to the closed type sensor 14 sealed with dry air. E is a constant voltage power supply, R3 and 'R4 are resistors forming bridge circuit B, and R5 is a resistor connected in series with bridge circuit B, which functions to limit the magnitude of the flowing current, and in this circuit, The resistance value is selected so that the temperature of the thermistor is approximately 200°C.

Now, the AH sensor 11 consisting of the resistors R1 and R2 is placed in an atmosphere of dry air, and the resistance values of the resistors R3 and R4 are adjusted so that the output V of the bridge circuit B becomes zero. next,
If we put this AH sensor +1 in the atmosphere of if and examine the relationship between its output ■ and absolute humidity, we find that the absolute humidity and AH
Although not shown, the output with the sensor 11 is in a linear relationship, and the absolute humidity can be directly read from the sensor output. Considering this qualitatively, the thermistors 13a and 14a of the above AH sensor are both I5o℃~
Since it is self-heated to 200 degrees Celsius, the thermistor 18a of the sensor 13 with ventilation holes receives air containing water vapor (humid air) due to changes in humidity, and its thermal conductivity is higher than that of the thermistor 18a of the sensor 14 containing dry air. Compared to +4a, the amount of water vapor itself varies greatly. In other words, the thermistor 13a exposed to humid air is cooled and the resistance R1
The resistance value increases and the balance of the bridge improves. This imbalance is what causes the absolute output to rise with linearity.

Next, the atmospheric temperature of the heating chamber 7 and A when the AH sensor 11 having the above characteristics is incorporated into the microwave oven 1.
Investigate the zero balance output characteristics of the H sensor. Ah
The zero balance of the sensor is the difference in the temperature coefficients of the two thermistors that make up the AH sensor.
This refers to the fact that a drift output of about several mV appears in the power output.

FIG. 6 shows the zero balance output characteristics of the AH sensor when the temperature of the heating chamber 7 is relatively low between 30°C and 40°C.
FIG. 7 shows the zero balance output characteristics of the AH sensor at a high temperature of 100°C to 150°C.

According to this, when the temperature is low, the zero balance output characteristic is constant and stable, but when the temperature is high, a drift output is obtained with a width of about ±5 mV, and the zero balance characteristic varies. As described above, when the temperature of the heating chamber is relatively high, the output of the AH sensor 11 is not constant when the food 5 is barely heated, that is, when the absolute humidity has not yet increased due to heating. Therefore, as shown in FIG. 8, when the food 5 is heated, the absolute humidity signal level A2 detected by the AH sensor 11 and the pre-stored absolute humidity signal level at the time of heating finish are -A20 (A2o:A
If the heating is controlled to end when the initial voltage of the H sensor matches the initial voltage of the H sensor, then in the case of the AH sensor + 1A, the finishing will be completed at time TA, and by finishing earlier than the desired finishing time Tc, it will be in an unheated state. In addition, in the case of the AH sensor 11B, finishing is completed at time TB, and as a result of finishing later than the desired finishing time TC, an overheating state occurs. In other words, variations in the zero balance output characteristics of the AH sensor II may cause variations in the finish of the food, making it difficult to obtain the optimal heating finish for a specific menu. This was done in consideration of the above points, and automatically detects the zero fluctuation state of the AH sensor (even if variations in lance output occur) in a high-temperature atmosphere, and selects and sets the cleaning time. At the same time, the output of the AH sensor at the end of cleaning is used as the initial value of the finish, and the finish level corresponding to each cooking menu is detected to obtain a uniform heated finish.

<Configuration> In order to achieve the above-mentioned object, the present invention includes a detection means for detecting the slope of the output characteristic of an absolute humidity sensor during the cleaning time, and a predetermined cleaning time that is selectively determined according to the output of the detection means. The present invention is characterized by comprising a cleaning time setting means for setting a cleaning time.

<Example> Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 9 is a circuit diagram of a main part of a microwave oven showing an embodiment of the present invention, FIG. 10 is a characteristic diagram explaining the operation of the AH sensor in FIG. 9, and FIG. 11 is a diagram showing the operation of the present invention. It is a flowchart showing an outline.

In the figure, parts having the same functions as those of the conventional example described above are given the same reference numerals and detailed explanations will be omitted.

Reference numeral 17 denotes a DC amplifier into which the output voltage V of the bridge circuit B is introduced, and is connected to the raw converter 18. 1
9 is a raw converter connected to the common terminal 20 of the resistors R3 and R4 of the bridge circuit B. Above ~ Raw converter 1
8 and 19- are connected to the microcomputer 22 via the interface 21, respectively. The microcomputer 22 includes a CPU that is the main body of calculation and control.
22a, a ROM 22b for storing programs and data for arithmetic fist control processing, and a RAM 22C for storing external programs and used for registers, flags, etc. 23 is a transistor that operates according to the output of the microcomputer 22; 24 is a relay having a relay coil connected in series with the transistor 23; its contact 25 is connected to a commercial power line 26 that supplies power to the magnetron 8; 27 is a transistor connected in series with a relay coil 30 having a relay contact 29 that controls a fan 9 that blows air into the heating chamber 7 and a relay contact 29 that controls ON/OFF of the fan motor 28; When 4 is pressed, the rHighj signal output from the microcomputer 22 via the interface 21 turns on the relay 30 and operates the fan motor 28.
A so-called cleaning operation, in which hot air, water vapor, etc. remaining in the heating chamber is sent out of the heating chamber, is started and is set to operate for a predetermined period of time.

Next, the operation of the embodiment of the present invention having the above configuration will be described in the ninth section.
This will be explained based on the drawings and FIG. 11.

If you press the menu selection key 3 on the operation panel 2 and then press the heating start key 4 (Sl), the rHighj signal output from the microcomputer 22 via the interface 21 turns on the cylinder 30 and turns on the fan. The so-called cleaning operation starts (S2), in which the motor 28 is activated and relatively high-temperature air, water vapor, etc. remaining in the heating chamber are sent out to the outside of the heating chamber. It is set.

Next, it is determined whether or not the inside of the heating chamber 7 is at a high temperature, that is, whether the atmosphere in which the AH sensor II is installed is at a high temperature or a relatively low temperature. This is the output voltage A of the common terminal 20 of the resistors R3 and R4 of the bridge B.
1 is measured (S3). As mentioned above, AH sensor I
I is composed of a heat-sensitive element called a thermistor,
The output voltage A1, which is the voltage across the AH sensor, changes linearly so that the voltage level decreases as the temperature increases. The output voltage Al is converted into a digital signal by the raw converter 19 and introduced into the microcomputer 22 via the interface 21.
Compare with the value 2 stored and set in 2b (54) L, A
If I<2, the microcomputer 22 determines that the heating chamber 7 is relatively low temperature, and in this case, 'AH
-t! Since this does not affect the zero balance output of the sensor, the cleaning time CT is set to 16 seconds (S5), which is used in the normal heating sequence. On the other hand, in the case of A1<2, since the heating chamber 7 is in a high temperature state, a sequence is entered to stabilize the zero balance output of the AH sensor II by setting the cleaning time longer than the normal 16 seconds.

Specifically, AH sesen-1 after time Tl from the start of heating
1, and the output voltage A2 of the AH sensor 11 after time T2 from the start of heating is A2 (TI).
2 (T2) in the RAM 22c (S6)
, (S7)L, these numbers are α−A 2 (T2 )
and A2 (71) and calculate (S8) L. If the value of α is 09≦α≦11, set the cleaning time CT to 16 seconds (S5),
α〉12. In the case of α<0.8, the level of the AH sensor changed greatly when changing from T1 to T2, so it was determined that the AH sensor had poor zero balance output characteristics, and the cleaning time was increased to 1 minute compared to the normal case. (S9), and the value of α is 08≦α≦0.9 or 1.1≦α≦
If it is within the range of 1.2, the cleaning time is controlled to be slightly shorter and set to 32 seconds (510) as shown in FIG. 10(b). In this way, by selecting and setting the cleaning time CT according to the zero balance output characteristics of the AH sensor 11, as shown in FIG.
If there is a difference between H sensor + 1A and AH sensor - JIB with a difference of -5 mV, the initial value A of the sensor will change when 1 minute of cleaning time has elapsed (Sll) for each.
20A and A20B are stored in R and AM22C respectively (
s+2)L, the microcomputer 22 outputs the rHighJ signal that turns on the transistor 23, and the relay 24 turns on, supplying commercial power to the magnetron 8, which starts operating and oscillates microwaves (513). .

The food 5 is heated in this way, and the AH
Initial value A20A of sensor 11A and IIB.

From A20B, the sensor output A2 is measured to see if it has reached a predetermined AH sensor output increase amount ΔH (S13). Then, this output A2 is A20A+ΔH or A
When it reaches 20B+ΔH, it is determined that the predetermined finishing p level has been reached (314), and the microwave heating is stopped (S16).
Then, cooking of food 5 is completed.

In this way, by adjusting the cleaning time, variations in the characteristics of the AH sensor can be corrected.

Effects> As explained above, the present invention includes a detection means for detecting the slope of the output characteristic of the absolute humidity sensor during the cleaning time, and a predetermined cleaning time selectively set according to the output of the detection means. Since the cleaning time setting means is provided, even if there are variations in the zero balance output characteristics of the absolute humidity sensor, the cleaning time can be adjusted according to the output characteristics. By detecting the finishing level corresponding to each cooking menu using the output of the humidity sensor as the initial value of the heating finish of the food, it is possible to easily obtain uniform heating and finishing.

[Brief explanation of the drawing]

Figure 1 is a front view of the microwave oven, Figure 2 is its schematic cross-sectional view, Figure 3 is an external view of the absolute humidity sensor, Figure 4 is a detailed cross-sectional view of Figure 3, and Figure 5 is the absolute humidity measurement circuit. Figures 6 and 7 are zero balance output characteristic diagrams of the absolute humidity sensor at low and high temperatures, respectively. Figure 8 is a heating finishing time characteristic diagram at high temperature conditions. Figure 9 is an example of the present invention. FIG. 10 is a characteristic diagram illustrating the operation of the absolute humidity sensor in FIG. 9, and FIG. 11 is a flowchart outlining the operation of the present invention. 2. Operation panel, 3. Menu selection key, 4. Heating start key, 7. Heating chamber, 8. Magneto. 9 ・Fan, +1・−・Absolute humidity sensor, 2 interface, 22 Microcomputer. 28 ・Fan motor. Agent Patent attorney Aihiko Fuku (2 others) Figure 1 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. It is characterized by comprising a detection means for detecting the slope of the output characteristic of the absolute humidity sensor during the cleaning time, and a cleaning time setting means for selectively setting a predetermined cleaning time according to the output of the detection means. microwave oven.