JPH0238961B2 - FUTSUTOKENSHUTSUSOCHI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a boiling detection device for an electric range, etc., which indirectly detects the water temperature in a water boiling container using a temperature sensing element provided in the center of a spiral heater. The purpose is to accurately detect boiling regardless of the type or amount of water.

Hereinafter, one embodiment of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of the boiling detection device of this embodiment. Reference numeral 1 denotes an AC power source, to which a heating means (heater) 3 and a power circuit 4 are connected via a power switch 2. Reference numeral 5 denotes a temperature sensing element (thermistor) which is pressed against the outer bottom surface of the water boiling container 16 and indirectly detects the water temperature. This temperature sensing element 5 has a resistance 6
The temperature detecting device 7 is connected to the temperature detecting device 7. The output of the temperature detection device 7 is input to an A/D converter 8, and the output is input to a slope detection device 9. 10 is a timer device, and 11 is a gate device. 12 is a storage device that temporarily stores the gradient value calculated by the gradient detection device 9; Reference numeral 13 denotes an arithmetic unit that compares and processes the gradient value stored in the storage device 12 and the sometimes changing gradient value outputted from the gradient detection device 9 to detect boiling. Note that this arithmetic processing is started by a command signal from the slope change determination device 14. 15
is a buzzer circuit operated by the output of the arithmetic unit 13. Note that 8 to 14 are devices built into a one-chip microcomputer.

The operation will be explained below.

First, when the power switch 2 is closed, the water boiling container 16 placed above is heated by the heater 3, and the water temperature rises. Thermistor 5 is container 1
Since the thermistor 5 is pressed against the outer bottom surface of the thermistor 6 (see FIG. 2), the temperature of the thermistor 5 rises as the water temperature rises. FIG. 3 shows the rise curves of these water temperatures and thermistor temperatures.

Further, a DC power source is formed by the power supply circuit 4, and the boiling detection device starts operating. First, the timer device 10 prohibits the operation of the slope detection device 9 for one minute. This happens when you add water or
Ignoring the fluctuations 19 and 20 of the temperature curve in the initial state,
This is to detect the gradient during normal temperature rise.
In particular, since the temperature gradient becomes large at fluctuation 20 of the temperature curve, the temperature gradient at this part is used as the reference temperature gradient to prevent the temperature gradient from increasing when boiling is detected, and to detect boiling before boiling. It prevents you from doing so. Furthermore, after one minute has elapsed, the timer device 10 provides a sampling signal to the A/D converter 8 approximately every second. Therefore, the A/D converter 8 samples the temperature information of the temperature sensing element 5 about every second, A/D converts it, and provides it to the slope detection device 9. At this time, the gate device 11 does not take in temperature information until the temperature of the thermistor 5 reaches 70°C.

When the heating progresses and the temperature of the thermistor 5 exceeds 70°C, the gradient detection device 9 starts calculating the gradient. This calculation method is based on the temperature of the thermistor being 2℃.
Count the time that passes as it rises. this time
T _N and temporarily stored in the storage device 12. T _N and
The contents of the storage device 12 are rewritten until the next T _N+1 is compared and T _N ≦T _N+1 , that is, until the temperature increase curve of the thermistor becomes upwardly convex (or straight). This process is performed by the slope change determination device 14. If T _N ≦T _N+1 is confirmed,
T _N+1 is stored in the storage device 12, and the arithmetic device 13
2×T _N+1 is calculated within the range, and this value is stored in the storage device again. Compare 2×T _N+1 with the values after T _N+2 , and at point 21 when 2×T _N+1 < T _N+M ,
The arithmetic unit 13 outputs an output and operates the buzzer circuit 15.

In summary, under certain conditions, that is, 1 minute after the start of heating, the thermistor temperature is 70℃ or higher, and the temperature rise curve is straight or upwardly convex. Only after that, gradient detection processing is performed, and a boiling detection signal is generated when the gradient reaches 1/2 of the initial value.

FIG. 2 shows the configuration of the sensor section. In the center of the outer bottom of the water boiling container 16 placed on the heater 3,
The temperature sensing element 5 wrapped in the sensor cover 17 is pushed upward by the spring member 18 and is pressed into contact with the sensor cover 17 . The sensor cover 17 is provided to block radiant heat from the heater 3 and allow the temperature sensing element 5 to detect the temperature of the water boiling container 16 with higher accuracy.

As mentioned above, FIG. 3 shows an increase curve of the thermistor temperature and water temperature. When heating is started by the heater 3, the thermistor temperature first receives heat from the heater 3 during the initial minute, and a fluctuation 20 occurs in the thermistor temperature. Since then, as the water temperature has increased, the thermistor temperature has steadily increased.
Initial temperature gradient detection is performed at 70℃ or higher, which is stable regardless of water volume, etc. When boiling begins and the water temperature stops rising, the thermistor temperature rise is also suppressed and the temperature gradient becomes smaller, so boiling can be detected at the time point 21 when the temperature gradient becomes 1/2 or less of the initial temperature gradient.
Next, when water is added and heating is started again in the same way, the temperature distribution is initially disturbed and there is a temperature fluctuation 19 for one minute. From then on, boiling detection can be performed in the same way as the first time.

In the above example, the conditions for performing the gradient detection process were that the thermistor temperature was 70°C or higher 1 minute after the start of heating, and the gradient was 1/2 of the initial value at the time of boiling detection. It goes without saying that these values may be changed accordingly.

As is clear from the above description, since the present invention is provided with a timer device that prohibits the operation of the slope detection device until a certain period of time has elapsed from the start of heating, it is possible to Since the reference temperature gradient is not memorized based on a sudden rise, the accuracy of boiling detection can be improved. Furthermore, since boiling is detected based on the ratio between the standard temperature gradient and the temperature gradient that changes from time to time, boiling can be reliably detected even if the absolute value of the temperature gradient changes due to changes in the amount of water or the kettle container. In addition, by providing a gate device that does not operate the gradient detection device until the temperature of the temperature sensing element reaches a predetermined temperature, there is no need to set the reference temperature gradient necessary for boiling detection until the water temperature stabilizes, and the detection accuracy is improved. Increase it further. Furthermore, by providing a gradient change determination device, a stable part of the temperature rise curve of the temperature sensing element and the temperature gradient in the vicinity can be used as a reference, and detection accuracy can be further improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a boiling detection device showing an embodiment of the present invention, FIG. 2 is a sectional view of the essential parts, and FIG. 3 is a temperature characteristic diagram of the essential parts of the same boiling detection device. 3... Heating means, 5... Temperature sensing element, 7... Temperature detection device, 9... Gradient detection device, 10... Timer device, 11... Gate device, 12... Storage device,
13... Arithmetic device, 14... Gradient change determination device.

Claims (1)

[Scope of Claims] 1. A heating means such as a heater that heats a water boiling container, a temperature sensing element that is brought into pressure contact with the outer bottom of the water boiling container and indirectly detects water temperature, and a temperature detection device that uses this temperature sensing element as a part. a gradient detection device that detects the gradient of the output of the temperature detection device; a timer device that prohibits the operation of the gradient detection device for a certain period of time from the start of operation of the heating means; A storage device that stores the output of the gradient detection device as a temperature gradient, and compares the stored value of this storage device with the output of the gradient detection device, and determines that the change in the slope of the temperature rise curve of the temperature sensing element has become 0 or negative. Until the output of this slope change determination device is output, the stored value in the storage device is rewritten with a new one, and at the time the output of the slope change determination device is output. The value stored in the storage device is fixed as a reference temperature gradient, the reference temperature gradient is compared with the subsequent output of the gradient detection device, and when the ratio becomes less than a predetermined ratio, the boiling detection output is determined. A boiling detection device consisting of a calculation device that performs 2. The boiling detection device according to claim 1, wherein the temperature detection device includes a gate device that outputs a signal that causes the gradient detection device to start detecting a gradient when the temperature of the temperature sensing element reaches a predetermined temperature. .