Microwave Ovens Limited

Microwave Owens Limited

Kenneth I Eke

Microwave oven with co-located microwave and hot air launch site

A microwave oven has a magnetron 26 cooled by a fan 30 which generates a flow of air which is admitted to the oven cavity 10 through an inlet aperture 32, leaving the cavity through an outlet aperture 36. A grill element 22 is located in the upper part of the cavity 10 and a turntable 24 is positioned in the lower part of the cavity 10. Where the air respectively enters and leaves the cavity, thermocouples monitor air inlet (Ti) and air outlet (To) temperatures. After cooking commences, the air inlet and air outlet temperatures are monitored. After a time dependent on the load of the food item being cooked, the plot of air outlet temperature against time crosses the plot of air inlet temperature against time. The crossover point 44 of the air inlet and air outlet temperatures is used to control the remaining cooking time and the duration of energisation of the magnetron and the grill element during the remaining cooking time.

Microwave ovens with air inlet and air outlet temperature sensors

A microwave oven has electrical resistance heating elements (38a, 38b), a fan (36) for passing air over the heating elements and through the oven cavity (10) and a magnetron for delivering microwave power to the oven cavity. The oven is intended for use in commercial establishments such as cafes, petrol filling stations or railway stations and is capable of occupying a stand-by mode pending insertion of a foot item into the oven cavity (10). During the stand-by mode the electrical resistance heating elements are energized at a lower power level (continuously or in pulses) in order to provide a reservoir of heat which speeds the cooking process. The oven is capable of occupying the stand-by mode continuously.

Microwave oven with stand-by mode

A microwave oven defrosts a food item by subjecting the food item to a first defrosting stage during which a flow of air is forced through the oven cavity by a fan, and microwave power is simultaneously delivered to the cavity, ceasing the first stage when the temperature of the air flow reaches a threshold value and subjecting the food item to a second defrosting stage during which the air flow is maintained continuously and the microwave power is pulsed in accordance with a pre-set program.

Microwave ovens and methods of defrosting food therein

A microwave oven has a magnetron for delivering microwave power to the oven cavity, and a fan (36) and electrical resistance heating element (38) for recirculating hot air through the cavity. The oven cooks cakes by subjecting the cakes to a first cooking stage during which hot air but no microwave power is produced, and a second cooking stage during which microwave power is produced but the electrical resistance heating element (38) is not energized, and a third cooking stage during which hot air power is applied and microwave power is produced for a certain proportion of the third cooking stage. The transitions between the stages are determined by the recirculated air temperature as detected by a thermocouple (40) positioned to detect the temperature of the air as the latter leaves the oven cavity.

Microwave ovens and methods of cooking food

A microwave oven having a cavity for receiving a food item to be cooked, primarily meat items, a magnetron for delivering microwave power to the cavity, and a forced hot air system, including a fan and an electrical resistance heating element which are both disposed in a compartment separated from the cavity by a dividing panel. The oven has a first thermistor for monitoring air temperature drawn from the oven cavity after a predetermined time, between eight and fifteen minutes, dependent upon the nature of the food item to be cooked. When the predetermined time is reached, a microprocessor determines the remaining cooking time to complete cooking by referring to an internal program that relates to the particular food item to be cooked. A second thermistor monitors temperature near the heating element and, through the microprocessor, controls the heating element. The microprocessor thus determines a decreasing maximum air temperature curve over the remaining cooking time which is to be executed from the predetermined time to the end of cooking by referring to an internal program for sensed temperature control, again relating to the particular food item to be cooked.

Microwave ovens for cooking primarily meat items

A microwave oven having a cavity for receiving a food item to be cooked, a magnetron for delivering microwave power to the cavity, and a forced hot air system including a fan and an electrical resistance heating element which are disposed in a compartment separated from the cavity by a dividing panel. The oven has a thermistor for monitoring the variation of hot air temperature over time and for determining the particular time at which the hot air temperature reaches a predetermined value. When the hot air temperature reaches the predetermined value, a microprocessor: (1) determines the remaining cooking time to complete cooking by referring to an internal program that relates the time of measurement with total cooking time, and (2) determines a maximum hot air temperature to be maintained from the time of measurement to the end of cooking by reference to a second internal program which relates the values of the time of measurement with the maximum desirable hot air temperature.

A microwave oven having a cavity for receiving food items to be cooked, primarily baked goods and frozen foods, a magnetron for delivering microwave power to the cavity, and a forced hot air system, including a fan and an electrical resistance heating element which are both disposed in a compartment separated from the cavity by a dividing panel. The oven has a thermistor for monitoring air temperature drawn from the oven cavity after a predetermined time, between four and eight minutes, from the commencement of cooking. Dependent upon the sensed temperature being below or above a predetermined threshold temperature between 130.degree. C. and 140.degree. C., a microprocessor determines a category for the food item being cooked with a corresponding final cooking temperature to be attained for completion of cooking by referring to an internal program that relates to the particular food item to be cooked. The delivery of hot air and magnetron power are terminated when the corresponding final cooking temperature is sensed by the thermistor.

Microwave ovens and methods for cooking primarily baked goods and frozen

A microwave oven has a magnetron which launches microwave power into a cavity of the oven through an aperture in the base of the cavity. A metal tray, which may be a shelf or a rotatable turntable is supported above the aperture in a predetermined disposition so that the oven when devoid of food presents a poor power match with the magnetron in terms of effectiveness of power transfer from the magnetron into the oven cavity. As a result, the dielectric load of food items placed in the oven determines the power coupled to the loaded oven from the magnetron and the power transfer automatically increases in proportion to the dielectric food load in the oven. A forced hot air system blows hot air through the cavity, so that food items on the tray are cooked by the simultaneous application of microwave power and the hot air.

Microwave oven with power transfer automatically responsive to

A microwave oven has a magnetron for producing microwave power and a resistance heating element over which air is forced by a fan to produce a forced flow of hot air through the oven cavity. A thermistor in the hot air flow senses the temperature of the hot air. Microwave power and hot air are produced simultaneously until the sensed hot air temperature reaches a predetermined threshold temperature (T1). For baked food items this represents the end of the cooking process, but for meat items there is a final cooking stage during which no hot air is forced through the cavity, the level of microwave power being doubled during the final stage. The end of the final stage occurs when the sensed temperature drops to a predetermined threshold (TS). The absence of forced hot air during the final stage makes the detection of the predetermined threshold temperature (TS) easier, because the slope of the hot air temperature/time curve is steeper than would be the case if hot air were produced to the end of the cooking process.

Microwave ovens having modified final cooking stages

A microwave oven has a trivet in the form of a perforated metal plate which is a receptacle for food, is metal and is supported on a turntable of the oven. The metal plate and the turntable are both insulated by stove enamel to prevent sparking. The plate and the turntable enclose a space which is thereby shielded from electrical fields generated in the microwave oven so that fats and juices draining into the space from food cooked above the trivet do not absorb substantial quantities of microwave power and therefore do not boil or smoke. A rack may be placed on the trivet to support food at a level higher than the trivet.

Trivet for a microwave oven

A microwave oven has a magnetron for supplying microwave power to a cavity of the oven, and an electrical resistance heating element over which air is blown by a fan to provide a forced flow of hot air through the cavity. The variation in hot air temperature is monitored, and the slope of the temperature/time variation is sensed after a predetermined time interval from the commencement of cooking with the oven in a cold condition. The sensed slope is then used to predict the time period it will take the hot air temperature to reach a predetermined threshold, and the microwave power and the hot air are discontinued after the predicted time period has elapsed.

An oven system comprises a grill unit and a microwave oven unit built into a standard kitchen unit framework or other structure for receiving same with the grill unit surmounting the microwave oven unit. A duct extends from the rear of the microwave oven unit, upwardly past the rear of the grill unit, over the top of the grill unit to a front exit. The rear wall of the cavity of the microwave oven unit has a vent communicating with the duct, and the rear wall of the cavity of the grill unit has a vent communicating with the duct. The microwave oven unit has a magnetron cooled by a blower which directs a flow of air through the duct, this flow being capable of venting both cavities.

Oven systems

A portable microwave oven is designed to be powered from a domestic power socket having a standard maximum power rating. The oven has two side walls, a base, a top wall, a rear wall and a closable front door together defining an oven cavity, a magnetron for supply microwave power to the cavity of the oven, a blower motor for generating a flow of cooling air for the magnetron, a rotatable turntable on the base of the cavity for supporting food thereon, a port in one of the side walls of the cavity, a vent in the rear wall of said vent leading to a vent outlet at the rear of the oven, a shutter mounted adjacent the port and movable between an open position in which the port is open and air is blown through the port and into the cavity by the blower motor and a closed position in which the port is closed by the shutter which prevents air delivered by the blower motor from reaching said cavity. Continuous microwave power is supplied to the cavity simultaneously with the supply of thermal power delivered by a fan forcing air over an electrical resistance heating element. The shutter is in the closed position when the electrical heating element is energized and in the open position to vent the cavity when the electrical heating element is de-energized, the blower motor being energized so long as the oven is switched on and a bypass duct being provided to direct at least some of the air delivered by the blower motor to a region adjacent the vent outlet to prevent condensation in this region.

A microwave oven delivers microwave power to the oven cavity simultaneously with thermal power provided by a circulation of hot air forced through the cavity by a fan. A temperature sensor in the cavity and timing means monitor the temperature/time variation. If a predetermined maximum temperature (e.g. 250.degree. C.) is reached in the cavity in a predetermined time (e.g. 30 minutes) from commencement of cooking with the oven in a cold condition, the oven automatically switches off to finish the cooking process. Most food items other than large meat or casserole dishes will be cooked within the predetermined time by this method. For larger meat and casserole dishes, where the maximum temperature is reached after the predetermined time, the delivery of microwave power is increased and the delivery of thermal power decreased when the maximum temperature is reached in order to complete cooking of these denser food items.

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Woldingham, United Kingdom

Kenneth I Eke