JPH03191924A - Electric water heater with temperature control - Google Patents

Abstract

PURPOSE:To prevent erroneous detection of boiling even if voltage is fluctuated to cause fluctuation in the ascending curve of water temperature or if gradually cooled hot water is heated and a bending point is generated on the ascending curve, by composing a device so that the boiling is effectively detected only when output is generated from a temperature comparing means. CONSTITUTION:In a nonvolatile storage means 6, the temperature data of previous boiling detection and the like are stored. Besides, according to the output of an atmospheric pressure detecting means 7, by a storage value correcting means 8, the storage value of said storage means 6 is corrected. The corrected temperature data and the output of a temperature detecting means 4 are compared with each other by a temperature comparing means 9, and when a difference between them is set to come within a specified value, then output is generated. Thus, by a boiling detecting means 10, it is discriminated to be boiling when both the output amounts of a gradient dulling detecting means 5 and the temperature comparing means 9 are obtained, and the electrification of a heater 2 is stopped, and at the same time, in the storage means 6, the output of temperature detecting means 4 is stored. A temperature at the time of previous boiling is kept stored, and in the area of a temperature lower than a temperature corrected according to atmospheric pressure, a device is composed not to perform the boiling detection 10, and so even if fluctuation and a bending point are generated on the ascending curve of water temperature due to the fluctuation of line voltage and the change of convection, the erroneous detection of boiling cannot be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an electric water heater such as a jar pot for boiling water and keeping it warm in general households.

2. Description of the Related Art Conventional electric water heaters of this type are known, for example, from Japanese Patent Application Laid-open No. 1986-
As shown in Japanese Patent No. 276522, there is a device that measures the temperature increase gradient of a temperature detection element that is pressed into contact with a container, and stops heating when this temperature increase gradient becomes small.

Problems to be Solved by the Invention However, in such conventional electric water heaters, when the commercial power supply fluctuates, the amount of heat generated by the heater, which is the heating means, fluctuates in proportion to the square of the power supply voltage, resulting in a rise in water temperature. There is a problem in that the curve fluctuates, and as a result, it is determined that the temperature rise has slowed down, and boiling is incorrectly detected before the water in the container has boiled.

Additionally, when the heated water cools slowly, the cooled water collects at the bottom of the container, creating a temperature difference between it and the top. When heating is started in this state, as shown in FIG. 4, convection initially occurs only in the bottom layer, and the temperature of this bottom layer increases. However, this temperature rise is rapid because only a small volume of water in the bottom layer is being heated. When the temperature difference between the upper layer and the bottom layer becomes sufficiently small, -
The air changes to convection that reaches the upper layer, and the temperature gradient in the upper layer becomes smaller.As shown in Figure 6, the temperature rise curve of the thermosensor creates a bend A, and this bend A is defined as the change point of the temperature gradient. There was also the problem that boiling was incorrectly detected. Alternatively, even after the water in the container boils, the temperature of the thermosensor increases due to radiation from the heater, as shown in Figure 6B, so the detection of the gradient change is delayed, and boiling is detected after the water continues to boil for a while. There was also the problem that there was a so-called late turnaround time. Furthermore, the boiling temperature of water changes depending on atmospheric pressure, so if you set the heat retention temperature high, if you use it at a high altitude or use it under low pressure due to changes in weather conditions, it will boil even while it is being kept warm. There was also the problem of not being able to set the temperature high.

The present invention has been made in view of the above-mentioned problems, and the problem is that fluctuations in the water temperature increase curve occur due to fluctuations in the voltage of the commercial power supply.
A first object of the present invention is to provide an electric water heater that does not erroneously detect boiling even if a bending point occurs in the rising curve when hot water whose temperature has been lowered by slow cooling is heated.

A second object is to provide an electric water heater that promptly and correctly detects boiling even if the temperature of the temperature sensing element continues to rise due to radiant heat after boiling.

A third object of the present invention is to provide an electric water heater that can accurately detect boiling even when the atmospheric pressure changes and can maintain heat at a temperature close to the boiling temperature.

Furthermore, as the boiling temperature changes due to changes in weather conditions, the fourth purpose is to provide an electric water heater that can change the heat retention temperature accordingly and set a higher heat retention temperature within the range that does not boil. do.

Means for Solving the Problems In order to achieve the above first object, the present invention provides a memory means for storing the output of the temperature detecting means when boiling is detected, an atmospheric pressure detecting means, and an atmospheric pressure detecting means. stored value correction means for correcting the stored value of the storage means based on the output of the detection means;
A temperature comparison means is provided which compares the corrected temperature data with the output of the temperature detection means and outputs an output when the difference is less than a predetermined value, and boiling is detected only when the temperature comparison means is outputting an output. It is configured to be effective.

In addition, in order to achieve the second object, the present invention compares the corrected temperature data and the output of the temperature detection means, and if the output of the temperature detection means exceeds the corrected temperature data, the difference is greater than or equal to a predetermined value. Equipped with a temperature comparison means that outputs when the
The structure is such that boiling is detected immediately when the temperature comparison means outputs an output.

In order to achieve the third object, the present invention includes a heat retention control means that performs heat retention control at a temperature lower by a predetermined value than the output of the temperature detection means when the boiling detection means outputs the output. It is something that

Furthermore, in order to achieve the fourth object, the present invention is such that the heat retention temperature is also corrected based on the output of the atmospheric pressure detection means.

The electric water heater of the present invention has the above-mentioned structure, so that even if the temperature rise of the hot water fluctuates due to fluctuations in the commercial power supply or a bending point occurs due to changes in convection, the electric water heater of the present invention maintains the previous boiling temperature at atmospheric pressure due to the above-mentioned configuration. Boiling is not detected in a temperature range lower than the temperature data corrected accordingly.

Further, even if the temperature of the temperature sensing element continues to rise after boiling, boiling is detected when the temperature exceeds the temperature data obtained by correcting the previous boiling temperature according to atmospheric pressure and rises by a predetermined value. Then, based on the temperature data at the time of boiling detection, the temperature is maintained at a high temperature close to the boiling temperature.

Further, even if the boiling temperature becomes low due to a drop in atmospheric pressure due to an approach of a typhoon during heat retention, the heat retention temperature is also corrected in accordance with the output of the atmospheric pressure detection means.

Embodiment A first embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing the configuration of essential parts of an embodiment of the present invention, in which an annular heater 2 is provided as a heating means at the outer bottom of a container 1, and a temperature-sensitive element (thermistor) is provided at the center of the heater 2. ) 3 is attached so as to be in pressure contact with the container 1, and the temperature of the water in the container 1 is indirectly detected by a temperature detecting means 4 of which the temperature sensing element 3 is a part.

When the heater 2 is energized to start heating, the gradient-slowing detecting means 5 calculates the temperature gradient from the output of the temperature detecting means 4, and detects the slowing of the temperature gradient at the boiling point. The operation of this gradient blunting detection means 5 is similar to that of the conventional example. On the other hand, the non-volatile storage means 6 stores temperature data at the time of previous boiling detection. Reference numeral 7 denotes an atmospheric pressure detecting means for detecting atmospheric pressure which varies depending on altitude and weather conditions.A stored value correcting means 8 corrects the stored value of the storing means 6 according to the output of this atmospheric pressure detecting means 7. A temperature comparing means 9 compares this corrected temperature data with the output of the temperature detecting means 4, and outputs when the difference is within a predetermined value. Then, the boiling detection means 10 determines that boiling has occurred when the outputs of both the gradient blunting detection means 5 and the temperature comparison means 9 are obtained, and at the same time, the temperature is stored in the storage means 6. The output of the detection means 4 is stored. Note that the temperature detection means 4 to boiling detection means 10 described above are realized by a one-chip microcomputer.

Next, the operation will be explained. The temperature detection means 4 includes:
As shown in FIG. 2, the voltage of the DC power source 11 is divided by the temperature sensing element 3 and the resistor 12, and this is A/D converted. Here, a thermistor is used as the temperature sensing element.

FIG. 3 shows the water temperature, the temperature of the thermistor 3, and the A/D.
The output of the converter 13 is shown, and the output of the thermistor 3 is shown.
In a region where the temperature is about 80° C. or higher, the A/D conversion output increases by 1 for each rise of about 0.5° C. Then, the slope blunting detection means 5 measures the time Tn required for this A/D conversion output to increase by 1, and calculates that Tnm≧2xT.
When the temperature gradient reaches n, that is, when the temperature gradient becomes 1/2, it is determined that the gradient has become slower and is output.

By the way, the temperature θ(
°C) is expressed as (A=64.500. B=0.1979'). The storage means 6 stores the output of the temperature detection means 4 at the time of previous boiling detection, corrected to the boiling temperature at atmospheric pressure of 1 atmosphere. The atmospheric pressure is detected by the atmospheric pressure detecting means 7, and the stored value correcting means 8 corrects the stored value in the storing means 6 based on the output of the atmospheric pressure detecting means 7. That is, the output value of the temperature detection means 4 corresponding to the boiling temperature of 100° C. at 1 atm pressure is stored in the storage means 6, for example, 2A in hexadecimal notation.
is memorized. Based on the output of the atmospheric pressure detection means 7, the temperature is corrected to a value corresponding to the boiling temperature at the atmospheric pressure at that time. Suppose that the output of the atmospheric pressure detection means 7 is 0.9.
Assuming that the pressure is 3 atm, the boiling temperature will be about 98°C from the above formula 0, which is about 2°C lower than when the pressure is 1 atm. Since the resolution of the temperature detection means 4 is approximately 0.5°C, the stored value correction means 8 subtracts 4, which corresponds to 2°C, to 26 in hexadecimal notation.
Output.

The temperature comparing means 9 compares the output of the stored value correcting means 8 and the output of the temperature detecting means 4, and determines that the output of the temperature detecting means 4 approaches the temperature data corrected by the stored value correcting means 8 and there is no difference. Outputs when the value is below a predetermined value. In this embodiment, this predetermined difference is set to 2, that is, approximately 1°C.

When the outputs of both the temperature comparing means 9 and the gradient blunting detecting means 5 are obtained, the boiling detecting means 10 determines that boiling is occurring and stops energizing the heater 2. Furthermore, if the output of the temperature detection means 4 at this time is 27 in hexadecimal, this means that the atmospheric pressure is 0.9 as described above.
This is the boiling temperature at 3 atmospheres, and since 4 is a much smaller value than at 1 atmosphere, the hexadecimal value 2B obtained by adding 4 is stored in the storage means 6 as the standard boiling temperature at 1 atmosphere.

After detecting boiling in this way, the heat retention control means 14
The temperature is kept slightly lower than the temperature corrected by the stored value correction means 8. Here, the temperature corrected by the memory value correction means 8 is the boiling temperature, which changes from time to time with changes in atmospheric pressure, so the heat retention temperature controlled by the heat retention control means 14 is equal to the boiling temperature. A constant temperature difference will always be maintained.

As is clear from the above explanation, the electric water heater of this embodiment memorizes the temperature at the previous boiling point, and does not detect boiling in a temperature range lower than the temperature corrected according to atmospheric pressure. With this configuration, even if fluctuations or inflection points occur in the water temperature increase curve due to fluctuations in power supply voltage or changes in convection, erroneous boiling detection cannot be performed. In addition, the heat retention temperature is corrected according to the atmospheric pressure based on the temperature when boiling is detected, so it can be kept warm at a high temperature close to the boiling temperature, and it will not start boiling even if the atmospheric pressure changes. There is no such thing.

Next, a second example will be described. The structure of this second embodiment is also similar to that of the first embodiment, as shown in FIG. In this embodiment, the temperature comparing means 9 outputs an output when the output of the temperature detecting means 4 exceeds the data corrected by the stored value correcting means 8 and the difference becomes a predetermined value of 4 or more. When either the gradient blunting detection means 5 or the temperature comparison means 9 outputs an output, it is determined that boiling has occurred and the power supply to the heater 2 is stopped. The configuration and operation other than that are the same as in the first embodiment.

With the above configuration and operation, even if the gradient blunting detection means 5 is delayed in detecting the point of gradient blunting, the temperature comparing means 9 will output an output when the temperature of the thermistor 3 has risen approximately 2 degrees above the previous boiling temperature. , the boiling detection means 10 stops energizing the heater 2 .

Although a heater was used as the heating means in this embodiment, it is also possible to use electromagnetic induction heating or induction heating using microwaves.

In addition, although non-volatile storage was used as storage means, external RAM backed up by batteries etc.
It goes without saying that the microcomputer itself may be backed up by using a RAM built in the microcomputer.

Effects of the Invention As is clear from the description of the embodiments above, the first effect of the present invention is
According to the above means, it is possible to prevent so-called premature cut-off, in which water boils erroneously detected before it boils, and it is also possible to keep the water warm at a temperature close to the boiling point in accordance with changes in atmospheric pressure. Furthermore, according to the second means, it is possible to prevent so-called late boiling, in which water continues to be heated even after it has boiled. Furthermore, since this is a so-called learning control in which boiling is detected based on the previous boiling temperature of each vessel, boiling can be detected with high accuracy regardless of variations in parts.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a configuration diagram of the main parts of an electric water heater with temperature control according to an embodiment of the present invention, Fig. 2 is a circuit diagram of its temperature detection means, and Fig. 3 is a diagram showing water temperature and temperature control. A characteristic diagram showing the relationship between the thermistor temperature and the output of the temperature detection means, Figures 4 and 5 are diagrams showing changes in water convection, and Figure 6 is a relationship between changes in water convection, water temperature, and thermistor temperature. FIG. 1... Container, 2... Heater, 3...
... Temperature sensing element (thermistor), 4 ... Temperature detection means, 5 ... Gradient blunting detection means, 6 ...
...Storage means, 7...Atmospheric pressure detection means, 8...
... Memory value correction means, 9 ... Temperature comparison means, 10 ... Boiling detection means, 14 ... Heat retention control means.

Claims (4)

[Claims] (1) A heating means that heats a container containing water, a temperature detection means that includes a temperature sensing element that is in pressure contact with the outside of the container and indirectly detects the water temperature, and a gradient of the output of this temperature detection means. a storage means for storing the output of the temperature detection means; an atmospheric pressure detection means for detecting atmospheric pressure; and a storage means for detecting the output of the atmospheric pressure detection means. temperature detection means for comparing the temperature data corrected by the memory value correction means with the output of the temperature detection means and outputting when the difference becomes less than or equal to a predetermined value; and a boiling detection means that stops energizing the heating means when both the output of the temperature comparison means and the output of the slope blunting detection means are obtained, and the storage means includes a boiling detection means that stops energizing the heating means. An electric water heater with temperature control configured to update the stored value when output. (2) A heating means that heats a container containing water, a temperature detection means that includes a temperature sensing element that is in pressure contact with the outside of the container and indirectly detects the water temperature, and a gradient of the output of this temperature detection means. a storage means for storing the output of the temperature detection means; an atmospheric pressure detection means for detecting atmospheric pressure; and a storage means for detecting the output of the atmospheric pressure detection means. and a memory value correction means for correcting the memory value of the memory value, and compares the temperature data corrected by the memory value correction means with the output of the temperature detection means, and determines whether the output of the temperature detection means exceeds the corrected temperature data. temperature comparison means that outputs an output when the difference becomes equal to or less than a predetermined value; and boiling detection that stops energizing the heating means when at least one of the output of the temperature comparison means and the output of the slope blunting detection means is obtained. 3. An electric water heater with temperature control, the storage means updating the stored value when the boiling detection means outputs the stored value. (3) The temperature control system according to claim 1 or 2, further comprising a heat retention control means for performing heat retention control at a temperature lower by a predetermined value based on the output of the temperature detection means when the boiling detection means outputs the output. Electric water heater. (4) The electric water heater with temperature control according to claim 3, wherein the heat retention control means corrects the heat retention temperature based on the output of the atmospheric pressure detection means.