US3624334A - Interlock circuitry for microwave oven - Google Patents
Interlock circuitry for microwave oven Download PDFInfo
- Publication number
- US3624334A US3624334A US24538A US3624334DA US3624334A US 3624334 A US3624334 A US 3624334A US 24538 A US24538 A US 24538A US 3624334D A US3624334D A US 3624334DA US 3624334 A US3624334 A US 3624334A
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- United States
- Prior art keywords
- door
- switch
- circuit condition
- switch means
- power
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- 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.)
- Expired - Lifetime
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- 230000007257 malfunction Effects 0.000 claims abstract description 6
- 230000008878 coupling Effects 0.000 claims description 10
- 238000010168 coupling process Methods 0.000 claims description 10
- 238000005859 coupling reaction Methods 0.000 claims description 10
- 230000005855 radiation Effects 0.000 claims description 8
- 238000010438 heat treatment Methods 0.000 claims description 7
- 238000010411 cooking Methods 0.000 claims description 6
- 239000007787 solid Substances 0.000 description 3
- 238000004804 winding Methods 0.000 description 2
- 238000001816 cooling Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 235000002020 sage Nutrition 0.000 description 1
Images
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
- H05B6/6414—Aspects relating to the door of the microwave heating apparatus
- H05B6/6417—Door interlocks of the microwave heating apparatus and related circuits
Definitions
- the present invention relates in general to microwave ovens and more particularly concerns interlock circuitry for use with a microwave oven to provide safe operation.
- the invention helps avoid harmful radiation from the microwave oven source and turns off the empty microwave oven when the oven door is closed with relatively inexpensive interlock circuitry capable of performing a number of interlock actions.
- Another object of the invention is to reduce the chance of an unsafe failure by providing dual interlocks, one of which interrupts the power to the microwave source directly; the other, indirectly, such as by way of a relay.
- Still another object of the invention is to provide for automatic turn-on of the magnetron filament when the oven is initially opened.
- Still another object of the invention is to provide interlock circuitry that automatically resets the oven timer to zero when the oven door is opened.
- Another object of the invention is to provide interlock circuitry which deenergized the microwave energy source after a suitable time delay when no food is in the oven and the oven door is shut.
- Still another object of the invention is to provide interlock circuitry which will interrupt the power to the filament and plate circuits of the microwave oven when the door is left open for at least a predetermined time interval.
- Still another object of the invention is to achieve one or more of the foregoing objects at low cost with apparatus relatively free from complexity.
- a microwave oven includes interiock circuitry with an input terminal coupled to an electric power supply, such as the l-volt AC line.
- First and second switching means initially carry power from the input terminal to the filament of a microwave energy source, such as a magnetron.
- Means are also provided for applying power to the plate of the microwave energy source after applying power to the filament thereof.
- the first and second switching means are also adapted to interrupt power to the plate when the door is opened.
- FIG. I is a schematic diagram showing the microwave interlock circuitry according to the invention.
- FIG. 2 shows an additional safety feature that may be used with the circuitry of FIG. 1.
- On-olf switch 12 and circuit breaker l4 carry AC energy to normally closed tube thermostat switch 16 in thermal contact with magnetron 40. If magnetron 40 overheats, switch 16 opens to interrupt power to magnetron 40.
- Switches 20 and 22 are shown in FIG. I with the door closed. Assuming that power has just been applied by turning switch 12 on, power flows from contact 20A to terminal 92A of relay contacts 92. Contacts 92 are then open, and magnetron 40 receives no power. Contacts 22A and 22C of switch 22 are then interconnected.
- switches 20 and 22 again assume the position shown in FIG. 1.
- the power across relay 80 is then transferred through contacts 22A and 22C of switch 22 and contact 69 of delay switch 68 to timer unit 100. If the door closes before the delay interval expires, contact 69 is still open, and timing unit 100 receives no power until the delay interval ends.
- Timing unit 100 includes a bank of switches 110, a bank of resistors 120, a switch release solenoid 102 and solid state timer 104.
- the switch bank 110 includes a number of switches 110A through 110F, typically mounted on the front of the microwave oven, and a plurality of switches 122A through 122F operative with respect switches 110A through lIOF to connect respective resistors 120A through 120F across terminals and 106 of solid state timer 104.
- Switch release solenoid 102 is coupled to all switch contacts to cause them to release, thus assuming the position shown in FIG. 1, when solenoid 102 is energized.
- Solid state timer 104 is operative when it receives an input on line 104A through one of the selected switches A through 1 10F.
- the timer 104 includes reset line 104B and output line 104C.
- Timer 104 also includes an internal switch (not shown) for coupling power from input line 104A and the common contact connected thereto to output line 104C for a time interval dependent upon the value of a resistor connected between terminals 105 and 106 associated with the internal delay switch (not shown). After this time interval, the internal switch interrupts the fiow of power to output line 104C and applies power to reset line 1043.
- an internal switch (not shown) for coupling power from input line 104A and the common contact connected thereto to output line 104C for a time interval dependent upon the value of a resistor connected between terminals 105 and 106 associated with the internal delay switch (not shown). After this time interval, the internal switch interrupts the fiow of power to output line 104C and applies power to reset line 1043.
- relay 90 unlatches to deenergize magnetron 40.
- the oven is then opened and either switch 20 or 22 is properly functioning, the power that is still available at contact 20C of switch 20 is coupled through contact 20B of switch 20 to relay 102 to assure that it has released or reset the timing unit 100.
- the circuitry of FIG. 1 provides for filament power turnoff after a predetermined time when the oven door is closed.
- Time delay switch 75 provides this feature.
- contact 76 opens, deenergizing relay 80 and turning off filament power.
- Relay 80 can again be energized only by opening the oven a second time.
- the safety interlock circuitry shown herein prevents harm to an operator of the oven if the oven is opened when the mag netron is radiating energy. A number of interlocks help prevent the escape of potentially harmful radiation under nearly all conditions.
- Switch 20 interrupts the power to magnetron 40 directly, and switch 22 interrupts the power indirectly through releasing relay 90 and opening contact 92. The chance of both interlock switches sticking at the same time is quite remote.
- FIG. 2 there is shown an added feature that may be used with the circuitry of FIG. 1.
- relay 80 is eventually deenergized and no power is fed to the filament or plate. If the door is left open, however, the filament could be energized indefinitely thereby significantly reducing its lifetime.
- the circuitry of FIG. 2 prevents this by limiting the on" time of the filament particularly when the door is left open.
- Relay 30 with associated contacts 32 and 34 and a time delay switch 24 having a heater element 26 and a contact 25 are connected so that if an operator of the oven leaves the door open for a predetermined time, all power to the magnetron is interrupted. This interlock is operative, when either switch 20 or switch 22 has malfunctioned, and the oven door is left open.
- switch 20 or switch 22 When the door is open and either switch 20 or switch 22 sticks in a door closed position, power is available by way of the operative switch, such as switch 20 contacts 208 and 20C, to beat heater element 26. This eventually latches relay 30, opens contacts 32 and 34 and interrupts power to the filament after a predetermined time, typically 180 seconds. When the oven is to be used again, the door has to be closed initially, thereby opening contact 20, deenergizing relay 30 and providing power to switch 22.
- the operative switch such as switch 20 contacts 208 and 20C
- Safety and interlock circuitry for use with a microwave oven having a door ad a source of microwave energy comprising;
- said first and second switch means being coupled from said input terminal and responsive to door for each assuming a first position when said door is open and a second position when said door is closed,
- said first and second switch means being arranged when said door is open to establish the first circuit condition when both said first and second switch means are in their first position
- Safety and interlock circuitry in accordance with claim 1 and comprising a first latching means coupled from said first and second switch means whereby said latching means is actuated when said door is opened and both said first and second switch means properly assume their first position.
- Safety and interlock circuitry in accordance with claim 1 wherein said means for setting said second circuit condition includes timing means for setting said preselected interval and means responsive to completion of said preselected interval for resetting said timing means.
- Safety and interlock circuitry in accordance with claim 4 and further comprising first time delay means for establishing a predetermined minimum time interval between occurrence of said first circuit condition and the occurrence of said second circuit condition in response to the occurrence of said first circuit condition.
- Safety and interlock circuitry in accordance with claim 1 and further comprising third time delay means responsive to said door left closed for interrupting power to said microwave energy source after a preselected time interval.
- Safety and interlock circuitry for use with a microwave oven having a door and a source of microwave energy comprising;
- time delay means coupled to at least one of said first and second switch means for interrupting said means for coupling said electron heating power after a predetermined time interval, when said door is open and at least one of said first and second switch means assumes its first position.
Abstract
Description
Claims (8)
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US2453870A | 1970-04-01 | 1970-04-01 |
Publications (1)
Publication Number | Publication Date |
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US3624334A true US3624334A (en) | 1971-11-30 |
Family
ID=21821111
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US24538A Expired - Lifetime US3624334A (en) | 1970-04-01 | 1970-04-01 | Interlock circuitry for microwave oven |
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Cited By (7)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3710065A (en) * | 1971-12-06 | 1973-01-09 | Litton Systems Inc | Magnetron power supply having in-rush current limiter |
US3780252A (en) * | 1972-07-20 | 1973-12-18 | Litton Systems Inc | Microwave oven power supply circuit |
US3842233A (en) * | 1973-05-31 | 1974-10-15 | Tappan Co | Microwave oven defrost circuit |
US3846607A (en) * | 1972-04-03 | 1974-11-05 | A Bucksbaum | Programming circuit for microwave ovens |
USRE28822E (en) * | 1972-04-03 | 1976-05-18 | Amana Refrigeration, Inc. | Safety interlock system for microwave ovens |
FR2314606A1 (en) * | 1975-06-12 | 1977-01-07 | Philips Nv | SAFETY SYSTEM FOR MICROWAVE OVENS |
US4096370A (en) * | 1977-06-15 | 1978-06-20 | Litton Systems, Inc. | Microwave oven door interlock switch system |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3317699A (en) * | 1964-09-16 | 1967-05-02 | Gen Electric | Power supply for a magnetron |
US3407279A (en) * | 1965-10-08 | 1968-10-22 | Melikian Inc Rudd | High frequency heating apparatus |
US3523170A (en) * | 1967-10-27 | 1970-08-04 | Technology Instr Corp Of Calif | Control system for microwave heater apparatus |
-
1970
- 1970-04-01 US US24538A patent/US3624334A/en not_active Expired - Lifetime
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3317699A (en) * | 1964-09-16 | 1967-05-02 | Gen Electric | Power supply for a magnetron |
US3407279A (en) * | 1965-10-08 | 1968-10-22 | Melikian Inc Rudd | High frequency heating apparatus |
US3523170A (en) * | 1967-10-27 | 1970-08-04 | Technology Instr Corp Of Calif | Control system for microwave heater apparatus |
Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3710065A (en) * | 1971-12-06 | 1973-01-09 | Litton Systems Inc | Magnetron power supply having in-rush current limiter |
US3846607A (en) * | 1972-04-03 | 1974-11-05 | A Bucksbaum | Programming circuit for microwave ovens |
USRE28822E (en) * | 1972-04-03 | 1976-05-18 | Amana Refrigeration, Inc. | Safety interlock system for microwave ovens |
US3780252A (en) * | 1972-07-20 | 1973-12-18 | Litton Systems Inc | Microwave oven power supply circuit |
US3842233A (en) * | 1973-05-31 | 1974-10-15 | Tappan Co | Microwave oven defrost circuit |
FR2314606A1 (en) * | 1975-06-12 | 1977-01-07 | Philips Nv | SAFETY SYSTEM FOR MICROWAVE OVENS |
US4117294A (en) * | 1975-06-12 | 1978-09-26 | U.S. Philips Corporation | Safety arrangement for microwave ovens |
US4096370A (en) * | 1977-06-15 | 1978-06-20 | Litton Systems, Inc. | Microwave oven door interlock switch system |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: MICRO-QUARTZ TECHNOLOGY CORPORATION, A CORP. OF MN Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:MICRO-TRONICS, LTD. A CORP. F MN.;REEL/FRAME:004004/0072 Effective date: 19820603 Owner name: MICRO-QUARTZ TECHNOLOGY CORPORATION, 1010 LYNDALE Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:MICRO-TRONICS, LTD. A CORP. F MN.;REEL/FRAME:004004/0072 Effective date: 19820603 |
|
AS | Assignment |
Owner name: MICRO-QUARTZ TECHNOLOGY CORPORATION 1010 LYNDALE A Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:MICRO-TRONICS, LTD., INC. A MN CORP.;REEL/FRAME:004024/0290 Effective date: 19820714 Owner name: MICRO-TRONICS, LTD., INC., 1010 LYNDALE AVE. NORTH Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:MICRO-TRONICS, INC. A WI CORP.;REEL/FRAME:004024/0294 Effective date: 19820603 |