JPS5942258B2 - humidity detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity detection device that can detect the humidity of a measurement target without the influence of the relative humidity of outside air.

In recent years, microwave ovens and open ovens have rapidly become popular in the field of cooking equipment.

However, with modern microwave ovens, it is extremely difficult to set the heating time for food. For this reason, there are quick reference charts for cooking times depending on the type of food and its amount, but there is a limit to the amount of information that can be written, and if it is written in too much detail,
It actually becomes harder to see. Therefore, this quick reference table is only a guideline and cannot be considered sufficient. Furthermore, this does not take into account the factors that determine the actual heating time, such as the humidity and final temperature of the target food before cooking. Therefore, the reality is that cooking mistakes often occur. The present inventors have actually confirmed that if these cooking devices detect the moisture coming out of food and cook accordingly, no cooking mistakes will occur for most menu items.

Specifically, it detects the humidity of the atmosphere in the cooking area, for example, in the case of a microwave oven.
If you stop the heating operation when it reaches a certain value,
This ensures that the food is cooked properly. However,
When a humidity-sensitive resistance element is used to detect humidity, the influence of the humidity of the outside air cannot be ignored.

That is, since the humidity in the air varies depending on the date and time, when the humidity in the air changes, it becomes difficult to control the heating by detecting the humidity of moisture generated from the heated object.

In other words, since the humidity in the air is used as the reference humidity, if the humidity in the air fluctuates, it becomes difficult to detect moisture generated from the heated object. Furthermore, the water vapor released when food is cooked causes condensation on the surface of the moisture-sensitive resistor.
Water desorption response becomes very poor. In other words, when a moisture-sensitive resistance element is at room temperature and comes into contact with water vapor, the temperature difference causes dew to condense on the surface, and once the dew adheres to the surface, the response deteriorates significantly. Put it away. In particular, if the resistance value of a humidity-sensitive resistance element is detected and the cooking operation is automatically stopped when the resistance value reaches a certain value due to a change in the humidity of the surrounding atmosphere, dew condensation will occur on the surface of the element immediately after electricity is turned on. The problem arises that the operation stops immediately. An object of the present invention is to provide a humidity detection device that eliminates such drawbacks.

Figure 1 shows that the relative humidity in the air is 40%, 50%,
60%, when water 11 is heated in a microwave oven, the change in resistance value of the moisture-sensitive resistance element provided in the microwave oven is shown. The X-axis in FIG. 1 is the heating time of the microwave oven, and the Y-axis is the resistance value of the humidity-sensitive resistance element. As is clear from the figure,
The resistance value of the moisture-sensitive resistance element decreases with heating time, but
It can be seen that the resistance range of the humidity-sensitive resistance element changes greatly depending on the change in the relative humidity in the air. Therefore, it is extremely difficult to accurately detect the moisture coming out of the heated object as it is. Therefore, in the humidity detection device of the present invention, the relative humidity on the surface of the element is reduced by heating the humidity sensing element,
By detecting humidity while maintaining a constant relative humidity, the influence of humidity changes in the air is removed, making it possible to accurately detect humidity changes due to moisture generated from the heated object. Note that the relative humidity to be maintained may be set to a value slightly lower than normal humidity. The humidity detection device of the present invention includes a humidity sensing resistor, a resistance heating element for heating the humidity sensing resistor, a humidity sensing circuit that converts a change in the resistance value of the humidity sensing resistor into an electrical signal, and a subtraction circuit that detects a deviation signal between the output signal of the humidity detection circuit and an electric signal corresponding to a set value of relative humidity; and a current holding circuit that supplies a current corresponding to the output signal of the subtraction circuit to the resistance heating element. a circuit that causes the resistance heating element to generate heat to heat the humidity-sensitive resistor to a temperature at which the relative humidity on the surface of the humidity-sensitive resistor matches a preset relative humidity value; The device is characterized in that it is configured to detect humidity while the temperature is maintained at the above temperature.

In the present invention, the humidity-sensitive resistor is made of, for example, a metal, a metal oxide, a compound semiconductor, or the like, and its electrical resistance changes depending on humidity.

The humidity sensitive resistor is configured to be heated by a resistance heating element, and this resistance heating element is made of metal, carbon, oxide semiconductor, or the like. In this way, the present invention maintains the relative humidity on the element surface at a constant value and standardizes the relative humidity on the element surface, thereby adjusting the humidity changes in the air that change depending on the date and time to a constant reference humidity level. , which enables stable humidity detection.

A detailed explanation will be given below based on examples.

Figures 2A, 2C, and 2C show a front view, side sectional view, and rear view of an example of the structure of a moisture-sensitive element used in the device of the present invention.
, 2 and 3 are respectively electrodes made of Ag-Pd metal, and 4
is a Cr2O3 based ceramic moisture sensitive resistor with a temperature of 1350°C.
We use products that have been baked for 2 hours.

The size of this moisture-sensitive resistor 4 is 6 mm in diameter and 0.3 mm in thickness.
It is disc-shaped. 5 is an alumina insulating board, vertical a, horizontal b,
Thickness c dimensions are 8mm, 112mm, and 10.6mu, respectively.
It is.

6 is a RUO2-based resistance heating element.

FIG. 3 shows the humidity-electrical resistance characteristics between electrodes 1 and 2 of the humidity-sensitive element shown in FIG.

Figure 4 shows an embodiment of the humidity detection device of the present invention constructed using the humidity sensing element shown in Figure 2, and 7 detects humidity by the output between electrodes 1 and 2 of the humidity sensing element. 8 is a subtraction circuit that detects the deviation between the electrical signal corresponding to a relative humidity value (reference relative humidity value) set slightly (20%) lower than normal humidity and the output signal of the humidity detection circuit 7. It is a circuit.

9 is an input terminal for applying an electric signal corresponding to the reference relative humidity value; 10 is an amplification circuit for amplifying the output deviation signal of the subtraction circuit 8; and 11 is an amplification circuit for amplifying the output deviation signal of the subtraction circuit 8; This is a current holding circuit that holds the current value after a current that compensates for humidity is passed through the resistance heating element 6.

In addition, 12 is a level detection circuit, which temporarily causes the resistance heating element 6 to generate strong heat, burns off and removes oil etc. attached to the humidity sensitive resistor 4, and then returns the original compensation current to the resistance heating element 6. 6
It is controlled so that it is supplied to Next, the operation of this device will be explained.

The relative humidity signal detected by the humidity detection circuit 7 is compared with the reference relative humidity signal applied to the terminal 9, and after the deviation signal is amplified by the amplifier 10, it is sent to the resistance heating element 6 by the current holding circuit 11. Feedback control of the current and set the current to a steady value. Thereafter, the current holding circuit 11 is held by an external signal, and the current at the above-mentioned steady-state value is transferred to the resistance heating element 6.
Continue to flow. Now, for example, when the humidity in the air is 50%, the humidity sensing resistor 4 is slightly heated by generating heat in the resistance heating element 6 of the humidity sensing element, and the relative humidity near the humidity sensing resistor 4 is The relative humidity is reduced to a reference relative humidity (eg 30%). Next, when the relative humidity drops to the reference relative humidity (30%), the resistance value of the humidity sensitive resistor 4 increases, and the humidity sensitive resistor 4, humidity detection circuit 7, subtraction circuit 8, amplification circuit 10, and current holding circuit 11 The feedback loop is kept steady. In this way, by passing current through the resistance heating element 6, the relative humidity corresponding to the resistance value of the humidity sensitive resistor 4 can be adjusted to a preset reference relative humidity.

Then, after fixing the current holding circuit 11 in this state, for example, the object to be heated is heated, and a change in relative humidity due to moisture generated from the object to be heated is detected. FIG. 5 shows the change in resistance of the humidity-sensitive resistor 4 when water 11 is heated in the microwave oven by installing the humidity-sensing element of the apparatus of the present invention inside the microwave oven. As shown in the figure, by standardizing the humidity level by matching the relative humidity on the surface of the humidity sensing element to the reference relative humidity, the humidity level remains constant regardless of the humidity fluctuations in the air (40%, 50%, 60%). humidity sensitivity can be obtained. Note that, if the device of the present invention is used for a while, oil components and the like will adhere to the moisture-sensitive resistor 4.

In such a case, due to the adhesion of the oil component, the moisture-sensitive characteristics of the humidity-sensitive resistor 4 are no longer exhibited, making it impossible to control the setting of the reference relative humidity on the surface of the humidity-sensitive resistor element as described above. That is, the control state of the field back loop (loop 4, 7, 8, 10, 11) cannot be maintained in equilibrium, and a large deviation signal is generated in the subtraction circuit 8. In this case, after the deviation signal is amplified by the amplifier 10, the deviation signal is detected by the level detection circuit 12, and when the deviation signal exceeds a certain value, the output current of the current holding circuit 11 is temporarily increased. After heating the resistance heating element 6 to burn off and remove oil components adhering to the humidity sensitive resistor 4, etc., the original compensation current is supplied to the resistance heating element 6 again.
The characteristics of the moisture-sensitive element can be regenerated by supplying the moisture to the moisture-sensitive element. However, when the operation of the current holding circuit 11 is fixed and the humidity sensing resistor 4 is maintained at a predetermined temperature to detect humidity, it is configured in advance to stop the operation of removing oil components by heating. There is a need. FIG. 6 shows the desorption response when water condenses, curve A is the characteristic of the conventional humidity sensing element, curve B is the characteristic of the humidity sensing element in this example,
When a current is instantaneously applied to the resistance heating element 6 to heat it, water adsorption/desorption responsiveness is improved.

By heating and maintaining the humidity-sensitive resistor, even if it comes into contact with the instantaneous moment that occurs during cooking, dew condensation does not occur on the surface, and humidity can be detected with high precision.

Note that the above-described humidity detection device is useful not only in microwave ovens and ovens, but also in cases where there is a risk of dew condensation occurring when the humidity sensing element comes into contact with the atmosphere to be detected.

As is clear from the above embodiments, according to the present invention, by controlling the amount of heat generated by the heating element for heating the humidity-sensitive resistor, the humidity of the measurement area can be controlled by eliminating the influence of the relative humidity of the outside world. Can be detected accurately.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram of a conventional humidity sensing element, and FIGS. Fig. 3 is a diagram showing the humidity-sensitive resistance characteristics of the same element, Fig. 4 is a block diagram showing an embodiment of the humidity detection device according to the present invention, and Fig. 5 is a diagram showing the humidity detection characteristics of the humidity-sensing element using the same device. 6 are characteristic diagrams showing water desorption responsiveness. 1, 2, 3...Electrode, 4...Moisture sensitive resistor, 5...Alumina insulating plate, 6...Resistance heating element, 7... ...Humidity detection circuit, 8...
・Subtraction circuit, 9...Reference humidity input terminal, 10.
... Amplifying circuit, 11 ... Current holding circuit,
12...Level detection circuit.

Claims (1)

[Claims] 1 A humidity-sensitive resistor, a resistance heating element for heating the humidity-sensitive resistor, a humidity detection circuit that converts a change in the resistance value of the humidity-sensitive resistor into an electrical signal, and an output signal of the humidity detection circuit. The resistor includes a subtraction circuit that detects a deviation signal from an electric signal corresponding to a set value of relative humidity, and a current holding circuit that supplies a current corresponding to the output signal of the subtraction circuit to the resistance heating element. A state where the humidity sensitive resistor is heated to a temperature at which the relative humidity on the surface of the humidity sensitive resistor matches a preset relative humidity value by causing a heating element to generate heat, and the humidity sensitive resistor is maintained at the above temperature. 1. A humidity detection device configured to detect humidity in a room.