JPS6345810B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a temperature control device for a water heater that heats and keeps a liquid in a container warm using a main heater and an auxiliary heater.

(b) Prior Art A conventional control device of this type is disclosed in Japanese Utility Model Publication No. 58-27708. In such devices, in order to set the temperature, in the case of a bimetal type thermostat, the distance between the bimetals must be changed, resulting in low accuracy, and only the auxiliary heater is energized when transitioning from the heating state to the keeping temperature state. Since the heat capacity of the heater is constant regardless of the amount of hot water in the container, there is a drawback that the temperature cannot be maintained at a constant temperature. Furthermore, it has the disadvantage that if the amount of hot water in the container decreases, it will continue to boil.

(c) Purpose of the invention In view of the above points, an object of the present invention is to maintain a substantially constant temperature regardless of the amount of liquid in a container and to prevent it from continuing to boil.

(d) Structure of the Invention For this purpose, the present invention provides a water heater that heats and keeps the liquid in a container warm by a main heater and an auxiliary heater, and a thermistor for detecting the temperature of the liquid in the container, and a thermistor for detecting the temperature of the liquid in the container. The detection output is compared with the first setting output that is variable by external operation, and the first setting output is
a first comparator having a differential;
a second comparator that compares the detection output of the thermistor with a second set output that is variable by the external operation but does not exceed a predetermined value by the constant voltage means and has a second differential; a first control circuit that controls energization/de-energization of the main heater based on a comparison output of a first comparator; and a first control circuit that controls energization/de-energization of the auxiliary heater based on a comparison output of the second comparator. It is constructed from a second control circuit.

(E) Embodiment An embodiment of the present invention will be described below in detail based on the drawings.
First, the structure of the water heater 1 will be described based on FIG. 1. Reference numeral 2 is a bottomed cylindrical exterior body with an open top surface, and an inner lid 3 closes the top opening 4 on the top surface of the exterior body 2. It is installed like this. An outer cover 5 is provided on the inner cover 3 so as to be openable and closable. Reference numeral 6 denotes a cylindrical container with a bottom, and a lower conduit 7 is provided vertically within the container 6, and an upper conduit 9 provided at a pouring port 8 is connected to the upper end of the lower conduit 7.

When the operating body 10 is pressed, the pump mechanism 11
This allows the liquid in the container 6 to be poured out through the pouring spout 8 via the conduits 7 and 9.

12 is wrapped around the lower outer periphery of the container 6.
13 is a 700W main heater and a 50W auxiliary heater attached to the bottom of the container 6. Reference numeral 14 denotes a temperature control device, and by moving a knob 15 from side to side, the set temperature of the liquid in the container 6 can be changed. 16 is a thermistor that detects the temperature of the liquid in the container 6, and 17 is a power plug connected to a commercial power source.

Next, the control circuit will be explained based on FIG. First, when the power plug 17 is connected to a commercial power source, the DC constant voltage generating circuit 18 generates a DC power source.
It is configured to generate VDD. Reference numeral 19 denotes a temperature detection circuit, and the thermistor 16 constituting this circuit has a characteristic that its resistance value decreases as the temperature rises, and is connected to a DC power supply VDD via a resistor _R1 . One end of the resistor _R2 is connected to ground, and the other end is connected to the thermistor 16 and the resistor _R1 . The connection point A is connected to the inverting input terminal of the first comparator 20 and also to the inverting input terminal of the second comparator 21. Further, one end of the resistor _R4 is connected to the ground, and the resistor R4 is connected to the DC power supply VDD via the variable resistor VR and the resistor _R3 . Further, the variable resistor VR whose resistance value can be changed by the temperature control device 14 is connected to the non-inverting input terminal of the comparator 20 constituting the main heater control circuit 22 via _R5 , and is also connected via the resistor _R6. The comparator 2 constituting the auxiliary heater control circuit 23
1 non-inverting input terminal.

Further, the output terminal of the comparator 20 is connected to the gate of the transistor 24 via a resistor _R7 , and to the DC power supply VDD via resistors _R7 and _R8 . The emitter of the transistor 24 is connected to the DC power supply VDD, and the core is connected to the diode _D1 and the main heater control relay 25, which are connected to ground.

On the other hand, the output terminal of the comparator 21 is connected to the gate of the transistor 26 via a resistor R ₉ and to the DC power supply VDD via resistors R ₉ and R ₁₀ . The emitter of the transistor 26 is connected to the DC power supply VDD, and the collector is connected to the diode D ₂ and the auxiliary heater control relay 27 which are connected to ground.

When the transistor 24 becomes conductive, the relay 25 is energized and the switch 25A is closed, so that the main heater 12 is energized. When the other transistor 26 becomes conductive, the relay 27
is excited, its switch 27A is closed, and the auxiliary heater 13 is energized.

In order to determine the input potentials of the comparators 20 and 21, the voltage applied to the resistor R ₆ is set so that the temperature at which the auxiliary heater 13 stops energizing is lower than the temperature at which the main heater 12 stops energizing. Make it greater than the voltage across resistor R ₅ .

Further, the hysteresis of the first comparator 20 and the second comparator 21 is determined by the feedback resistor R ₁₁ and the resistor R ₅ , the feedback resistor R ₁₂ and the resistor R ₆ , respectively. Therefore, the hysteresis of the first comparator 20 is
The temperature is set to a value lower than the temperature at which the output of the comparator 21 changes from high level to low level.

Furthermore, the resistance value of the variable resistor VR can be changed by external operation, that is, by moving the knob 15 of the temperature control device 14, and the temperature can be set arbitrarily, so that if the set temperature is set to a relatively high temperature, it will continue to boil. To prevent this from happening, one end is connected to a DC power supply.
A Zener diode 28 as a constant voltage means connected to VDD is connected to a connection point B between the non-inverting input terminal of the second comparator 21 and the resistor _R6 . That is, the input level to the non-inverting input terminal of the second comparator 21 is prevented from rising above a predetermined voltage by the diode 28, and is set such that the temperature at which the auxiliary heater 13 stops being energized is, for example, 95° C. or lower. can do.

In this way, the main heater 1
2, energization start temperature of auxiliary heater 13, energization stop temperature of auxiliary heater 13, main heater 1
The operation will be described below assuming that the energization stop temperature of the auxiliary heater 13 is set to 2 and the energization stop temperature of the auxiliary heater 13 does not exceed 95°C.

First, assume that the container 6 of the water heater 1 is fully filled with water, and the power plug 17 is connected to a commercial power source. At this time, when the temperature is set to 92°C by the temperature controller 14, both comparators 2 and 2 are set by the variable resistor VR.
The operating temperature when transitioning from the low level output state of 0 and 21 to the high level output state is 95°C, respectively.
Assuming that the operating temperature of the first comparator 20 when transitioning from the high level output state to the low level output state is 89.5°C, and that of the second comparator 21 is 91°C. This will be explained below.

A DC power supply VDD is generated by a DC constant voltage generation circuit 18 from a commercial power supply. As mentioned above, since the temperature of the water in the container 6 is low, the thermistor 16
detects low temperature and the resistance value is large, both comparators 20 and 2
In both cases, the potential of the inverting input terminal is higher than that of the non-inverting input terminal, and a low level is output. Therefore, both transistors 24 and 26 become conductive, and the main heater control relay 2
5 and the auxiliary heater control relay 27 are energized and their own switches 25A and 27A are closed, so the main heater 12 and the auxiliary heater 13 are energized and the water in the container 6 is heated.

When the water temperature in the container 6 eventually rises and reaches 93.5°C, the second comparator 21 outputs a high level, the transistor 26 becomes non-conducting, the auxiliary heater control relay 27 is demagnetized, and the switch 27A is opened to turn on the auxiliary heater. The heater 13 is de-energized. However, main heater 1
2 is in an energized state and continues heating. When the temperature reaches 95° C., the first comparator 20 outputs a high level signal, and the switch 25A is similarly opened to stop energizing the main heater 12. As a result, the water temperature will gradually decrease.

When the water temperature decreases and reaches 91℃, the resistance value of the thermistor 14 also increases and the second comparator 2
The potential of the inverting input terminal of No. 1 becomes higher than the potential of the non-inverting input terminal. Therefore, the comparator 21 outputs a low level, the transistor 26 becomes conductive, the relay 27 is energized, the switch 27A is closed, and only the auxiliary heater 13 is energized. In this way, the temperature is controlled by energizing or de-energizing the auxiliary heater 13. Therefore, it can be maintained at approximately 92°C. Of course, at this time, if the amount of hot water in the container 6 is small, the energizing time of the auxiliary heater 13 will be short, and if it is large, the energizing time will be long. Therefore, even if the amount of hot water is low, there will be no empty cooking and no unnecessary power consumption.

Then, when the amount of hot water decreases, the outer lid 5 and the inner lid 3
When the water is opened and water is replenished through the top opening 4, the water temperature decreases and becomes heated, and both the comparators 20 and 21 output a low level due to the thermistor 16, so the main heater 12 and the auxiliary heater 13
will be energized and controlled again as described above.

Hereinafter, a case will be described in which the set temperature is set to 94° C. by operating the knob 15 of the temperature control device 14 in order to change the set temperature. In this case, the second comparator 2
It is supposed to be 93°C when the output of No. 1 changes from high level to low level, and conversely, it should be 95.5°C when it changes from low level to high level. However, as mentioned above, the Zener diode 28 is connected to the non-inverting input terminal of the second comparator 21, so that the second comparator 21
1 is maintained at a constant voltage so that the voltage does not rise above a predetermined voltage despite the operation of the knob 15 described above. Therefore, it is possible to prevent the temperature from rising above 95°C.

(F) Effects of the Invention As described above, the present invention allows the main heater and the auxiliary heater to be controlled with a thermistor serving as a single temperature detector, and the set temperatures of the main heater and the auxiliary heater can be set simultaneously with a single operation. It is easy to adjust the temperature. In addition, since the set voltage of the second comparator for controlling the auxiliary heater is prevented from exceeding a predetermined voltage, it is possible to control the temperature so that it does not rise above the predetermined temperature despite the temperature adjustment.
Since the water does not continue to boil, the amount of water does not decrease.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view of a water heater to which the control device of the present invention is applied, Fig. 2 is a front view of the temperature control device, and Fig.
The figure is an electric circuit diagram showing an embodiment of the control device of the present invention. 12...Main heater, 13...Auxiliary heater, 16
...Thermistor, 20...First comparator, 21...
...Second comparator, 24, 26...transistor,
25...Main heater control relay, 27...Auxiliary heater control relay, _R11 , _R12 ...Feedback resistance, 28...
...Zener diode.

Claims (1)

[Claims] 1. In a water heater that heats and keeps the liquid in a container warm by a main heater and an auxiliary heater, there is a thermistor that detects the temperature of the liquid in the container, and a first thermistor that is variable depending on the detection output of the thermistor and external operation. a first comparator that compares a set output and has a first differential; and a second setting that is variable depending on the detection output of the thermistor and the external operation but does not exceed a predetermined value by a constant voltage means. a second comparator that compares the output and has a second differential; and a first control circuit that controls energization/de-energization of the main heater based on the comparison output of the first comparator. and a second control circuit that controls energization/de-energization of the auxiliary heater based on the comparison output of the second comparator.