JPH031824A - Electric kettle - Google Patents

Abstract

PURPOSE:To prevent erroneous detection of boiling when a time taken for a predetermined temperature width rise is not N times longer than a predetermined time, by setting the predetermined time to a comparative value when the time taken for the predetermined temperature width rise in heating is shorter than the predetermined time. CONSTITUTION:When a temperature rise detecting means 3 detects predetermined temperature width rise, a controlling means 4 stores contents of time since the beginning of heating of a clock means 7 in a memory means 8 and further compares the value of the memory means 8 with a predetermined time to store the predetermined time in the memory means 8 if the predetermined time is longer and send an OFF signal to a heating means 5 when the time taken for the predetermined temperature width rise of at least N times that in the data is reached. A temperature detecting element 1 is constituted of a thermistor 1a and a resistance 1b, the resistance value of the former being increased when the temperature is low and reduced when the temperature is high so that the corresponding voltage is outputted to the temperature rise detecting means 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electric water heater for heating and keeping a liquid contained in a container warm.

2. Prior Art A conventional electric water heater of this type is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-12
0815, the boiling detection performed within a predetermined time after the start of heating and the boiling detection performed below a predetermined temperature (warming temperature) are invalidated to prevent erroneous boiling detection.

In other words, the temperature rise is small for a while after the start of heating due to a delay in thermal response, and at this time there are warm and cold parts in the heated object, causing ripples in the temperature rise curve. Erroneous boiling detection that occurs during this period is invalidated, and if this occurs after a predetermined period of time has elapsed, the boiling detection is invalidated if the temperature at that time is below a predetermined temperature.

Problems to be Solved by the Invention However, with such a conventional configuration, even in the worst case, although the temperature can be raised to above the heat retention temperature, it is not possible to bring the temperature to boiling reliably.

For example, when a container filled with enough water is gradually cooled down to the insulating temperature, the hot water that has lowered its temperature first will accumulate at the bottom of the container, creating a temperature difference in the upper layer of the water. When reheating in this state, convection continues for a while centered on the bottom heated by the heating element, and eventually changes to convection from the bottom to the top. When the convection is centered at the bottom, it is like heating a small volume of hot water, and the temperature curve rises very steeply, but when the convection changes over the entire area, the temperature curve becomes gentler. If a comparison value is made at a point where the temperature curve rises steeply, this value will be small and boiling will be detected when the convection changes over the entire body.

Therefore, in the present invention, if the state where the liquid is not heated continues,
Focusing on the fact that there is a temperature difference between the top and bottom of the water as it cools,
If the time for the temperature to rise within the specified temperature range during heating is shorter than the specified time, it is assumed that the data is when the convection does not change overall, and the specified time is used as a comparison value, and if it does not become longer than N times the specified time, This is to prevent erroneous boiling detection.

Means for Solving the Problems The electric water heater of the present invention includes a heating element that heats a liquid in a container, a heating means that controls energization of the heating element, and a temperature sensor that detects the temperature of the liquid in the container. an element, a temperature rise detection means for detecting that the temperature detection element increases by a predetermined width, a timer for timing the time for the temperature rise detection means to increase by a predetermined width, and a value of the timer for When the temperature rise detection means detects a rise in a predetermined temperature range, the value of the time measurement means at that time is stored in the storage means, and if the value of the storage means is shorter than a predetermined time, the temperature increase detection means stores the value of the time measurement means at that time, and if the value of the storage means is shorter than a predetermined time, the temperature rise detection means detects a rise in a predetermined temperature range. is stored in the storage means, and when the temperature sensing element detects that the time for the temperature to rise by a predetermined range is longer than the value stored in the storage means by I)N times, the heating means is turned off. This means that a means has been established.

Effect: By having the above-described structure, the present invention prevents erroneous heating because even if a comparison time is set for boiling detection when there is an unstable factor at the start of heating, boiling is not detected in a shorter time than a predetermined time. Boiling can be detected correctly without stopping the system.

Embodiment FIG. 1 shows a block diagram showing an embodiment of the electric water heater of the present invention.

The structure and operation of the electric water heater of the present invention will be explained.

In the figure, / is a temperature detection element that is brought into contact with the bottom of the container λ, and a voltage output corresponding to the temperature can be obtained by the temperature rise detection means 3. The temperature rise detection means 3 determines whether the temperature has risen by a predetermined range (here, 0.5 degrees) based on the obtained output, and transmits the output to the control means. j is a heating means, and the heating element 6 is controlled by the output of the control means≠. Reference numeral 7 denotes a clock means, which performs counting and clearing in response to a signal from the control means≠. ♂ is a storage means, which stores the data of the clock means 7 according to a command from the control means≠. When the humidity increase detection means 3 detects an increase in temperature within a predetermined range, the control means ≠ stores the content of the time at which the timer 7 starts heating at that time.
to be memorized. Furthermore, the value of this storage means and the predetermined time (
6 seconds here), and if the predetermined time is longer, this predetermined time is stored in the storage means r, and if the time for the predetermined temperature range to rise is longer than N times this data, the heating means j This is to transmit an off signal to the

FIG. 2 is a circuit diagram showing a specific configuration of an embodiment of the present invention.

The temperature sensing element/ is composed of a thermistor/a and a resistor/b. When the temperature is low, the resistance value of the thermistor/a is large, and when the temperature is high, the resistance value is small, and the voltage is adjusted accordingly. It is output to the temperature rise detection means 3. The temperature rise detection means 3 is composed of an A/D converter, and converts the output of the temperature detection element into a binary code and outputs it. The heating means includes a transistor ta, a relay contact tb, and a relay coil tc.
Consists of transistors! When a is turned on, current flows through relay coil JC, closes relay contact tb, and heats the heating element. // is a microcomputer (hereinafter abbreviated as microcomputer) that constitutes the control means 7, the timekeeping means 7, and the storage means g, and is configured to realize these functions by executing a program. Next, the flow of the process will be explained based on FIGS. 3 and 4.

If the temperature is reheated during keeping warm or the temperature drops below the set value (here, the temperature is 5°C lower than the keep warm temperature), My Fun// turns on heating means j and executes the heating treatment routine shown in Figure 3. Let's do it. Here, in step 3/ the clock means 7
is cleared, the output of the temperature rise detection means 3 is inputted in step 32, and it is determined in step 33 whether the temperature has increased by a predetermined range.If the temperature has not increased, the timer is counted in step 31r, and the temperature has increased by a predetermined range. Repeat step 3 → step 33 → step 3 until When the temperature rises by a predetermined range in step 33, the time value from the start of heating of the timer means 7 is stored in the storage means r in step 3j, and the timer means 7 is cleared in step 3j. Next, in step 36, the stored value of the storage means is compared with a predetermined time, and if it is less than the predetermined time, the value of the storage means is updated to the predetermined time in step 37. When the comparison data is stored in the storage means ♂ in this manner, a boiling detection processing routine as shown in FIG. 4 is performed.

In FIG. 4, the output of the temperature rise detection means 3 is input to the microcomputer/l in step 1A2, and it is determined in step 1A2 whether the temperature has increased by a predetermined range. If the temperature has not increased by the predetermined range, step ≠ evening Then, the timer means 7 counts and returns to step 44/. If the temperature has increased by a predetermined width in step≠2, the value counted by the timer 7 and the value multiplied by N in the storage device g are compared in step≠3. Here, clocking means 7
If the counted value of 0 is small, the timer 7 is cleared at step ≠ B, and the process returns to step ≠ / to start counting the rising time of the predetermined temperature range anew. If the value counted by the timer 70 at step 3 is longer, the heating means is turned off at step 3, and boiling is detected.

Effects of the Invention According to the present invention, since the comparison time used when detecting boiling is set to be longer than a predetermined time at any time, the temperature increase gradient of the temperature sensing element changes depending on the temperature difference between the top and bottom of the hot water. Even if a bending point exists, it is ignored, so there is no possibility of erroneous boiling detection, and as a result, correct boiling detection can always be carried out.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of an electric water heater according to an embodiment of the present invention, Fig. 2 is a specific circuit diagram of the electric water heater, and Fig. 3 shows the process during heating of the electric water heater. FIG. 4 is a flowchart showing the boiling detection process of the electric water heater. /: temperature detection element, la: thermistor, /b: resistance,
2: Container, 3: Temperature rise detection means, Hiroshi: Control means, 5: Heating means, J'a: ) transistor, tb: Relay contact, jC: Relay coil, B: Heating element, 7:
Timekeeping means, lr: Storage means, //: Microcomputer. Patent Applicant Matsushita Electric Industrial Co., Ltd. 1st Prisoner/: Gekishin Susu J 2. Actual! : Yoshi;1)! Otsu=no! 'Jimζyo ai3-3・
5-1 Yono → L 1ε sentence b 2 Soku stop Figure 2 Woni → E electric 7 g 10 Ha Ien electric O〃-Mike 4 nhi 1-7 Figure 3

Claims (1)

[Claims] a heating element that heats the liquid in the container; a heating means that controls energization of the heating element; a temperature detection element that detects the temperature of the liquid in the container; temperature rise detection means for detecting temperature rise detection means; clock means for timing the time for temperature rise detection means to rise by a predetermined range; storage means for storing the value of said time measurement means; When an increase in the width is detected, the value of the timer at that time is stored in the storage means, and if the value of the storage means is shorter than a predetermined time, a predetermined time is stored in the storage means, and the temperature sensing element An electric water heater comprising a control means for turning off the heating means when it is detected that the time for temperature rise is N times longer than the value stored in the storage means.