General Electric Company

Chemetron

Peter H Smith

Fred F Holub

Richard L Stottmann

Raymond L Dills

Charles M Loring, Jr

Thomas L Wilson

Finis E Gentry

Richard L Stottman

A duty cycle power control circuit for a magnetron including a power transformer having a primary winding, a secondary anode winding for supplying anode voltage to the magnetron and a secondary filament winding for energizing the filament of the magnetron. In the illustrative embodiment the power transformer primary winding comprises a main winding and a serially connected standby winding. Duty cycle controlled switching devices are effective in a standby state to connect the main winding in series with the standby winding across an external power supply and are effective in the power on state to disconnect the standby winding and connect the main winding directly across the external power supply. The ratio of the standby winding turns to main winding turns is selected such that when the standby winding is serially connected to the main winding the anode voltage supplied at the secondary of the power transformer is below the minimum anode voltage level for microwave energy generation and when the standby winding is disconnected from the main winding the secondary anode voltage is greater than this minimum anode voltage level; in either instance the filament voltage is sufficient to maintain the filament temperature high enough to avoid moding in the magnetron.

Power control circuit for magnetron

Method and apparatus for testing microwave oven cavities during the oven fabrication process after the cavity forming operation is complete. The cavity to be tested is positioned front frame resting on a test plate containing a non-protruding microwave power source and choke/ferrite attenuators. The power source radiates into the interior of the cavity and microwave leakage is measured at the cavity exterior.

Apparatus and method for production line leakage testing of microwave

A domestic combination microwave and electric self-cleaning oven of the type providing a plurality of operating modes including a microwave mode and a self-cleaning mode is provided with an arrangement for preventing an undesirable buildup of humid air in the cavity when operating in the microwave modes. The venting arrangement includes a restricted air inlet passageway provided to allow outside air to enter the cavity. Air is vented from the cavity through an air exhaust passageway. A catalytic oxidation unit is provided in the air exhaust passageway to decompose gases generated when the oven is operating in the self-cleaning mode. The restricted air inlet passageway is configured to limit unaugmented air flow into the cavity to a level sufficient to facilitate the proper operation of the oxidation unit during operation in the self-cleaning mode. A humidity sensor for sensing the relative humidity of the air exiting the cavity through the exhaust passageway is provided in combination with a blower operative when energized to substantially augment the flow of air into the cavity and blower control circuitry responsive to the sensor and operative to energize the blower when the sensed relative humidity level exceeds a predetermined threshold level. The control circuitry enables energization of the blower only when operating in the microwave modes so that only the unaugmented air flow occurs in other operating modes.

Combination microwave and thermal self-cleaning oven with an automatic

A system and method for defrost detection particularly applicable to a microwave oven having an excitation system which normally exhibits relatively little change in voltage standing wave ratio and phase for loads of widely varying dielectric constant values. A discontinuity is periodically introduced into the waveguide coupling microwave energy from the source to the cooking cavity. This discontinuity is effective to cause a substantial change in the magnitude and phase of the electromagnetic field in the waveguide for food objects in the frozen state, while causing relatively little change in these parameters for the same food objects in the thawed state. Hence, the presence of the discontinuity in the waveguide provides a readily detectable difference in field strength at the sensor location in the waveguide between an object in its frozen state and the same object in its thawed state. A sensor responsive to the strength of the electromagnetic field at a predetermined location in the waveguide generates an output signal representative of field strength at that location. This output signal is sampled with the discontinuity present in the waveguide to detect a predetermined relationship between the signal and a reference which when detected indicates the food load has converted from its frozen state to its thawed state.

Automatic defrost sensing arrangement for microwave oven

A microwave oven having a cooking cavity for receiving objects to be heated during the oven cooking cycle arranged to permit continuous circulation of air through the cavity during the cooking cycle, an exhaust flow path to the oven exterior formed externally of the cavity for circulating air exiting the cavity, and sensing means responsive to vapors and/or gases carried by the exiting air positioned in the exhaust flow path, is provided with a pyrolytic converter positioned in the exhaust flow path upstream of the sensing means for converting non-gaseous contaminants carried by the exiting air during the cooking cycle to gaseous form. Removal of non-gaseous contaminants from the air exiting the cooking cavity upstream of the sensor prevents accumulation of such contaminants from interferring with proper sensor operation without interrupting the cooking cycle and without requiring periodic manual cleaning of the sensor device.

Food emission sensing

A method and apparatus for anticipating the occurrence of a fire in the cooking cavity of a microwave oven. The oven is provided with a blower for continuously circulating outside air through the cooking cavity to carry away gases by food loads being heated therein. A sensor responsive to the concentration of gases in the circulating air monitors the gas concentration level and generates an output signal representative thereof. Sensor monitoring circuitry responsive to the sensor output signal is operative to determine the rate of change of the gas concentration level, and a detect a characteristic rate of change indicative of the load being heated closely approaching its combustion point. Upon detection of the characteristic rate of change, power to the oven is turned off and and indication is provided to the user that a combustion condition in the oven cavity is imminent.

Automatic fire detection for a microwave oven

A touch control arrangement which employs a touch panel comprising a plurality of touch keys and a network of electrically connected capacitive elements; an oscillator which incorporates the network of capacitive elements in its timing circuit; and a microprocessor coupled to the output of the oscillator and operative to control various appliance operating components as determined by the frequency of the oscillator output signal. The keys of the touch panel are operatively coupled to the network of capacitive elements such that actuation of a key or pad by the user changes the equivalent capacitance of the timing circuit causing the oscillator a generate a control signal at the frequency associated with the actuated key.

Touch control arrangement for data entry

Method and apparatus for detecting the boiling point of liquids being heated by a cooking appliance and automatically reducing the output power of the heat source, once the boiling point has been reached, to a level which will sustain a desired evaporation rate, by measuring the initial weight of the liquid to be heated; energizing the heat source at a predetermined power level, periodically measuring the weight of the liquid as the heating process continues; computing the rate of change of the weight of the liquid, and reducing the power level of the heat source to a lower power level when the computed rate of change exceeds a reference rate and increasing the power level when the computed rate of change is less than the reference rate once the boiling point has been reached. The first occurrence of a measured weight decrease greater than the reference rate signifies that the boiling point of the liquid has been reached.

Method and apparatus for limiting the evaporation rate of liquids heated

A weight measuring arrangement for a cooking appliance in which a surface heating unit also functions as a scale platform. A three arm cantilever beam supports the heating unit. A set of four strain gages measures the strain of the three support arms, with one gage each being attached to each of two identical support arms and the remaining two gages being attached to the third arm, which arms are constructed such that the strain measured by each of the gages secured to the third arm is one-half that measured by each of the gages secured to the two identical arms when the ends of all three arms are equally deflected by a utensil placed on the surface unit for heating. The gages are electrically connected in a Wheatstone bridge network such that the output voltage from the bridge network is proportional to the weight of the load carried on the surface unit. This arrangement can be used to monitor the weight of the items being heated, throughout the heating period.

Weight measuring arrangement for cooking appliance surface unit

An improved phase shifting device for varying the phase of the standing wave in a hollow rectangular waveguide is provided which is particularly applicable to microwave cooking appliances. A metallic septum is constructed at the end of the waveguide remote from the microwave source which extends inwardly into the waveguide from the adjacent waveguide end wall parallel to the narrow walls of the waveguide and electrically connects the broad walls of the waveguide, thereby dividing the waveguide into two sub-waveguides, each of which exhibits a cut-off characteristic at the operating frequency. The leading edge of the septum provides a short circuit termination reference point for the waveguide. The moving parts comprise a pair of dielectric plugs, each of which is received in a respective one of the sub-waveguides for selective movement in tandem from a reference position completely within the sub-waveguides to one or more phase shifting positions in which the plugs extend forward of the septum leading edge toward the microwave source. The shift in the phase of the standing wave varies linearly with the extent of forward displacement of the plugs relative to the septum leading edge. The plugs are selectively moved in tandem relative to the reference position in the sub-waveguides to provide the desired phase shift.

Microwave phase shifting device

Food thawing apparatus is disclosed specifically adapted for use in a refrigeration appliance. An enclosure having good thermal communication with surrounding environment is provided with a pair of planar electrodes defining a food thawing zone. One of the electrodes is movable to allow insertion of a frozen food load. A high frequency, relatively low wattage power supply provides uniform energy distribution throughout the feed load for gentle heating (thawing). Frequencies of 27.12 MHz or 43 MHz are suggested along with a power level of 100 watts or below, preferably 35-80 watts.

Apparatus for thawing frozen food

A utensil detection arrangement for an induction heating apparatus which provides a signal indicative of an off-center position of a cooking utensil supported on a cooking surface which overlies an induction heating coil. The detection arrangement comprises a conductive loop configuration located intermediate the heating coil and the cooking utensil in a plane parallel to the plane of the cooking surface and concentric with respect to the axis of the coil. The conductive loop is linked with the magnetic flux generated by the induction heating coil, which flux changes as a result of the position of a cooking utensil with respect to the axis of the coil and thereby generates a signal which changes in amplitude as a result of utensil position.

Utensil location sensor for induction surface units

A microwave oven cavity excitation system for promoting time-averaged uniformity of microwave energy distribution within the cooking cavity. Circularly-polarized microwave energy is radiated from a feed waveguide into an adjacent cooking cavity by means of an aperture, such as an X-slot, in the feed waveguide properly electrically located laterally within the feed waveguide so as to nominally radiate an electric field having circular polarization properties and, overall, shaped as an approximate hemisphere. A cross-sectional slice of the field, for example in the plane of the food supported on a conventionally-located shelf, is circular in shape. The radiating X-slot is controllably and selectively electrically moved laterally with respect to the waveguide centerline with the result that the sectional shape of the resulting field changes from circular to elliptical, with the degree and orientation of the ellipse depending upon the direction and degree of movement of the coupling aperture with respect to the waveguide centerline. The shape of the field is constantly varied through various elliptical configurations during operation, to provide the desired time-averaged uniformity of energy distribution through a suitably-programmed controller.

Microwave oven cavity excitation system providing controlled electric

A microwave oven including a resonant cavity humidity sensor operated by microwave energy sampled from the power produced for the cooking operation. The arrangement provides for a flow of moist air from the cooking cavity through an active resonant chamber and a flow of dry air from the atmosphere through a passive resonant chamber. Control circuitry governs the microwave energy flow into the cooking cavity in response to moisture conditions in the cavity so indicated by the sensor.

Microwave oven humidity sensing arrangement

Food thawing apparatus is disclosed specifically adapted for use in a refrigeration appliance. An enclosure having good thermal communication with surrounding environment is provided with a pair of planar electrodes defining a food thawing zone. One of the electrodes is movable to allow insertion of a frozen food load. A high frequency, relatively low wattage power supply provides uniform energy distribution throughout the food load for gentle heating (thawing). Frequencies of 27.12 MHz or 43 MHz are suggested along with a power level of 100 watts or below, preferably 35-80 watts.

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Anchorage, KY, United States of America

Peter H Smith