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EP0142958A2 - Mikrowellenherd und Verfahren zum Kochen von Speisen - Google Patents

Mikrowellenherd und Verfahren zum Kochen von Speisen Download PDF

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Publication number
EP0142958A2
EP0142958A2 EP84307554A EP84307554A EP0142958A2 EP 0142958 A2 EP0142958 A2 EP 0142958A2 EP 84307554 A EP84307554 A EP 84307554A EP 84307554 A EP84307554 A EP 84307554A EP 0142958 A2 EP0142958 A2 EP 0142958A2
Authority
EP
European Patent Office
Prior art keywords
microwave
power
oven
cavity
thermal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP84307554A
Other languages
English (en)
French (fr)
Other versions
EP0142958A3 (de
Inventor
Kenneth Ian Eke
Percy George Giles
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Microwave Ovens Ltd
Original Assignee
Microwave Ovens Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Microwave Ovens Ltd filed Critical Microwave Ovens Ltd
Publication of EP0142958A2 publication Critical patent/EP0142958A2/de
Publication of EP0142958A3 publication Critical patent/EP0142958A3/de
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/647—Aspects related to microwave heating combined with other heating techniques
    • H05B6/6482—Aspects related to microwave heating combined with other heating techniques combined with radiant heating, e.g. infrared heating
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/6408—Supports or covers specially adapted for use in microwave heating apparatus
    • H05B6/6411—Supports or covers specially adapted for use in microwave heating apparatus the supports being rotated
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/6447—Method of operation or details of the microwave heating apparatus related to the use of detectors or sensors
    • H05B6/645—Method of operation or details of the microwave heating apparatus related to the use of detectors or sensors using temperature sensors

Definitions

  • This invention relates to microwave ovens and to methods of cooking food.
  • a portable domestic microwave oven made for the UK market has a higher power rating and there is therefore more power available to supply to the cavity, than is the case with ovens made for the Japanese or US markets.
  • this increase in available power does not automatically mean a shorter cooking time and a better result.
  • Any increase in the thermal power delivered to the cavity causes the cavity temperature to rise more quickly and for the temperature sensing means to cause the thermal heating means to cycle on and off.
  • An increase in microwave power does not, beyond certain limits, decrease the cooking time.
  • the main limitation on reducing cooking times is the thermal conductivity of the food.
  • Microwave energy at the conventional oven frequency of 2450 Megahertz has a penetration into the food of only a few centimetres, so whatever microwave power is used this factor places a limit on reducing cooking times.
  • the invention aims to overcome this problem by using a lower microwave frequency.
  • a microwave oven comprises a microwave generator for supplying microwave power to a cavity of the oven, thermal heating means for supplying thermal power to the. cavity simultaneously with the microwave power, the thermal heating means including an electrical heating element and a recirculating fan for recirculating air over the heating element and through the cavity, wherein the microwave generator has an operating frequency of less than 1000 Megahertz. This lower microwave frequency has a greater penetration into the food items being cooked, typically around 10 centimetres. This means that even large food items having a total thickness of 20 centimetres are penetrated by the microwave energy, so that heating and therefore cooking are extremely rapid.
  • the generation of thermal power is arranged to match the microwave power, preferably so that the temperature/time curve rises steadily from zero (corresponding to a cold start) and reaches the desired maximum temperature at the completion of the cooking time, without interruption or reduction in the supply of thermal power.
  • a method of cooking food in a microwave oven comprises delivering thermal power and microwave power simultaneously into a cavity of the oven, the thermal power being delivered by hot air recirculated by a fan over an electrical heating element, and wherein the microwave power is delivered at an operating frequency of less than 1000 Megahertz.
  • the microwave power is produced by a magnetron or klystron having a frequency of 915 Megahertz (suitable for the USA) or 896 Megahertz (suitable for the United Kingdom and mainland Europe). It is possible for the magnetron or klystron to have an operating frequency which lies between 915 Megahertz and 896 Megahertz and which is suitable for use either in the USA or in the UK or mainland Europe.
  • the invention may be applied to a portable domestic microwave oven intended to be powered from a domestic plug/socket, but the invention is also applicable to full size domestic ovens and to large commercial ovens having higher power ratings.
  • the lower microwave frequency increases penetration into the food items being cooked, thereby enabling higher thermal power to be applied by the recirculated hot air, whilst retaining the necessary balance between thermal power and microwave power.
  • mains power (from a 35A cooker input) is applied from the left hand side of Figure 1 through a fuse 10 and a magnetron thermostat 12.
  • a triac 14 controlled by a first timer governs the supply of power to a cavity lamp 16 and a blower 18 for the magnetron.
  • a further triac 20 which is controlled by another timer and through which current must pass before reaching a triac 22 and a parallel network comprising a convection motor 24, a relay 26 for operating a flap or damper, a diode 28 in parallel with a triac 30, and a thermal heating element 32.
  • the convection motor 24 drives a fan for blowing air over the element 32, this forced flow of hot air being recirculated through the oven cavity so as to produce thermal power for browning the food to supplement the microwave power.
  • a triac 34 forms a microwave on/off switch, and inductive coils 36 transmit power through one or more capacitors 38, 40 and 42 to the magnetron 44.
  • the oven has the usual door-latch switch 46, monitor switch 48, and cook/start switch 50.
  • a turntable motor 52 is provided to drive a rotating turntable on which the food is placed in the oven cavity.
  • the oven may also have a radiant grill element 51 at the top of the oven cavity.
  • a portion of the oven cavity is shown schematically at 54, the cavity 54 being vented through a moisture vent 56.
  • Figure 2 is a plot of air temperature (at a location immediately downstream of the element 32) against time.
  • Curve A shows the temperature/time variation for an empty oven. After time x from a cold start, the air temperature has reached a predetermined threshold Tl (e.g. 250°C), at which point the oven is switched off. Curve A represents one extreme in that it is not possible for the air temperature to reach Tl in a time less than x.
  • Curve B shows the temperature/time variation when the oven is heavily loaded, e.g. by a dense joint of meat. For curve B, the predetermined threshold temperature Tl is reached after time y from a cold start. Curve B represents the other extreme and for all other food items in the oven the temperature/time curve will be somewhere between curve A and curve B and the temperature Tl will be reached (and therefore cooking completed) at a time intermediate x and Y.
  • Tl e.g. 250°C
  • the predetermined threshold temperature Tl is detected by temperature sensing means in the form of a thermistor 64 which, when temperature Tl is attained, produces an electrical signal to switch off power to the element 32 and to the magnetron 44 to signify the end of cooking. Hence, all food items are cooked when temperature Tl is reached, commencing with the oven in a cold condition.
  • the triacs shown in Figure 1 are connected to a microprocessor control circuit to which the thermistor 64 is also connected.
  • the operation of the microprocessor control circuit is governed by manually operated control pads of the oven.
  • the triac 34 is also closed and current flows through the coils 36, the magnetron 44 being operated at its low power level through the capacitor 38 because switches 60, 62 are open.
  • the heating element 32 delivers thermal power (1000) watts) and the magnetron delivers microwave power (250 watts).
  • the temperature time variation is shown by curve C in Figure 2, the temperature rising steadily from zero as the thermal power and the microwave power are applied simultaneously and continuously until the thermistor 64 registers that temperature T1 has been attained at time z.
  • a signal is sent to the microprocessor control circuit which switches off the gate supply to triac 20, thereby causing simultaneous cessation of thermal and microwave power and leaving the oven in a stand-by mode. Cooking is then complete. In this stand-by mode, the damper relay 26 is opened and cooling air from the magnetron blower 18 is directed into the oven cavity to cool the latter. A further pad marked RESET/OFF must be touched to turn the oven off completely.
  • the capacitor 40 and switch 60 enable an intermediate level of microwave power to be selected, and the capacitor 42 and switch 62 are provided to enable a third, higher level of microwave power to be selected for microwave only operation.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Electric Ovens (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)
  • General Preparation And Processing Of Foods (AREA)
  • Constitution Of High-Frequency Heating (AREA)
EP84307554A 1983-11-11 1984-11-01 Mikrowellenherd und Verfahren zum Kochen von Speisen Withdrawn EP0142958A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8330179 1983-11-11
GB838330179A GB8330179D0 (en) 1983-11-11 1983-11-11 Microwave ovens

Publications (2)

Publication Number Publication Date
EP0142958A2 true EP0142958A2 (de) 1985-05-29
EP0142958A3 EP0142958A3 (de) 1985-10-30

Family

ID=10551640

Family Applications (1)

Application Number Title Priority Date Filing Date
EP84307554A Withdrawn EP0142958A3 (de) 1983-11-11 1984-11-01 Mikrowellenherd und Verfahren zum Kochen von Speisen

Country Status (4)

Country Link
EP (1) EP0142958A3 (de)
JP (1) JPS60114634A (de)
AU (1) AU3524784A (de)
GB (1) GB8330179D0 (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2722559A1 (fr) * 1994-07-12 1996-01-19 Samsung Electronics Co Ltd Four a micro-ondes
EP0783240A3 (de) * 1995-12-30 1998-03-25 Lg Electronics Inc. Kombinierter Grill-, Konvektions- und Mikrowellenofen und Verfahren zum Kochen
US11412584B2 (en) 2017-12-08 2022-08-09 Alkar-Rapidpak, Inc. Ovens with metallic belts and microwave launch box assemblies for processing food products

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3699976A (en) * 1969-01-27 1972-10-24 Japan Monopoly Corp Method for killing tobacco leaf bug inhabitants and their eggs
DE2555154A1 (de) * 1975-01-22 1976-07-29 Elektromaschinen Ag Umluftbackofen
US4221948A (en) * 1976-11-17 1980-09-09 Jean Olivier A L Apparatus for subjecting a material to electromagnetic waves
GB2081060A (en) * 1978-06-09 1982-02-10 Special Metals Corp A method of improving the susceptibility of a material to microwave energy heating
GB2137860A (en) * 1983-03-15 1984-10-10 Microwave Ovens Ltd Microwave ovens and methods of cooking food

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3699976A (en) * 1969-01-27 1972-10-24 Japan Monopoly Corp Method for killing tobacco leaf bug inhabitants and their eggs
DE2555154A1 (de) * 1975-01-22 1976-07-29 Elektromaschinen Ag Umluftbackofen
US4221948A (en) * 1976-11-17 1980-09-09 Jean Olivier A L Apparatus for subjecting a material to electromagnetic waves
GB2081060A (en) * 1978-06-09 1982-02-10 Special Metals Corp A method of improving the susceptibility of a material to microwave energy heating
GB2137860A (en) * 1983-03-15 1984-10-10 Microwave Ovens Ltd Microwave ovens and methods of cooking food

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2722559A1 (fr) * 1994-07-12 1996-01-19 Samsung Electronics Co Ltd Four a micro-ondes
EP0783240A3 (de) * 1995-12-30 1998-03-25 Lg Electronics Inc. Kombinierter Grill-, Konvektions- und Mikrowellenofen und Verfahren zum Kochen
US11412584B2 (en) 2017-12-08 2022-08-09 Alkar-Rapidpak, Inc. Ovens with metallic belts and microwave launch box assemblies for processing food products
US11751296B2 (en) 2017-12-08 2023-09-05 Alkar-Rapidpak, Inc. Ovens with metallic belts and microwave launch box assemblies for processing food products

Also Published As

Publication number Publication date
EP0142958A3 (de) 1985-10-30
AU3524784A (en) 1985-05-30
JPS60114634A (ja) 1985-06-21
GB8330179D0 (en) 1983-12-21

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Inventor name: GILES, PERCY GEORGE

Inventor name: EKE, KENNETH IAN