ELECTRICAL HEATING UNIT
United States Patent 3848111
An electrical heating unit including a plate or panel of a glassy material having in intimate physical contact with a surface of the plate, in a selected area of the plate surface, a 240 volt heating element comprising a pair of electrical resistance conductors extending in sinuous parallel paths over the contacted area of the panel surface, and circuit means for normally connecting the conductors across opposite terminals of a 240 volt source of electrical energy with a single set of temperature responsive contacts included in the circuit means for interrupting electrical energy to the conductors when the temperature of the heating unit reaches a preselected maximum temperature.
US Patent References:
Heating pad
McFarlan et al. - April 1938 - 2114396
Heating unit
Nathanson - January 1957 - 2777930
Shunts for printed circuit meters
Parker - July 1960 - 2945180
Electric food warmers
Salton - March 1961 - 2976386
Multi-layer film heaters in strip form
Hurko - December 1962 - 3067315
Heating pad
McFarlan et al. - April 1938 - 2114396
Heating unit
Nathanson - January 1957 - 2777930
Shunts for printed circuit meters
Parker - July 1960 - 2945180
Electric food warmers
Salton - March 1961 - 2976386
Multi-layer film heaters in strip form
Hurko - December 1962 - 3067315
Application Number:
05/400217
Publication Date:
11/12/1974
Filing Date:
09/24/1973
View Patent Images:
Export Citation:
Assignee:
Corning Glass Works (Corning, NY)
Primary Class:
Other Classes:
338/308, 219/522, 174/262, 219/448.110, 174/260, 219/466.100, 338/61
International Classes:
H05B3/26; H05B3/74; H05B3/22; H05B3/68
Field of Search:
219/203,212,213,435,436,441,451,452,453,464,494,522,528,543,549 338/61,62,63,212,308,309 174/68.5
US Patent References:
| 3130289 | Collapsible heating pad for travelling | April 1964 | Katzman et al. | |
| 3496336 | ELECTRIC HEATER | February 1970 | Hingorany et al. | |
| 3668367 | ELECTRICALLY HEATED PADS OR BLANKETS | June 1972 | Williams | |
| 3754118 | FLEXIBLE IMMERSION HEATER | August 1973 | Booker | |
| 3757087 | HEATING ELEMENTS | September 1973 | Bernard | |
| 3758747 | ELECTRIC MATTRESS | September 1973 | Rohr |
Primary Examiner:
Mayewsky, Volodymyr Y.
Attorney, Agent or Firm:
Gregg Jr., Charles Patty Clarence W. R.
Claims:
What is claimed is
1. An electrical heating unit comprising;
2. A heating unit as in claim 1 and in which said conductors each comprise a narrow continuous strip of a metallic film.
3. A heating unit as in claim 1 and in which said conductors each comprise a narrow strip of foil.
4. A heating unit as in claim 1 and in which said glassy material is a glass-ceramic material.
5. A heating unit as in claim 2 and in which said glassy material is a glass-ceramic material.
6. A heating unit as in claim 3 and in which said glassy material is a glass-ceramic material.
1. An electrical heating unit comprising;
2. A heating unit as in claim 1 and in which said conductors each comprise a narrow continuous strip of a metallic film.
3. A heating unit as in claim 1 and in which said conductors each comprise a narrow strip of foil.
4. A heating unit as in claim 1 and in which said glassy material is a glass-ceramic material.
5. A heating unit as in claim 2 and in which said glassy material is a glass-ceramic material.
6. A heating unit as in claim 3 and in which said glassy material is a glass-ceramic material.
Description:
BACKGROUND OF THE INVENTION
In an electrically heated appliance employing a heating unit comprising a panel or plate of a glassy material having heating elements including narrow continuous strips of electrical resistance heating conductors in intimate physical contact with or integrally bonded to an area of one of the surfaces of the panel of the heating unit, electrical leakage can occur through the material of such a panel at certain times such as when the temperature of the panel exceeds by a selected allowed margin, a normal maximum operating temperature for such panel. Such electrical leakage can at times present the possibility of an electrical shock. For example, kitchen ranges having smooth continuous cooktops made of a glassy material, such as a glass-ceramic material, are becoming increasingly popular. The cooktop of such a range comprises a panel of said glassy material which may be the panel of a heating unit such as that discussed above. In actuality, such a panel usually provides for two or more of said heating units, each such unit including a selected area of the panel defining a heating area on the upper surface of the panel. As mentioned above, electrical leakage through the material of such a cooktop can present the possibility of an electrical shock. For example, a housewife handling an electrically conductive cooking vessel in contact or resting on a cooktop cooking surface of the type mentioned, is subject to a possible electric shock if an electrical leakage such as that mentioned occurs. This is especially true, of course, if the housewife handling the vessel is also in good contact with an electrical ground such as an electrically conductive part of the cooking range itself or any other electrically conductive and electrically grounded item in the immediate environs of the range. Accordingly, it is an object of the present invention to provide electrical heating units of the class mentioned using 240 volt heating elements and which include, to the extent possible, a reduction in the possibility of an electrical shock due to an inadvertent electrical leakage through the glassy material of the panels used in the heating units.
Other objects and characteristic features of the invention will become apparent as the description proceeds.
SUMMARY OF THE INVENTION
The invention is believed to be adequately summarized in the foregoing abstract of the disclosure and, therefore, for the sake of brevity and to prevent repetition and redundancy to the extent possible, no further summary of the invention will be given nor is any considered to be necessary.
BRIEF DESCRIPTION OF THE DRAWING
The single drawing FIGURE comprises a bottom plan view of an electrical heating unit embodying the invention, such view including electrical circuit means for energizing such unit from a suitable source of electrical energy.
PREFERRED EMBODIMENT OF THE INVENTION
Referring to single drawing FIGURE in detail, there is shown a surface 11 of an area 12 of a plate or panel 10 of a glassy material and which may, for example, be an area of the lower surface of a smooth glass-ceramic cook-top of a kitchen range such as previously discussed. A 240 volt heating element 13 comprises a pair of first and second suitable electrical resistance conductors 14 and 15 which extend parallel with or adjacent to each other in sinuous, winding, serpentine or back-and-forth parallel paths over part of surface 11 of area 12 of panel 10, such conductors 14 and 15 being in intimate physical contact or made to be integral with said part of surface 11. Conductors 14 and 15 may, for example, comprise narrow continuous strips of a conductive film bonded to the surface of said part of area 12 as disclosed in U.S. Pat. 3,067,315, issued Dec. 4, 1962, to Bohdan Hurko, or the conductors 14 and 15 may be cut from a relatively thin foil of an electrical resistance heating material and secured to said part of surface 11 by a suitable adhesive or cement. However, it is pointed out that conductors 14 and 15 need not necessarily be a conductive film or foil but may be electrical resistance wires which are held against said surface 11 in any suitable manner such as being so held by a suitable backing sheet of a heat resistant and electrically non-conductive material, as is well known in the art.
A first electrical circuit or circuit means comprising wires 16 and 17, is provided for connecting first corresponding ends 14a and 15a of conductors 14 and 15, respectively, to fixed and movable members a and b, respectively, of a set of normally closed temperature actuated or responsive contacts of a thermostat or thermally sensitive switch T. Thus, such first electrical circuit or circuit means connects conductors 14 and 15 in series with each other when the set of contacts a-b are in their closed or circuit closing condition. Second and third electrical circuits or circuit means, comprising wires or leads 18 and 19 are provided for connecting second corresponding ends 14b and 15b of conductors 14 and 15, respectively, to the alternatingly positive (+) and negative (-) terminals, respectively, of a commercial 240 volt source PS of alternating electrical current, the neutral or grounded terminal of such source being designated N.
The above mentioned thermostat or thermally actuated switch T does not, per se, form part of the present invention but such switch may, for example, be any of the well known types of thermostats or thermally actuated switches which include a set of temperature actuated contacts, such as contacts a-b in the drawing, which normally occupy or are in a closed position or condition for completing an electrical circuit therethrough and which are actuated to an open or circuit interrupting position or condition when a temperature sensed by the thermostat or switch reaches a preselected maximum temperature. It will be understood by those skilled in the art that a thermostat such as T is intended to actuate its contacts a-b to an open condition when the temperature of area 12 of surface 11 of panel 10, for example, reaches a preselected maximum normal temperature, that is, a maximum temperature reached under normal operating conditions.
The positive and negative numerical values or designations shown on conductors 14 and 15 represent one set of instantaneous values of voltage potentials in the approximate regions of the conductors where the numerical values are shown, when the heating element 13 is connected with the source PS of alternating current as hereinbefore described. The values of voltage potentials in the lengths of the conductors between the regions indicated by said numerical values increase or decrease in accordance with the directions of movement along said lengths, as will be readily apparent from a brief glance at the drawing by those skilled in the art. It is pointed out that electrical leakage through the material of the panels 12 is effectively cancelled out due to the opposite polarities of the parallel paths of conductors 14 and 15 as discussed below.
OPERATIONAL EXAMPLE OF THE INVENTION
A brief operational example of the manner in which the invention disclosed reduces the possibility of electrical shock if and when electrical leakage occurs through the material of a panel such as 10 will now be set forth.
Referring to the drawing, it will be assumed that ends 14b and 15b of conductors 14 and 15 are connected across power source PS as shown and as previously discussed, and that ends 14a and 15a of the conductors are connected to each other through the set of contacts a-b of switch or thermostat T as also shown in the drawing and previously discussed. If, for example, electrical leakage occurs in area 12 of panel 10 in the region designated by the letter L in the drawing, such leakage, assuming for the purposes of the present example that the leakage path has an electrical resistance of one megohm, for example, may be at approximately a 105 volt potential or higher. Such a voltage potential could present the possibility of an electrical shock to a housewife handling an electrically conductive vessel as previously discussed. By the parallel arrangement of conductors 14 and 15 as shown in the drawings, some of said electrical leakage would probably flow between adjacent points on the closely parallel conductors 14 and 15 in said region L and thus be cancelled out. However, that part of the leakage which is not so cancelled could flow to a conductor such as, for example, a metal cooking vessel resting on the surface of region L and could, of course, present the possibility of an electric shock to said housewife is said parallel arrangement of conductors were not used. That is to say, said parallel arrangement of conductors provides for said part of the electric leakage to flow between adjacent points on the bottom of said vessel and thus be effectively cancelled to reduce the possibility of electric shock to said housewife. This is, of course, similarly true throughout the lengths of conductors 14 and 15, that is, in any of the regions of the area 12 over surface 11 of which conductors 14 and 15 extend.
It is pointed out that ends 14a and 15a of conductors 14 and 15 could be directly connected with each other if contacts of switch or thermostat T were interposed in the circuitry connecting ends 14b and 15b of conductors 14 and 15 across power source PS. However, in such case, if only a single set of contacts such as set a-b of switch T are interposed in one of the wires 18 or 19, when such set of contacts are in their open or circuit interrupting condition, the above discussed protection against electrical shock would not be provided, because both conductors 14 and 15 would be at the same instantaneous polarity with respect to the grounded terminal N of power source PS. Therefore, if ends 14a and 15a of conductors 14 and 15 were in direct connection with each other as mentioned, a set of contacts such as a-b of thermostat or switch T must be interposed in each of the wires 18 and 19 to attain the desired protection against electrical shock such as discussed above.
It is also desired to here make reference to the copending U.S. Pat. application of James P. Hocker and entitled "Electrical Heating Unit," such application being filed on even date herewith and assigned to the same assignee as the present application. Such copending application discloses another 240 volt electrical heating unit reducing the possibility of electrical shock in a manner similar to that discussed herein but using electrical resistance conductors connected in a different manner across a commercial 240 volt source of alternating current.
Although there is herein shown and described only one form of an electrical heating unit embodying the invention, it will be understood that various changes and modifications may be made therein within the purview of the appended claims without departing from the spirit and scope thereof.
In an electrically heated appliance employing a heating unit comprising a panel or plate of a glassy material having heating elements including narrow continuous strips of electrical resistance heating conductors in intimate physical contact with or integrally bonded to an area of one of the surfaces of the panel of the heating unit, electrical leakage can occur through the material of such a panel at certain times such as when the temperature of the panel exceeds by a selected allowed margin, a normal maximum operating temperature for such panel. Such electrical leakage can at times present the possibility of an electrical shock. For example, kitchen ranges having smooth continuous cooktops made of a glassy material, such as a glass-ceramic material, are becoming increasingly popular. The cooktop of such a range comprises a panel of said glassy material which may be the panel of a heating unit such as that discussed above. In actuality, such a panel usually provides for two or more of said heating units, each such unit including a selected area of the panel defining a heating area on the upper surface of the panel. As mentioned above, electrical leakage through the material of such a cooktop can present the possibility of an electrical shock. For example, a housewife handling an electrically conductive cooking vessel in contact or resting on a cooktop cooking surface of the type mentioned, is subject to a possible electric shock if an electrical leakage such as that mentioned occurs. This is especially true, of course, if the housewife handling the vessel is also in good contact with an electrical ground such as an electrically conductive part of the cooking range itself or any other electrically conductive and electrically grounded item in the immediate environs of the range. Accordingly, it is an object of the present invention to provide electrical heating units of the class mentioned using 240 volt heating elements and which include, to the extent possible, a reduction in the possibility of an electrical shock due to an inadvertent electrical leakage through the glassy material of the panels used in the heating units.
Other objects and characteristic features of the invention will become apparent as the description proceeds.
SUMMARY OF THE INVENTION
The invention is believed to be adequately summarized in the foregoing abstract of the disclosure and, therefore, for the sake of brevity and to prevent repetition and redundancy to the extent possible, no further summary of the invention will be given nor is any considered to be necessary.
BRIEF DESCRIPTION OF THE DRAWING
The single drawing FIGURE comprises a bottom plan view of an electrical heating unit embodying the invention, such view including electrical circuit means for energizing such unit from a suitable source of electrical energy.
PREFERRED EMBODIMENT OF THE INVENTION
Referring to single drawing FIGURE in detail, there is shown a surface 11 of an area 12 of a plate or panel 10 of a glassy material and which may, for example, be an area of the lower surface of a smooth glass-ceramic cook-top of a kitchen range such as previously discussed. A 240 volt heating element 13 comprises a pair of first and second suitable electrical resistance conductors 14 and 15 which extend parallel with or adjacent to each other in sinuous, winding, serpentine or back-and-forth parallel paths over part of surface 11 of area 12 of panel 10, such conductors 14 and 15 being in intimate physical contact or made to be integral with said part of surface 11. Conductors 14 and 15 may, for example, comprise narrow continuous strips of a conductive film bonded to the surface of said part of area 12 as disclosed in U.S. Pat. 3,067,315, issued Dec. 4, 1962, to Bohdan Hurko, or the conductors 14 and 15 may be cut from a relatively thin foil of an electrical resistance heating material and secured to said part of surface 11 by a suitable adhesive or cement. However, it is pointed out that conductors 14 and 15 need not necessarily be a conductive film or foil but may be electrical resistance wires which are held against said surface 11 in any suitable manner such as being so held by a suitable backing sheet of a heat resistant and electrically non-conductive material, as is well known in the art.
A first electrical circuit or circuit means comprising wires 16 and 17, is provided for connecting first corresponding ends 14a and 15a of conductors 14 and 15, respectively, to fixed and movable members a and b, respectively, of a set of normally closed temperature actuated or responsive contacts of a thermostat or thermally sensitive switch T. Thus, such first electrical circuit or circuit means connects conductors 14 and 15 in series with each other when the set of contacts a-b are in their closed or circuit closing condition. Second and third electrical circuits or circuit means, comprising wires or leads 18 and 19 are provided for connecting second corresponding ends 14b and 15b of conductors 14 and 15, respectively, to the alternatingly positive (+) and negative (-) terminals, respectively, of a commercial 240 volt source PS of alternating electrical current, the neutral or grounded terminal of such source being designated N.
The above mentioned thermostat or thermally actuated switch T does not, per se, form part of the present invention but such switch may, for example, be any of the well known types of thermostats or thermally actuated switches which include a set of temperature actuated contacts, such as contacts a-b in the drawing, which normally occupy or are in a closed position or condition for completing an electrical circuit therethrough and which are actuated to an open or circuit interrupting position or condition when a temperature sensed by the thermostat or switch reaches a preselected maximum temperature. It will be understood by those skilled in the art that a thermostat such as T is intended to actuate its contacts a-b to an open condition when the temperature of area 12 of surface 11 of panel 10, for example, reaches a preselected maximum normal temperature, that is, a maximum temperature reached under normal operating conditions.
The positive and negative numerical values or designations shown on conductors 14 and 15 represent one set of instantaneous values of voltage potentials in the approximate regions of the conductors where the numerical values are shown, when the heating element 13 is connected with the source PS of alternating current as hereinbefore described. The values of voltage potentials in the lengths of the conductors between the regions indicated by said numerical values increase or decrease in accordance with the directions of movement along said lengths, as will be readily apparent from a brief glance at the drawing by those skilled in the art. It is pointed out that electrical leakage through the material of the panels 12 is effectively cancelled out due to the opposite polarities of the parallel paths of conductors 14 and 15 as discussed below.
OPERATIONAL EXAMPLE OF THE INVENTION
A brief operational example of the manner in which the invention disclosed reduces the possibility of electrical shock if and when electrical leakage occurs through the material of a panel such as 10 will now be set forth.
Referring to the drawing, it will be assumed that ends 14b and 15b of conductors 14 and 15 are connected across power source PS as shown and as previously discussed, and that ends 14a and 15a of the conductors are connected to each other through the set of contacts a-b of switch or thermostat T as also shown in the drawing and previously discussed. If, for example, electrical leakage occurs in area 12 of panel 10 in the region designated by the letter L in the drawing, such leakage, assuming for the purposes of the present example that the leakage path has an electrical resistance of one megohm, for example, may be at approximately a 105 volt potential or higher. Such a voltage potential could present the possibility of an electrical shock to a housewife handling an electrically conductive vessel as previously discussed. By the parallel arrangement of conductors 14 and 15 as shown in the drawings, some of said electrical leakage would probably flow between adjacent points on the closely parallel conductors 14 and 15 in said region L and thus be cancelled out. However, that part of the leakage which is not so cancelled could flow to a conductor such as, for example, a metal cooking vessel resting on the surface of region L and could, of course, present the possibility of an electric shock to said housewife is said parallel arrangement of conductors were not used. That is to say, said parallel arrangement of conductors provides for said part of the electric leakage to flow between adjacent points on the bottom of said vessel and thus be effectively cancelled to reduce the possibility of electric shock to said housewife. This is, of course, similarly true throughout the lengths of conductors 14 and 15, that is, in any of the regions of the area 12 over surface 11 of which conductors 14 and 15 extend.
It is pointed out that ends 14a and 15a of conductors 14 and 15 could be directly connected with each other if contacts of switch or thermostat T were interposed in the circuitry connecting ends 14b and 15b of conductors 14 and 15 across power source PS. However, in such case, if only a single set of contacts such as set a-b of switch T are interposed in one of the wires 18 or 19, when such set of contacts are in their open or circuit interrupting condition, the above discussed protection against electrical shock would not be provided, because both conductors 14 and 15 would be at the same instantaneous polarity with respect to the grounded terminal N of power source PS. Therefore, if ends 14a and 15a of conductors 14 and 15 were in direct connection with each other as mentioned, a set of contacts such as a-b of thermostat or switch T must be interposed in each of the wires 18 and 19 to attain the desired protection against electrical shock such as discussed above.
It is also desired to here make reference to the copending U.S. Pat. application of James P. Hocker and entitled "Electrical Heating Unit," such application being filed on even date herewith and assigned to the same assignee as the present application. Such copending application discloses another 240 volt electrical heating unit reducing the possibility of electrical shock in a manner similar to that discussed herein but using electrical resistance conductors connected in a different manner across a commercial 240 volt source of alternating current.
Although there is herein shown and described only one form of an electrical heating unit embodying the invention, it will be understood that various changes and modifications may be made therein within the purview of the appended claims without departing from the spirit and scope thereof.