Boiling point detection method, device, circuit and cooking utensil
阅读说明：本技术 沸点检测方法、装置、电路及烹饪器具 (Boiling point detection method, device, circuit and cooking utensil ) 是由 杨华 陈坚权 张涛 于 2021-08-23 设计创作，主要内容包括：本发明公开了一种沸点检测方法、装置、电路及烹饪器具。该方法包括：获取以烹饪器具中液体作为介质的电容的电容值,和该液体的温度；若该电容值和该温度满足预设条件,则判断该液体达到沸点；该预设条件为：在前一段时间该温度逐渐升高、该电容值逐渐变小,在后一段时间该温度保持不变、而该电容值发生持续的波动变化。本发明通过监测温度和电容值的变化是否满足预设的条件,从而判断温度是否达到沸点,该方法简单可靠。该方法广泛应用于烹饪器具。(The invention discloses a boiling point detection method, a boiling point detection device, a boiling point detection circuit and a cooking utensil. The method comprises the following steps: acquiring a capacitance value of a capacitor taking liquid in the cooking appliance as a medium and a temperature of the liquid; if the capacitance value and the temperature meet preset conditions, judging that the liquid reaches the boiling point; the preset conditions are as follows: the temperature is gradually increased and the capacitance value is gradually reduced in the former period, and the temperature is kept unchanged in the latter period while the capacitance value is subjected to continuous fluctuation change. The invention judges whether the temperature reaches the boiling point by monitoring whether the change of the temperature and the capacitance value meets the preset condition, and the method is simple and reliable. The method is widely applied to cooking appliances.)
1. A boiling point detection method, comprising:
acquiring a capacitance value of a capacitor taking liquid in a cooking appliance as a medium and a temperature of the liquid;
if the capacitance value and the temperature meet preset conditions, judging that the liquid reaches a boiling point;
the preset conditions are as follows: the temperature gradually rises and the capacitance value gradually becomes smaller in the former period, and the temperature is kept unchanged in the latter period, while the capacitance value is subjected to continuous fluctuation change.
2. The method of claim 1, wherein determining that the liquid reaches a boiling point if the capacitance value and the temperature satisfy a predetermined condition comprises:
if the absolute value of the difference between the capacitance value at the current moment and the average value of the capacitance values at two times before the current moment exceeds a preset threshold value, namely | capa- (capa1+ capa2)/2| > (X), the current capacitance value is considered to generate a fluctuation change once, 1 is added to the total fluctuation times of the capacitance, and N is equal to N + 1;
if the total number of times of the capacitance fluctuation is larger than or equal to a preset threshold value, namely N > ═ Y, the temperature is judged to reach the boiling point;
here, capa is a capacitance value acquired at the current time, capa1 and capa2 are capacitance values respectively acquired at the previous two times of the current time, X is a threshold value of capacitance change, N is a total number of times of capacitance value fluctuation, and Y is a threshold value of the number of times of capacitance value fluctuation.
3. A boiling point detection apparatus, comprising:
the data acquisition module is used for acquiring the capacitance value of a capacitor taking liquid in the cooking appliance as a medium and the temperature of the liquid;
the boiling point judging module is used for judging that the liquid reaches the boiling point if the capacitance value and the temperature meet preset conditions;
the preset conditions are as follows: the temperature gradually rises and the capacitance value gradually becomes smaller in the former period, and the temperature is kept unchanged in the latter period, while the capacitance value is subjected to continuous fluctuation change.
4. The apparatus of claim 3, wherein the boiling point determining module comprises:
a first condition judgment unit, configured to consider that the current capacitance value has a primary fluctuation change if an absolute value of a difference between the capacitance value at the current time and an average value of the capacitance values at two times before the current time exceeds a predetermined threshold, that is, | capa- (capa1+ capa2)/2| >;
the counting unit is used for counting the total fluctuation times of the capacitance value, wherein N is N + 1;
a second condition judgment unit, configured to judge that a boiling point condition is reached if the total number of times of capacitance fluctuation is greater than or equal to a predetermined threshold, that is, N > -Y;
here, capa is a capacitance value acquired at the current time, capa1 and capa2 are capacitance values respectively acquired at the previous two times of the current time, X is a threshold value of capacitance change, N is a total number of times of capacitance value fluctuation, and Y is a threshold value of the number of times of capacitance value fluctuation.
5. A boiling point detection circuit, comprising:
the first metal electrode and the second metal electrode form a capacitor together with liquid in the cooking utensil; the first metal electrode and the second metal electrode are used as polar plates of the capacitor, and the liquid is used as a medium of the capacitor;
a capacitance sampling circuit;
a temperature sampling circuit; and
a processor connected to the capacitance sampling circuit and the temperature sampling circuit, respectively, the processor being provided with a computer program for performing the method according to claim 1 or 2.
6. The circuit of claim 5, wherein the capacitance sampling circuit comprises:
a first capacitor; the first end of the first capacitor is connected with the first metal electrode and is grounded, and the second end of the first capacitor is connected with the second metal electrode;
a first resistor; the first end of the first resistor is connected with the second metal electrode, and the second end of the first resistor is connected with the processor.
7. The circuit of claim 5, wherein the temperature sampling circuit comprises:
the thermistor comprises a thermistor, a second resistor, a third resistor and a second capacitor;
the first end of the thermistor is powered by a power supply, and the second end of the thermistor is connected with the first end of the second resistor and the first end of the third resistor; the second capacitor is coupled in parallel between the second resistor second end and the third resistor second end; the second end of the second resistor is connected with the processor; and the second end of the third resistor is grounded.
8. The circuit of claim 7, wherein the first metal electrode and the second metal electrode are metal foils, and the metal foils are copper foils or aluminum foils;
the processor, the capacitance sampling circuit and the temperature sampling circuit are all arranged on the control circuit board; the first metal electrode and the second metal electrode are respectively connected with the control circuit board.
9. The circuit of claim 8, wherein the control circuit board is further provided with an alarm device, and if the liquid level in the cooking utensil is lower than a standard liquid level, an alarm prompt sound is given through the alarm device.
10. A cooking appliance, comprising:
the cup body is used for containing liquid, and the outer wall of the cup body is an insulator;
a heating structure for heating the cup body; and
the boiling point detection circuit of any one of claims 5 to 9;
wherein the first metal electrode and the second metal electrode are both arranged on the outer wall of the cup body.
Technical Field
The invention relates to the technical field of intelligent household appliances, in particular to a boiling point detection method, a boiling point detection device, a boiling point detection circuit and a cooking appliance.
Background
It is well known that the boiling point varies with altitude. As the altitude increases, the air pressure decreases and the boiling point of water decreases as the air becomes thinner, and thus it is necessary to detect the boiling point of the cooking appliance. The conventional boiling judging method has the following problems:
(1) an anti-overflow device is added, so that the hardware cost is increased;
(2) the operating mode is switched according to the use environment of the cooking appliance, for example, multiple operating modes such as "plateau" and "plain" are provided for the user to select, and the user sets the corresponding operating mode in advance before heating, that is, sets the temperature corresponding to the boiling point in advance, but the operation is cumbersome and may cause misoperation.
(3) If the detected temperature does not rise any more within a prescribed time, it is determined that the liquid reaches the boiling point, but this may cause the liquid to overflow.
The boiling point judging methods all have certain defects, so that a new boiling point judging method needs to be developed to conveniently detect the boiling point of the cooking utensil.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art. Therefore, an object of the present invention is to provide a boiling point detection method, device, circuit and cooking utensil, which can safely and reliably detect the boiling point of the cooking utensil when the cooking utensil is applied in different altitude places.
The technical scheme adopted by the invention is as follows:
in a first aspect, the present invention provides a boiling point detection method, comprising: acquiring a capacitance value of a capacitor taking liquid in the cooking appliance as a medium and a temperature of the liquid; if the capacitance value and the temperature meet preset conditions, judging that the liquid reaches the boiling point; the preset conditions are as follows: the temperature is gradually increased and the capacitance value is gradually reduced in the former period, and the temperature is kept unchanged in the latter period while the capacitance value is subjected to continuous fluctuation change.
Further, if the capacitance value and the temperature satisfy a predetermined condition, determining that the liquid reaches a boiling point includes: if the absolute value of the difference between the capacitance value at the current moment and the average value of the capacitance values at two times before the current moment exceeds a preset threshold value, namely | capa- (capa1+ capa2)/2| > (X), the current capacitance value is considered to generate a fluctuation change once, 1 is added to the total fluctuation times of the capacitance, and N is equal to N + 1; if the total number of times of the capacitance fluctuation is larger than or equal to a preset threshold value, namely N > -Y, the temperature is judged to reach the boiling point; here, capa is a capacitance value acquired at the current time, capa1 and capa2 are capacitance values respectively acquired at the previous two times of the current time, X is a threshold value of capacitance change, N is a total number of times of capacitance value fluctuation, and Y is a threshold value of the number of times of capacitance value fluctuation.
In a second aspect, the present invention provides a boiling point detection apparatus, comprising: the data acquisition module is used for acquiring the capacitance value of a capacitor taking liquid in the cooking appliance as a medium and the temperature of the liquid; the boiling point judging module is used for judging that the liquid reaches the boiling point if the capacitance value and the temperature meet preset conditions; the preset conditions are as follows: the temperature is gradually increased and the capacitance value is gradually reduced in the former period, and the temperature is kept unchanged in the latter period while the capacitance value is subjected to continuous fluctuation change.
Further, the boiling point judgment module comprises: a first condition judgment unit, configured to consider that the current capacitance value has a primary fluctuation change if an absolute value of a difference between the capacitance value at the current time and an average value of the capacitance values at two times before the current time exceeds a predetermined threshold, that is, | capa- (capa1+ capa2)/2| >; the counting unit is used for counting the total fluctuation times of the capacitance value, wherein N is N + 1; a second condition judgment unit for judging that the boiling point condition is reached if the total number of times of the capacitance fluctuation is greater than or equal to a predetermined threshold value, that is, N > -Y; here, capa is a capacitance value acquired at the current time, capa1 and capa2 are capacitance values respectively acquired at the previous two times of the current time, X is a threshold value of capacitance change, N is a total number of times of capacitance value fluctuation, and Y is a threshold value of the number of times of capacitance value fluctuation.
In a third aspect, the present invention provides a boiling point detection circuit, comprising: the first metal electrode and the second metal electrode form a capacitor together with liquid in the cooking utensil; the first metal electrode and the second metal electrode are used as polar plates of the capacitor, and the liquid is used as a medium of the capacitor; a capacitance sampling circuit; a temperature sampling circuit; and a processor connected to the capacitance sampling circuit and the temperature sampling circuit, respectively, the processor being provided with a computer program for executing the above method.
Further, the capacitance sampling circuit includes: a first capacitor; the first end of the first capacitor is connected with the first metal electrode and grounded, and the second end of the first capacitor is connected with the second metal electrode; a first resistor; the first end of the first resistor is connected with the second metal electrode, and the second end of the first resistor is connected with the processor.
Further, the temperature sampling circuit includes: the thermistor comprises a thermistor, a second resistor, a third resistor and a second capacitor; the first end of the thermistor is powered by a power supply, and the second end of the thermistor is connected with the first end of the second resistor and the first end of the third resistor; the second capacitor is connected between the second end of the second resistor and the second end of the third resistor in parallel; the second end of the second resistor is connected with the processor; the second end of the third resistor is grounded.
Furthermore, the first metal electrode and the second metal electrode adopt metal foils, and the metal foils are copper foils or aluminum foils; the processor, the capacitance sampling circuit and the temperature sampling circuit are all arranged on the control circuit board; the first metal electrode and the second metal electrode are respectively connected with the control circuit board.
Further, an alarm device is further arranged on the control circuit board, and if the liquid level in the cooking appliance is lower than a standard liquid level, an alarm prompt sound is sent out through the alarm device.
In a fourth aspect, the present invention provides a cooking appliance comprising: the cup body is used for containing liquid, and the outer wall of the cup body is an insulator; a heating structure for heating the cup body; and the boiling point detection circuit as described above; wherein, the first metal electrode and the second metal electrode are both arranged on the outer wall of the cup body.
The invention has the beneficial effects that:
the invention adopts the monitoring to judge whether the capacitance value and the temperature of the liquid in the cooking utensil as a medium meet the preset conditions or not, thereby judging whether the temperature reaches the boiling point or not. The technical problems of inconvenience and unreliability in boiling point detection in the prior art are solved, and the boiling point of the liquid can be detected safely and reliably.
The invention is widely applied to cooking appliances.
Drawings
FIG. 1 is a perspective view of one embodiment of a cooking appliance of the present invention;
FIG. 2 is a graph of the capacitance of the capacitor formed by the two metal electrodes of FIG. 1 as a function of temperature;
FIG. 3 is a schematic flow chart diagram of one embodiment of the boiling point detection method of the present invention;
FIG. 4 is a flowchart illustrating an embodiment of step S12 of FIG. 3;
FIG. 5 is a graph of data on fluctuations in capacitance values for an embodiment of the method of FIG. 4;
FIG. 6 is a schematic structural diagram of an embodiment of the boiling point detecting device of the present invention;
FIG. 7 is a schematic structural diagram of an embodiment of a boiling point detection circuit of the present invention;
FIG. 8 is a schematic diagram of an embodiment of the capacitive sampling circuit of FIG. 7;
FIG. 9 is a schematic diagram of an embodiment of the temperature sampling circuit of FIG. 7.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. Referring to fig. 1, fig. 1 is a perspective view of a cooking appliance according to an embodiment of the present invention. As shown in fig. 1, the cooking appliance includes: a cup body 1 for containing liquid and a control circuit board (not shown). The outer wall of the cup body 1 is an insulator, a first metal electrode 11 and a second metal electrode 12 are arranged on the outer wall, and the first metal electrode 11 and the second metal electrode 12 are two pieces of metal foils. The first metal electrode 11 and the second metal electrode 12 are respectively connected to the control circuit board. It is understood that the first metal electrode 11 and the second metal electrode 12 form a capacitor, and the medium between the capacitors is the liquid.
The control circuit board is respectively provided with a capacitance sampling circuit, a temperature sampling circuit and a processor, and the processor is respectively connected with the capacitance sampling circuit and the temperature sampling circuit.
The working principle of the invention is as follows: the dielectric constant of the liquid differs at different temperatures. In the following examples, the liquid is water, and the dielectric constant of water is related to the temperature as shown in table one below:
temperature t/. degree.C
Dielectric constant ε (F/m)
0
87.90
5
85.90
10
83.97
15
82.04
20
80.22
25
78.41
30
76.63
35
74.85
40
73.20
45
71.50
50
69.91
55
68.30
60
66.77
65
65.25
70
63.77
75
62.34
80
60.90
85
59.55
90
58.15
95
56.88
100
55.58
Watch 1
From table one, it can be seen that: as the temperature gradually increases, the dielectric constant of water gradually decreases. Therefore, the capacitance of the capacitor formed by the first metal electrode 11 and the second metal electrode 12 changes with the temperature.
Specifically, please refer to fig. 2 for the relationship between the capacitance and the temperature. As shown in fig. 2, during the water heating process, the temperature and capacitance values change as follows:
(1) the temperature is gradually increased, and when the temperature is increased to about 97 ℃, the temperature is kept unchanged, namely the boiling point is reached.
(2) Before the temperature reaches the boiling point, the capacitance value is gradually reduced, but the capacitance value is not greatly fluctuated in the process; when the temperature reaches the boiling point, the capacitance value is not reduced any more, but the capacitance value fluctuates continuously and greatly.
The reasons for the above process are: during the heating in the initial stage, the dielectric constant of water is gradually reduced along with the temperature rise, so that the capacitance value is reduced; when the temperature reaches the boiling point, in the process that water boils from small to large, the capacitance fluctuation is increased due to the boiling of the water and the generation of foam caused by the boiling, namely the capacitance is gradually increased or decreased. Therefore, whether the temperature reaches the boiling point or not can be judged according to the capacitance value and the change of the temperature.
Example one
Referring to fig. 3, fig. 3 is a schematic flow chart of a boiling point detection method according to an embodiment of the invention. As shown in fig. 3, the method is executed by a processor disposed on a control circuit board, and includes the steps of:
s11: acquiring a capacitance value of a capacitor taking liquid in the cooking appliance as a medium and a temperature of the liquid;
in step S11, the capacitance and the temperature are collected at intervals, where the interval has a value ranging from 1 to 6 seconds, for example, the temperature and the capacitance can be collected at intervals of 3 seconds.
S12: and if the capacitance value and the temperature meet preset conditions, judging that the temperature of the liquid reaches the boiling point.
In step S12, the preset conditions are: the temperature is gradually increased and the capacitance value is gradually reduced in the former period, and the temperature is kept unchanged in the latter period while the capacitance value is subjected to continuous fluctuation change. Specifically, whether the preset condition is met or not can be judged by monitoring data change between the capacitance value at the current moment and the capacitance value at the previous moment, and data change between the temperature at the current moment and the temperature at the previous moment and combining the duration of the data change.
In step S12, the fluctuation of the capacitance value is quantized to accurately determine whether the capacitance value has a continuous fluctuation. Referring to fig. 4, fig. 4 is a flowchart illustrating an embodiment of step S12 of fig. 3. As shown in fig. 4, this step includes:
s121: judging that | capa- (capa1+ capa2)/2| > | X;
s122: if yes, N is N + 1;
s123: judging that N > is Y;
s124: if so, the temperature is judged to reach the boiling point.
In the calculating step, capa is a capacitance value acquired at the current time, capa1 and capa2 are capacitance values respectively acquired at two times before the current time, X is a threshold value of capacitance change, N is a total number of times of capacitance fluctuation, and Y is a threshold value of the number of times of capacitance fluctuation. It is explained here that the threshold value X of the capacitance change and the threshold value Y of the number of capacitance fluctuations may be determined based on experimental data.
In the method of fig. 4, the absolute value of the difference between the capacitance value at the current time and the average value of the capacitance values of two times before the current time is used as an index of the fluctuation change of the capacitance value, and if the absolute value exceeds a set threshold, it is determined that the current capacitance value fluctuates; and whether the temperature reaches the boiling point is judged by monitoring whether the total number of times of capacitance value fluctuation reaches a set threshold value. Experimental data show that the judgment method is accurate and reliable. It is understood that in other embodiments, other data indicators may be used to measure the fluctuation degree of the capacitance value, and are not limited herein.
Referring to fig. 5, fig. 5 is a graph of data showing fluctuation of capacitance in an embodiment of the method of fig. 4. In fig. 5, the capacitance value is acquired every 6S, and t is a fluctuation value of the capacitance value, i.e., t ═ capa- (capa1+ capa 2)/2. The capacitance change threshold value X is set to 10 and the capacitance fluctuation number threshold value Y is set to 6, so that when the number of times of | t | > 10 exceeds 6, it is determined that the temperature reaches the boiling point.
In this embodiment, whether the temperature reaches the boiling point is determined by monitoring whether the capacitance and the temperature satisfy the preset conditions. The technical problems that the boiling point of the cooking utensil is inconvenient to detect and unreliable in the prior art are solved, and the boiling point of the cooking utensil can be detected safely and reliably.
Example two
Referring to fig. 6, fig. 6 is a schematic structural diagram of a boiling point detecting device according to an embodiment of the present invention. The boiling point detection device is disposed on the processor on the control circuit board, as shown in fig. 6, the device includes: a data acquisition module 11 and a boiling point judgment module 12.
The data acquisition module 11 is used for acquiring the capacitance value of a capacitor taking liquid in the cooking appliance as a medium and the temperature of the liquid.
A boiling point determining module 12, configured to determine that the liquid reaches a boiling point if the capacitance value and the temperature meet preset conditions; the preset conditions are as follows: the temperature is gradually increased and the capacitance value is gradually reduced in the former period, and the temperature is kept unchanged in the latter period while the capacitance value is subjected to continuous fluctuation change.
Wherein, the boiling point judging module 12 includes: a first condition judgment unit 121, a counting unit 122, and a second condition judgment unit 123.
A first condition determining unit 121, configured to determine that the current capacitance value has a primary fluctuation change if | capa- (capa1+ capa2)/2| > is X;
a counting unit 122, configured to count the total number of times of capacitance value fluctuation, where N is N + 1;
a second condition judgment unit 123 configured to judge that the boiling point condition is reached if N > ═ Y;
here, capa is a capacitance value acquired at the current time, capa1 and capa2 are capacitance values respectively acquired at the previous two times of the current time, X is a threshold value of capacitance change, N is a total number of times of capacitance value fluctuation, and Y is a threshold value of the number of times of capacitance value fluctuation.
Specifically, please refer to embodiment one for a working method of the data obtaining module 11 and the boiling point determining module 12, which is not described herein again.
EXAMPLE III
Referring to fig. 7, fig. 7 is a boiling point detection circuit disposed on the cooking appliance of fig. 1, the boiling point detection circuit including: the device comprises a first metal electrode, a second metal electrode, a capacitance sampling circuit, a temperature sampling circuit and a processor.
The first metal electrode and the second metal electrode form a capacitor together with liquid in the cooking utensil; the first metal electrode and the second metal electrode are used as polar plates of the capacitor, and the liquid is used as a medium of the capacitor. The capacitance sampling circuit is respectively connected with the first metal electrode and the second metal electrode. The capacitance sampling circuit and the temperature sampling circuit are respectively connected with the processor, and the processor is provided with a computer program for executing the method according to the first embodiment.
Referring to fig. 8, fig. 8 is a schematic structural diagram of an embodiment of the capacitance sampling circuit of fig. 7. The capacitance sampling circuit is electrically connected with the first metal electrode (induction sheet 1) and the second metal electrode (induction sheet 2) respectively. As shown in fig. 8, the capacitance sampling circuit includes: a first capacitor C1 and a first resistor R1.
The first end of the first capacitor C1 is connected to the first metal electrode and grounded, and the second end of the first capacitor C1 is connected to the second metal electrode.
The first end of the first resistor R1 is connected to the second metal electrode, and the second end of the first resistor R1 is connected to the processor.
The working principle of the capacitance sampling circuit is as follows:
the capacitance formed by sensor chip 1 and sensor chip 2 is denoted as C0. Before the liquid is not heated, Pin _01 is firstly used as an input voltage end of the capacitance sampling circuit to charge the capacitor C0 and the first capacitor C1. When the liquid is heated, the capacitor C0 gradually discharges with the increase of the temperature, the capacitance value of the capacitor C0 gradually decreases, and at this time, Pin _01 serves as the output voltage end of the capacitance sampling circuit, and we can detect that the output voltage of Pin _01 gradually changes. Since the output voltage of Pin _01 has a certain conversion relation with the capacitance value of the capacitor C0, the capacitance value of the capacitor C0 can be obtained by monitoring the output voltage of Pin _ 01.
Referring to fig. 9, fig. 9 is a schematic structural diagram of an embodiment of the temperature sampling circuit of fig. 7. As shown in fig. 9, the temperature sampling circuit includes: a thermistor NTC1, a second resistor R2, a third resistor R3 and a second capacitor C2.
The first end of the thermistor NTC1 is powered by a power supply VCC, and the second end of the thermistor NTC1 is connected with the first end of the second resistor R2 and the first end of the third resistor R3; the second capacitor C2 is coupled between the second terminal of the second resistor R2 and the second terminal of the third resistor R3; a second end of the second resistor R2 is connected with the processor; the second end of the third resistor R3 is grounded. The working principle of the temperature sampling circuit is as follows:
when the liquid is heated, the thermistor NTC1 senses the change of the temperature along with the rise of the temperature, the resistance value of the thermistor NTC1 changes, and the output voltage of Pin _ NTC1 is affected. The resistance value of the thermistor NTC1 can be obtained by monitoring the voltage of Pin _ NTC 1; according to the resistance value of the thermistor NTC1, the value of the temperature is obtained. Therefore, the output voltage of Pin _ ntc1 has a certain conversion relation with the temperature, and the temperature can be obtained by monitoring the output voltage of Pin _ ntc 1.
In summary, in the embodiment, the processor can obtain the capacitance of the capacitor C0 by monitoring the output voltage of Pin _01, and obtain the temperature by monitoring the output voltage of Pin _ ntc 1. After the capacitance value and the temperature are obtained, whether the temperature reaches the boiling point can be judged through the algorithm described in the first embodiment. When the temperature reaches the boiling point, the processor controls the heating mechanism to perform the next action.
Further, be provided with alarm device on this control circuit board, if the liquid level in this cooking utensil is less than standard liquid level, then send out through this alarm device and report an emergency and ask for help or increased vigilance suggestion sound to remind people to operate.
The working principle of detecting the liquid level in the cooking appliance is as follows, continuing with water as an example:
(1) the dielectric constant of water at different temperatures is calculated by the formula:
the formula I is as follows: in epsilon-4.474226-4.54426E-3 t, where E is a constant, epsilon is the dielectric constant of water, and t is temperature.
From the formula one, if the temperature t is known, the dielectric constant ε of water can be obtained.
(2) The calculation formula of the relationship among the dielectric constant epsilon of water, the capacitance C formed by the metal foil and the area S of the water level overflowing the metal foil is as follows:
the formula II is as follows:wherein S is the area of the water level over the metal foil, C is the capacitance value of the capacitor formed by the metal foil, k is the constant of the electrostatic force, d is the thickness of the metal foil, and epsilon is the dielectric constant of the water.
From the above, knowing the temperature t and the capacitance C, the area S of the water level over the metal foil can be calculated, and the current level value of the cooking appliance can be obtained. And comparing the current liquid level value with the standard liquid level value, and if the current liquid level value does not reach the standard value, controlling an alarm device to give an alarm prompt sound by the processor.
Example four
The invention also comprises a cooking appliance, which comprises a cup body for containing liquid, wherein the outer wall of the cup body is an insulator; a heating structure for heating the cup body; and a boiling point detection circuit as described in embodiment three; wherein, the first metal electrode and the second metal electrode are both arranged on the outer wall of the cup body.
In the present invention, the metal foil may be a copper foil or an aluminum foil or a metal foil of other materials, and the cooking utensil includes: a wall breaking machine, a soybean milk machine, a water boiling kettle and a health preserving kettle, which are not limited herein.
In summary, the invention provides a boiling point detection method, a boiling point detection device, a boiling point detection circuit and a cooking appliance. The invention adopts the monitoring to judge whether the capacitance value and the temperature of the liquid in the cooking utensil as a medium meet the preset conditions or not, thereby judging whether the temperature reaches the boiling point or not. The technical problems of inconvenience and unreliability in boiling point detection in the prior art are solved, and the boiling point of the liquid can be detected safely and reliably.
The invention also judges whether the temperature reaches the boiling point by monitoring whether the total times of capacitance value fluctuation reaches a set threshold value, thereby further improving the detection precision of the detection method.
In addition, the circuit structures of the capacitance sampling circuit and the voltage sampling circuit of the control circuit board are simple and easy to implement.
In addition, the cooking utensil can also detect whether the liquid level is lower than the standard liquid level, so that idle burning is prevented.
The invention can not only detect the boiling point, but also detect the liquid level. From the production perspective, the hardware used by the invention has simple structure, low requirement on the production process and low cost.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.