CA1130847A - Fuse circuitry - Google Patents
Fuse circuitryInfo
- Publication number
- CA1130847A CA1130847A CA317,409A CA317409A CA1130847A CA 1130847 A CA1130847 A CA 1130847A CA 317409 A CA317409 A CA 317409A CA 1130847 A CA1130847 A CA 1130847A
- Authority
- CA
- Canada
- Prior art keywords
- panel
- heating means
- fuse
- door
- heater
- 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
Abstract
S P E C I F I C A T I O N
TO ALL WHOM IT MAY CONCERN:
BE IT KNOWN that I, THOMAS REHBERG, a citizen of the United States of America, residing at 17931 LaHaigh, Homewood, in the County of Cook and State of Illinois, have invented a new and useful improvement in FUSE CIRCUITRY
of which the following is a specification.
ABSTRACT OF THE DISCLOSURE
A control system for use in electrically heated glass panel refrigerator doors to substantially prevent electrical shock if the glass panel is accidentally broken. The control system has an interlock switch for effectively disconnecting the power source from both the panel heater and the door heater of the electrically heated refrigerator door should breakage occur.
The interlock switch includes a thermal responsive device, such as a fuse, and a fuse heater. If the glass panel is accidentally broken causing the panel heater to become dangerously exposed, the fuse heater is activated to generate a sufficient amount of heat to blow the fuse which opens the circuit to quickly and safely deactivate both the panel heater and the door heater.
TO ALL WHOM IT MAY CONCERN:
BE IT KNOWN that I, THOMAS REHBERG, a citizen of the United States of America, residing at 17931 LaHaigh, Homewood, in the County of Cook and State of Illinois, have invented a new and useful improvement in FUSE CIRCUITRY
of which the following is a specification.
ABSTRACT OF THE DISCLOSURE
A control system for use in electrically heated glass panel refrigerator doors to substantially prevent electrical shock if the glass panel is accidentally broken. The control system has an interlock switch for effectively disconnecting the power source from both the panel heater and the door heater of the electrically heated refrigerator door should breakage occur.
The interlock switch includes a thermal responsive device, such as a fuse, and a fuse heater. If the glass panel is accidentally broken causing the panel heater to become dangerously exposed, the fuse heater is activated to generate a sufficient amount of heat to blow the fuse which opens the circuit to quickly and safely deactivate both the panel heater and the door heater.
Description
113C~8~
BACKGROUND ~F THE INVENTION
This invention relates to electrically heated glass panel refrigerator doors, and more partlcularly, to a control system for substantially preventing electrical shock when the glass panel of a ~efrigerator door is accidentally broken.
Glass panel refrigerator doors, such as the type shown in U.S. Patents 2,987,7B2; 3,131,421; 3,499,245; and 3,629,972, have a glass panel mounted in a movable metal door frame. In order to keep the glass panel substantially fogless and frost free and to substantially prevent the frame from "sweating" and collect-ing moisture, the glass panel and frame are equipped with an electric panel heater and door heater, respectively. Typically, the electric panel heater includes a heating element such as a transparent electrically conductive coating on one of the inacces-sible surfaces of the panel.
Normally, the electrically heated glass panel and frame do not present any shock hazard because the panel and door heaters are inaccessible, however, if the glass panel is acci-dentally broken, the electrically conductive or "live" panel heater and/or door heater may become accessible, creating a hazardous condition which can cause electrical shock to persons who accidentally touch or contact the broken panel.
It is therefore desirable to provide an electrically heated glass panel refrigerator door system which substantially prevents electrical shock if the glass panel of the refrigerator door is accidentally broken. While various protective devices and circuits, such a those found in U.S. Patents 3,4~9,551;
3,475,594; and 3,52~,753, have been previously employed with v~rying degress of success in an attempt to solve this problem, 30 there still exists the need for a new and improved system which is reliable, quick ~nd fail-safe.
~13C~8~7 SUMMARY OF THE INVENTION
A new and improved electrically heated glass panel refrigerator door system is provided to prevent electrical shock if the glass panel of the refrigerator door is accidentally broken.
According to the invention there is provided an electrically heated glass panel refrigerator door system, com-prising: a glass-like panel assembly for permitting viewing of products in a refrigerator and a movable door frame securing said panel assembly for access into said refrigerator, said panel assembly including at least one transparent glass-like pane having a normally inaccessible surface; panel heating means for heating said panel assembly to substantially prevent the condensation of moisture and the formation of frost on said panel assembly so that said panel assembly is substantially fogless and frost free, said panel heating means including bus bar means and an electrically conductive coating connected to said bus bar means on said normally inaccessible surface of said transparent glass-like pane, said bus bar means including a first bus bar and a second bus bar spaced from said first bus bar and connected to said electrically conductive coating;
door heating means for heating said door frame to substantially prevent the condensation of moisture and the formation of frost on said door frame; power supply means for energizing said door heating means and said panel heating means; and interlock switch .
means connected to and between said power supply means and said panel and door heating means for effectively disconnecting and deactivating said door heating means and said panel heating means from said power supply means in response to an unsafe condition when said transparent glass-like pane is accidentally broken causing the electrical resistance of said panel heating means to increase with said panel heating means being dangerously ~13(:~8~
accessible, said interlock switch means including fuse heating means for emitting heat in response to said unsafe condition, said fuse heating means connected in parallel with said panel heating means and in series with said door heating means to pass effective heating current when said panel heating means resistance increases, and thermal responsive means operatively associated with said fuse heating means for opening said circuit connection between said power supply means and said door and panel heating means in response to said heat from said fuse heating means to substantially prevent electrical shock from both said door heating means and said accessible panel heating means on said broken pane.
In the illustrative embodiment the fuse heating means includes a tubular ceramic heater which circumscribes the thermal responsive means.
The interlock switch means can include a plurality of thermal responsive devices and a plurality of fuse heaters to increase the safety and reliability of the control system.
A more detailed explanation of the invention is pro-vided in the following description and appended claims taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic circuit diagram of an elec-trically heated glass panel refrigerator door system in accord-ance with principles of the present invention; and FIGURE 2 is a fragmentary schematic circuit diagram illustrating a portion of another electrically heated glass panel refrigerator door system in accordance with principles of the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT
Referring to Figure 1 of the drawings, an electrically heated glass panel refrigerator door system 10 has a glass panel 1~ 3~347 refrigerator door 12. Such refrigerator doors are desirably used in supermarkets, convenient food stores, beverage stores and the like in refrigerated display cases and cabinets from which purchasers may select refrigerated beverages, foods and other products. The doors may be employed on self-contained refrigerator cabinets or i.n connection with walk-in coolers or other built-in refrigerated display facilities and commercial refrigerators which have shelves or bins to hold and display products for sale. Such doors are used for both normal temper-ature -4a-.~
113C~
and low temperature refrigeration. Normal temperature appli-cations involve the display of dairy products and the like at a temperature slightly above the freezing temperature. Low tem-perature applications involve the display of frozen foods, ice cream and the like, at a temperature well below freezing. Desir-ably, the customer selects the products or merchandise by look-ing through the glass-like panel assembly 14 of door 12, opening the door 12 and removing the merchandise from the refrigerator.
Preferably, the refrigerator door 12 is of a swinging or pivotally hinged type of construction, such as the type shown in U.S. Patents 2,987,782; 3,131,421 and 3,499,245, although othe~
types of refrigerator doors can be used with this system such as the sliding ~ype construction shown in U.S. Patent 3,508,361.
The glass-like panel assembly 14 of refrigerator door 12 generally takes the form of a glass panel mounted in a movable rectangular metal door frame 16. Panel assembly 14 desirably is of the insulated type and includes a plurality of parallel light-transmissive and preferably transparent glass-like panes 14a made of glass or impact-resistant plastic to clearly display and per-mit viewing of the merchandise or products in the refrigerator.Preferably, the panel assembly 14 has three glass panes, although in some circumstances it may be desirable to use one, two, four or even more glass panes.
Spaces are hermetically sealed between the edges of the pane to provide dead air spaces therebetween, so that moisture will be excluded from the dead air spaces between the panes. The dry air between the panes generally has good insulating value.
While such spaces are typically filled with dry air, they can be filled with an inert gas, such as nitrogen.
~L13~)8~7 In order to prevent the glass panel assembly 14 from "fogging up" and accumulating frost, which would interfere with full visibility of the products in the refrigerator, the door 12 is equipped with panel heating means such as an electrical panel heater 18 having an electrical heating element, which preferably takes the form of a transparent electrically conduc~ive coating 18a or layer on one of the normally inaccessible surfaces of the glass panes 14a. Desirably, the electrically conductive coating 18a is intimately bonded ox fused to the rear or inner surface of the front glass pane such as shown in U.S. Patent 3,475,594 and prevents the condensation of moisture as well as formation of frost on the panel assembly 14 so that the panel assembly is substan-tially fogless and frost free. The ends of the electrically con-ductive coating are connected to bus bar means, such as first and second opposed bus bars or leads 18b and 18c, respectively. The bus bars are connected to wires or lines 22b and 22c which pass through the door and are suitably connected to power supply means, such as an electrical power source 24 or line.
In order to prevent the condensation of moisture and the formation of frost on the metal door frame 16, the door frame is provided with door heating means, such as one or more internal door heaters 20, which can take the form of heating cables mounted in the hollow core of the door frame, such as shown in U.S. Patent 3,499,245. The door heater 20 is connected to bus bars 18b and 18c by lines 22b and 22~, respectively, and is connected to an outlet of the power source 24 via line wires 26b, 26c and 26d.
The power source or line is adapted to supply an alternating current at 110 volts and 60 cycles or any other desirable voltage and frequency.
113~8~7 In accordance with principles of the present inven-tion a novel interlock switch means, such as interlock switch 28 is provided to effectively disconnect and deactivate the panel heater 18 and door heater ~0 if the glass panel assembly 14 is accidentally shattered or otherwise broken. The interlock switch generally defines a control system or circuit which is generally reliable, quick and substantially fail-safe.
The interlock switch 28 is connected between the power source 24 and the door heater 20 and panel heater 18 via lines 26b and 26d, and desirably draws little power so as to not sub-stantially interfere with the heating function of the door heater 20 and panel heater 18. In the preferred form, the interlock switch 28 includes heating means, such as a fuse heater 28a, connected to thermal responsive means, such as a thermal respon-sive device or fuse 28b. The fuse heater 28a emits or generates heat in response to an unsafe or hazardous condition when the glass panel assembly is broken, causing the fuse to activate or blow thereby effectively disconnecting the door heater 20 and panel heater 18 from the power source 24. In the illustrative embodiment, the fuse heater 28a takes the form of an elongated tubular ceramic heater which longitudinally surrounds and circum-scribes fuse 28b and desirably has leads connected in parallel to or shunted across the opposed end leads of fuse 28b. The tubular ceramic heater construction generally includes a ceramic sleeve into which is embedded a pair of conductive termin~l rings adjacent the ends of the sleeve, and a heating coil of finely wrapped wire positioned between and connected to the conductivè
terminal rings. While the described ceramic heater is preferred, it may be desirable in some circumstances to use a different type of fuse heater construction such as a heater or thermal ~13C)847 activating device which is operatively associated with but does not necessarily surround the fuse 28b.
Normally, the fuse heater 28a is shunted out of the circuit and is not activated and therefore passes little or no current.
If the gl~ss panel is accidentally broken, one or both of the bus bars 18b or 18c, as well as the electrical conductive coating 18a may be severed, causing the panel heater 18 to become danger-ously aceessible, however, in the present circuit such situation causes the fuse heater 28 to energize in series with the door heater 20 and panel heater 18. When energized, the fuse heater 28a generates a sufficient amount of heat to cause the fuse 28b to melt thereby opening the circuit or line 26d between the power source 24 and the door heater 20 and panel heater 18 which effectively deactivates and disconnects the door heater and panel heater from the power source 24. In this manner, the hot leads 22b and 22c to the bus bars 18b and 18c and the door heater 20 are quickly and safely neutralized to avoid pos-sible electric shock or other haxm to patrons or other individuals who may accidentally make physical contact with the panel heater, broken pane or door heater.
When a 300 ohm ceramic resistor heater was used in conjunction with a thermal fuse which opened at about 154F. in a refrigerator door having a 300 ohm door heater and a 150 ohm resistance in the electrically conductive coating, the fuse opened in about 15 to 18 seconds after the glass panel and bus bars were severed. Other values for the ceramic heater, fuse, door heater and electrically conductive coating can be chosen when desired.
It may be desirable in many circumstances to provide an extra margin of safety to the circuitry of the present inven-tion by providing a plurality of interlock switches, including at least one interlock switch connected to one of the conductive lines of the power-source and at least one other interlock switch connected to another conductive line of the power source.
One such circuit for accomplishing this result is illustrated in Figure 2, in which a pair of interlock switches 128 and 130 are connected to lines 126d and 126c, respectively, of the power source 124. Each of the interlock switches includes heating means, such as a fuse heater 128a or 130a, operatively associated with or connected to thermal responsive means, such as a thermal responsive device or fuse 128b or 130b, with the fuse heaters 128a and 130a connected in series to each other along line 126b and fuses 128b and 130b connected to power lines 126d and 126c, respectively. The other end leads of fuse heaters 128a and 130a are connected to door heater 120 and first bus bar 118bl respec-tively, while the other end leads of fuses 128b and 130b are connected to the second bus bar 118c and door heater 120, and the first bus bar 118b, respectively, so that fuse heaters 128a and 130a are shunted across fuses 128b and 130b. Preferably, the fuse heaters 128a and 130a and fuses 130a and 130b are of the same type of construction as described in relationship to the fuse heater 28a and fuse 28b of Figure 1, although in some circumstances it may be desirable to use other types of fuse heaters or fuses.
The other components of the circuit 110 shown in Figure 2 are substantially similar to the other components of the circuit 10 shown in Figure 1 and for ease of illustration and understanding, the similar parts of the circuit 110 shown in Figure 2 have been given numbers similar to the parts of the circuit 10 in Figure 1, but increased by a hundred, such as door heater 120, panel heater 118, glass panel assembly 114, etc. The operation of circuit 110 is substantially the same as the operation of 1~30~7 circuit 10 of Figure 1 with the additional safety and reliability feature of two interlock switches 128 and 130 which effectively disconnect both power lines 126c and 126d from the panel heater 118 and door heater 120 when the panel assembly is accidentally broken.
Although embodiments of this invention have been shown and described, it is to be understood that various modifications and substitutions can be made by those skilled in the art with-out departing from the novel spirit and scope of this invention.
What is desired to be protected and secured by Letters P t t of tho Unitoa-~atoc is- :
a en
BACKGROUND ~F THE INVENTION
This invention relates to electrically heated glass panel refrigerator doors, and more partlcularly, to a control system for substantially preventing electrical shock when the glass panel of a ~efrigerator door is accidentally broken.
Glass panel refrigerator doors, such as the type shown in U.S. Patents 2,987,7B2; 3,131,421; 3,499,245; and 3,629,972, have a glass panel mounted in a movable metal door frame. In order to keep the glass panel substantially fogless and frost free and to substantially prevent the frame from "sweating" and collect-ing moisture, the glass panel and frame are equipped with an electric panel heater and door heater, respectively. Typically, the electric panel heater includes a heating element such as a transparent electrically conductive coating on one of the inacces-sible surfaces of the panel.
Normally, the electrically heated glass panel and frame do not present any shock hazard because the panel and door heaters are inaccessible, however, if the glass panel is acci-dentally broken, the electrically conductive or "live" panel heater and/or door heater may become accessible, creating a hazardous condition which can cause electrical shock to persons who accidentally touch or contact the broken panel.
It is therefore desirable to provide an electrically heated glass panel refrigerator door system which substantially prevents electrical shock if the glass panel of the refrigerator door is accidentally broken. While various protective devices and circuits, such a those found in U.S. Patents 3,4~9,551;
3,475,594; and 3,52~,753, have been previously employed with v~rying degress of success in an attempt to solve this problem, 30 there still exists the need for a new and improved system which is reliable, quick ~nd fail-safe.
~13C~8~7 SUMMARY OF THE INVENTION
A new and improved electrically heated glass panel refrigerator door system is provided to prevent electrical shock if the glass panel of the refrigerator door is accidentally broken.
According to the invention there is provided an electrically heated glass panel refrigerator door system, com-prising: a glass-like panel assembly for permitting viewing of products in a refrigerator and a movable door frame securing said panel assembly for access into said refrigerator, said panel assembly including at least one transparent glass-like pane having a normally inaccessible surface; panel heating means for heating said panel assembly to substantially prevent the condensation of moisture and the formation of frost on said panel assembly so that said panel assembly is substantially fogless and frost free, said panel heating means including bus bar means and an electrically conductive coating connected to said bus bar means on said normally inaccessible surface of said transparent glass-like pane, said bus bar means including a first bus bar and a second bus bar spaced from said first bus bar and connected to said electrically conductive coating;
door heating means for heating said door frame to substantially prevent the condensation of moisture and the formation of frost on said door frame; power supply means for energizing said door heating means and said panel heating means; and interlock switch .
means connected to and between said power supply means and said panel and door heating means for effectively disconnecting and deactivating said door heating means and said panel heating means from said power supply means in response to an unsafe condition when said transparent glass-like pane is accidentally broken causing the electrical resistance of said panel heating means to increase with said panel heating means being dangerously ~13(:~8~
accessible, said interlock switch means including fuse heating means for emitting heat in response to said unsafe condition, said fuse heating means connected in parallel with said panel heating means and in series with said door heating means to pass effective heating current when said panel heating means resistance increases, and thermal responsive means operatively associated with said fuse heating means for opening said circuit connection between said power supply means and said door and panel heating means in response to said heat from said fuse heating means to substantially prevent electrical shock from both said door heating means and said accessible panel heating means on said broken pane.
In the illustrative embodiment the fuse heating means includes a tubular ceramic heater which circumscribes the thermal responsive means.
The interlock switch means can include a plurality of thermal responsive devices and a plurality of fuse heaters to increase the safety and reliability of the control system.
A more detailed explanation of the invention is pro-vided in the following description and appended claims taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic circuit diagram of an elec-trically heated glass panel refrigerator door system in accord-ance with principles of the present invention; and FIGURE 2 is a fragmentary schematic circuit diagram illustrating a portion of another electrically heated glass panel refrigerator door system in accordance with principles of the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT
Referring to Figure 1 of the drawings, an electrically heated glass panel refrigerator door system 10 has a glass panel 1~ 3~347 refrigerator door 12. Such refrigerator doors are desirably used in supermarkets, convenient food stores, beverage stores and the like in refrigerated display cases and cabinets from which purchasers may select refrigerated beverages, foods and other products. The doors may be employed on self-contained refrigerator cabinets or i.n connection with walk-in coolers or other built-in refrigerated display facilities and commercial refrigerators which have shelves or bins to hold and display products for sale. Such doors are used for both normal temper-ature -4a-.~
113C~
and low temperature refrigeration. Normal temperature appli-cations involve the display of dairy products and the like at a temperature slightly above the freezing temperature. Low tem-perature applications involve the display of frozen foods, ice cream and the like, at a temperature well below freezing. Desir-ably, the customer selects the products or merchandise by look-ing through the glass-like panel assembly 14 of door 12, opening the door 12 and removing the merchandise from the refrigerator.
Preferably, the refrigerator door 12 is of a swinging or pivotally hinged type of construction, such as the type shown in U.S. Patents 2,987,782; 3,131,421 and 3,499,245, although othe~
types of refrigerator doors can be used with this system such as the sliding ~ype construction shown in U.S. Patent 3,508,361.
The glass-like panel assembly 14 of refrigerator door 12 generally takes the form of a glass panel mounted in a movable rectangular metal door frame 16. Panel assembly 14 desirably is of the insulated type and includes a plurality of parallel light-transmissive and preferably transparent glass-like panes 14a made of glass or impact-resistant plastic to clearly display and per-mit viewing of the merchandise or products in the refrigerator.Preferably, the panel assembly 14 has three glass panes, although in some circumstances it may be desirable to use one, two, four or even more glass panes.
Spaces are hermetically sealed between the edges of the pane to provide dead air spaces therebetween, so that moisture will be excluded from the dead air spaces between the panes. The dry air between the panes generally has good insulating value.
While such spaces are typically filled with dry air, they can be filled with an inert gas, such as nitrogen.
~L13~)8~7 In order to prevent the glass panel assembly 14 from "fogging up" and accumulating frost, which would interfere with full visibility of the products in the refrigerator, the door 12 is equipped with panel heating means such as an electrical panel heater 18 having an electrical heating element, which preferably takes the form of a transparent electrically conduc~ive coating 18a or layer on one of the normally inaccessible surfaces of the glass panes 14a. Desirably, the electrically conductive coating 18a is intimately bonded ox fused to the rear or inner surface of the front glass pane such as shown in U.S. Patent 3,475,594 and prevents the condensation of moisture as well as formation of frost on the panel assembly 14 so that the panel assembly is substan-tially fogless and frost free. The ends of the electrically con-ductive coating are connected to bus bar means, such as first and second opposed bus bars or leads 18b and 18c, respectively. The bus bars are connected to wires or lines 22b and 22c which pass through the door and are suitably connected to power supply means, such as an electrical power source 24 or line.
In order to prevent the condensation of moisture and the formation of frost on the metal door frame 16, the door frame is provided with door heating means, such as one or more internal door heaters 20, which can take the form of heating cables mounted in the hollow core of the door frame, such as shown in U.S. Patent 3,499,245. The door heater 20 is connected to bus bars 18b and 18c by lines 22b and 22~, respectively, and is connected to an outlet of the power source 24 via line wires 26b, 26c and 26d.
The power source or line is adapted to supply an alternating current at 110 volts and 60 cycles or any other desirable voltage and frequency.
113~8~7 In accordance with principles of the present inven-tion a novel interlock switch means, such as interlock switch 28 is provided to effectively disconnect and deactivate the panel heater 18 and door heater ~0 if the glass panel assembly 14 is accidentally shattered or otherwise broken. The interlock switch generally defines a control system or circuit which is generally reliable, quick and substantially fail-safe.
The interlock switch 28 is connected between the power source 24 and the door heater 20 and panel heater 18 via lines 26b and 26d, and desirably draws little power so as to not sub-stantially interfere with the heating function of the door heater 20 and panel heater 18. In the preferred form, the interlock switch 28 includes heating means, such as a fuse heater 28a, connected to thermal responsive means, such as a thermal respon-sive device or fuse 28b. The fuse heater 28a emits or generates heat in response to an unsafe or hazardous condition when the glass panel assembly is broken, causing the fuse to activate or blow thereby effectively disconnecting the door heater 20 and panel heater 18 from the power source 24. In the illustrative embodiment, the fuse heater 28a takes the form of an elongated tubular ceramic heater which longitudinally surrounds and circum-scribes fuse 28b and desirably has leads connected in parallel to or shunted across the opposed end leads of fuse 28b. The tubular ceramic heater construction generally includes a ceramic sleeve into which is embedded a pair of conductive termin~l rings adjacent the ends of the sleeve, and a heating coil of finely wrapped wire positioned between and connected to the conductivè
terminal rings. While the described ceramic heater is preferred, it may be desirable in some circumstances to use a different type of fuse heater construction such as a heater or thermal ~13C)847 activating device which is operatively associated with but does not necessarily surround the fuse 28b.
Normally, the fuse heater 28a is shunted out of the circuit and is not activated and therefore passes little or no current.
If the gl~ss panel is accidentally broken, one or both of the bus bars 18b or 18c, as well as the electrical conductive coating 18a may be severed, causing the panel heater 18 to become danger-ously aceessible, however, in the present circuit such situation causes the fuse heater 28 to energize in series with the door heater 20 and panel heater 18. When energized, the fuse heater 28a generates a sufficient amount of heat to cause the fuse 28b to melt thereby opening the circuit or line 26d between the power source 24 and the door heater 20 and panel heater 18 which effectively deactivates and disconnects the door heater and panel heater from the power source 24. In this manner, the hot leads 22b and 22c to the bus bars 18b and 18c and the door heater 20 are quickly and safely neutralized to avoid pos-sible electric shock or other haxm to patrons or other individuals who may accidentally make physical contact with the panel heater, broken pane or door heater.
When a 300 ohm ceramic resistor heater was used in conjunction with a thermal fuse which opened at about 154F. in a refrigerator door having a 300 ohm door heater and a 150 ohm resistance in the electrically conductive coating, the fuse opened in about 15 to 18 seconds after the glass panel and bus bars were severed. Other values for the ceramic heater, fuse, door heater and electrically conductive coating can be chosen when desired.
It may be desirable in many circumstances to provide an extra margin of safety to the circuitry of the present inven-tion by providing a plurality of interlock switches, including at least one interlock switch connected to one of the conductive lines of the power-source and at least one other interlock switch connected to another conductive line of the power source.
One such circuit for accomplishing this result is illustrated in Figure 2, in which a pair of interlock switches 128 and 130 are connected to lines 126d and 126c, respectively, of the power source 124. Each of the interlock switches includes heating means, such as a fuse heater 128a or 130a, operatively associated with or connected to thermal responsive means, such as a thermal responsive device or fuse 128b or 130b, with the fuse heaters 128a and 130a connected in series to each other along line 126b and fuses 128b and 130b connected to power lines 126d and 126c, respectively. The other end leads of fuse heaters 128a and 130a are connected to door heater 120 and first bus bar 118bl respec-tively, while the other end leads of fuses 128b and 130b are connected to the second bus bar 118c and door heater 120, and the first bus bar 118b, respectively, so that fuse heaters 128a and 130a are shunted across fuses 128b and 130b. Preferably, the fuse heaters 128a and 130a and fuses 130a and 130b are of the same type of construction as described in relationship to the fuse heater 28a and fuse 28b of Figure 1, although in some circumstances it may be desirable to use other types of fuse heaters or fuses.
The other components of the circuit 110 shown in Figure 2 are substantially similar to the other components of the circuit 10 shown in Figure 1 and for ease of illustration and understanding, the similar parts of the circuit 110 shown in Figure 2 have been given numbers similar to the parts of the circuit 10 in Figure 1, but increased by a hundred, such as door heater 120, panel heater 118, glass panel assembly 114, etc. The operation of circuit 110 is substantially the same as the operation of 1~30~7 circuit 10 of Figure 1 with the additional safety and reliability feature of two interlock switches 128 and 130 which effectively disconnect both power lines 126c and 126d from the panel heater 118 and door heater 120 when the panel assembly is accidentally broken.
Although embodiments of this invention have been shown and described, it is to be understood that various modifications and substitutions can be made by those skilled in the art with-out departing from the novel spirit and scope of this invention.
What is desired to be protected and secured by Letters P t t of tho Unitoa-~atoc is- :
a en
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrically heated glass panel refrigerator door system, comprising: a glass-like panel assembly for permitting viewing of products in a refrigerator and a movable door frame securing said panel assembly for access into said refrigerator, said panel assembly including at least one transparent glass-like pane having a normally inaccessible surface; panel heating means for heating said panel assembly to substantially prevent the condensation of moisture and the formation of frost on said panel assembly so that said panel assembly is substantially fogless and frost free, said panel heating means including bus bar means and an electrically conductive coating connected to said bus bar means on said normally inaccessible surface of said transparent glass-like pane, said bus bar means including a first bus bar and a second bus bar spaced from said first bus bar and connected to said electrically conductive coating; door heating means for heating said door frame to substantially prevent the condensation of moisture and the formation of frost on said door frame; power supply means for energizing said door heating means and said panel heating means; and interlock switch means connected to and between said power supply means and said panel and door heating means for effectively disconnecting and deactivating said door heating means and said panel heating means from said power supply means in response to an unsafe condition when said transparent glass-like pane is accidentally broken causing the electrical resistance of said panel heating means to increase with said panel heating means being dangerously accessible, said interlock switch means including fuse heating means for emitting heat in response to said unsafe condition, said fuse heating means connected in parallel with said panel heating means and in series with said door heating means to pass effective heating current when said panel heating means resis-tance increases, and thermal responsive means operatively associated with said fuse heating means for opening said circuit connection between said power supply means and said door and panel heating means in response to said heat from said fuse heating means to substantially prevent electrical shock from both said door heating means and said accessible panel heating means on said broken pane.
2. An electrically heated glass panel refrigerator door system in accordance with claim 1 wherein said thermal respon-sive means is an electrically conductive fuse adapted to melt and interrupt current flowing between said power supply means and said door and panel heating means.
3. An electrically heated glass panel refrigerator door system in accordance with claim 1 wherein said fuse heating means include at least one tubular ceramic heater substantially circumscribing said thermal responsive means.
4. An electrically heated glass panel refrigerator door system in accordance with claim 1 wherein: said thermal respon-sive means include a plurality of thermal responsive devices, and said fuse heating means include a plurality of fuse heaters.
5. An electrically heated glass panel refrigerator door system in accordance with claim 4 wherein: said power supply means include a first line and a second line, and said thermal responsive means include a first thermal responsive device connected to said first line and a second thermal responsive device connected to said second line, and said fuse heating means include a first fuse heater operatively associated with said first thermal responsive device, and a second fuse heater connected in series to said first fuse heater and operatively associated with said second thermal responsive device.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86560077A | 1977-12-29 | 1977-12-29 | |
| US865,600 | 1977-12-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1130847A true CA1130847A (en) | 1982-08-31 |
Family
ID=25345855
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA317,409A Expired CA1130847A (en) | 1977-12-29 | 1978-12-05 | Fuse circuitry |
Country Status (2)
| Country | Link |
|---|---|
| AU (1) | AU527447B2 (en) |
| CA (1) | CA1130847A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10690391B2 (en) | 2013-03-15 | 2020-06-23 | Whirlpool Corporation | Appliance using heated glass panels |
-
1978
- 1978-12-05 CA CA317,409A patent/CA1130847A/en not_active Expired
- 1978-12-14 AU AU42552/78A patent/AU527447B2/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10690391B2 (en) | 2013-03-15 | 2020-06-23 | Whirlpool Corporation | Appliance using heated glass panels |
Also Published As
| Publication number | Publication date |
|---|---|
| AU527447B2 (en) | 1983-03-03 |
| AU4255278A (en) | 1979-07-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |