GB2431784A

GB2431784A - Anti dry-boil control for kettle using rate of change of temperature

Info

Publication number: GB2431784A
Application number: GB0523558A
Authority: GB
Inventors: George Mohan Zhang; Yaolun Wang
Original assignee: Crastal Technology Shenzhen Co Ltd
Current assignee: Crastal Technology Shenzhen Co Ltd
Priority date: 2005-11-18
Filing date: 2005-11-18
Publication date: 2007-05-02
Anticipated expiration: 2025-11-18
Also published as: GB2431784B; GB0523558D0

Abstract

A system for control of domestic heating appliances, such as electric kettles, using temperature measurements of the appliance where the rate of change of the temperature with respect to time is calculated and compared to a threshold. If the rate is above the threshold, the heater power is switched off thus avoiding dry-boiling or dry-burning of the appliance, such as when too little or no water is put in the kettle. Preferably the second differential may also be calculated and compared to a threshold if the first differential is less that a threshold, and the heater power turned off if the second differential is above the threshold. A maximum temperature limit and maximum heating time limit may also be set and if either is exceeded, the heater is switched off.

Description

1 2431784

ANTI-DRY BURNING CONTROL METHODS AND APPARATUS

Field of the Invention

This invention relates to apparatus and methods for anti-dry burning control. More particularly, but not exclusively, it relates to controlling anti-dry burning of an electric kettle.

Background of the Invention

The electric kettle delivers convenience to our daily lives, whether it is at home or at work. The current anti-dry burning technology of an electric kettle uses a fuse protector. When a user accidentally turns on an electric kettle containing little or no water, the rising temperature of the heating element will break the fuse protector thereby turning off the heating power supply in order to protect the electric kettle. However, one of the major drawbacks of this method is that the control circuit in the electric kettle may not turn off the heating power supply in time due to the inaccuracy in estimating the temperature rise. As a result, the electronic circuit elements in the electric kettle may suffer damage.

Another known method of anti-dry burning control is by applying a birnetal anti-dry burning switch. In an event that dry burning occurs, the rising temperature within the electric kettle will cause the anti-dry burning switch to turn the heating power supply off. Again, this method suffers a similar drawback to that mentioned in the previous paragraph.

Sunmary of the Invention Embodiments of the invention include apparatus and methods for anti-dry burning control of an electric kettle.

Aspects of the present invention aims to provide an anti-dry burning control method to estimate the temperature rise inside an electric kettle and to turn off the heating power supply in an event when dry burning occurs.

In a first aspect of the present invention, there is provided a method of controlling an anti-dry burning feature of a domestic appliance, the controlling method comprising the steps of: determining the temperature of said domestic appliance; determining the rate of change of said detennined temperature; and outputting a heating control signal if said determined rate of change is above a preset rate of change value.

According to the above aspect of the present invention, said controlling method further comprises the step of initialising circuit elements of said domestic appliance.

Preferably, said step of initialising said circuit elements of said domestic appliance comprises setting up a monitoring means, a processing means and a circuit control means.

Preferably, said step of determining the temperature of said domestic appliance comprises measuring the real-time temperature of said domestic appliance.

Preferably, in the case that said determined rate of change is less than said preset rate of change value, the method further comprises the steps of comparing said rate of change value with a corresponding rate of change value from a preceding point in time, to obtain a measure of the rate of change of the rate of change of temperature, comparing said measure with a preset temperature acceleration value, and outputting a control signal if said measure exceed said preset acceleration value.

In an embodiment of the present invention, there is provided the step of setting a maximum heating time, and outputting said control signal if the continuous heating time is greater than said maximum heating time.

In another embodiment of the present invention, there is provided the step of setting a maximum heating temperature, and outputting said control signal if the heating temperature is greater than said maximum heating temperature.

Preferably, the step of storing said rate of change of temperature and said rate of change of the rate of change of temperature is performed for any particular healing cycle, Preferably, the step of clearing said stored rate of change of temperature and said rate of change of the rate of change of temperature when the step of said switching off heating power supply is performed.

In another embodiment of the present invention, the step of switching off said heating power supply upon receipt of said heating control signal is performed.

Preferably, the step of activating a continuous alarm is performed when the step of switching off said heating power supply is performed.

Compared with the existing methods, the present invention provides an accurate method of estimating the temperature rise in a domestic appliance and provides a timely control of power cut to avoid any possible damage to the domestic appliance.

Detailed Description

The present invention will be described further in detail on the basis of the attached diagram and examples.

Figure 1 illustrates a flow diagram of a process operated by an appliance in accordance with a specific embodiment of the invention.

The operation for controlling anti-dry burning in an electric kettle will now be described with reference to Figure 1. The first step of the method comprises initialising the circuit elements of the electric kettle. During the initialisation process, a sensor, microprocessor and control circuit are set up. In a second step, the control circuit turns on the heating power supply which in turn triggers the sensor to monitor the temperature of the electric kettle in real time. Then, the microprocessor calculates the temperature change rate in accordance with the detected temperature, and compares the temperature change rate with a preset value. If the temperature change rate is greater than the preset value, a signal is sent to the control circuit to turn off the heating power supply and an alarm is activated. However, if the temperature change rate is less than the preset value, the microprocessor calculates the rate of change of the rate of change of temperature. If the rate of change of the rate of change of temperature is greater than the preset value, the microprocessor sends a signal to the control circuit to turn off the power supply and the alarm is activated. If the rate of change of the rate of change of teniperature is less than the preset value, the microprocessor takes the temperature change rate to one second earlier and returns to the main program to prepare for the anti-dry burning control for the next period.

Meanwhile, the microprocessor sets up the maximum heating time and the signal is sent to the control circuit to turn off the heating power supply and the alarm is activated if the continuous heating time is greater than the maximum heating time. The microprocessor also sets up the maximum heating temperature and the signal is sent to the control circuit to turn off the heating power supply and the alarm is activated if the heating power supply is greater than the maximum heating power supply.

The microprocessor stores the temperature change rate and the rate of change of the rate of change of temperature of each continuous heating.

The control circuit turns on the heating power supply and turns off the heating power supply and activates the alarm when the continuous heating time is greater than or equal to the preset maximum heating time. When the continuous heating time is less than the preset maximum heating time, the sensor detects the heating temperature. The heating power supply is turned off and alarm is activated when the heating power supply is greater than the preset maximum heating temperature. If the heating temperature is less than the preset maximum heating temperature, then the microprocessor calculates the temperature change rate and compares it with the preset value when the temperature change rate is greater than the preset value, the heating power supply is turned off and alarm is activated; if the temperature change rate is less than the preset value, the microprocessor calculates the rate of change of the rate of change of temperature varied with time -when the rate of change of the rate of change of temperature is greater than the preset value, the heating power supply is turned off and alarm is activated; when the rate of change of the rate of change of temperature is less than the preset value, the microprocessor takes the current temperature change rte and compares it again with the preset value so as to calculate the rate of change of the rate of change of temperature for next period. The preset values, such as maximum heating time, maximum heating temperature, temperature change rate and the rate of change of the rate of change of temperature, can be obtained by means of experiment for electric kettles of different capacities and heating powers and can be saved in the microprocessor in the form of constants.

The modular converting port in the microprocessor is connected with the resistors of various voltage-dividing values for electric kettles with different capacities and heating powers. The modular converting results are different to various voltage dividing values.

Such different converting results are utilized as the query codes to obtain the necessary computation period, preset temperature change rate, the rate of change of the rate of change of temperature and preset maximum heating time. Therefore, the chips of the same software can be applicable to electric kettles of different models and powers.

Example I -capacity: 175L; heating power: 2000W; computation period: 6s; preset temperature change rate: 8 KIs; rate of temperature acceleration: 2 K1s2.

Example 2 -capacity: I 75L; heating power: 3000W; computation period: 2s; preset temperature change rate: 8 K/s; rate of temperature acceleration: 2 K1s2.

Example 3 -capacity: I 75L; heating power: I 000W; computation period: lOs; preset temperature change rate: 8 KIs; rate of temperature acceleration: 2 K1s2.

Claims

CLAIMS: I. A method of controlling an anti-dry burning feature of a

domestic appliance, the controlling method comprising the steps of: determining the temperature of said domestic appliance; detennining the rate of change of said determined temperature; and outputting a heating control signal if said determined rate of change is above a preset rate of change value.

2. A method in accordance with claim I further comprising the step of initialising circuit elements of said domestic appliance.

3. A method in accordance with claim 2 wherein said step of initialising said circuit elements of said domestic appliance comprises setting up a monitoring means, a processing means and a circuit control means.

4. A method in accordance with any preceding claim wherein the step of determining the temperature of said domestic appliance comprises measuring the real-time temperature of said domestic appliance.

5. A method in accordance with any preceding claim wherein, in the case that said determined rate of change is less than said preset rate of change value, the method further comprises the steps of comparing said rate of change value with a corresponding rate of change value from a preceding point in time, to obtain a measure of the rate of change of the rate of change of temperature, comparing said measure with a preset temperature acceleration value, and outputting a control signal if said measure exceed said preset acceleration value.

6. A method in accordance with any preceding claim and including setting a maximum heating time, and outputting said control signal if the continuous heating time is greater than said maximum heating time. n

7. A method in accordance with any preceding claim and including setting a maximum heating temperature, and outputting said control signal if the heating temperature is greater than said maximum heating temperature.

8. A method in accordance with any preceding claim including, for any particular heating cycle, storing said rate of change of temperature and said rate of change of the rate of change of temperature.

9. A method in accordance with claim 8 further include clearing the stored rate of change of temperature and said rate of change of the rate of change of temperature when the step of said switching off heating power supply is performed.

10. A method in accordance with any preceding claim including switching off said heating power supply upon receipt of said heating control signal.

11. A method in accordance with claim 10 further comprising the step of activating a continuous alarm when the step of switching off said heating power supply is performed.

12. An apparatus for controlling an anti-dry burning feature of a domestic appliance, said apparatus comprising: monitoring means operable to determine temperature of said domestic appliance; processing means for processing said determined temperature; and circuit control means operable to output a heating control signal to cause switching off of the heating power supply of said domestic appliance; 13. The apparatus of claim 12, wherein said monitoring means is operable to determine the real-time temperature of said domestic appliance.

14. The apparatus of claim 12 or claim 13, wherein said processing means is operable to calculate the rate of change of temperature in accordance with the determined temperature.

15. The apparatus of any one of claims 12 to 14 wherein, in the case that said determined rate of change is less than said preset rate of change value, said processing means is further operable to compare said rate of change value with a corresponding rate of change value from a preceding point in time, to obtain a measure of the rate of change of the rate of change of temperature, compare said measure with a preset temperature acceleration value, and to output a control signal if said measure exceed said preset acceleration value.

16. The apparatus of any one of claims 12 to 15, wherein said processing means is operable to set up a maximum heating time, and to send a signal to said circuit control means if the continuous heating time is greater than said maximum heating time.

17. The apparatus of any one of claims 12 to 16, wherein said processing means is operable to set up a maximum heating temperature, and to send a signal to said circuit control means if the heating temperature is greater than said maximum heating temperature.

18. The apparatus of any one of claims 12 to 17, wherein said processing means is operable to store said rate of change of temperature and said rate of change of the rate of change of temperature, for any particular heating cycle.

19. The apparatus of claim 18, wherein said processing means is operable to clear the stored rate of change of temperature and rate of change of the rate of change of temperature when said circuit control means switches off said heating power supply.

20. The apparatus of any one of claims 12 tol 9, wherein said circuit control means is operable to switch off said heating power supply upon receipt of said signal from said processing means.

21. The apparatus of claim 20, wherein said circuit control means is operable to activate an alarm when said domestic appliance is switched off.

22. A method as substantially hereinbefore described with reference to the accompanying drawing.

23. An apparatus as substantially hercinbefore described with reference to the accompanying drawing.

Amendments to the claims have been flied as follows A method of controlling an anti-dry burning feature of a domestic appliance, the controlling method comprising the steps of: determining the temperature of said domestic appliance; determining the rate of change of said determined temperature; outputting a heating control signal if said determined rate of change value is above a preset rate of change value; and comparing said rate of change value with a corresponding rate of change value from a preceding point in time, to obtain a measure of the rate of change of the rate of change of temperature if said determined rate of change value is less than said preset rate of change value.

2. A method in accordance with claim 1 further comprising the step of initialising circuit elements of said domestic appliance.

3. A method in accordance with claim 2 wherein said step of initialising said circuit elements of said domestic appliance comprises setting up a monitoring means, a processing means and a circuit control means.

4. A method in accordance with any preceding claim wherein the step of determining the temperature of said domestic appliance comprises measuring the real-time temperature of said domestic appliance.

5. A method in accordance with any preceding claim and including comparing said measured rate of change of the rate of change temperature with a preset temperature acceleration value, and outputting a control signal if said measure exceed said preset acceleration value.

6. A method in accordance with any preceding claim and including setting a maximum heating time, and outputting said control signal if the continuous heating time is greater than said maximum heating time.

7. A method in accordance with any preceding claim and including setting a maximum heating temperature, and outputting said control signal if the heating temperature is greater than said maximum heating temperature.

8. A method in accordance with any preceding claim including, for any particular heating cycle, storing said rate of change of temperature and said rate of change of the rate of change of temperature.

9. A method in accordance with any preceding claim including switching off said heating power supply upon receipt of said heating control signal.

10. A method in accordance with claim 9 further include clearing the stored rate of change of temperature and said rate of change of the rate of change of temperature when the step of said switching off heating power supply is performed.

11. A method in accordance with claim 9 or claim 10 further comprising the step of activating a continuous alarm when the step of switching off said heating power supply is performed.

12. An apparatus for controlling an anti-dry burning feature of a domestic appliance, said apparatus comprising: monitoring means operable to determine temperature of said domestic appliance; processing means for processing said determined temperature, said processing means is operable to measure the rate of change of the rate of change of said determined temperature if said determined rate of change is less than a preset rate of change value; and circuit control means operable to output a heating control signal to cause switching off of the heating power supply of said domestic appliance if said determined rate of change is above said preset rate of change value. t2-

13. The apparatus of claim 12, wherein said monitoring means is operable to determine the real-time temperature of said domestic appliance.

14. The apparatus of claim 12 or claim 13, wherein said processing means is operable to calculate the rate of change of temperature in accordance with the determined temperature.

15. The apparatus of any one of claims 12 to 14 wherein, said processing means is further operable to compare said measured rate of change of the rate of change with a preset temperature acceleration value, and to output a control signal if said measure exceed said preset acceleration value.

16. The apparatus of any one of claims 12 to 15, wherein said processing means is operable to set up a maximum heating time, and to send a signal to said circuit control means if the continuous heating time is greater than said maximum heating time.

17. The apparatus of any one of claims 12 to 16, wherein said processing means is operable to set up a maximum heating temperature, and to send a signal to said circuit control means if the heating temperature is greater than said maximum heating temperature.

18. The apparatus of any one of claims 12 to 17, wherein said processing means is operable to store said rate of change of temperature and said rate of change of the rate of change of temperature, for any particular heating cycle.

19. The apparatus of any one of claims 12 to 18, wherein said circuit control means is operable to switch off said heating power supply upon receipt of said signal from said processing means.

20. The apparatus of claim 19, wherein said processing means is operable to clear the stored rate of change of temperature and rate of change of the rate of change of temperature when said circuit control means switches off said heating power supply.

21. The apparatus of claim 19 or claim 20, wherein said circuit control means is operable to activate an alarm when said domestic appliance is switched off.

22. A method as substantially hereinbefore described with reference to the accompanying drawing.

23. An apparatus as substantially hereinbefore described with reference to the accompanying drawing.