Communications: electrical – Condition responsive indicating system – Specific condition
Utility Patent
1999-07-19
2001-01-02
Hofsass, Jeffery A. (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S588000, C340S589000, C340S600000, C340S643000, C219S464100
Utility Patent
active
06169486
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a monitoring and a control system for determining and controlling the temperature of a cooktop, and more particularly a system having one or more sensors and one or more filters to sense infrared radiation emanating from the cooktop in an area above a controllable radiating energy source, and the level of infrared radiation being representative of the temperature of the cooktop.
Recently, standard porcelain enamel cooktop surfaces of domestic ranges have been replaced by smooth surface, high resistivity cooktops located above one or more heat sources, such as electrical heating elements, or gas burners. The smooth surface cooktops improve cleanability because there are no seams or recesses in which debris can accumulate. The continuous cooktop surface also prevents spillovers from coming into contact with the heating elements or burners. Such cooktops may be milkwhite, opaque, glass ceramic or crystal and glass material sold under various trade names. Glass ceramic material is used frequently because of its low coefficient of thermal expansion and smooth top surface that provides a pleasing appearance.
The high thermal mass of the glass ceramic material has a slow thermal response, thereby requiring a longer time to heat up and cool down. The heat is stored in the glass ceramic cooktop, as well as in the sheathed heating element, or the insulating support block or pad for the heating element. When open coil heaters are used at a spaced distance below the cooktop, there is also poor thermal coupling between the heat source and the glass ceramic cooktop. In order to transfer a requisite amount of heat from an open coil heater to the glass ceramic plate, the heat source has to operate at a higher temperature than otherwise, which creates problems, such as poor system efficiency, high heat losses, component overheating and high cooktop temperatures. Glass ceramic cooktops in surface units with open coil heaters also may present a safety hazard in the event the cooktop is broken.
Another type of surface cooking units utilize solid state, induction cooking systems. The basic mechanism of induction cooking comprises an alternating magnetic field coupled across a gap with a utensil bottom, which acts as a single turn secondary winding. One or more induction heating coils are located below a ceramic, glass, or plastic cooking surface which may be in the form of a substantially unbroken utensil support plate. A complete induction surface cooking unit preferably employs a static power conversion circuit including a filter and an inverter for converting a filtered unidirectional voltage to ultrasonic power for driving the induction heating coil. Components for cooking, in addition to the gating circuit for the inverter power devices, include an inhibit circuit for selectively inhibiting operations of the inverter, start-up and shut-down devices coupled to the inhibit and gating circuits for controlling transients and the application and removal of voltage from the inverter, a protection device, output power adjusting devices and user controls. The power output of the inverter is modulated to change the heating level in the utensil and, therefore, the temperature at which the food is cooked. Static power converters, especially those with semiconductor components, require protection to prevent malfunction and failure under abnormal circuit conditions, such as over voltages and over currents. Furthermore, the coupled utensil is the inverter load and the reflected impedance changes the inverter's electrical parameters. There are severe load requirements if the unit is to be operable with a variety of utensils of different sizes and materials, under both load and no-load conditions. The requirement for automatic and continuous operation means that the circuit design must anticipate circumstances that could cause failure or temporary shutdown.
Thus, a need exists for a system to determine the temperature of the cooktop and to utilize a signal generated by the system to aid in the automatic control of the heat source, provide user feedback to increase safety, to increase the life of the components and to increase energy savings.
SUMMARY OF THE INVENTION
A monitoring and control system is disclosed for determining the temperature of, and controlling the temperature of a cooktop, which preferably is glass ceramic, having an upper surface and a lower surface. At least one controllable heat source is located below the lower surface of the cooktop to heat the cooktop area above the heat source, and at least one sensor is provided to sense infrared radiation from the glass ceramic cooktop above the heat source. The level of infrared radiation selected in a particular band is representative of the temperature of the cooktop.
The sensor provides a signal indicative of the temperature of the cooktop which can then be used to control the heat source in order to protect the cooktop from extreme temperatures, or the signal may be utilized to provide an indication of a hot cooktop surface to alert the user. The signal can also be utilized to provide automatic control of the heat source to maintain a predetermined temperature, or to prevent exceeding a maximum cooking temperature on the cooktop above the heat source.
The present invention utilizes an optical detector to “look” at the cooktop or detect the level of infrared radiation in a particular band to detect the temperature thereof. The cooking surface temperature can then be controlled using the absolute temperature and the associated temperature gradient through the thickness of the cooktop to provide a signal which may be used to protect the glass ceramic from extreme temperatures, provide an indication of a hot surface after the heat source has been turned off, and/or to provide a temperature-based control of the heat source.
The signal used in the system originates in the infrared radiation from the cooktop. The existence and the level of the infrared radiation from the cooktop can be measured using an optical sensor assembly opening into the heating chamber between the heat source and the cooktop. The level of infrared radiation is representative of the temperature of the cooktop. The range of wavelengths sensed by the optical sensor can be controlled to enable the sensor to monitor either the surface temperature of the cooktop, or the internal temperature of the cooktop. This information can also be used to determine the heat flux through the cooktop by also considering the temperature gradient through the cooktop by using two different wavelength ranges of sensitivity.
The system according to the present invention envisions the measurement of the temperature of the cooktop using an optical sensor to sense some portion of the underside of the cooktop from a location at the edge, side, or bottom of the heat source. An optical waveguide may be utilized to direct the infrared radiation onto the detector. However, due to the thermal environment and manufacturing considerations, the optical waveguide may not extend into contact with the underside of the cooktop. In this situation, there may be significant signal interference resulting from reflections from the cooktop surface. Filters used to select wavelength ranges may be utilized to filter out the reflective component of the radiation and to avoid interference by other sources of radiation.
The transmission band of the filters may be tailored to select the specific wave length ranges for determining the temperature of the surface of the cooktop, or to determine the sub-surface temperature of the cooktop. For instance, infrared radiation substantially around the 5&mgr; (microns) range may be utilized to detect the surface temperature, while wavelengths equal to or greater than 3.5&mgr; range, for example, may be utilized to measure the sub-surface temperature of the cooktop. Wavelengths substantially closer to the 7&mgr; range may be sensed in the instance where there are large temperature gradients in the cooktop.
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Berkcan Ertugrul
Saulnier Emilie Thorbjorg
Breedlove Jill M.
General Electric Company
Hofsass Jeffery A.
Pr{acute over (e)}vl Daniel
Thompson John F.
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