CA1070771A - Safety inter-locking arrangement for microwave oven door - Google Patents
Safety inter-locking arrangement for microwave oven doorInfo
- Publication number
- CA1070771A CA1070771A CA254,381A CA254381A CA1070771A CA 1070771 A CA1070771 A CA 1070771A CA 254381 A CA254381 A CA 254381A CA 1070771 A CA1070771 A CA 1070771A
- Authority
- CA
- Canada
- Prior art keywords
- switch
- door
- switches
- oven
- circuit
- 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.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
- H01H9/20—Interlocking, locking, or latching mechanisms
- H01H9/22—Interlocking, locking, or latching mechanisms for interlocking between casing, cover, or protective shutter and mechanism for operating contacts
- H01H9/226—Interlocking, locking, or latching mechanisms for interlocking between casing, cover, or protective shutter and mechanism for operating contacts the casing containing electrical equipment other than and operated by the switch
-
- 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
Abstract
--ABSTRACT OF THE DISCLOSURE
A safety interlock system for microwave ovens com-prising first and second interconnected switches activated by the oven door. Each switch has make-and-break contacts.
The first switch interrupts the current to the microwave source when the door is opened and the second switch moni-tors the operation of the first switch. The switches are connected in series with a fuse so that a malfunction of either of the switches makes the oven immediately unusable.
A delay element is connected within one switch and the first switch is arranged to operate before the second switch when the door is initially opened.--
A safety interlock system for microwave ovens com-prising first and second interconnected switches activated by the oven door. Each switch has make-and-break contacts.
The first switch interrupts the current to the microwave source when the door is opened and the second switch moni-tors the operation of the first switch. The switches are connected in series with a fuse so that a malfunction of either of the switches makes the oven immediately unusable.
A delay element is connected within one switch and the first switch is arranged to operate before the second switch when the door is initially opened.--
Description
'H~ ~8?-3 Mels/L0 ~7~'7~ 3-5-]~76 "A sa~ety a:rrangement for microwave o~ens".
The inven-tion relates to a safety arrangement in microwave ovens compr:is:ing a first switch contro].led by the oven door and adaptecl to interrupt the current supply to the microwave generator of the oven at the openi~g of the door and a second, moni-toring swi-tch also controlled by the door and adapted to monitor the function of the first switch, both switches having the shape of make-and-break contacts, the ~ixed contact elelne/lts af which are mutually interconnected in such manner that a current path between the movable contact elemeIlts only arises, when the two switches assume different positions, a c;o called "landing swltch~ circui.t, i..e. one switch assu,mes the position it has whcn the door i9 closed and the second switch assumes the position it has when the door is open or vice versa, and the movable contact elements o~ which are included in a current path, com-pri.sing a circuit element, which, when the said current path is closed, makes the oven unusable.
When using such a sa:~ety arrangement the oven is made unusable as soon as arly of -the switches sticks in the one or the other position. The two swi.tches therefore can be regarded as monitoring each other, i.e. the first switch, which in reality is the monitored switch, will at -the same time monitor the second switch, which is added only for the purpose to monitor the first switch.
rthermore there is often at leas-t one further .
~.
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switch (micro-switch), which indirectly interrupts the genera-tion of microwave energy as soon as the oven door is opened.
Safety authorities require or will require that if one of the switches, used for interrupting the current supply to the microwave generator in dependence upon the opening of the door, is out of function the oven shall be made unusable within one second after the beginning of the opening of the door. With the expression "made unusable" is then meant that it shall not be possible to put the oven into function without help of a serviceman, who then also repairs the primary cause to the malfunction, i.e. replaces the faulty switch.
In the safety arrangement in the introduction, with a first switch in the shape of a make-and-break contact for interrupting the current supply to the microwave generator and a second switch also in the shape of a make-and-break contact for monitoring the first switch, which switches are inter-connected so as to form a circuit of the "landing switch" type, which is connected to a circuit element for making the oven unusable if the current path through the said "landing switch"
circuit is closed it is a probLem that it is difficult in practice to avoid that the said "landing switch" circuit is closed for a short while during opening and closing of the door, even if both switches Eunction properly. Closing of the said path will namely as mentioned take place as soon as the two switches assume different positions. The only way to bring about that there will be no closing of the current path containing the circuit element, which makes the oven unusable, thus will be to ensure that the two switches function exactly in the same moment at the . ~,...
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opening and the closing of the door. This, however, is impossible to achieve in practice. Consequently there will always be a short exitation of the said circuit element at the opening and the closing of the door even when the two switches function properly. The length of this exitation will be dependent upon the speed of the door motion and thus the time of exitation of the said element, which makes the oven unusable, can be extended in case of a slow door motion.
Now, if the activation time for the said circuit element is made so short that the arrangement fulfills the safety requirements it may happen, if no special measures ~ , were taken, that the said element is also activated by the exitation, which is caused by properly functioning switches at a slow door motion. Say for example that the said element is adjusted so as to function and make the oven unusable within 0.2 - 0.5 seconds after the beginning of the opening ;~
of the door in case of a real error on the switches. In order to achieve that the oven is not made unusable unintentionally in case of properly functioning switches at a slow door motion it then must be ensured that the difference between the time moments, when the two switches function at the opening and closing of the door, under no circumstances can amount to 0.2 - 0.5 seconds. This may be difficult to achieve and con-sequently it may happen that the oven is made unusab~le even in case of functioning switches.
~7~7~
According to the present invention there is provided a safety interlock arrangement for a microwave oven having a door and a microwave generator, comprising a first switch controlled by the oven door and connected to interrupt the current supply circuit to the microwave generator of the oven upon opening of the door, a second monitoring switch also controlled by the oven door and connected to monitor the operation of the first switch, both switches having make-and-break contacts with fixed contact elements thereof mutually interconnected to form a "landing switch" circuit in which a current path between the movable contact elements of the switches only arises when the two switches assume different relative positions, said switches each having predetermined first and second positions when the door is closed and when the door is open respectively, means connecting the movable contact elements of the switches in a current path including a circuit control element which, when the said current path is closed, makes the oven unusable, the two switches being arranged so that the first switch operates before the second monitoring switch upon the opening of the door, and a delay means for delaying activation of said circuit control element and included in an internal branch of the "landing switch" circuit leading to that fixed contact element in the first switch which comes in contact with the movable contact element thereof when the door is open.
By the invention it is thus intentionally ensured that the current path through the "landing switchl' circuit .
is momentarily closed during opening and closing of the door, but this always in a special way, namely through the branch :
leading to the make contact (at the opening of the door) in ~ -5-~L~7~q7~
the first swi-tch, in which the delay means is included, Hereby the circuit element, which makes the oven unusable, will be delayed and will not have time to react for the short lasting excitation through the delay means, which takes place when both switches function properly and the door is opened.
In the contrary i-f the first switch sticks in the ~ , position it shall have, when the door is clo,sed, in which it delivers supply voltage to the microwave generator, which is the only really dangerous condition to be monitored, the delay means will not be effective because the current path , ~. .. .
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~' ' '., ~ . ~ ,' '.
~ -5a-~ ' ' ' ~ , ~ P~IN 8223 ~ 7 7 ~ 3-5~76 then will be closed through -the second branch in the "landing swLtch" circuit, wh:ich leads to the brealc contact in the first switch (a-t the opening of the door) not containing any delay means. Thus the circuit elemen-t which makes the oven unusable, will in this case be excited without delay.
By the invention thus the safety arrangenlent can be brought to functioll for mak-ing the oven unusable rapidly in case of faulty switch without risk that -the oven is rnade unusable unintentionally due to slow door motion.
The invention is illustrated in the accompanying drawings, in which shows a e:ircuit cliagram for a Isnown switch failure monitoring device, which is bas:ic for the arrangement aceorcling to the invention, fi~_~ shows a perspective view of an oven provided with door switches, which are arranged in accordance with the invention, ~ and fig ~ shows a colnplete circuit diagram for a microwave oven with a safe-ty arrangement accordiMg to the invention.
F:ig 1 shows a sw:l-tch failure monitoring ~evice as described in D~IEW (US Department of Health, Education and Welfare) publication No. (FDA) 72-~0~1 of May, 1972. In fig 1- RE1 is a power relay having a first contact S1 ~Thich is normally closed and a second contact S5 which is normally open., RE2 is a -time-delay relay having a contact S4 which ., ~C~741 773~ ;
is normally open and S3, S2 are switches operated by the oven door. The switches S3 and S2 have both the shape of make-and-break contacts and are shown in the position they have when ~he door is closed. Relay contact Sl and the switch S3 ~the break contact part of the same) are arranged in the supply line from the mains to the load B. The switch S2 is a monitoring switch for monitoring the function of S3. The fixed contact elements in switches S2 and S3 are interconnected in such manner that the current path between their movable 10 contact elements will be closed only when the switches assume ;
different positions~ so called "landing switch" circuit.
This "landing switch" circuit is connected in series with the relay RE2 across the mains supply. Contact S~ of relay RE2 is connected in series with relay REl or energizing this relay REl in response to energization of RE2 and contact S5 is a holding current contact for REl.
The function is as follows.
In normal operation both relays REl and RE2 are non-energized and contact Sl is closed. Mains supply voltage can be fed to the load B through Sl and S3, if the door is closed and S3 assumes the shown position. When the door is opened ~-switch S3 will interrupt the current supply to the load but no actuation of relay RE2 will take place, because there is no current path through S2, S3 in any condition of the door.
The switches S2, S3 are mechanically so adjusted that they are actuated at approximately the same time~ whereby there ~7V77~
will substantially neither be any e~citation of the relay RE2 during the closing and opening o the door.
However, if any of the switches S2, S3 sticks in the one or the other position the current path through S2, S3 will be closed at opening or closing of the door, whereby relay RB2 is energized. Contact S~ closes and en~ergizes the relay REl, which is kept energized via contact S5. When REl is actuated contact Sl is opened and no voltage can be supplied to the load B. Thus, if either of the switches S3 or S2 fails to function normally the described arrangement will render the system inoperative until the cause of the failure is corrected.
Figure 2 shows a simplified perspective view of a micro-wave oven, which comprises door switches included in a safety arrangement according to the invention. In Figure 2 His an oven envelope, K is an oven cavity, D is an oven door and S13 and S12 are switches actuated by the door. The actuation of the S13, S12 takes place via an actuating arm A, which is attached ~ ;
to the door. S13 is a switch, which interrupts the current supply to the microwave source at the opening of the door and corresponds to S3 in Figure 1. S12 is a monitoring switch and corresponds to S2 in Figure 1. According to the invention the door switch arrangement is such that S13 is always activated before S12 at the opening of the door, which is schematically indicated in Figure 2 thereby that the actuating surface al3 for the switch S13 on the actuating arm A is at a lower level , ~6~7~77~
than the corresponding actuating sur~ace al2 for the switch S12 .
Fig. 3 shows a complete circuit diagram for a micro-wave oven provided with a safety arrangement according to the invention. In Fig. 3 reference numeral 2 designates a magnetron, which is supplied with voltage from the mains via relay switches S8, Sll actuated by a relay RE7 and the said door switch S13. Both switches S13 and S12 are make-and-break contacts and generally arranged in the same manner as S3 and S2 in Fig. 1 ("landing switch" circuit). Contacts S8, Sll are normally open and brought to close by actuation of the relay RE7. Relay RE7 i5 energized through a start switch S6, a door switch S14 and a device represented by the block 1, which i.e.
comprises a timer. The relay RE7 furthermore has a normally open contact S10 which is a self--holding contact for RE7 and a normally closed contact S9. The contact S9 is arranged in series with a buzzer RE4 and a time circuit 3, which i~
adapted to bring the buzzer to emit sound a short time after the pre-set heating time has elapsed. LA5 is a lamp which indicates that heating goes on.
According to the invention a resistance R15, which can be a temperature dependent resistor with negative tempera-ture coefficient (NTC), is connected in one o -the internal branches in the "landing switch" circuit S12, S13, namely in that branch which leads to the make contact (at the opening of the door) of S13. This door operated "landing switch" circuit S13, R15, S12 is connected across the mains supply in series , 7~
with a second temperature dependent resistance R16 and a fuse VL17, which fuse also lies in the excita~ion path for the relay RE7. R16 prevents short-circuiting of the mains supply via the fuse.
The function is as follows.
The oven is started by closing contact S6, whereby relay RE7 is energized and kept energized through contact S10. Magnetron 2 gets supply voltage via door switch S13 and relay contacts S8l Sll. When the pre-set time has elapsed heating is terminated thereby that the timer 1 de-energizes relay RE7. Should the oven door be opened, while supply voltage is still fed to the magnetron, switch S13 will interrupt the current supply to the magnetron.
In normal operation of the door switches S12, S13 the switch S13 will as mentioned always function before S12 at the opening o the door, so that the movable contact element in S13 or a short moment will assume the opposite position as compared with the one shown, while S12 is still in the shown position. At the closing of the door switch S12 will return to the shown position, while S13 is still in the opposite position. In both cases a current path will be closed momentarily in the "landing switch"
circuit, which path comprises the NTC-resistance R15. During this short time of closing in S12, S13 the fuse VL17 gets voltage viaR~ and ~6. By the fact tha~ both resistances R15 and R16 are connected in series with VL17 it will take a relatively long time, 1 10 seconds, preferably 2-3 seconds, before the fuse is burnt-off. This will minimize the risk for burning of the fuse at normal operation of the switches.
~n the contrary if for example S13 got stuck in the shown position, in which it delivers voltage ~o the magnetron and which is the only really dangerous condition, a current path is colsed in the "landing switch" circuit at the opening o the door through that branch, which com-prises no resistance. The fuse VL17 gets voltage through R16 alone and will be burnt-off within a timeS which is shorter than 0.5 seconds, preferably 0.2 to 0.3 seconds, as counted from the beginning of the opening of the door. When the fuse VL17 is burnt-off the relay RE7 is deenergized -10- : .
' ~ ' ~ 7~3~77~
and the voltage supply to the magnetron is stopped via the relay contacts ~-S8, and Sll. If S12 gets stuck in the opposite position than the shown ~non- !
dangerous) the same will happen at the closing of the door. If S12 gets stuck -in the shown position or S13 in the opposite position (both cases non-dangerous) the fuse VL17 will get voltage via R15 and R16 in series, so that it will be burn-t-off after a time delay at the opening and closing respectively of the door.
Thus, by the described arrangement if any of the switches S12 or S13 is faulty~ the oven is made inoperative, in the dangerous case without delay at the opening of the door, and cannot be started again unless the fuse and the defective switch is replaced. Furthermore the glow lamp LA5 receives voltage through RE7 - R16 - S12/S13~and emits light also when the door is open, which is a warning. At the same time block 3 is activated through RE7 -R16 S12/I3 which involves that the buzzer RE4 emits sound as soon as S14 is closed (= the door is closed). This is also a warning. If the starting knob S6 is pushed down with the door closed the lamp LA5 will emit light and the block 3 is activated through the block 1-S14-S6.
The buzzer will also emit sound as a current path through RE4 is formed (the block l-S14-S9-Rfi4-the block 3). Also this is a warning.
In order to achieve desired delay a temperature independent re-sistance R18 can be arranged in series with the temperature dependent re-sistance R16. It is also possible to connect several temperature dependent resistances in series for the same purpose.
Instead of a fuse also other current circuit elements with a corresponding function may be used, for example relays, switching units with semi-conductors, as thyristors or the like. The switch S14 may possibly be omitted and the current supply to the relay coil be interrupted by the first switch (S13). Alternatively the said switch S14 which interrupts the current to the relay coil> can instead be supervised and combined with a supervision switch (corresponding to S12) in described manner. Of course, also both switches S13 and S14 can be supervised by special switches, as S12.
The inven-tion relates to a safety arrangement in microwave ovens compr:is:ing a first switch contro].led by the oven door and adaptecl to interrupt the current supply to the microwave generator of the oven at the openi~g of the door and a second, moni-toring swi-tch also controlled by the door and adapted to monitor the function of the first switch, both switches having the shape of make-and-break contacts, the ~ixed contact elelne/lts af which are mutually interconnected in such manner that a current path between the movable contact elemeIlts only arises, when the two switches assume different positions, a c;o called "landing swltch~ circui.t, i..e. one switch assu,mes the position it has whcn the door i9 closed and the second switch assumes the position it has when the door is open or vice versa, and the movable contact elements o~ which are included in a current path, com-pri.sing a circuit element, which, when the said current path is closed, makes the oven unusable.
When using such a sa:~ety arrangement the oven is made unusable as soon as arly of -the switches sticks in the one or the other position. The two swi.tches therefore can be regarded as monitoring each other, i.e. the first switch, which in reality is the monitored switch, will at -the same time monitor the second switch, which is added only for the purpose to monitor the first switch.
rthermore there is often at leas-t one further .
~.
~Q~7~37~7~
switch (micro-switch), which indirectly interrupts the genera-tion of microwave energy as soon as the oven door is opened.
Safety authorities require or will require that if one of the switches, used for interrupting the current supply to the microwave generator in dependence upon the opening of the door, is out of function the oven shall be made unusable within one second after the beginning of the opening of the door. With the expression "made unusable" is then meant that it shall not be possible to put the oven into function without help of a serviceman, who then also repairs the primary cause to the malfunction, i.e. replaces the faulty switch.
In the safety arrangement in the introduction, with a first switch in the shape of a make-and-break contact for interrupting the current supply to the microwave generator and a second switch also in the shape of a make-and-break contact for monitoring the first switch, which switches are inter-connected so as to form a circuit of the "landing switch" type, which is connected to a circuit element for making the oven unusable if the current path through the said "landing switch"
circuit is closed it is a probLem that it is difficult in practice to avoid that the said "landing switch" circuit is closed for a short while during opening and closing of the door, even if both switches Eunction properly. Closing of the said path will namely as mentioned take place as soon as the two switches assume different positions. The only way to bring about that there will be no closing of the current path containing the circuit element, which makes the oven unusable, thus will be to ensure that the two switches function exactly in the same moment at the . ~,...
, .
~7~77~
opening and the closing of the door. This, however, is impossible to achieve in practice. Consequently there will always be a short exitation of the said circuit element at the opening and the closing of the door even when the two switches function properly. The length of this exitation will be dependent upon the speed of the door motion and thus the time of exitation of the said element, which makes the oven unusable, can be extended in case of a slow door motion.
Now, if the activation time for the said circuit element is made so short that the arrangement fulfills the safety requirements it may happen, if no special measures ~ , were taken, that the said element is also activated by the exitation, which is caused by properly functioning switches at a slow door motion. Say for example that the said element is adjusted so as to function and make the oven unusable within 0.2 - 0.5 seconds after the beginning of the opening ;~
of the door in case of a real error on the switches. In order to achieve that the oven is not made unusable unintentionally in case of properly functioning switches at a slow door motion it then must be ensured that the difference between the time moments, when the two switches function at the opening and closing of the door, under no circumstances can amount to 0.2 - 0.5 seconds. This may be difficult to achieve and con-sequently it may happen that the oven is made unusab~le even in case of functioning switches.
~7~7~
According to the present invention there is provided a safety interlock arrangement for a microwave oven having a door and a microwave generator, comprising a first switch controlled by the oven door and connected to interrupt the current supply circuit to the microwave generator of the oven upon opening of the door, a second monitoring switch also controlled by the oven door and connected to monitor the operation of the first switch, both switches having make-and-break contacts with fixed contact elements thereof mutually interconnected to form a "landing switch" circuit in which a current path between the movable contact elements of the switches only arises when the two switches assume different relative positions, said switches each having predetermined first and second positions when the door is closed and when the door is open respectively, means connecting the movable contact elements of the switches in a current path including a circuit control element which, when the said current path is closed, makes the oven unusable, the two switches being arranged so that the first switch operates before the second monitoring switch upon the opening of the door, and a delay means for delaying activation of said circuit control element and included in an internal branch of the "landing switch" circuit leading to that fixed contact element in the first switch which comes in contact with the movable contact element thereof when the door is open.
By the invention it is thus intentionally ensured that the current path through the "landing switchl' circuit .
is momentarily closed during opening and closing of the door, but this always in a special way, namely through the branch :
leading to the make contact (at the opening of the door) in ~ -5-~L~7~q7~
the first swi-tch, in which the delay means is included, Hereby the circuit element, which makes the oven unusable, will be delayed and will not have time to react for the short lasting excitation through the delay means, which takes place when both switches function properly and the door is opened.
In the contrary i-f the first switch sticks in the ~ , position it shall have, when the door is clo,sed, in which it delivers supply voltage to the microwave generator, which is the only really dangerous condition to be monitored, the delay means will not be effective because the current path , ~. .. .
' ''"' "
: ' ."
. ~, .
~' ' '., ~ . ~ ,' '.
~ -5a-~ ' ' ' ~ , ~ P~IN 8223 ~ 7 7 ~ 3-5~76 then will be closed through -the second branch in the "landing swLtch" circuit, wh:ich leads to the brealc contact in the first switch (a-t the opening of the door) not containing any delay means. Thus the circuit elemen-t which makes the oven unusable, will in this case be excited without delay.
By the invention thus the safety arrangenlent can be brought to functioll for mak-ing the oven unusable rapidly in case of faulty switch without risk that -the oven is rnade unusable unintentionally due to slow door motion.
The invention is illustrated in the accompanying drawings, in which shows a e:ircuit cliagram for a Isnown switch failure monitoring device, which is bas:ic for the arrangement aceorcling to the invention, fi~_~ shows a perspective view of an oven provided with door switches, which are arranged in accordance with the invention, ~ and fig ~ shows a colnplete circuit diagram for a microwave oven with a safe-ty arrangement accordiMg to the invention.
F:ig 1 shows a sw:l-tch failure monitoring ~evice as described in D~IEW (US Department of Health, Education and Welfare) publication No. (FDA) 72-~0~1 of May, 1972. In fig 1- RE1 is a power relay having a first contact S1 ~Thich is normally closed and a second contact S5 which is normally open., RE2 is a -time-delay relay having a contact S4 which ., ~C~741 773~ ;
is normally open and S3, S2 are switches operated by the oven door. The switches S3 and S2 have both the shape of make-and-break contacts and are shown in the position they have when ~he door is closed. Relay contact Sl and the switch S3 ~the break contact part of the same) are arranged in the supply line from the mains to the load B. The switch S2 is a monitoring switch for monitoring the function of S3. The fixed contact elements in switches S2 and S3 are interconnected in such manner that the current path between their movable 10 contact elements will be closed only when the switches assume ;
different positions~ so called "landing switch" circuit.
This "landing switch" circuit is connected in series with the relay RE2 across the mains supply. Contact S~ of relay RE2 is connected in series with relay REl or energizing this relay REl in response to energization of RE2 and contact S5 is a holding current contact for REl.
The function is as follows.
In normal operation both relays REl and RE2 are non-energized and contact Sl is closed. Mains supply voltage can be fed to the load B through Sl and S3, if the door is closed and S3 assumes the shown position. When the door is opened ~-switch S3 will interrupt the current supply to the load but no actuation of relay RE2 will take place, because there is no current path through S2, S3 in any condition of the door.
The switches S2, S3 are mechanically so adjusted that they are actuated at approximately the same time~ whereby there ~7V77~
will substantially neither be any e~citation of the relay RE2 during the closing and opening o the door.
However, if any of the switches S2, S3 sticks in the one or the other position the current path through S2, S3 will be closed at opening or closing of the door, whereby relay RB2 is energized. Contact S~ closes and en~ergizes the relay REl, which is kept energized via contact S5. When REl is actuated contact Sl is opened and no voltage can be supplied to the load B. Thus, if either of the switches S3 or S2 fails to function normally the described arrangement will render the system inoperative until the cause of the failure is corrected.
Figure 2 shows a simplified perspective view of a micro-wave oven, which comprises door switches included in a safety arrangement according to the invention. In Figure 2 His an oven envelope, K is an oven cavity, D is an oven door and S13 and S12 are switches actuated by the door. The actuation of the S13, S12 takes place via an actuating arm A, which is attached ~ ;
to the door. S13 is a switch, which interrupts the current supply to the microwave source at the opening of the door and corresponds to S3 in Figure 1. S12 is a monitoring switch and corresponds to S2 in Figure 1. According to the invention the door switch arrangement is such that S13 is always activated before S12 at the opening of the door, which is schematically indicated in Figure 2 thereby that the actuating surface al3 for the switch S13 on the actuating arm A is at a lower level , ~6~7~77~
than the corresponding actuating sur~ace al2 for the switch S12 .
Fig. 3 shows a complete circuit diagram for a micro-wave oven provided with a safety arrangement according to the invention. In Fig. 3 reference numeral 2 designates a magnetron, which is supplied with voltage from the mains via relay switches S8, Sll actuated by a relay RE7 and the said door switch S13. Both switches S13 and S12 are make-and-break contacts and generally arranged in the same manner as S3 and S2 in Fig. 1 ("landing switch" circuit). Contacts S8, Sll are normally open and brought to close by actuation of the relay RE7. Relay RE7 i5 energized through a start switch S6, a door switch S14 and a device represented by the block 1, which i.e.
comprises a timer. The relay RE7 furthermore has a normally open contact S10 which is a self--holding contact for RE7 and a normally closed contact S9. The contact S9 is arranged in series with a buzzer RE4 and a time circuit 3, which i~
adapted to bring the buzzer to emit sound a short time after the pre-set heating time has elapsed. LA5 is a lamp which indicates that heating goes on.
According to the invention a resistance R15, which can be a temperature dependent resistor with negative tempera-ture coefficient (NTC), is connected in one o -the internal branches in the "landing switch" circuit S12, S13, namely in that branch which leads to the make contact (at the opening of the door) of S13. This door operated "landing switch" circuit S13, R15, S12 is connected across the mains supply in series , 7~
with a second temperature dependent resistance R16 and a fuse VL17, which fuse also lies in the excita~ion path for the relay RE7. R16 prevents short-circuiting of the mains supply via the fuse.
The function is as follows.
The oven is started by closing contact S6, whereby relay RE7 is energized and kept energized through contact S10. Magnetron 2 gets supply voltage via door switch S13 and relay contacts S8l Sll. When the pre-set time has elapsed heating is terminated thereby that the timer 1 de-energizes relay RE7. Should the oven door be opened, while supply voltage is still fed to the magnetron, switch S13 will interrupt the current supply to the magnetron.
In normal operation of the door switches S12, S13 the switch S13 will as mentioned always function before S12 at the opening o the door, so that the movable contact element in S13 or a short moment will assume the opposite position as compared with the one shown, while S12 is still in the shown position. At the closing of the door switch S12 will return to the shown position, while S13 is still in the opposite position. In both cases a current path will be closed momentarily in the "landing switch"
circuit, which path comprises the NTC-resistance R15. During this short time of closing in S12, S13 the fuse VL17 gets voltage viaR~ and ~6. By the fact tha~ both resistances R15 and R16 are connected in series with VL17 it will take a relatively long time, 1 10 seconds, preferably 2-3 seconds, before the fuse is burnt-off. This will minimize the risk for burning of the fuse at normal operation of the switches.
~n the contrary if for example S13 got stuck in the shown position, in which it delivers voltage ~o the magnetron and which is the only really dangerous condition, a current path is colsed in the "landing switch" circuit at the opening o the door through that branch, which com-prises no resistance. The fuse VL17 gets voltage through R16 alone and will be burnt-off within a timeS which is shorter than 0.5 seconds, preferably 0.2 to 0.3 seconds, as counted from the beginning of the opening of the door. When the fuse VL17 is burnt-off the relay RE7 is deenergized -10- : .
' ~ ' ~ 7~3~77~
and the voltage supply to the magnetron is stopped via the relay contacts ~-S8, and Sll. If S12 gets stuck in the opposite position than the shown ~non- !
dangerous) the same will happen at the closing of the door. If S12 gets stuck -in the shown position or S13 in the opposite position (both cases non-dangerous) the fuse VL17 will get voltage via R15 and R16 in series, so that it will be burn-t-off after a time delay at the opening and closing respectively of the door.
Thus, by the described arrangement if any of the switches S12 or S13 is faulty~ the oven is made inoperative, in the dangerous case without delay at the opening of the door, and cannot be started again unless the fuse and the defective switch is replaced. Furthermore the glow lamp LA5 receives voltage through RE7 - R16 - S12/S13~and emits light also when the door is open, which is a warning. At the same time block 3 is activated through RE7 -R16 S12/I3 which involves that the buzzer RE4 emits sound as soon as S14 is closed (= the door is closed). This is also a warning. If the starting knob S6 is pushed down with the door closed the lamp LA5 will emit light and the block 3 is activated through the block 1-S14-S6.
The buzzer will also emit sound as a current path through RE4 is formed (the block l-S14-S9-Rfi4-the block 3). Also this is a warning.
In order to achieve desired delay a temperature independent re-sistance R18 can be arranged in series with the temperature dependent re-sistance R16. It is also possible to connect several temperature dependent resistances in series for the same purpose.
Instead of a fuse also other current circuit elements with a corresponding function may be used, for example relays, switching units with semi-conductors, as thyristors or the like. The switch S14 may possibly be omitted and the current supply to the relay coil be interrupted by the first switch (S13). Alternatively the said switch S14 which interrupts the current to the relay coil> can instead be supervised and combined with a supervision switch (corresponding to S12) in described manner. Of course, also both switches S13 and S14 can be supervised by special switches, as S12.
Claims (7)
- Claim 1.
A safety interlock arrangement for a microwave oven having a door and a microwave generator, comprising a first switch controlled by the oven door and connected to interrupt the current supply circuit to the microwave ge-nerator of the oven upon opening of the door, a second moni-toring switch also controlled by the oven door and connected to monitor the operation of the first switch, both switches having make-and-break contacts with fixed contact elements thereof mutually interconnected to form a "landing switch" circuit in which a current path between the movable contact elements of the switches only arises when the two switches assume different relative positions, said switches each having pre-determined first and second positions when the door is closed and when the door is open respectively, means connecting the movable contact elements of the switches in a current path including a circuit control element which, when the said cur-rent path is closed, makes the oven unusable, the two switches being arranged so that the first switch operates before the second monitoring switch upon the opening of the door, and a delay means for delaying activation of said circuit con-trol element and included in an internal branch of the "landing switch" circuit leading to that fixed contact element in the first switch which comes in contact with the movable contact element thereof when the door is open. - Claim 2.
A safety interlock arrangement as claimed in claim 1 wherein said delay means comprises a negative temperature dependent resistor. - Claim 3.
A safety interlock arrangement as claimed in claim 1 further comprising a temperature dependent resistor included in the common branch of said current path that includes the two switches and said circuit control element. - Claim 4.
A safety interlock arrangement as claimed in claim 1 wherein the current supply circuit of the microwave generator further comprises a relay contact of an electro-magnet which in the operative condition of the microwave generator is kept closed by said electromagnet , a third door operated switch connected to keep the current supply circuit of the electromagnet closed in the closed position of the oven door and to interrupt a holding current path for the electromagnet upon opening of the door, and means further connecting said circuit control element in the holding current path for the electromagnet thereby to inter-rupt the holding circuit of the electromagnet when said cir-cuit control element is activated. - Claim 5.
A safety interlock arrangement as claimed in claim 4 wherein one terminal of said current path including the two switches and the circuit control element is connected to one pole of a supply current source for the oven and a second terminal thereof is connected to a junction point between the electromagnet winding and one terminal of said circuit control element, and means connecting the other terminal of the circuit control element to the second pole of the supply current source. - Claim 6.
A safety interlock arrangement as claimed in claim 1 wherein said circuit control element is a fuse. - Claim 7.
A safety interlock arrangement as claimed in claim 1 wherein the movable contacts of said first and second switches contact the respective break and make contacts thereof in the closed and open positions of the oven door, respectively, and said delay means interconnects the make-and-break contacts of the first and second switches, respectively, and means connecting the movable contact of the first switch to a terminal of the oven supply current source, the break contact of the first switch to the microwave generator current supply circuit, and the movable contact of the second switch to said circuit control element.
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7506751A SE391391B (en) | 1975-06-12 | 1975-06-12 | MICROWAVE SAFETY DEVICE INCLUDING AN POWER SWITCH CONTROLLED BY THE OVEN DOOR |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1070771A true CA1070771A (en) | 1980-01-29 |
Family
ID=20324855
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA254,381A Expired CA1070771A (en) | 1975-06-12 | 1976-06-09 | Safety inter-locking arrangement for microwave oven door |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4117294A (en) |
| JP (1) | JPS527048A (en) |
| CA (1) | CA1070771A (en) |
| DE (1) | DE2625477C3 (en) |
| FR (1) | FR2314606A1 (en) |
| GB (1) | GB1530676A (en) |
| SE (1) | SE391391B (en) |
Families Citing this family (32)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS549037A (en) * | 1977-06-22 | 1979-01-23 | Toshiba Corp | Output contoller circuit for electronic range |
| JPS6015041Y2 (en) * | 1977-07-20 | 1985-05-13 | 松下電器産業株式会社 | High frequency heating device |
| JPS6314246Y2 (en) * | 1979-07-26 | 1988-04-21 | ||
| CA1137174A (en) * | 1978-12-19 | 1982-12-07 | Keiichiro Doi | Error alarm system in a microwave oven |
| DE2941338A1 (en) * | 1979-10-12 | 1981-05-07 | Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt | Safety circuit for microwave oven - has fuse in series with relay coil and resistor |
| EP0105054B1 (en) * | 1982-10-01 | 1987-02-04 | Square D Starkstrom GmbH | Circuit for the active control of limit switches arranged in pairs |
| DE3244675A1 (en) * | 1982-12-02 | 1984-06-07 | Bosch-Siemens Hausgeräte GmbH, 7000 Stuttgart | Monitoring device for a protection device |
| DE3337141A1 (en) * | 1983-10-12 | 1985-04-25 | Bosch-Siemens Hausgeräte GmbH, 7000 Stuttgart | Safety device for a microwave oven |
| JPH0317150Y2 (en) * | 1985-02-15 | 1991-04-11 | ||
| FR2595179B1 (en) * | 1986-02-28 | 1988-05-06 | Labo Electronique Physique | MICROWAVE OVEN PROVIDED WITH CONTROL MEANS REDUCING THE RISK OF LOAD-FREE OPERATION |
| JPH03283384A (en) * | 1990-03-30 | 1991-12-13 | Toshiba Corp | Power circuit for microwave oven |
| DE4023280C2 (en) * | 1990-07-21 | 1995-06-14 | Miele & Cie | Safety device for microwave ovens |
| US5780792A (en) * | 1996-06-21 | 1998-07-14 | Amana Company L.P. | Interlock switch for appliances |
| FR2767615B1 (en) * | 1997-08-22 | 2000-02-04 | Legrand Sa | ELECTRONIC COMPLIANCE MOUNTING |
| US6396239B1 (en) * | 2001-04-06 | 2002-05-28 | William M. Benn | Portable solar generator |
| US20050236408A1 (en) * | 2004-04-08 | 2005-10-27 | Maytag Corporation | Door position sensing system for cooking appliance including combination heating system |
| US7009147B1 (en) | 2005-01-12 | 2006-03-07 | Maytag Corporation | Operational modes for a cooking appliance employing combination cooking technology |
| KR101484945B1 (en) * | 2008-12-04 | 2015-01-22 | 삼성전자 주식회사 | Microwave oven |
| US20130008895A1 (en) * | 2011-07-06 | 2013-01-10 | General Electric Company | Double line break |
| US20160116171A1 (en) * | 2014-10-22 | 2016-04-28 | General Electric Company | Oven airflow control |
| US10085592B1 (en) | 2015-09-10 | 2018-10-02 | Brava Home, Inc. | Sequential broiling |
| US11388788B2 (en) | 2015-09-10 | 2022-07-12 | Brava Home, Inc. | In-oven camera and computer vision systems and methods |
| AU2016321324B2 (en) | 2015-09-10 | 2022-06-02 | Brava Home, Inc. | In-oven camera |
| US10064244B2 (en) | 2015-09-10 | 2018-08-28 | Brava Home, Inc. | Variable peak wavelength cooking instrument with support tray |
| US11156366B2 (en) | 2015-09-10 | 2021-10-26 | Brava Home, Inc. | Dynamic heat adjustment of a spectral power distribution configurable cooking instrument |
| CN105785879A (en) * | 2016-04-29 | 2016-07-20 | 佛山市顺德区美的洗涤电器制造有限公司 | Door switch circuit used for household appliances and the household appliances |
| US10223933B1 (en) | 2017-08-09 | 2019-03-05 | Brava Home, Inc. | Multizone cooking utilizing a spectral-configurable cooking instrument |
| WO2019033089A1 (en) | 2017-08-11 | 2019-02-14 | Brava Home, Inc. | Configurable cooking systems and methods |
| CN111587609B (en) * | 2017-11-06 | 2023-01-06 | 布拉瓦家居公司 | Spectral power density configuration in a cooking appliance |
| US11206949B1 (en) | 2017-11-15 | 2021-12-28 | Brava Home, Inc. | High power density toaster |
| US11422037B2 (en) | 2018-03-15 | 2022-08-23 | Brava Home, Inc. | Temperature probe systems and methods |
| US10502430B1 (en) * | 2018-10-10 | 2019-12-10 | Brava Home, Inc. | Particulates detection in a cooking instrument |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1133050B (en) * | 1960-08-04 | 1962-07-12 | Siemens Elektrogeraete Gmbh | RF radiation focus |
| US3211871A (en) * | 1962-12-26 | 1965-10-12 | North American Aviation Inc | Control device with switches actuated by cams defining a helical trace |
| DE1515171A1 (en) * | 1964-10-01 | 1969-06-19 | Siemens Elektrogeraete Gmbh | HF radiation stove with a device to prevent HF radiation when the oven door is open |
| US3624334A (en) * | 1970-04-01 | 1971-11-30 | Sage Laboratories | Interlock circuitry for microwave oven |
| US3699300A (en) * | 1971-11-30 | 1972-10-17 | Norris Industries | System for detecting safety switch failure |
| US3766437A (en) * | 1972-04-03 | 1973-10-16 | Amana Refrigeration Inc | Safety interlock system for microwave ovens |
| SE363463B (en) * | 1972-09-27 | 1974-01-14 | Husqvarna Vapenfabriks Ab | |
| US3857067A (en) * | 1972-12-13 | 1974-12-24 | Department Of Health Education | Switch failure monitoring device |
| US3829809A (en) * | 1973-03-26 | 1974-08-13 | Micro Devices Corp | Thermal limiter construction and electrical switch and system utilizing the same |
-
1975
- 1975-06-12 SE SE7506751A patent/SE391391B/en not_active IP Right Cessation
-
1976
- 1976-06-05 DE DE2625477A patent/DE2625477C3/en not_active Expired
- 1976-06-08 US US05/693,944 patent/US4117294A/en not_active Expired - Lifetime
- 1976-06-09 CA CA254,381A patent/CA1070771A/en not_active Expired
- 1976-06-09 GB GB23884/76A patent/GB1530676A/en not_active Expired
- 1976-06-09 JP JP51066647A patent/JPS527048A/en active Granted
- 1976-06-11 FR FR7617669A patent/FR2314606A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| DE2625477C3 (en) | 1980-01-24 |
| FR2314606B1 (en) | 1982-02-12 |
| JPS527048A (en) | 1977-01-19 |
| SE391391B (en) | 1977-02-14 |
| DE2625477B2 (en) | 1979-05-10 |
| GB1530676A (en) | 1978-11-01 |
| DE2625477A1 (en) | 1976-12-23 |
| JPS5734635B2 (en) | 1982-07-23 |
| FR2314606A1 (en) | 1977-01-07 |
| SE7506751L (en) | 1976-12-13 |
| US4117294A (en) | 1978-09-26 |
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Legal Events
| Date | Code | Title | Description |
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| MKEX | Expiry |