JPS643492B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an electric water heater such as a jar pot.

(Prior art) Conventionally, in the case of electric water heaters, an overtemperature rise preventer such as a temperature fuse is thermally attached to the container, and heating by the heating means is stopped when the temperature of the container rises abnormally due to dry baking, for example. This is designed to prevent burnout due to heat. However, the operating temperature of overheating preventers is generally set at a high temperature of 100°C or higher due to the relationship with the hot water retention temperature, or the relationship with the boiling temperature in the case of boiling type devices, so the temperature of the overheat preventer is set at a high temperature of 100℃ or higher. The temperature of the water heater reaches a high temperature of 100℃ or more, and there is a risk of deterioration due to the heat in various parts of the water heater.In addition, if you open the lid by mistake and touch the container at such times, you may get burned. It was not safe.

(Purpose) The present invention has been made in view of the above points, and calculates the temperature rise gradient during boiling water based on the signal from the heat-sensitive element that senses the temperature change of hot water via the container, and based on the calculation result. By controlling the heating means, for example, dry baking can be quickly detected and overheating can be prevented, thereby eliminating the conventional inconvenience.

(Example) First, the configuration of the present invention will be described with reference to FIG. 1. The present invention comprises a container for storing hot water, a heating means for heating the container to raise the temperature of the hot water, and a heating means for controlling the temperature change of the hot water. A heat-sensitive element that senses through the container, a temperature gradient calculation means that calculates a temperature increase gradient during boiling water based on a signal from the heat-sensor element, and a temperature rise gradient calculated by the calculation means and a preset temperature rise gradient for heating. and a control means for stopping the heating by the heating means when it is determined that the dry firing state is determined as a result of the comparison with a reference value.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIG. 2, 1 is an AC power supply, 2 is a water heater that heats a container to raise the temperature of hot water, 3 is a heat-retaining heater that also heats a container and raises the temperature of hot water,
4 is a heat retention control switch that turns on and off by sensing the temperature change of hot water; 5 is a first relay switch; 6
is a second relay switch, 7 is a microcomputer, 8 is a power supply circuit for the microcomputer 7,
Reference numeral 9 includes a heat-sensitive element that senses the temperature change of hot water through a container and sends a signal to the microcomputer 7 via a temperature detection circuit 10, and 11 includes four light emitting diodes (hereinafter simply referred to as LEDs) 11a to 11d. A status display unit that displays each status of water boiling, boiling, warming, and dry baking; 12 is a display drive circuit that controls the status display unit 11 based on signals from the microcomputer 7; 13 is a display drive circuit that controls the status display unit 11 based on signals from the microcomputer 7; This is a relay drive circuit that controls relay switches 5 and 6. The microcomputer 7 includes a CPU, ROM, RAM, electronic timer, and interface.
The CPU control program is stored, and the RAM is
Used as data memory for the CPU. On the other hand, an electronic timer counts a predetermined time based on instructions from the CPU and outputs a signal after the predetermined time. The above CPU reads the status of each part on the input side via the interface, and
By reading the control program from the ROM, each section on the output side necessary for executing a predetermined operation is controlled.

Next, the control will be explained according to the flowchart shown in FIG. Now, when you turn on the power,
By turning on the first and second relay switches 5 and 6 via the relay drive circuit 13, electricity is supplied to both the heaters 2 and 2 for boiling water and keeping the water warm, and heating is started by these heaters 2 and 3. display
The LED 11a is turned on via the display drive circuit 12 to display the water boiling state.

Then, when the temperature sensed by the heat-sensitive element 9 becomes higher than the predetermined temperature t, the sensed temperature _t1 at this time is read, and a timer count is started by setting a time _T1 (for example, about several seconds to 10 seconds), and the time T1 is set. Read the sensed temperature t ₂ at the time when ₁ has elapsed, then read the temperature t ₁ ,
The temperature increase gradient x is calculated based on the relationship between t ₂ and time T ₁ .

Here, to explain the temperature increase gradient x,
Fig. 4 shows the temperature change of the heat-sensitive element 9 during normal boiling, and Fig. 5 shows the temperature change of the heat-sensitive element 9 during abnormal boiling, that is, during dry-baking. It can be seen that the temperature rise gradient is much steeper than that during normal water boiling. Therefore, based on these data, a reference value x ₁ is determined in advance, and by comparing the temperature rise gradient obtained as a result of calculation with the reference value x ₁ , it is possible to determine whether or not dry baking is being performed. It can be determined whether or not exists.

Now, if the temperature increase gradient x obtained by calculation is larger than the reference value x ₁ and it is determined that dry firing is occurring, the LED 11a is turned off via the display drive circuit 12, and the LED 1
1d is turned on to switch from boiling water display to dry boiling display, and at the same time, both relay switches 5 and 6 are turned off via the relay drive circuit 13, and both heaters 2 and 3 are turned off.
To stay safe, stop heating.

If the temperature increase gradient x is smaller than the reference value _x1 , then it is determined whether or not the hot water is in a boiling state, and if it is not in a boiling state, the above determination is repeated from the calculation of the temperature increase gradient again.

The temperature increase gradient during boiling is zero, and based on the reference value x ₂ (≒0) for boiling state determination, the boiling state of the water can be determined by comparing this value x ₂ with the temperature increase gradient x obtained from the calculation result. Determine.

Therefore, the temperature increase gradient x obtained by calculation
When the relationship between x and reference value _x2 becomes x≦ _x2 and a boiling state is determined, the first relay switch 5 is turned off via the relay drive circuit 13, and only the second relay switch 6 is turned on. , the LED 11a is turned off via the display drive circuit 12, and the LED 11b is turned off.
Light up to switch from boiling water display to boiling display. Then, the LED 11b is turned off after a certain period of time _T2 has elapsed, and thereafter the LED 11c is turned on to indicate the heat retention state.

When the first relay switch 5 is turned off, only the heat retention circuit is activated and the heat retention control switch 4 is turned off.
By turning ON and OFF, the power supply to the heat-retaining heater 3 is controlled, and hot water is kept at a temperature of, for example, about 93°C.

During heat retention, it is repeatedly determined whether the temperature sensed by the heat-sensitive element 9, that is, the temperature of the hot water, is below the reboiling reference temperature (for example, 85°C). When the temperature drops to below 85℃,
The above operation will be performed again.

As described above, in this embodiment, dry baking and boiling can be determined based on the temperature rise gradient, so that there is no need to provide a conventional excessive temperature rise preventer. In addition, dry firing can be detected when the temperature of the container is low, and there is no risk of deterioration due to heat in the various parts of the water heater, which is extremely safe from the standpoint of safety. Note that it is desirable that the temperature t, which is the dry firing determination start temperature, be set as low as possible, especially when considering the risk of burns. However, if only the thermal deterioration in each part of the water heater is considered, the temperature may be set as high as about 80°C.

In addition, in the above embodiment, when calculating the temperature increase gradient, the time T ₁ is kept constant, and the temperature difference (t ₂ −
t ₁ ), but the temperature difference may be kept constant and the time required during this time may be measured to determine the temperature increase gradient.

In addition, the present invention is not limited to the embodiments described above and shown in the drawings, and can of course be implemented with appropriate changes within the scope of the invention, such as notifying dry firing with a buzzer. .

(Effects) As described above, according to the configuration of the present invention, dry baking can be quickly detected and heating can be stopped before the temperature of the container reaches a high temperature, and the conventional inconveniences can be solved.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of the present invention, Fig. 2 is a circuit diagram showing an embodiment of the invention, Fig. 3 is a control flowchart of the same as above, Fig. 4 is a diagram showing temperature changes during boiling water, FIG. 5 is a diagram showing temperature changes during dry baking. 2...Kettle heater, 3...Warmth retention heater, 5,
6... Relay switch, 7... Microcomputer, 9... Heat sensitive element.

Claims (1)

[Scope of Claims] 1. A container for storing hot water, a heating means for heating the container to raise the temperature of the hot water, a heat-sensitive element for sensing temperature changes in the hot water via the container, and a signal from the heat-sensitive element. a temperature gradient calculation means that calculates a temperature increase gradient during boiling water based on the temperature increase gradient calculated by the calculation means and a preset reference value for dry baking, and determines the dry baking state as a result. and control means for stopping heating by the heating means when the electric water heater is heated.