CA1329828C - Method of determining whether power supply or magnetron has failed - Google Patents

Abstract

CONTROLLING DEVICE FOR ELECTRIC APPARATUS

Abstract The present invention relates to an apparatus and method for determining whether the power supply or the magnetron has failed in a power supply circuit for powering a magnetron. The circuit comprises a magnetron and a dual half wave doubler circuit having dual first and second circuit portions which include first and second transformers, respectively. A sensing unit is provided for sensing the magnitude of a first current flowing in the primary of the first transformer. Another sensing unit is provided for sensing the magnitude of a second current flowing in the primary of the second transformer. A comparator is provided for comparing the magnitude of the first and second currents to determine if the first current is more than a certain amount greater than the second current or is the second current is more than a certain amount greater than the first current, whereby it is determined whether the power supply has failed.

Description

This is a di~ision of copending Canadian Patent Application Serial Number 571,162 which was filed on July 5, 1988.
The present invention relates to safety means for heating apparatus for an electric oven or an electronic range having a digital control portion, or for compound ovens or the like, or for other apparatus such as a washing machine or cooler. The safety means detects errors of the input power supply voltage, and failures of the respective heating means and control means, and displays the nature of the failure and stops the electric appliance.
Present day appliances are considerable in their diversity.
In terms of heating apparatus there are single function electronic ranges, single function electric ovens, appliances intended for higher outputs by having two-high frequency generating devices mounted therein, compound appliances having both thermal heating and high-frequency heating to realize alternative or simultaneous heatlng. Accordingly, the components for use in such appliances have greatly increased in number. For example, a high-frequency heating apparatus with two high-frequency heating devices therein requires a h~gh-tension transformer, a high-tension capacitor, a magnetron and a high-tension diode, which are the function ~ ;
components, and a relay apparatus and so on ~or controlling these part~. The ~requency o~ failure o~ the ~unctional components increase~ with their number. Failure o~ the ~unctional components can cau~e abnormal currents to ~low to cause ~ire or insulation deterioration.
Al~o, more time iq taken to locate which component is out o~
order, 50 as to repair it, because the number o~ components is so large. ;
Many input voltages are provided, because o~ inter-natlonalizatlon Or the appliances. For example, slnce 208V and 230V ~re available in the same outlet in the North America area, th- wrong oonnection o~ an appliance can be made by mista~e. For xample, when the tap on the primary ~ide o~ a low-ten~ion 3g tran~ormer and a high-ten~ion trans~ormer o~ high-~requency hoatlng apparatus having a digital control portion i8 set at 208V, but the ~p~Aratus i~ connected to a power supply o~ 230V, a voltaqe that i~ higher by approximately 10% than normal is outputted ~t the seoondary side, with the disadvantage that the ~ ", ' .
',:, ,' ''; ,; ' `' ' ,. , ''' ','.',, .,,, ''''''`'~ ' )' " ' ': ` '; :,"`;', '' ' . "" , - 2 - 1329g28 service life of components of the apparatus, such as a magnetron, is considerably shortened. When the tap on the primary side is set at 230V, the high-frequency output becomes smaller than normal if a power-supply of 208V is connected to it, making the cooking time longer.
In the operation of a sheathed heater or the like the heating output varies by approximately 20% for a change of 10~ input voltage (being proportional to the square of the voltage), with the inconvenience that either the heating becomes excessi~e or the temperature does not reach the desired level. Such errors are often not found out until after use.
If the contacts of relay devices are melted due to a malfunction, the high-frequency heating may continue, whether or not desired, to produce excessive heating and dangerous conditions. The magnetron may be injured to shorten its service li~e.
The present invention has been developed with a view to substantially solving the above-described disadvantages and has ~or its essential object to provide means for quickly stopping an electrical appliance when a malfunction occurs.
Another ob;ect o~ the present invention i8 to provide in an electrlcal appliancè means ~or quickly and sa~ely stopping only th~ ~aulty ~unction, i~ the appliance has other heating functions that are operating normally and can continue to do so.
In accordance with one aspect o~ the invention there is provided in a power supply circuitry ~or powering a magnetron, a method o~ determining whether the power supply or the magnetron has ~ailed, comprising the steps o~: providing a magnetron which ie powered by a dual hal~ wave doubler c~rcuit having dual ~irst and second circuit portions including ~irst and second trans~ormers respectively; sensing the magnitude of a first current rlowing in the primary Or the ~irst trans~ormer: sensing the magnltude o~ a second current ~lowing ln the primary o~ the ~econd tran~ormer; and comparing the magnitudes Or the ~irst and 3~ ~eoond aurrents to determine i~ the ~irst current is more than a cerlain amount greater than the second current or i~ the ~econd current i8 more than a certain amount greater than the ~irst ourrent, whereby it i5 determined whether the power supply has railed . ,.

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~ n accordance with another aspect of the invention there is provided in power supply circuitry for powering a magnetron, an apparatus for determining whether the power supply or the magnetron has failed, comprising: a magnetron; a dual half wave doubler circuit for powering the magnetron, the dual half wave doubler circuit having dual first and second circuit portions including first and second transformers respectively; means for sensing the magnitude of a first current flowing in the primary of the first transformer: means for sensing the magnitude of a second current flowing in the primary of the second transformer; and means for comparing the magnitude of the first and second currents to determine if the first current is more than a certain amount greater tnan the second current or if the second current is more than a certain amount greater than the first current, whereby it is determined whether the power supply has failed.
The present invention will be described in detail hereinbelow in con~unction with the invention described in copending Canadian Patent Application Serial Number ~71,162 which was filed on July 5, 1988, with the aid of the accompanying drawings.
Like parts are designated by like reference numerals, and in which:
Fig. 1 is a block diagram o~ a heating apparatus showing a ~irst embodiment o~ the present invention:
Fig. 2 is a circuit diagram thereof;
Fig. 3 iB a ~low chart o~ a major control portion thereof;
Fig. 4 iB a sectional view o~ the body o~ a heating apparatus having a plurality o~ heating means, in a second embodiment:
Fig. 5 is a circuit diagram thereo~; and Fig. 6 i~ a ~low chart thereror.
There i5 shown in Fig, 1, a heating apparatus according to one pre~erred embodiment o~ the present invention. A keyboard 3 con~tltutlng lnput mean~ is arranged on an operation panel 2 Or a hlgh-~requency heating apparatus 1 80 that the user can instruct a contral system. Fluorescent display tube~ 23 constitute display ~ ;
3S m~an~ ror di~playing the operational instructlons ~329828 and cooking details. A main controller 4 in~ermittently controls the heating ope~ation of a magnetron 9 in accordance with the input information of the keyboard 3.
A temperature sensor 5 is mounted in an exhaust guide ll.
A voltage detecting means 7 detects the voltage of a power supply 6, and a ~urrent detecting means 8 detects the load current of the apparatus.
A fan lO cools the magnetron 9 and blows cooling air into the heating chamber, whereby to discharge the compartment heat, steam and so on through the exhaust guide ll. ' A door 12 is provided in the front opening of the apparatus 1.
Fig. 2 is a circuit diagram thereof.
Power from the AC primary power-supply 6 is fed to a irst intermittent relay 14 and a second intermittent relay 15, through a fuse 13 and a first door switch 16 which is turned on or off by closing or opening of the door 12, and into a high-tension transformer 18 through a second door switch 17.
This power is boosted to approximately 2,000V by the transformer 18, and is rectified in a voltage doubler by a high-tension capacitor l9 and a high-tension diode 20, to operate the magnetron 9. ~he power 6 is also fed into a low-tension transformer 21 that outputs a low voltage to feed power to, the controller 4 etc. The voltage detecting means 7 extracts a voltage peoportional RA ~ R at a split between a resistor RA 69 and a resi8tor ~ 70 on the secondary side of the transformer 21, inctead Oe directly mea~uring the AC primary voltage, and inputs this information into the controller 4. A
current transformer 22 acts as the current detecting means ~ ' 8 and is used to input into the contcoller 4 a voltage indicative oF the load current on the AC primary side.

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The temperature sensor 5 inputs into the controller 4 variations in a resistance value caused by temperature changes. The information from the keyboard 3 is also ~i inputted into the controller 4.
The outputs from the controller 4 are the display outputs to the flourescent display 23, and intermittent control signals to the first intermittent relay 14 and to the second intermittent relay 15.
The operation is shown in Fig. 3.
The heating method and heating time are selected by the keyboard 3 to start the heating operation (step 24), which starts the intermittent control of the relays.
~oth the first and second intermittent relays are turned on ~step 25). The input voltage is detected (step 26) by the voltage detecting means 7. The voltage value is compared with a predetermined memory value by comparing means, to determine whether or not the voltage value is within the range of 208V+10~ of the rated input voltage (step 27). I~ the voltage value is more than 10%
different from the rated input voltage, this abnormality is considered to be an input voltage error and is shown on the display 23 (step 28). Simultaneously the intermittent relays are stopped to suspend the heating operation.
The pswer-supply current is then detected by the current detecting means 8 (step 29). At this time, it is decLded whether or not the second intermittent relay 15 should be kept on ~step 30).
I~ the current value i9 larger than normal, namely 3A or more (step 31) with the second intermittent relay 15 of~, the abnormality is considered to be a melted contact, and the abnormality is shown (step 28) by the display 23 to stop both the ~irst and second intermittent relays 14 and 15 (step 32).
The Pluorescent display 23 employs a combination "'"' ,' ~"','' . .

132~28 of letters and numerals in a readily understood manner.
A comparing operation is also carried out to determine whether the current value is larger or smaller than 12A~10~ with the second intermittent relay 15 ON
(step 33). If the current ~alue is larger, the cause is considered to ~e a heater disconnection of the magnetron 9. If it is smaller, the cause is considered to be a short of the high-tension capacitor 19 (step 34). These factors are shown by the display 23 (step 28J so that the first and second intermittent relays 14 and 15 are stopped (step 32). The exhaust temperature is detected by the temperature sensor 5 (step 35) to compare such exhaust temperature with a given temperature (step 36). If the exhaust temperature is high, it is considered to be an lS abnormality in heating, which is shown (step 28) on the display 23 to stop the first and second intermittent relays 14 and 15. Things are judged to be abnormal, to stop the heating operation as described above. Thereafter when the keyboard 3 is operated to provide a given input operation (step 69) the abnormal display is released (step 70), so that the heating operation can be carried out again.
It is to be noted that an abnormal heating function causes the abnormal function to come to a stop again, with the normal ~unctions being able to be used as they are.
A high-frequency heating apparatus having a plurality of magnetrons will be described hereinafter as a ~econd embodiment. In order to increase the h~gh-Erequency output (Figs. 4 and 5) magnetrons 9,9' are respectively pcovided in two waveguLdes 38, 38' with the 3ame ~peci~ications and being respectively disposed in the upper and lower portLons oE the heating chamber 37.
The power, converted into the necessary operating , - 7 - 132~828 voltages, is fed to the magnetrons 9 and 9' from a high-tension circuit composed of two similar high-tension . ..... .
transformers 18, 18', high-tension capacitors 19, 19' and ~:
high-tension diodes 20, 20'.
S Current transformers 22, 22' are provided as current detection means 8 on the AC primary side.
The current transformers 22, 22' are magnetically coupled with coils 40, 40' wound on iron cores 39, 39', and coils 41', 41' insulated therefrom and wound likewise 10 on the iron coils 39,39'. .
The current transformers 22, 22', together with the other components,.are mounted on a base plate 42 constituting a control portion. When the high-fre~uency heating apparatus is operating, current flows through the ..
lS coils 40, 40', likewise also the coils 41, 41' to excite .. :.
the eespective iron cores 39, 39'. The magnetic flux causes a voltage in the coils 41, 41', corresponding to ~: :
the current on the primary side. The voltages generated ; :
in coils 41, 41' are connected to rectification smoothing circuits 43, 43' to convert them into DC. The number of the respective coils, the size of the iron cores, the capacitor of the rectification circuits, and the values of ~ .. ;
the resistors are so set that the output voltage converted ~
into this direct current is proportional to the current :.
25 value flowing on the AC primary side. In the specific ..
embodiment the output voltage is adapted to become 4V when .
the current flowing through coils 40, 40' is lOA, and to become 0.4V when the current is lA. The outputs o~ the ..
eectLfication imoothing circuits 43, 43' are connected to an input 45 o a microcomputer circuit 44 which is the maln controller 44.
The clrcuit 44 is connected to a ~ey-board 3' for . : .
controlling the apparatus, a fluorescent display 23' ;
8howing the operating condition, a third intermit~ent relay :, "'.', ' ' ,,".,, .~". .
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132~8~8 46 for interrupting the high-frequency heatin~ operation, a fourth intermittent relay 47, and a lamp eelay 49 to be used for interruption of a lamp 48 within the heating chamber, in accordance with a procedure programmed in advance. The circuit 44 is operated by power provided through a low-tension transformer 21', converted into direct current.
A voltage input 50 receives an output voltage on t'ne secondary side of the transformer 21', and is provided in the circuit 44 to observe the voltage on the AC primary side. The apparatus has a door 12 at the front of the heating chamber 37 for containing ~ood 51. A third door switch 52 has a contact for opening and closing operations in accordance with opening and closing of the door 12 to interrupt the input into the high-tension transformers 18, 18'. There is also a fuse 53 to interrupt any excessi~e current flowing on the AC primary side.
The control operation will be described with the use of the flow chart of Fi9. 6.
The value of the input voltage (step 54) is assessed to ~udge whether it is within the range of the predetermined voltage ~step 55). If the voltage value is oEf by 15~ or more with respect to the rated voltage, both the third and fourth intermittent relays 46 and 47 are turned off to prevent the high frequency from being generated (step 56). In the other embodiment, it is po~sible that the operatLon not be effected from the beginning if the voltage is abnormal, with the voltage detection being provided even during the inoperative condition o~ the apparatus. The operation is continued when the voltage is within the normal range, to temporarlly store the voltage generated in the coil 41 of the current tcans~ormer 22 ~converted to DC) in the memory ~RAM1. This is assumed to be K ~step 57). Similarly the DC output from the coil 41' of the current transformer 22' is stored. This is assumed to be L (step S9). These v~lues are then compared. When K is larger than L, a K/L
opera~ion is effected (step 60). If the result is negative, i.e., L is larger than K, an (L/R) operation is effected (step 61). In the specific embodiment, it is judged whether or not the ratio is larger tnan 1.2.
Namely, a judgment is caused to be made as to whether (step 62) the difference between K and L is 20% or more. ~ -If the ratio is smaller than 1.2 (namely, it is judged that nothing is wrong with the two magnetrons, this ratio being within the variations normally caused by the dispersion of the load), the routine returns to normal.
If K is larger than L with a difference between them of 20%, the higher value is sensed (step 63) with respect to the rated value of K to judge whether or not the difference is positive or negative (step 64).
If this value is positive, the current K is considered abnormally large, since it is 1.2 times as much as the value of L ànd furthermore is larger than the rated cucrent of K. In the secondary circuit of the high-tension transformer 18, a number N2 ~or judging that the high~tension capacitor 19 has been short-circuited is measured. If this condition has continued five times or more, the output to the third intermittent relay 46 is cut, the contact of the third intermittent relay 46 being opened to cut only the abnormal cureent flowing into the high-tension transformer 18. F03 showing this abnormality i9 shown on the display 23 (step 65).
~f the value is negative, the value of L is conside~ed abnormally lower as compared wlth the normal value. In the secondary circuLt o~ the high-tension transformer 18', it iq judged that thece i9 a short-ciecult o~ the high-tension diode 20', magnetron 9', '''~ '","',.

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When the number Nl has continued five times oc more, the fourth intermittent celay 47 is opened to tur~ off the cuerent flowing to the high-tension transformer 18'. The S display 23' shows FO4 (step 66). Once the third intermittent relay 46 or the fourth intermittent relay 47 has been opened, the program is kept in the relay until the power supply is cut off.
If L is larger than K, with a difference of 20%
or more, the higher value is compared with the rated value of L to judge whether or not the difference is positive or negative (step 67). If this value is positive, the currents L is assumed to be abnormal. In the secondary -circuit of the high-tension transformer 18', there is lS judged to be a short-circuit condition of the high-tension capacitor 19, to measure the number N3. If this condition has continued five times or more, the fourth intermittent relay 47 is opened to turn ofE only the input to the high-tension transformer 18'. The display 23 shows FO2 to notify the user of this abnormality (step 68). If the value is negative, the K value is abnoemally low. ~t is judged that the high-tension diode 20 and the magnetron 9 in the secondary circuit of the high-tension transformer 18 have been short-circuited, or a portion of the secondary circuit has been opened. The number N4 is counted. When this condition has continued five times or more, the third intermittent relay 46 is opened to turn oF~ only the input to the high-tension transformer 18.
The dlsplay 23 shows FOl. This measurement is effected eve~y 0.1 second~
The above-descrLption Ls given for two magnetrons. When more magnetrons are provided, there will be a corresponding number o~ current detecting means. The dieeerehce between each two is based on the calculation of 13~9828 A-B, B-C, C ... ... X-A obtained from the detected signals A, B, C ... ... X. It is judged whether or not each difference is more than normal. When there is such a difference, the circuit whece the failure occurred is determined by comparing the current size with the rated current as in the described embodiment, whereby to open the relay contact of only the circuit in which the failure has arisen.
As is clear from the foregoing description, information obtained from the voltage detecting means, the current detecting means and the temperature detecting means is compared with predetermined information by a digital control portion in heating apparatus. The abnormality can be detected immediately and can be seen at a glance in the display. Also, if the abnormality arises during a heating operation, such heating operation can be stopped automatically to ensure safety. Since the location of the abnormality is determined, repair is simpli~ied.
Other heating means can operate continuously even if one of them fails in heating apparatus having a plurality of heating means. When two high-frequency generating devices (magnetrons) are provided, the cooking; g time becomes longer, but the operation can be completed by the single magnetron.
The measured input voltage is stored in the memory under constant conditions by use of the ~ :
predetermined voltage detecting means to compare the memorized value with the qubse~uent power voltage values.
This enables hlghly precise measurement and detection, wlth the result that there is a considerable cost reduction as compared with high-priced circuit components.
Although the present invention has been ~ully descrlbed in connection with the preferred embodiments ',~

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- 12 - ~329828 thereof with reference to the accompanying drawinqs, it is to be noted that various changes and modifications are ~ ~
apparent to those skilled in the art. Such changes and :
modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

Claims (14)

1. In a power supply circuitry for powering a magnetron, a method of determining whether the power supply or the magnetron has failed, comprising the steps of:
providing a magnetron which is powered by a dual half wave doubler circuit having dual first and second circuit portions including first and second transformers respectively;
sensing the magnitude of a first current flowing in the primary of the first transformer;
sensing the magnitude of a second current flowing in the primary of the second transformer; and comparing the magnitudes of the first and second currents to determine if the first current is more than a certain amount greater than the second current or if the second current is more than a certain amount greater than the first current, whereby it is determined whether the power supply has failed.

2. The method of claim 1, further comprising the steps of:
comparing the first and second currents; and determining whether the sum of the first and second currents is out of specification by more than a first criterion, and determining whether the magnitudes of said first and second currents are closer to each other than a second criterion, whereby it is determined whether the magnetron has failed.

3. The method of claim 1, further comprising the steps of:
indicating that the first power supply portion of the doubler has failed if the second current is more than said certain amount greater than the first current; and indicating that the second power supply portion of the doubler has failed if the first current is more than said certain amount greater than the second current.

4. The method of claim 2, further comprising the steps of:
indicating that the first power supply portion of the doubler has failed if the second current is more than said certain amount greater than the first current; and indicating that the second power supply portion of the doubler has failed if the first current is more than said certain amount greater than the second current.

5. The method of claim 2, further including the steps of:
determining whether the first or second currents have become much larger than normal.

6. The method of claim 4, wherein the power supply circuitry is used for power an electrodeless lamp.

7. The method of claim 1, wherein said certain amount greater comprises about 20% greater.

8. The method of claim 2, wherein said first criterion comprises about 20% and wherein said second criterion comprises about a 20% difference.

9. In power supply circuitry for powering a magnetron, an apparatus for determining whether the power supply or the magnetron has failed, comprising:
a magnetron;
a dual half wave doubler circuit for powering the magnetron, the dual half wave doubler circuit having dual first and second circuit portions including first and second transformers respectively;
means for sensing the magnitude of a first current flowing in the primary of the first transformer;
means for sensing the magnitude of a second current flowing in the primary of the second transformer; and means for comparing the magnitude of the first and second currents to determine if the first current is more than a certain amount greater than the second current or if the second current is more than a certain amount greater than the first current, whereby it is determined whether the power supply has failed.

10. The apparatus of claim 9, further comprising:
means for comparing the first and second currents;
means for determining whether the sum between the first and second currents is out of specification by more than a first criterion; and means for determining whether the magnitudes of the first and second currents are closer to each other than a second criterion, whereby it is determined whether the magnetron has failed.

11. The method of claim 3, further comprising the step of:
prohibiting the close of switching means having been failured after deciding as a failured one.

12. The method of claim 3, further comprising the step of:
indicating the failure of switching means after deciding as a failured one.

13. The apparatus of claim 9, further comprising a means for prohibiting the power supply only to the failured switching means after deciding as a failured one.

14. The apparatus of claim 9, further comprising an indicating means for indicating the failure of switching means after deciding as a failured one.