JP2676827B2 - Electric water heater - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electric water heater used in general households.

2. Description of the Related Art In a conventional electric water heater, as shown in FIG. 4, a charging / discharging circuit 2 is composed of resistors 101, 102, a capacitor 103, and a transistor 104 to form a charging / discharging waveform as shown in FIG. On the other hand, a comparator (comparator) 5 to which the resistors 105 and 106 whose constants are determined according to a predetermined temperature and the divided voltage of the thermistor (temperature sensitive resistance element) 3 are input, and the output of this comparator 5 are received to the heater. And the energization control means 6 for controlling the energization of.

The charging / discharging circuit 2 turns off the transistor 104 from the charging start voltage determined by the divided voltage of the resistors 101 and 102, and charges for the time T _{1 with} the _first time constant τ ₁ determined by the resistor 101 and the capacitor 103. The comparator 5 compares the charging voltage with the divided voltage of the thermistor 3 and the resistor 105, and when the charging voltage exceeds the divided voltage, inverts the output to "H" level. When the temperature of the thermistor 3 rises, the divided voltage level between the thermistor 3 and the predetermined resistor 4 increases, so that the time t required from the start of charging to the reversal of the output of the comparator 5 increases. Further, the energization control means 6 measures the required time t, and the thermistor 3 changes every moment.
The temperature is calculated relatively, the rate of change of the temperature is further investigated, and boiling is detected by detecting the extremely slow rate of change of the temperature.

Although temperature detection using such relative temperature is effective, accuracy is not sufficient due to variations in the capacitor 103 and the like. On the other hand, in order to keep the hot water temperature at a predetermined temperature, it is necessary to detect the temperature with high accuracy and control the energization of the heater. Therefore, at the time of discharge, the voltage that is uniquely determined by a predetermined temperature is compared with the divided voltage to detect the temperature.

After the charging is completed, the charging / discharging circuit 2 turns on the transistor 104.
Then, the discharge is performed for the time T _{2 with} the _second time constant τ ₂ determined by the parallel resistance value of the resistors 101 and 102 and the capacitor 103. In order to compare the temperature of the thermistor 3 and a predetermined temperature during this discharge, the comparator 5 detects the divided voltage of the thermistor 3 and the resistor 106 and the voltage after the time T ₃ (T ₃ <T ₂ ) from the start of the discharge. The discharge voltage V ₃ at which the discharge is completed is compared. Further, the energization control means 6 determines whether the temperature of the thermistor 3 is higher or lower than a predetermined temperature from the output level of the comparator 5 in order to keep the hot water temperature at a predetermined temperature. In this way, by using the capacitor 103 for both charging and discharging, the influence of variations is canceled out, and highly accurate detection is performed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in such a conventional electric water heater, when the heat retention temperature that can be set increases, a reference voltage level is required for each heat retention temperature. It is necessary to create such a charge / discharge waveform. However, when the charge / discharge waveform of FIG. 6 is used, the time t _e required from the start of charging to the inversion of the output of the comparator 5 is the same as the temperature of the thermistor 3 because the charging start voltage of each waveform differs depending on the temperature of heat retention. different t _h, as a result, there is a problem that makes a difference to the relative temperature by insulation temperature set.

The present invention solves such a problem. Even when the heat retention temperature that can be set is increased, the temperature of the thermistor at the time of discharge is compared with a predetermined temperature determined by the set heat retention temperature, and then the charge / discharge waveform is compared. Correction to make the charging start voltage equal regardless of the heat retention temperature so that the same relative temperature can be obtained even at different heat retention temperatures, and one of multiple heat retention temperatures can be selected. The purpose is to provide a container.

Means for Solving the Problems To solve the above problems, the electric water heater of the present invention is:
A warming temperature selecting means for selecting one from a plurality of warming temperatures, and when a high temperature is selected by this warming temperature selecting means, after charging from a predetermined reference voltage with a first time constant, a second Repeated discharge to the reference voltage with the time constant of
On the other hand, when a low temperature is selected by the heat retention temperature selection means, after charging from the reference voltage with the first time constant, after discharging for a predetermined time with the third time constant smaller than the second time constant, the second time A charging / discharging circuit that repeats charging to the reference voltage with a time constant of, and a divided voltage of a temperature-sensitive resistance element and a predetermined resistance for detecting the voltage and the hot water temperature at a predetermined time of the charging / discharging as a comparison. And a current-carrying control means for controlling the power supply to the heater. The current-carrying control means detects the relative temperature from the time required from the start of charging to the reversal of the output of the comparator during charging. Then, the electric heater is controlled by the rate of change thereof, and the electric heater is controlled by the output of the comparator during discharge.

Operation According to the above configuration, when a low heat retention temperature is set, the divided voltage of the temperature-sensitive resistance element and the predetermined resistance value at the time of discharging and the charging voltage of the charging / discharging circuit are compared, and then the charging start voltage is reached. Since the charge / discharge circuit can be charged and the discharge waveform can be corrected, the charge waveform will be the same regardless of the set temperature,
As a result, the same relative temperature can be obtained regardless of the heat retention temperature by measuring the time from the start of charging until the output of the comparator is inverted.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram of an electric water heater according to an embodiment of the present invention, in which 1 is a heat retention temperature selecting means for selecting one from a plurality of predetermined heat retention temperatures, and 2 is a heat retention temperature. A charging / discharging circuit that repeats a charging / discharging waveform having a reference voltage level of the heat retention temperature selected by the selecting means 3, 3 is a thermistor for detecting the hot water temperature, 4 is a predetermined resistance whose constant is determined by a predetermined temperature, Reference numeral 5 is a comparator that receives the divided voltage of the thermistor 3 and a predetermined resistor 4 and the voltage of the charge / discharge circuit 2 for a predetermined time, and 6 is a comparator 5.
Is an energization control means for controlling the energization of the heater by receiving the output of.

FIG. 2 is a circuit diagram of an electric water heater according to an embodiment of the present invention, in which heat retention temperatures that can be set are 95 ° C. and 85 ° C.
It is. The charging / discharging circuit 2 is composed of a resistor 7, resistors 8 and 9 whose constants are determined to be about 1: 3 in accordance with the keeping temperature of 95 ° C and 85 ° C, a capacitor 10 and transistors 11 and 12, and a predetermined resistor. 4 is composed of resistors 13 and 14 and transistors 15 and 16 whose constants are uniquely determined for comparison at the time of charging and discharging. Hereinafter, the resistance values of the resistors 7, 8, 9, respectively R _7,
It is represented as R ₈ and R ₉ , and the capacitance of the capacitor 10 is represented as C.

When the heat retention temperature of 95 ° C. is selected by the heat retention temperature selection means 1, the operation of the circuit shown in FIG. 2 is almost the same as the operation of the circuit shown in FIG. 4, and the charge / discharge circuit 2 is shown in FIG. In order to repeat the charging / discharging waveform as shown in I, first, the resistance 7,
From the charge start voltage determined by the divided voltage of 8 to transistor 11
By turning on and off, the battery is charged for the time T ₁ with the first time constant τ ₁ where τ ₁ = CR ₇ , and with the second time constant τ ₂ where τ ₂ = C (R ₇ R ₈ ). Discharging is performed for time T ₂ . The comparator 5 compares the divided voltage of the thermistor 3 and the resistor 13 with the charging voltage of the charging / discharging circuit 2 at the time of charging, and at the time of discharging, the time T _{3 has} elapsed from the start of discharging and the discharging voltage and the thermistor 3 are almost completed. And the divided voltage V ₃ of the resistor 13 are compared. The energization control means 6 measures the time t required from the start of charging until the output of the comparator 5 is reversed to detect the temperature relatively, and controls the energization to the heater by the rate of change. During discharge, the output of the comparator 5 determines whether the temperature of the thermistor 3 is higher or lower than 95 ° C., and the energization of the heater is controlled.

On the other hand, when the heat retention temperature of 85 ° C. is selected by the heat retention temperature selection means 1, the charging / discharging circuit 2 first generates the charging / discharging waveform shown by II in FIG. The transistor 11 is turned off from the charging start voltage determined by the piezoelectric voltage, and the charging is performed for the time T ₁ with the first time constant τ ₁ . When this charging is completed, the transistors 11 and 12 are turned on at the same time, and τ ₃ = C (R ₇
It is discharged for a time T ₄ (T ₄ = T ₃ ) with a _third time constant τ ₃ (τ ₃ <τ ₂ ) which is R ₈ R ₉ ). After the discharge is completed, the transistor 12 is turned off, the second time constant τ ₂ is charged for T _{2 to} T ₄ , and the waveform is corrected. The energization control means 6 measures the time t required from the start of charging to the reversal of the output of the comparator 5 to detect the temperature relatively, as in the case where the heat retention temperature is 95 ° C., and the time T ₄ from the start of discharge. Whether the temperature of the thermistor 3 is higher than 85 ° C due to the output of the comparator 5 later,
Determine whether it is low and control the energization to the heater. Fig. 3,
When the charging start voltage of the charge / discharge waveform of FIG. 6 is calculated by the numerical values used in this embodiment, when the waveform is not corrected (FIG. 6), the temperature is kept at 95 ° C. and 85 ° C., respectively. 2.0
The difference is 0V and 1.61V, which is 0.39V, but when the waveform is corrected (Fig. 7), the difference is 2.00V and 1.97V, respectively, which is 0.03V. As is clear from this result, when the charge / discharge waveform shown in FIG. 3 is used, there is almost no difference in the discharge start voltage due to the difference in the heat retention temperature.
Has no effect on relative temperature sensing.

In this example, the heat retention temperatures that can be set are 95 ° C and 85 ° C.
However, the predetermined heat retention temperature that can be set is not limited to two. Further, although T ₃ = T ₄ is set in the above embodiment, the same effect can be obtained even if T ₃ ≠ T ₄ .

EFFECTS OF THE INVENTION As described above, according to the present invention, in an electric water heater that selects one of a plurality of predetermined heat retention temperatures as a heat retention temperature, a charge / discharge waveform used for temperature detection of a low heat retention temperature is set to Since the correction is performed after the temperature is compared with the predetermined temperature, the charging start voltages become equal, and as a result, relative temperature detection can be accurately performed regardless of the set heat retention temperature.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electric water heater showing an embodiment of the present invention, FIG. 2 is a circuit diagram of the electric water heater, and FIG.
Charge / discharge waveform diagram used in the charge / discharge circuit of FIG. 4, FIG. 4 is a circuit diagram of a conventional electric water heater, FIG. 5 is a charge / discharge waveform diagram used in the charge / discharge circuit of FIG. 4, and FIG. FIG. 6 is a charge / discharge waveform chart used in the charge / discharge circuit when the heat retention temperature is increased using the circuit of FIG. 1 ... Insulated temperature selection means, 2 ... Charge / discharge circuit, 3 ... Thermistor (temperature sensitive resistance element), 5 ... Comparator (comparator), 6 ... Energization control means.

Front page continuation (72) Inventor Sadatoshi Tanabe 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP 62-144614 (JP, A) JP 62-144615 (JP) , A) Actual development Sho 52-57238 (JP, U)

Claims (1)

(57) [Claims] Claim: What is claimed is: 1. A warming temperature selecting means for selecting one of a plurality of warming temperatures, and a predetermined time constant from a predetermined reference voltage when a high temperature is selected by the warming temperature selecting means. After charging, discharging is repeated up to the reference voltage with a second time constant, while when a low temperature is selected by the heat retention temperature selection means, after charging with a first time constant from the reference voltage, a second time is reached. A charging / discharging circuit that repeats charging to the reference voltage with a second time constant after a predetermined time of discharging with a third time constant smaller than the constant, and a voltage and hot water temperature at a predetermined time of the charging / discharging. It has a comparator for comparing the divided voltage of the temperature sensitive resistance element and a predetermined resistance as an input, and an energization control means for controlling energization to the heater, and the energization control means starts charging after charging. By the time the output of the comparator is inverted Electric water heater which controls the energization of the heater, at the time of discharge and controlling the power supply to the heater by the output of the comparator by its rate of change to detect the relative temperature from time to.