JP2850424B2 - Electric water heater - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric water heater, such as a jar pot, that keeps water warm in ordinary households.

2. Description of the Related Art In a conventional electric water heater of this type, for example, as shown in Japanese Patent Application Laid-Open No. 61-276522, a temperature rise gradient of a temperature detecting element pressed against a container is measured, and this temperature rise is measured. In some cases, heating was stopped when the gradient became smaller.

Problems to be Solved by the Invention However, in such a conventional electric water heater, as shown in FIG. 3, since the temperature of the temperature-sensitive element rises due to radiation from the heater even after the water boils,
There has been a problem in that the detection of a change in the gradient is delayed and the boiling is continued for a while and then the boiling is detected.

An object of the present invention is to solve the above-mentioned problem and to provide an electric water heater that accurately detects boiling.

Means for Solving the Problems The present invention, in order to achieve the above object, a heating means for heating a container containing water, and a temperature-sensitive element for indirectly detecting the water temperature by pressing against the outer bottom of the container, A temperature detecting unit having the temperature sensing element as a part, and detecting a temperature gradient based on an output of the temperature detecting unit to enable the boiling detection. When the temperature becomes higher than the temperature, the boiling detection is enabled, and when any one of the boiling detections is detected, the heating means is stopped.

Operation According to the present invention, since the boiling point is detected when the temperature exceeds the previous boiling temperature, the boiling point is not detected.

Embodiment An embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of a main part of the present embodiment.
An annular heater 2 is provided on the outer bottom of the container 1 as a heating means, and a temperature-sensitive element (thermistor) 3 is attached to the center of the container 1 so as to be in pressure contact with the container 1. The temperature of the water in the container 1 is indirectly detected by the temperature detecting means 4. When the heater 2 is energized to start heating, the temperature gradient detecting means 5 detects a temperature gradient from the output of the temperature detecting means 4 and stores the value in the first storage means 6 under predetermined conditions. Here, the predetermined condition is that the temperature rise curve is convex at one minute or more and 80 ° C. or more after the start of heating, which is the same as the above-mentioned conventional example. Then, the gradient comparing means 7 compares the value stored in the first storage means 6 with the output of the temperature gradient detecting means 5 and outputs when the ratio becomes lower than a predetermined ratio.

On the other hand, the temperature comparing means 8 compares the output of the temperature detecting means 4 with the value stored in the non-volatile second storage means 9 and outputs the output when the output of the temperature detecting means 4 becomes equal to or more than the stored value. I do. When one of the output of the gradient comparing means 7 and the output of the temperature comparing means 8 is obtained, the boiling detecting means 10 detects the boiling and stops the energization of the heater 2, and the temperature at this time. The output of the detecting means 4 is
Is stored in the storage means 9.

The temperature detecting means 4, temperature gradient detecting means 5, first storage means 6, gradient comparing means 7, temperature comparing means 8 and boiling detecting means 10 are realized by a one-chip microcomputer.

Here, the temperature detecting means 4 divides the DC power supply 11 with the temperature sensitive element 3 and the resistor 12 as shown in FIG.
A / D conversion is performed by the A / D converter 13. FIG. 3 shows the A / D conversion output, the water temperature, and the temperature of the temperature-sensitive element 3. Are increased one by one. Then, the gradient comparing means 7 measures the time Tn required for the A / D conversion output to increase by one, and determines that if the temperature gradient becomes Tn + m + 1 ≧ 2 × Tn, that is, if the temperature gradient becomes half, it is determined that the gradient becomes slower due to boiling. And output.

Further, the nonvolatile second storage means 9 stores 4 as an initial value when the water temperature is 100 ° C. Therefore, even if the gradient detection by the gradient comparing means 7 is delayed, when the temperature of the temperature sensing element 3 reaches about 102 ° C., the temperature comparing means 8 outputs and stops heating. On the other hand, when the boiling is correctly detected by the gradient comparing means 7,
The output value of the temperature detection means 4 at that time is stored in the second storage means 9
, The heating is stopped immediately even if the gradient detection is delayed.

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

Although the nonvolatile memory is used as the second storage means, an external RAM backed up by a battery or the like may be used instead, or the microcomputer itself may be used by using the RAM built in the microcomputer. Needless to say, backups may be made.

Effects of the Invention As is apparent from the above description of the embodiments, according to the present invention, it is possible to prevent a so-called delay that continues heating even after water boils.

Further, since the so-called learning control is performed in which the boiling detection is performed based on the previous boiling temperature in each body, the boiling can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a circuit diagram of a temperature detecting means of the embodiment, and FIG. 3 is a characteristic diagram showing a relationship between a water temperature, a temperature of a thermosensitive element, and an output of the temperature detecting means. It is. DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Heater (heating means), 3 ... Temperature sensing element, 4 ... Temperature detection means, 5 ... Temperature gradient detection means, 6
... first storage means, 7 ... gradient comparison means, 8 ... temperature comparison means, 9 ... second storage means, 10 ... boiling detection means.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Noda 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-60-41915 (JP, A) JP-A-63 -290526 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) A47J 27/21

Claims (1)

(57) [Claims] 1. Heating means for heating a container containing water,
It has a temperature sensing element that is in pressure contact with the outer bottom of the container and indirectly detects the water temperature, and a temperature detection unit that includes the temperature sensing element as a part, and detects a temperature gradient based on an output of the temperature detection unit. While enabling the boiling detection, it enables the boiling detection when the temperature detected by the temperature detecting means becomes higher than the temperature at the time of the previous boiling detection, and turns on the heating means when any one of the boiling detections is detected. Electric water heater to stop.