The present invention relates to a method and apparatus for detecting a change in water vapor above a cooktop surface, and more particularly, to a method and apparatus for detecting a change in water vapor above a cooktop surface by analyzing the water absorption of a predetermined wavelength of radiation directed above the cooktop surface.
Boiling water, other liquids or foods, collectively referred to herein as liquids, is one of the most common uses for a cooktop and/or range. It is typically desirable to closely monitor the boil phase and/or state of the liquid during the cooking process. The boil phase and/or state is monitored for a number of reasons. First, many cooking processes require that the liquid be attended to upon identification of a particular boil phase and/or state, such as, for example, stirring or adding ingredients. In addition, the boil phase and/or state may be monitored to reduce heat after the liquid reaches a boil, such as, for example, to reduce the liquid to a simmer or to prevent boil-over. Boil-over can result in a burned-on mess or, in the case of a gas powered heat source, the cooking flame can become extinguished. Moreover, a liquid not monitored upon boiling can boil dry which can result in the burning of the food, damage to vessels or other detrimental situations. Conventionally, the boil phase and/or state is monitored visually. Such visual monitoring can interfere with the ability of a user to prepare other foods or be otherwise fully productively disposed during heating of the liquid. Moreover, a busy or inexperienced user may fail to accurately identify a boil phase and/or state of interest in a timely manner.
For cooktops and ranges having energy sources using electric, inductive or gas power, the determination of the boil phases and/or states of a liquid being heated on the cooktop and/or range has traditionally focused on temperature monitoring or sensing. Various temperature sensors have been proposed for sensing the temperature of a surface heating source, a cooking vessel positioned on a cooktop surface or the contents of the vessel positioned on the cooktop. These temperature sensors can also be used to control the energy supplied to the heating source based upon the sensed temperature. In particular, such sensors have commonly been proposed for use in connection with glass-ceramic cooktops and/or ranges. Temperature-based sensing systems can indirectly or inferentially provide information regarding a boil phase and/or state of a liquid contained in a vessel being heated on the cooktop surface. However, some temperature-based sensing systems may not reliably determine the boil phase and/or state. This unreliability is partially based on the fact that the correlation between temperature and boil phase and/or state depends on a number of variables, such as, for example, the type of liquid, the amount of liquid, any additives, the position of the vessel and the physical characteristics of the vessel.
In addition, some conventional cooktops and/or ranges identify the boil phases and/or states of a liquid by analyzing acoustic emissions produced by the liquid during heating. Various signal processing circuits and other processors are implemented to analyze the acoustic emission and determine the boil phases and/or states of the liquid. However, these acoustic sensing systems also are dependent upon a number of variables, such as, for example, the position of the vessel and the physical characteristics of the vessel.
The boil phases and/or states that the liquid passes through during heating can be identified by scientific names which characterize the physical changes of the heated liquid. The term xe2x80x9cconvectionxe2x80x9d may be used to describe a pre-simmer phase in which the initial heating of the liquid from ambient to a temperature approaching the boiling point occurs. xe2x80x9cPop-cornxe2x80x9d or a xe2x80x9cpingxe2x80x9d is a term that may be used for a simmer onset phase in which the first signs of coalescence of nucleation of gases dissolved in the liquid and gases produced by the heating appear at sites within the vessel, for example, at surface irregularities along the bottom and side walls of the vessel, and such gas bubbles begin to travel towards the surface of the liquid to escape. These bubbles collapse when leaving the hotter inner surface of the vessel. xe2x80x9cJetxe2x80x9d nucleation occurs in a simmer phase, in which gas bubbles are formed more frequently and are of larger size, and in which the bubbles also more rapidly rise to the upper surface of the liquid to escape. The boil phase may also be termed xe2x80x9crolling boilxe2x80x9d, and at this stage, the liquid is highly agitated by the increased number of gas bubbles formed causing water vapor to escape from the liquid. The vaporizing of the water in the vessel increases the amount of water vapor, also termed humidity, above the vessel and the cooktop surface. Therefore, each of the boil phases and/or states is characterized by an increase in water vapor above the cooktop surface. Thus, it would be desirable to have a system and method that detects a change in the water vapor above the cooktop surface as a way to determine the boil phase and/or state of the liquid being heated.
In one representative embodiment, an apparatus for detecting a change in water vapor above a cooktop surface is provided. The apparatus comprises a radiation source that is positioned below the cooktop surface. The radiation source generates and emits radiation. The emitted radiation has at least a predetermined water vapor absorption wavelength. In one embodiment, the radiation source emits the radiation at a predetermined reflectance angle to the cooktop surface such that the emitted radiation is split into a first radiation beam and a second radiation beam. In another embodiment, the radiation source emits the radiation to a beam splitter that splits the emitted radiation into a first radiation beam and a second radiation beam. The first radiation beam is directed through and above the cooktop surface. The second radiation beam comprises reference radiation. A reflective surface is positioned above the cooktop surface and reflects the first radiation beam toward the cooktop surface. A radiation sensor is positioned below the cooktop surface and detects the reflected first radiation beam. The radiation sensor generates a sensor output that corresponds to the reflected radiation beam. A reference radiation sensor is positioned below the cooktop surface and receives the second radiation beam. The reference radiation sensor generates a reference output corresponding to the second radiation beam. A processor is connected to the radiation sensor and the reference radiation sensor, the processor receiving the sensor output and the reference output and determining a change in water vapor above the cooktop surface by analyzing the sensor output and the reference output.
In another representative embodiment, a method for detecting a change in water vapor above a cooktop surface is provided. The method comprises the steps of generating radiation at a position below the cooktop surface. The generated radiation has at least a predetermined water absorption wavelength. In one embodiment, the generated radiation is emitted to a beam splitter. In another embodiment, the generated radiation is emitted at a predetermined reflectance angle with respect to the cooktop surface. The radiation is split into at least a first radiation beam and a second radiation beam. The first radiation beam is directed through the cooktop surface to a position above the cooktop surface. In addition, the first radiation beam is reflected toward the cooktop surface using a reflective surface. The reflected first radiation beam passes through the cooktop surface, and the reflected first radiation beam is detected using a radiation sensor that is positioned below the cooktop surface. The radiation sensor generates a sensor output. The sensor output corresponds to the reflected first radiation beam. The second radiation beam is directed toward a reference sensor. Also, the second radiation beam is detected using the reference sensor. The reference sensor generates a reference output that corresponds to the second radiation beam. The sensor output and the reference output are analyzed at the predetermined water absorption wavelength of the generated radiation. A change in water vapor above the cooktop surface is determined from the analysis.