JP2563538B2 - Electric water heater - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electric water heater such as a jar pot that heats water by heating water in a general household.

2. Description of the Related Art A conventional electric water heater of this type is disclosed in, for example, Japanese Patent Laid-Open No. 61-27.
As shown in Japanese Patent No. 6522, the time required to rise per unit temperature of a temperature detector pressed against a container heated by a heating element is measured, and this time is compared with a predetermined value to obtain a value smaller than a predetermined value. The power supply to the heating element was stopped when it was too short.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in an electric water heater having such a configuration,
As shown in FIG. 7, in the fluctuation 1 of the temperature curve immediately after the start of heating and the fluctuation 2 of the temperature curve when water is added, there is a problem that the heating is erroneously stopped because the temperature rises rapidly. It was

That is, the unit temperature in the conventional electric water heater is generally set to 0.5 to 2 degrees, and in the fluctuations 1 and 2, a larger temperature fluctuation than this suddenly occurs. On the other hand, the unit temperature cannot be increased so much as to quickly detect the temperature saturations 3 and 4 due to boiling. This is for the following reason. Assuming that the heat quantity of the heater is P [w], the volume of water to be heated is V [cc], and the thermal efficiency is K, the time ΔT required for the temperature rise of Δd is J: Constant 4.2 [cal / J], so water capacity 3000 [cc], heater heat 700
Considering the case of [w], thermal efficiency 90 [%], and temperature rise 2 [° C], Becomes As shown in Fig. 8, when it takes an average of 40 seconds to rise normally by 2 [° C], considering the dispersion of measured values due to convection of water, etc., it is usually 1.5 in order to judge the saturation of temperature rise due to boiling. It is not preferable because the boiling detection is delayed until the time point of 6 even though the boiling point is expected to be doubled and the boiling point is actually 5 times. This delay increases as the unit temperature increases.

In view of such problems of the present invention, it is an object of the present invention to provide an electric water heater that can correctly detect the presence or absence of water in a container without lowering the accuracy of boiling detection.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention provides a temperature-sensitive element which is different from the first set temperature in addition to the unit temperature gradient calculating means.
When the time required for the temperature to rise to the second set temperature higher than the set temperature is measured and the time is output within a predetermined time, the air-baked detection means receives the output of the air-baked detection means or the boiling detection means. And a heating stopping means for stopping energization of the heater.

Action Since the electric water heater of the present invention is configured as described above, the first set temperature and the second set temperature can be set independently of the unit temperature gradient calculating means for boiling detection. As a result, if the temperature difference between the first set temperature and the second set temperature is set to be larger than the fluctuation of the temperature curve immediately after heating or when water is added, heating will not be stopped by mistake, The presence or absence of water can be detected correctly.

Embodiment One embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of a main part showing a configuration of an electric water heater in an embodiment of the present invention, 7 is a container, 8 is an annular heater for heating the container 7, and 9 is a bottom part of the container 7. The temperature of the water is indirectly detected by a temperature sensitive element (thermistor) that is pressed against. Reference numeral 11 is a unit temperature gradient calculating means for sequentially obtaining a temperature gradient each time the temperature detected by the thermistor 9 rises by a unit temperature from the output of the temperature detecting means 10. A storage unit 12 temporarily stores the output of the unit temperature gradient calculating unit 11. 13 is a boiling detection means, and this boiling detection means 13
Is to detect the boiling point by comparing the gradient value stored in the storage means 12 with the gradient value which is output from the unit temperature gradient computing means 11 and which changes from time to time. Reference numeral 14 is an air-baking detection means, which measures the time required for the temperature detected by the thermistor 9 to rise from the first set temperature to the second set temperature, performs comparison calculation processing with a predetermined value, and detects air-baking. Is. Reference numeral 15 is a heating stop means, which receives the output of either the boiling detection means 13 or the bakeout detection means 14 and stops the energization of the heater 8.
Note that 10 to 15 are realized by a one-chip microcomputer (hereinafter referred to as a microcomputer).

Next, the operation will be described. FIG. 2 shows a circuit diagram of a main part of this embodiment. In FIG. 2, the same components as those in FIG. 1 are designated by the same reference numerals. Reference numeral 16 is the microcomputer.

First, the operation of the temperature detecting means 10 will be described. Resistance 17
The timer means 20 measures the time until the charging potential b of the integrating circuit composed of the capacitor 18 and the capacitor 18 becomes equal to the divided potential a of the thermistor 9 and the resistor 19. 21 and 22 are resistors and transistors for charging the capacitor 18, which are timer means.
The capacitor 18 is charged by 20 each time the timing ends.
23 is a comparator.

FIG. 3 shows the input potentials a and b of the comparator 23 and the timer means 2
The relationship of the count value t of 0 is shown.
It shows the case of 90 ℃ and 95 ℃. That is, since the thermistor 9 has a negative temperature characteristic, the higher the temperature is, the higher the divided potential a becomes, and as a result, the time until the potential b of the capacitor 18 reaches the divided potential a becomes longer. . As a result, the output of the timer means 20 (time count t) becomes a value substantially proportional to the temperature of the thermistor 9. This is the so-called A / D
This is conversion, and the output of the timer means 20 is converted into the temperature detection means 10
Output. FIG. 4 is a flow chart showing the operation of the timer means 20.

Next, operations of the unit temperature gradient calculating means 11 and the boiling detecting means 13 will be described. FIG. 5 is a diagram showing how the output of the temperature detecting means 10 increases as the temperature of the thermistor 9 rises, and the count value t increases every time the temperature of the thermistor 9 rises by 1 ° C.
Shows an example in which is incremented by 1. Unit temperature gradient calculation means
The input 11 of the output t of the temperature detecting means 10 measures the time when the output t changes, that is, the time T required for the thermistor 9 to rise in unit temperature. Then, in the middle of the heating time T _N is temporarily stored in the storage unit 12, N + M-th time T _{N + M} to boiling detected at 24 is greater than a predetermined compared to T _N. In the present embodiment, since the predetermined ratio with the unit temperature gradient is set to 1/2, the time required to increase the unit temperature is the reciprocal, and therefore it is twice or more, and T _{N + M} ≧ 2 · T _N is the condition for boiling detection.

Next, the operation of the burnout detecting means 14 will be described. In FIG. 2, reference numeral 25 is a second comparator, and the input potential c of the thermistor 9 is the first due to the resistors 27, 28 and 29.
Is set to be equal to the partial voltage potential a at the set temperature (50 ° C. in this embodiment). Reference numeral 26 is a third comparator, and the input potential d is also set to be equal to the divided potential a when the thermistor 9 is at the second set temperature (60 ° C. in this embodiment). FIG. 6 is a flow chart showing the operation of the burnout detecting means 14, and waits for the output e of the second comparator 25 to change from Low to High in steps 202 to 203. Therefore, when the thermistor 9 is below 50 ° C., the timer remains cleared. Next, until the temperature of the thermistor 9 exceeds 50 ° C. and reaches 60 ° C., the output e of the second comparator 25 is High and the output f of the third comparator 26 is Low. It cycles through the loop of 206 and counts up the timer (measures time). Then, when the temperature of the thermistor 9 exceeds 60 ° C., the output f of the third comparator 26 also becomes High. Therefore, the time measurement is ended, and it is determined in step 207 whether the time is longer or shorter than the predetermined time or short. However, if the time is shorter than the predetermined time, it is output to the energization stopping means 15 in step 208. In the present embodiment, as the boundary condition guided by the burnout detecting means 14, the amount of water in the container 7 is 100 [cc] or less, the amount of heat of the heater 8 is 700 [w], and the thermal efficiency is 90.
%, The difference between the first set temperature and the second set temperature is 10 [° C.] Therefore, the predetermined time is set to 7 seconds.

Then, the energization stopping means 15 receives the output of either the baking detecting means 14 or the boiling detecting means 13, outputs an off signal to the transistor 30, and contacts 31b of the relay 31.
Is opened to stop energizing the heater 8. Therefore, even if the user mistakenly energizes the container 7 with no water, it is possible to detect this and stop energizing the heater 8. The first set temperature and the second set temperature are the boiling detection means 13
Since it can be set independently of, the temperature difference can be made sufficiently larger than the shaking immediately after the start of heating or when water is added, and as a result, erroneous firing detection can be prevented.

EFFECTS OF THE INVENTION As is clear from the description of the above embodiments, according to the present invention, it is possible to accurately detect the presence or absence of water in a container without reducing the accuracy of boiling detection. is there.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric water heater according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a block diagram of essential parts of the electric water heater, and FIG. FIG. 4 is a flow chart showing the operation of the temperature detecting means, FIG. 5 is a flow chart showing the operation of the boiling detecting means, and FIG. 6 is a flow chart showing the operation of the baking detecting means. FIG. 7 is a temperature characteristic diagram for explaining the problems of the conventional example, and FIG. 8 is a temperature characteristic diagram for explaining the boiling detection operation. 7 ... Container, 8 ... Heater, 9 ... Temperature sensitive element, 10 ... Temperature detecting means, 11 ... Unit temperature gradient calculating means, 12 ... Storage means, 13 ... Boiling detecting means, 14 ... Empty Bake detection means, 15
…… A means of stopping energization.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Noda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Shigeo Hamaoka 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. In the company

Claims (1)

(57) [Claims] 1. A container heated by a heater, a temperature-sensitive element that is pressed against the outer bottom portion of the container and indirectly detects the water temperature, and a temperature detecting means including the temperature-sensitive element as a part. A unit temperature gradient calculating means for sequentially calculating a temperature gradient for each unit temperature rise based on the output of the temperature detecting means, a storage means for temporarily storing the output of the unit temperature gradient calculating means, and a storage of the storage means. A value is compared with the output of the unit temperature gradient calculating means, and a boiling detecting means for outputting when the ratio becomes equal to or lower than a predetermined ratio, and the unit temperature gradient calculating means, the temperature sensing element is provided separately. Bake-out detection means for measuring the time required for the temperature rise from the first set temperature to reach the second set temperature higher than the first set temperature and outputting it within a predetermined time, and this bake-out Detection means or the boiling detection hand Electric water heater with a current supply stopping means for stopping the energization of the heater receiving one of the outputs of.