JPH05277030A - Electric water boiler - Google Patents

Abstract

PURPOSE:To provide the water boiler which can detect existence or lack of a liquid in a container without using a liquid quantity detecting function right after a heater is energized, irrespective of the temperature at the measurement start, and quickly and accurately stop energizing the heater. CONSTITUTION:Numeral 4 in the diagram is a switch for starting boiling-mode heating, 14 is a heater having a calorific value enough to rise the temperature of a liquid in a container and boil the liquid. Symbol 1-a is a relay contact, and 1-b is a relay coil which makes and breaks the relay contact 1-a according to the output generated from a microcomputer 9. Aymbol A is a temperature detecting section which detects temp. variation of the liquid in the container with a negative characteristic thermistor 8 and is composed of a part of the microcomputer 9 and its associated circuitry. The microcomputer 9 is a one-chip microcomputer which consists of CPU, ROM, RAM, I/O port, and A/D converter, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric water heater such as a general household jar pot for boiling water to keep it warm.

[0002]

2. Description of the Related Art Conventionally, as described in Japanese Patent Laid-Open No. 61-64217, a temperature difference for a certain period of time is measured in the process of boiling water, and the temperature rise gradient is calculated to obtain a constant temperature gradient. An electric water heater has been proposed, which stops heating when the temperature exceeds the limit and detects empty cooking.

However, in such a water heater, it is necessary to wait for the calculation of the temperature rise gradient after the elapse of a certain period of time before detecting the boiling.

In order to detect air-cooking quickly, it is sufficient to shorten the above-mentioned certain time, but if A / D conversion or the like is used for temperature measurement at this time, A / D conversion error, liquid convection, etc. Therefore, there is a problem that the temperature is erroneously read and it is detected that the cooking is not performed even when the cooking is not performed. Therefore, it is necessary to extend the certain time to some extent.

Further, as a temperature detecting method, a negative characteristic thermistor is generally used, and the temperature is detected by a voltage obtained by dividing the constant voltage by the thermistor and the resistor. Therefore, in the thermistor resistance value before and after the resistance value, The sensitivity is good, and the sensitivity tends to deteriorate as it deviates from the thermistor resistance value. In general, the thermistor resistance value near the boiling point of water is used as the resistance value, so at a temperature of about 50 ° C, about 1 /
The sensitivity becomes about 1/4 at about 2 and 25 ° C. and about 1/8 at about 0 ° C., which causes a problem that a considerable amount of time elapses before detecting empty cooking.

Risk of burns from contact with the container of the human body,
In consideration of the discoloration of the container, the heat deterioration of the components of the heating element, etc., it is required that the detection of empty cooking be performed quickly and accurately.

[0007]

DISCLOSURE OF THE INVENTION The present invention is to solve the above-mentioned requirements, and it is possible to measure whether the measurement start temperature is low or high in the container from the start of energization of the heating element of the heating means. The present invention provides an electric water heater capable of detecting the presence or absence of liquid or lack thereof without using a liquid amount detection function, and capable of quickly and accurately stopping energization of a heating element.

[0008]

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a circuit diagram of an electric water heater. Reference numeral 15 is an AC power source, and 14 is a bottomed cylindrical container 16 as shown in FIG. A heating element of a heating means having a heating value, 1-a is a relay contact connected in series with the heating element 14, 1-b is a relay coil for opening and closing the relay contact 1-a by an output generated from the microcomputer 9, 2 Is a diode, 3 is a transistor,
4 is a switch for starting the boiling mode, 10 is a light emitting diode, 11 is a resistance, and A is a temperature detecting unit for detecting a temperature change of the liquid in the container 16 by the negative characteristic thermistor 8 through the container 16 as shown in FIG. It is composed of a part of the microcomputer 9 and peripheral circuits.

The microcomputer 9 includes a CPU and RO
It is a one-chip microcomputer including M, RAM, an input / output port, an A / D converter, and the like.

The temperature detecting section A comprises a negative characteristic thermistor 8, voltage dividing resistors 5, 6, and 7, open drain output terminals O ₁ and O _{2 of a} microcomputer 9, and an A / D converter. The outputs O ₁ and O ₂ of 9 are alternately turned on and off in a constant cycle, and the thermistor 8
At the high temperature resistance value (about 110 ° C.) as the value of the resistor 5, the value of the value + the resistors 6 and 7 the resistance value at the low temperature of the thermistor (about 25 ° C.), the output O ₂ of the microcomputer 9
The voltage across the resistor 5 when ON is ON and the voltage across the resistor 7 when the output O ₁ is ON are averaged over the constant period, and the value is almost proportional at temperatures from 0 ° C to 120 ° C. The resistance of the negative characteristic thermistor 6 depending on the characteristics.
The temperature signal is calculated by adjusting the ratio of the resistor 7 and the resistor 7. I
Reference numeral ₁ is an input terminal of the microcomputer 9, and O ₃ and O ₄ are open drain output terminals of the microcomputer 9 (O ₄ has a built-in pull-up resistor).

FIG. 2 shows the RO in the microcomputer 9.
It shows a flowchart stored in M, and will be described according to a program procedure.

First, in step 1, a boiling mode for heating water to a boiling point is started by inputting a switch or the like.
In step 2, the heating element 14 is energized. Step 3
Then, start a timer for preventing idle cooking for a fixed time (about 12 to 30 seconds). In step 4, the temperature signal arithmetically processed by the temperature detector A is read, and in step 5, it is determined whether or not it is boiling based on the temperature signal read by another program. When boiling is determined,
In step 6, the energization of the heating element is stopped. If boiling is not determined, the process proceeds to step 7. In step 7, it is determined whether or not it is the first reading of the temperature signal after the timer is set, and if it is the first reading of the temperature signal t, the value t is read in step 8
Stores and t _o to AM, returns to the step 4. When the temperature signal t is read for the second time or later in step 7, the process proceeds to step 9, and the difference between the temperature signal t read in step 9 and the first temperature signal t _o is compared with a constant value B. .
The constant value B may be a value of a temperature difference at a constant time (time set by a timer) in the minimum allowable amount (about 0.2 liter) when the liquid contained in the container boils. In step 9, when the temperature difference (t-t _o) is equal to or greater than B, then stops the energization of the heating element as an empty炊displays. If it is less than B, it is judged in step 10 whether or not the timer has passed the fixed time, and if it has not passed the fixed time, the process returns to step 4. Step 1
When the fixed time has elapsed at 0, the timer is reset at step 11 and the process returns to step 3. Then, steps 3 to 11 are repeated.

Here, in the case of detecting the air cooking using the flowchart of FIG. 2, if hot water is added after the power supply to the heating element is started, the rising temperature (t _o -t) exceeds the constant temperature B. , A malfunction occurs in which the power supply to the heating element is stopped and the cooking is displayed even though it is not cooking. In order to improve such malfunction, as shown in the flowchart of FIG.
After detecting the first round of empty炊, after rising temperature after a predetermined time stably _{(t-t o <1 ℃} ), again returns to step 2, n times (2-3 times) for a predetermined time wait if elevated temperature again (t-t _o) is not scooped a predetermined temperature B, empty炊検unloading of the first round is also reset to repeat steps 11 step 3 as described above. N times the fixed time (2 to 3 times)
When the temperature rise (t-t _o) is beyond the predetermined temperature B within, the energization is stopped again heating element may be configured to empty炊display.

[0015]

As described above, according to the present invention, immediately after the heating element of the heating means is energized, even if the temperature at the initial stage of energization is low (0 ° C.) or high, a certain time When the temperature rises inside exceeds a certain temperature, the presence or absence of liquid in the container can be detected with few malfunctions without using a liquid level detection device, and the power supply to the heating element can be stopped quickly and accurately. Therefore, it is safe and it is possible to eliminate the inconvenience that occurs in the conventional technique.

[Brief description of drawings]

FIG. 1 is an electronic circuit diagram of an electric water heater according to an embodiment of the present invention.

FIG. 2 shows a flowchart stored in a ROM in a microcomputer according to an embodiment of the present invention (claim 1).

FIG. 3 is a vertical sectional view of an electric water heater according to an embodiment of the present invention.

FIG. 4 shows a flowchart stored in a ROM in a microcomputer according to an embodiment of the present invention (claim 2).

[Explanation of symbols]

 1-a relay contact 1-b relay coil 4 boiling mode start switch 5, 6, 7 partial pressure resistance 8 negative characteristic thermistor 9 microcomputer 14 heating element 15 AC power supply 16 container

Claims (2)

[Claims] 1. A bottomed cylindrical container, heating means for heating the container to raise the temperature of the liquid in the container, and a heating value sufficient to boil the liquid, and a temperature change of the liquid. Using a negative characteristic thermistor that senses through a container, the liquid temperature is 0 ° C to 120 ° C.
A temperature detecting device capable of detecting a temperature at a constant gradient at 0 ° C., and a temperature rise measuring means capable of measuring a rising temperature within a fixed time determined by a set time of a timer for each unit time and measuring the rising temperature within the fixed time. And an electric water heater equipped with a stop means for stopping the energization of the heating means when the temperature rise exceeds a predetermined temperature. 2. After the temperature rise within a certain time exceeds a certain temperature, the heating means is de-energized, and after the temperature rise is stabilized for a certain time, the heating means is re-energized.
The rising temperature is measured within a certain period of time, and when the constant temperature again exceeds n times the certain period of time, the energization of the heating means is stopped,
An electric water heater designed to be displayed.