JPH01109684A - Boiling detecting device - Google Patents

Abstract

PURPOSE:To improve the precision for boiling detection by detecting the temperature change rate after the preset time from the heating start, determining the set temperature, measuring the time until the set temperature is attained from the heating start, and determining the time until the boiling is completed in response to the value. CONSTITUTION:A microcomputer 19 is operated. The computer 19 first feeds a high-frequency current to a heating coil 29. The temperature detection signal by a thermistor 26 is inputted after the preset time elapses, and the temperature change rate is calculated. The set temperature is determined based on this temperature change rate. The set temperature thus determined and the temperature from the temperature thermistor 26 are compared, if the temperature from the temperature thermistor 26 is judged to reach the set temperature, the time from the heating start is integrated. The time until the stop is then determined based on the integrated time. If the computer judges that the time until the stop has elapsed, it judges as the boiling completion and stops the current feed to the heating coil 29.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a boiling detection device that heats water in a pot or the like and detects when the water boils.

BACKGROUND OF THE INVENTION Conventional boiling detection devices are applied to sheathed heater stoves, gas stoves, and the like. Figure 5 shows the configuration of the sheathed heater stove. In the figure, 1 is a spiral sheathed heater attached to a main body 2, and a steel 3 is placed directly on top of the sheathed heater. 4 is a temperature detection device for detecting the temperature of the pot 3, and is attached to the bottom of the pot 3 by pressure contact with a spring or the like. In the case of the above configuration, the output of the temperature detection device X4 shows a clear inflection point (boiling point) as shown in A of FIG. However, in the case of an induction heating cooker or the like in which the temperature detecting device 4 is attached via the top plate 6 as shown in FIG. 6, as shown in FIG. It draws a curve. That is, since the temperature detection device 4 is disposed via the top plate 5 on which the pot 3 is placed, the temperature of the pot is not directly detected.

Furthermore, if the thermal coupling between the container and the temperature sensor is poor,
As shown in C of FIG. 7, a curve with no bending points and a smaller rate of change than curve B is drawn.

Problems to be Solved by the Invention However, in the configuration of conventional induction heating cookers, etc., there is no bending point in the temperature curve, so even a small error in reading the temperature change can result in a large difference in the boiling point. It had some problems.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to detect boiling with high accuracy even when there is a slight change in temperature reading.

Means for Solving the Problems In order to achieve the above objects, the present invention provides a temperature sensing means thermally coupled to a container containing water heated by a heating source, and a temperature signal from the temperature sensing means. Temperature change detection means calculates a temperature change rate based on the temperature change detection means, and a temperature change signal from the temperature change detection means is inputted after a predetermined time after heating starts, and a set temperature is determined based on this temperature change rate. a temperature determining means; a timer means for counting the cumulative time from the start of heating when the temperature signal from the temperature detecting means and the set temperature become the same; inputting the cumulative time from the timer means; The structure includes a time determining means for determining the time until boiling is completed based on the time.

Operation According to the above configuration, first, the rate of temperature change after a predetermined time after heating is started is detected. That is, if the thermal coupling between the temperature sensing means and the container is poor, the set temperature will also be low, and by detecting the rate of temperature change, the set temperature can be determined correctly even if the thermal coupling changes.

Furthermore, since the time from the start of heating until the set temperature is reached is measured, and the time until boiling is completed is determined according to the measured value, errors in detecting the rate of temperature change can be corrected. In other words, when a high rate of temperature change is detected, the time required to complete boiling is shortened, and when a low rate of change is detected, the time required to complete boiling is determined to be longer, thereby reducing errors in the boiling point and increasing accuracy. Can be done.

EXAMPLE Hereinafter, the configuration of a boiling detection device in an example of the present invention will be explained with reference to FIG. In the figure, reference numeral 11 denotes a container containing water 12, and this container 11 is thermally coupled to a temperature detection means 13. A temperature change detection means 14 calculates a temperature change rate using the temperature detected by the temperature detection means 13 as an input signal, and a temperature change detection means 14 that uses the temperature detected by the temperature change detection means 14 as an input signal to calculate the temperature change rate from the temperature detection means 13 at the set temperature. A temperature determining means 16 for determining the temperature; a timer means 16 for counting the accumulated time from the start of heating when the set temperature of the temperature determining means 15 and the temperature of the temperature detecting means 13 match; A time determining means 17 that determines the time to stop the operation of the heating source 21 using the counted accumulated time as an input signal, and a heating source driving means 20
control means 18 for stopping the operation of the heating source 21 that heats the container 11 by controlling the temperature of the container 11;
It is composed of a null microcomputer 19 including a PU, ROM, RAM $-j, and input/output; t''-).

An example in which the boiling detection device having the above configuration is used in an induction heating cooker is shown in FIG. 2. In FIG. 2, 22 is an AC power source, which is connected to a rectifier circuit 24 via a power switch 23. On the DC side of this rectifier circuit 24, a temperature thermistor 26 and a resistor 27 are connected in series, which are attached to the back surface of a top plate 26 on which a container 11 containing water 12 is placed, and which are thermally coupled to the container 11. The body is connected, connection point a
The microcomputer 19 inputs the voltage (temperature signal) as a digital signal via the A/D converter 28. Further, on the DC side of the rectifier circuit 24, a heating coil 29 for inductively heating the container 11 is provided. A common photography capacitor 30 and a switching element 31 are connected. The switching element 31 is turned on and off by the driving transistor 32, and causes a high frequency current to flow through the heating coil 29.

Next, the operation of the microcomputer 19 will be explained with reference to FIG. First, in step 41, the driving transistor 32 is operated, the switching element 31 is turned on and off, and a high frequency current is caused to flow through the heating coil 29. If it is determined in step 42 that the predetermined time has elapsed, the temperature detection signal from the thermistor 26 is inputted in step 43, and step 4
4. Calculate the temperature change rate. Then, in step 45, a set temperature is determined based on this temperature change rate. The determination of this set temperature will be explained in detail with reference to FIG.

The temperature change rate ΔT after the elapse of the predetermined time t0 is determined by the value ΔT~ΔT3 (ΔT1<ΔT2<
ΔT3). Assuming that the temperature change rate ΔT is read as ΔT1, the set temperature is determined to be T1 based on this temperature change rate ΔT1.

ΔT2. Similarly, in the case of ΔT3, T2. It is decided to be T3.

That is, when the two temperature change rates are small, the set temperature is determined to be low. Comparing the set temperature determined in this way with the temperature from the temperature thermistor 26,
If it is determined in step 46 that the temperature of the temperature thermistor 26 has reached the set temperature, the time t from the start of heating is calculated in step 47. Next, in step 48, step 47
The time until stopping is determined based on the time accumulated in . In FIG. 4, this determination of the time until the stop will be explained in detail. If the cumulative time is tl, the time until boiling tB is determined to be tl-B. t2. Similarly, t3 is “2-B,”
g to B. That is, if the cumulative time is short, the time until stopping is lengthened. If it is determined in step 49 that the time until the stop determined in this manner has elapsed, boiling is determined to be completed in step 6o, and in step 61, the driving transistor 32 is turned off and the energization of the heating coil 29 is stopped.

Effects of the Invention As is clear from the above embodiments, according to the present invention, even if the thermal coupling between the temperature sensing means and the container changes, the coupling change is determined by the rate of temperature change, and the rate of change is determined based on the rate of change. Since the set temperature is changed accordingly, errors caused by changes in thermal coupling can be reduced. Furthermore, since the set temperature is set lower than the boiling point, reading errors can also be reduced. Furthermore, even if there is an error in the rate of temperature change, the time required to complete boiling is determined based on the time it takes to reach the set temperature again, so the error can be corrected at that point, and boiling can always be detected with high accuracy.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a boiling detection device according to an embodiment of the present invention, Fig. 2 is a circuit block diagram of an induction heating cooker using the same device, and Fig. 3 is a flow chart showing the operation of the same microcomputer. Figure 4 is a control characteristic diagram of the present invention, Figure 6 is a side sectional view of a sheathed heater, Figure 6 is a side sectional view of an induction heating cooker, and Figure 7 is a characteristic diagram showing temperature changes detected by a temperature detection element. It is. 11... Container, 13... Temperature detection means, 14... Temperature change detection means, 15...
・Temperature determining means, 16... Timer means, 17
...Time determining means. Name of agent: Patent attorney Toshio Nakao and 1 other person19
-11 Micro Combi-eder Fig. 1 Fig. 3 Fig. 4 ta t(tZ Z3 t:B
Figure 5

Claims (1)

[Claims] A temperature detection means thermally coupled to a container containing water to be heated by a heating source; a temperature change detection means for calculating a temperature change rate based on a temperature signal from the temperature detection means; After a predetermined time, a temperature determining means inputs a temperature change signal from the temperature change detecting means and determines a set temperature based on the rate of temperature change; A boiling device comprising: a timer means for counting the cumulative time from the start of heating when the time becomes the same; and a time determining means for inputting the cumulative time from the timer means and determining the time until completion of boiling based on the cumulative time. Detection device.