JPS6014149A - Detector for absolute humidity - Google Patents

Abstract

PURPOSE:To make it possible to use an absolute humidity sensor having an inferior zero balance by connecting a low resistance in series to two thermistors constituting the absolute humidity sensor to adjust a difference of temperature characteristics between thermistors. CONSTITUTION:A DC constant voltage source E is connected between input terminals B1 and B2, and an output terminal B3 is connected to the input terminal of a DC amplifier 16, and an output terminal B4 is connected to the positive input terminal of the DC amplifier 16. If a temperature drift to the positive side is generated in an absolute humidity sensor 10 in case of a variance of temperature, a low resistance RC is inserted in series to a thermistor resistance R2 between the compensating thermistor R2 of a bridge circuit and the input terminal B2. If a temperature drift to the negative side is generated in the absolute humidity sensor 10, the low resistance RC is inserted in series to a thermistor R1 between the input terminal B1 of the bridge circuit and the detecting thermistor R1. Thus, the absolute humidity sensor 10 is compensated into a superior zero balance state.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an absolute humidity detection device, and more particularly to an absolute humidity detection device that enables cost reduction.

BACKGROUND ART It is known to use an absolute humidity sensor (hereinafter referred to as an AH sensor) as a sensing element in an automatic food finishing control device for a microwave oven. As shown in Figure 1, A
The H sensor 10 is composed of a closed sensor 13 and an open sensor 12, and includes a closed container 1 filled with dry air.
A thermistor 13a is connected to the inside of 2 through wire 13b.
It is connected and supported between the book terminals 13c and 13C. In addition, the thermistor 12a is connected to two terminals 12C112 through wires 12b inside the container 12e opened to the outside.
It is connected and supported between C and C. This thermistor 13a
and 12a have the same characteristics.

Furthermore, in order to equalize the temperature of the closed container 13e and the open container 2e, the containers 13e and 12e are connected by a heat equalizing tube 14 made of a thermally conductive material. The AH sensor formed in this way is supported on one terminal block 11 as shown in FIG.
covered. The above-mentioned terminals 13c, 13c, 12c, 12
Lead wires 16, 16, 17 . ]7
4 that penetrates the terminal block 11 and protrudes below the terminal block 1]
They are connected to wooden terminals 18, respectively.

The thermistor AH sensor measures absolute humidity by utilizing the difference in thermal conductivity between humid air and dry air, and the principle circuit for humidity measurement is shown in FIG. -1' in Figure 3
-1 is a thermistor corresponding to the open type sensor 12 equipped with a ventilation hole 12d, and is a temperature compensation thermistor corresponding to the closed type sensor 13 which is filled with dry air after I. E is a constant voltage power supply, Iζ3. I (4 is bridge circuit B
The resistors R and S forming the circuit are resistors connected in series to the bridge circuit J3. The resistor IζS functions to limit the size of the small current that flows, and in this circuit the resistance value is selected so that the temperature of the thermistor is about 200° C. due to Joule heat.

Now, put the humidity sensor consisting of resistors 1 (□, 1 (2) in a dry air atmosphere, and the output of bridge circuit B is 11V.
Adjust the resistance value of resistor 4 so that it becomes zero at B7. Next, place this sensor in a humid atmosphere and
The relationship between the output voltage VB and absolute humidity is investigated. An example of the absolute humidity-output characteristics thus measured is shown in FIG. Fourth
As is clear from the figure, the absolute humidity and the sensor output voltage have a nearly linear relationship, and the absolute humidity can be directly read from the sensor output voltage.

If we consider this qualitatively, the thermistor 12a is an AH sensor used in microwave ovens.

13a (Fig. 1) are both self-heated to 150 to 200°C by Joule heat, so the open type sensor 12
The thermistor 12a, that is, the detection side thermistor □ receives air containing water vapor (humid air) due to humidity changes,
The thermal conductivity of the thermistor 13a of the closed type sensor 13 containing dry air, that is, the compensation side thermistor 2, varies greatly depending on the amount of water vapor itself. In other words, when the thermistor is exposed to humid air, the □ is cooled and its resistance increases, causing the bridge to become unbalanced. This imbalance results in an output that is linear and corresponds to the absolute humidity.

5 and 6 are a plan view and a front view, respectively, of a microwave oven using the above-mentioned AI-1 sensor. Turntable 3 due to the electromagnetic waves emitted
Food 34 placed on food 3 is heated. The gas containing water vapor generated from the food 34 by this heating is sent to the fan 35.
is sent into the exhaust duct 36, and this exhaust tact 3
6 and is discharged to the outside of the microwave oven 30 via an exhaust port 37. AI-I sensor 10 is installed on the inner surface of Senki duct 36.
The absolute humidity of the gas passing through the exhaust duct 36 is detected. As shown in FIG. 7, the front surface of this microwave oven is provided with an operation panel 1, a menu selection key 2, and a heating start key 3 on the operation panel 1.

An example of a specific circuit configuration of a microwave oven using the above-mentioned AI sensor is shown in FIG. In FIG. 8, the same reference numbers as in FIGS. 2, 3, 5, 6, and 7 indicate the same or equivalent parts.

In FIG. 8, E is a DC constant voltage source, 16 is a DC amplifier, 17 is an A/D converter that converts the analog output of the DC amplifier 16 into a digital value, and 18 is an interface with a microcomputer or microprocessor 19. The interface circuit, microcomputer or microprocessor 19 includes a CPU 19a which is the main body of calculation and control, and an R which stores programs for calculation and control processing, table data based on the table in FIG.
It includes an OM 19b and a RAM 19c used for storing external programs and for registers, flags, and the like.

20 is a transistor that operates according to the output of the microprocessor 19; 21 is a relay having a relay coil connected in series to the transistor 20; its contact is connected to a commercial power supply line 22 that supplies power to the magnetron 6;

In operation, first, the menu selection key 2 on the operation panel 1 is pressed, and then the heating start key 3 is pressed. The microprocessor 19 receives this start signal and outputs a 'High' signal to the transistor 20 via the interface circuit 18.
Send a level signal and turn on relay 2]. Then-
Magnetron 6 oscillates and the food is heated. At this time, the AI-1 sensor 10 disposed in the exhaust passage 9
Detects water vapor emitted from food. Δ1■Sensor 10
The output ゛magnetic pressure is sent to DC amplifier 1 via bridge circuit B.
The signal is amplified by A/1) converter 17, converted into a digital signal, and inputted to microprocessor 19 via interface circuit 18. Input data is CPU
19a, a point-by-point comparison is made with the optimum finish level value for each temperature previously stored in the ROM 191), and the operation of the magnetron 6 is continued until that level is reached. A lot of water vapor is generated from the food, and the sensor 1
0 detects the absolute amount and when the optimum finish level is reached, the microprocessor 19 controls the interface circuit 18.
A ``I-o1'' level signal is applied to the transistor 20 through the ``I-o1'' level signal. The relay 21 is then deenergized and its contacts open. Immediately, the oscillation of the Macnetron 6 stops, and cooking heating is stopped. Heating stop control is generally performed as described above, but since the capture of sensor output, processing of sensor data in the microprocessor 19, etc. are already known, details will be omitted.

7 crystallinity characteristics of thermistors R1' and R2, which are fixed in the AH sensor.If the so-called B constant is uniform, no matter how much the ambient temperature T of the AtI sensor changes, the thermistor
(Both 0 and R2 exhibit the same change. Therefore, the output voltage VB of the bridge circuit B (FIG. 3) does not vary depending on the ambient temperature T, as shown by the solid line in FIG. 9. In this case, A I- The I sensor has a good so-called zero balance in which no temperature drift occurs.

By the way, the above explanation is based on the case where the zero balance of the A I-I sensor is maintained well, but it is generally difficult to make the temperature characteristics of the two thermistors "1 ' R2 uniform from a manufacturing point of view. In other words, the SE' D balance is normally < out of alignment. If the zero balance is unbalanced, the bridge circuit will have an output voltage V13 from the beginning due to temperature drift, as shown by the dashed line and dashed line in Figure 9. Furthermore, as the output voltage V]3 increases, the amount of change in the output voltage Vn increases as the ambient temperature increases. Looking at this in terms of the output voltage V8H of the absolute humidity detection device, we can see that the factors that change the output voltage VAI+ include water vapor generated from the food, as well as the heating atmosphere temperature T.
The change in the output voltage VB of the bridge circuit due to the rise in VB is also superimposed. Therefore, as shown in FIG. 10, the output I' of the absolute humidity detection device with one heating time U
The change in 1 pressure VA n becomes a curve as shown by a dashed line or a broken line. That is, the time to reach the reference level VAHO may be shorter or longer than the optimal heating time u1 when zero balance is good. That is -
This causes a problem in that the degree of processing of the food becomes unstable.

Conventionally, the only way to maintain the same quality of food despite the imbalance of the zero balance of the A I-I sensor as described above is to select a sensor thermistor with a good zero balance. There was no.

Therefore, the yield of the Δ11 sensor deteriorates, and even if it is mass-produced, there is a limit to what can be used, and the cost of the AI-1 sensor increases.

Purpose The present invention has been made in view of the above-mentioned problems, and its purpose is to provide an absolute humidity detection device which can also be used with A, I (sensors) with poor zero balance.

Abstract: In an absolute humidity detection device that detects the absolute humidity of humid air from the temperature change of the thermistor due to the difference in thermal conductivity between humid air and dry air using a bridge circuit having two thermistors exposed to humid air and dry air, respectively. , connect a low resistance in series to the thermistor of the bridge circuit, and
This corrects the unbalance of the bridge circuit due to temperature drift caused by uneven temperature characteristics of the thermistors.

Example An embodiment of the present invention will be described below.

The results of an experiment using a sensor with good zero balance in the circuit shown in FIG. 3 above are shown in FIG. 1J. In this case, since the zero balance is good, the output voltage Vn of the bridge circuit B is zero volts as shown by the solid line with respect to a change in temperature. Therefore, if a low resistance of, for example, 10 or less is inserted between the input terminal B1 of the bridge circuit j3 and the detection side thermistor, the output voltage VB of the bridge circuit B will change as shown by the dashed line with respect to the change in temperature T. drift to the + side.

Conversely, if a low resistance of 1Ω or less is inserted between the compensation side thermistor R2 and the input terminal B2, the output voltage VB will drift to one side as shown by the broken line. This result, on the contrary,
When using an A I-1 sensor with poor zero balance, inserting a low resistance into the bridge circuit can improve the 111
+1' indicates that the degree drift can be corrected.

The bridge circuits shown in FIGS. 12 and 13 are circuits that perform correction using the method described above. This bridge circuit is replaced with the bridge circuit I3 of the microwave oven circuit shown in FIG. That is, input terminals 13□, 8
A DC constant voltage source E is connected between 2 and 2, the output terminal 133 is connected to the single power terminal of the DC amplifier 16, and the output terminal B4 is connected to the 10 input terminal of the DC amplifier 16. The output terminal of the DC amplifier 16 is connected to an A/D converter 17 (FIG. 8).

In this case, the AI-1 sensor 10 has poor zero balance, and the temperature characteristics of the detection side thermistor □ exposed to humid air and the compensation side thermistor R2 exposed to dry air are uneven. Resistors R3 and R4 are connected oppositely to these two thermistors R1 and R2.

Now, if the A I-I sensor 10 experiences a temperature drift on the + side with respect to temperature changes, as shown by curve a in FIG. 14, as shown in FIG. 2 and input terminal B2.
Insert a low resistance Rc in series with 2. In addition, if the Al-1 sensor has a temperature drift on one side due to temperature changes as shown in the curve shown in Fig. 14, then the input terminal B0 of the bridge circuit and the detection side should be connected as shown in Fig. 13. A low resistance Rc is inserted between the thermistor and the thermistor in series.

In this way, the output voltage VB of the bridge circuit becomes zero volts as shown by curve C in FIG. 14 with respect to temperature changes. In other words, by inserting a correction resistor into the bridge circuit, the deviation due to the temperature drift of the A I-I sensor itself and the deviation due to the inserted resistor cancel each other out. The output of the circuit's magnetic pressure becomes zero volts.

FIG. 15 shows the amount of correction for temperature changes when the above-mentioned correction resistor Rc is inserted on the detection thermistor side or the compensation thermistor side, using the resistance value of the correction resistor RC as a parameter. The larger the resistance value of the correction resistor Rc, the larger the correction amount.

Figure 16 shows the heating pattern of food in a microwave oven equipped with a conventional absolute humidity detection device (shown by the solid line) and the heating pattern of food in a microwave oven equipped with an absolute humidity detection device with a correction resistor inserted in the bridge circuit (shown by the broken line). ), and when a correction resistor is inserted - Since the resistance value of the correction resistor is small, there is no effect on humidity detection sensitivity, and food heating is performed in the same pattern as when no correction is performed.

As mentioned above, the zero balance correction of the A I-I sensor due to this low resistance has no effect on the humidity detection sensitivity when heating a food, and only corrects the zero balance due to the problematic temperature drift. can be done.

Effects As explained above, in the present invention, by using a bridge circuit having two thermistors exposed to moist air and dry air respectively, the temperature change of the thermistor due to the difference in thermal conductivity between humid air and dry air is detected. In the absolute humidity detection device that detects the absolute humidity of As a result, even two thermistors with uneven temperature characteristics can be used as an All sensor in a microwave oven, and
The yield of the I-I sensor is improved, and the price of a microwave oven equipped with this AI-1 sensor can be reduced. Furthermore, it is possible to improve the quality of food cooked in a microwave oven.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the A [1 sensor, Figure 2 is a diagram showing the assembled state of the AH sensor on the terminal block, Figure 3 is a circuit diagram showing the circuit principle of humidity measurement, and Figure 4 is the absolute humidity. -Graphs showing output characteristics, FIGS. 5 and 6, are A1. FIG. 7 is a diagram showing a schematic configuration of a microwave oven using an I sensor, FIG. 7 is a diagram showing a front configuration of a microwave oven, FIG. 8 is a circuit diagram showing a circuit configuration of a microwave oven using an A I4 sensor, and FIG.
The figure is a graph showing the ambient temperature - bridge circuit output 'city pressure characteristic, Figure 10 is a graph showing the heating time - absolute humidity detection device output characteristic, and Figure 11 is a graph showing the A I with good zero balance.
(A graph showing the temperature-output voltage characteristics when using the sensor. Figures 12 and 13 are circuit diagrams showing an embodiment of the present invention. Figure 14 is a graph showing the temperature-output voltage characteristics when using the sensor. Figure 15 is a graph showing the temperature-output voltage characteristics when correction is performed, Figure 15 is a graph showing the temperature-output voltage characteristics using the resistance value of the correction resistor as a parameter, and Figure 16 is '
It is a graph showing the heating pattern of food in a microwave oven. (0. ) Fig. 5 Fig. 6 Fig. 1 Fig. 7 Fig. 9 Fig. 10 -〉h口瑵明 (1, t) Fig. 11 Ongaku T ('C) Fig. 12 Fig. 13 Fig. 14 T ( 'C) Figure 15 ↑ T ('C) Figure 16 Mφ

Claims (1)

[Claims] (1) A bridge circuit having a first thermistor exposed to humid air, a second thermistor exposed to dry air, and two resistors on opposite sides of these two thermistors, In an absolute humidity detection device that obtains a signal corresponding to the absolute humidity of humid air at the output terminal of the bridge circuit from the temperature change of the thermistor caused by the difference in thermal conductivity between humid air and dry air, the thermistor of the bridge circuit An absolute humidity detection device, characterized in that a low resistance is connected in series with the thermistor to correct unbalance of the bridge circuit due to temperature drift caused by uneven temperature characteristics of the two thermistors.