US3526753A

US3526753A - Anti-shock control devices for electrically heated glass

Info

Publication number: US3526753A
Application number: US600201A
Authority: US
Inventors: Daniel J Aisanich; Frederic A Richter
Original assignee: Ardco Inc
Current assignee: Ardco Inc
Priority date: 1966-12-08
Filing date: 1966-12-08
Publication date: 1970-09-01
Anticipated expiration: 1987-09-01
Also published as: GB1175336A

Description

Sept. 1 1970 D. J. AISANICH ETAL 3,526,753

ANTI-SHOCK CONTROL DEVICES FOR ELECTRICALLY HEATED GLASS 2 Sheets-Sheet 1 Filed Dec. 8. 1966 -F1G.Z

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Sept. 1, 1970 J A|$AN|H ETAL 3,526,753

ANTI-SHOCK CONTROL DEVICES FOR ELECTRICALLY HEATED-GLASS Filed Dec. 8, 1966 2 Sheets-Sheet 2 United States Patent 3,526,753 ANTI-SHOCK CONTROL DEVICES FOR ELECTRICALLY HEATED GLASS Daniel J. Aisanich and Frederic A. Richter, Chicago, Ill.,

assignors to Ardco, Inc., Chicago, 11]., a corporation of Illinois Filed Dec. 8, 1966, Ser. No. 600,201 Int. Cl. H05b 1/02 US. Cl. 219-522 21 Claims ABSTRACT OF THE DISCLOSURE A current responsive control relay device effectively disconnects the power from electrically heated glass when breakage occurs, to obviate any shock hazard. In the first embodiment, the relay device comprises a bimetal switch which is operated from a first to a third position by a voltage responsive heater. The bimetal switch is maintained in the third position by the heat generated in the bimetal by the flow of the main load current. When breakage of the heater occurs, the bimetal switch returns to an intermediate position, in which it is maintained by a reduced current through the voltage responsive heater. In the second embodiment, the relay device comprises a normally open bimetal switch across which a high value resistor is connected. The bimetal switch is closed by the heat developed in such resistor, and is kept closed by the heat generated in the bimetal itself by the main load curent, and also the heat generated in a series con nected resistor. When breakage of the electrically heated glass occurs, the bimetal switch is opened. The resistor has a high value to obviate any shock hazard. Inthe fourth embodiment, the series connected resistor is not needed. In the fifth embodiment, a compensating bimetal is employed to carry one of the contacts for the bimetal switch, to compensate for variations in the ambient temperature. In the third embodiment, the relay device comprises normally open contacts operable by an electromagnet having a voltage responsive coil and a current responsive coil. The voltage responsive coil is connected across the contacts so as to cause initial closure thereof. Such closure is maintained by the load current through the current responsive coil. The voltage responsive coil has a high resistance to obviate any shock hazard.

This invention relates to electrically heated glass panels and pertains particularly to control devices for obviating any electrical shock hazard when such glass panels are accidentally broken.

An electrically heated glass panel generally comprises a plurality of parallel panes of glass. An electrically conductive coating, layer or the like is provided on one of the inaccessible or inner surfaces of one of the panes. The glass panel is heated by causing an electrical current to pass through the electrically conductive coating. Electrically heated glass has many applications, but is particularly useful for refrigerator doors. Display doors utilizing electrically heated glass are frequently employed on refrigerated cabinets and compartments for supermarkets and other stores, to hold frozen foods, ice cream, dairy products and other foods and beverages requiring refrigeration. The electrical heating of the glass prevents the condensation of moisture on the glass. Such condensation tends to occur under conditions of high atmospheric humidity, even though the glass is of the insulating type, having a plurality of parallel panes with dead air spaces therebetween.

Under normal conditions, electrically heated glass does not present any shock hazard, because the electrically conductive coating or element is between the panes of glass and is inaccessible. However, if breakage of the 3,526,753 Patented Sept. 1, 1970 "Ice glass occurs due to some accident, the electrically conductive coating or other element may become accessible to the touch so that an electrical shock hazard may possibly exist.

The general object of the present invention is to obviate any such shock hazard when electrically heated glass is accidentally broken.

A further object is to provide a new and improved control device whereby the electrical power is effectively disconnected from the electrically heated glass when breakage occurs. The supply of power may be disconnected entirely, or may be so diminished that no shock hazard will exist.

Another object is to provide a new and improved control device or relay which effectively disconnects the electrical power in response to the interruption of the heating current due to the breakage of the glass.

A further object is to provide a new and improved control device which is effective to supply substantially full power to the electrically heated glass under normal conditions, while being operative to terminate or diminish the supply of power to a harmless level, when the heating current is interrupted by the breakage of the glass.

Another object is to provide a new and improved control device which utilizes a relay arrangement for applying full power initially and for maintaining the full supply of power as long as the heating current is uninterrupted, while being effective to disconnect or diminish the power when the heating current is interrupted by the breakage of the glass.

A further object is to provide a control device of the foregoing character in Which the relay arrangement may be of the thermal or magnetic type.

Another object is to provide such a new and improved control device which is effective and dependable in operation, yet is low in cost.

Further objects and advantages of the present invention will appear from the following description taken with the accompanying drawing, in which:

FIG. 1 is a diagrammatic illustration of an anti-shock control device to be described as one embodiment of the present invention.

FIG. 2 is a circuit diagram of a modified anti-shock device constituting a second embodiment.

FIG. 3 is a diagrammatic illustration of a third antishock device, constituting another embodiment.

FIG. 4 is a circuit diagram of a modified anti-shock device, constituting a fourth embodiment, similar to that illustrated in FIG. 2.

FIG. 5 is a diagrammatic illustration of another antishock device, constituting a fifth embodiment, which is compensated for ambient temperature variations.

FIG. 6 is a circuit diagram of another modified antishock device, similar to the one illustrated in FIG. 1.

FIG. 7 is an elevational view showing the mechanical construction of the anti-shock device represented by FIG. 4.

FIG. 8 is an end view of the device shown in FIG. 7.

FIG. 9 is an elevational view of the anti-shock device represented by FIG. 5.

As already indicated, FIG. 1 illustrates an anti-shock control device 10 which is employed to control the supply of electric power to an electrically heated glass panel 12. Such glass panels are applicable to refrigerators of all kinds, both domestic and commercial, but are particularly valuable for display-type refrigerators as employed in supermarkets or other stores. Thus, the illustrated panel 12 is shown in an application in which it is mounted in a display refrigerator door 14, which may be of the general type disclosed and claimed in the Kurowski Pat. Nos. 2,987,782 and 3,131,421.

The illustrated glass panel 12 comprises three

parallel panes

16, 17 and 18 with

spacers

19 and 20 between the edge portions thereof. However, the panel may comprise more or less than three panes. Thus, the panel may have two, four or even more panes of glass.

The illustrated

panes

16, 17 and 18 are mounted in a frame or retainer 22.

Insulating spaces

24 and 25 are provided between the panes 16-18. The

spaces

24 and 25 are normally filled with dry air, which provides good heat insulation and obviates any condensation of moisture in the

spaces

24 and 25. The door 14 comprises an outer frame 26, preferably made of metal, in which the glass panel 12 is mounted.

An electrically conductive coating or layer 28 is provided on one of the inaccessible surfaces of one of the panes 16-18. Such coatings are known to those skilled in the art. The coating 28 may be transparent so that it does not interfere with visibility through the glass panel. The coating 28 may be intimately bonded or fused to the glass pane. In the illustrated construction, the conductive coating 28 is on the rear surface of the front or outer pane 17.

Suitable leads 30 and 32 are connected to the conductive coating 28 adjacent the opposite edges of the glass panel 12. The leads 30 and 32 are brought out of the edges of the glass panel so that electrical power may be supplied thereto.

The electrical power is derived from an ordinary electrical line 34 comprising

line wires

36 and 38. The electrical line 34 may be adapted to supply alternating current at 110 volts and 60 cycles, or any other suitable voltage and frequency.

The control device 10 is connected between the line 34 and the electrically heated glass panel 12 and is effective to supply full electrical power to the glass panel during normal operation. If the glass panel is broken, the control device 10 disconnects the electrical power from the glass panel so that no shock hazard will exist, even though the broken edges of the conductive coating 28 are accessible to the touch.

The illustrated control device 10 comprises a thermal relay or switching device 40 utilizing a bimetallic strip or bimetal 42. A contactor or switch member 44 is mounted on the free end of the bimetal 42. When the bimetal 42 is at room temperature, the contactor 44 engages a switch contact 46. If the bimetal 42 is heated, it curls so as to cause the contactor 44 to move from the first contact 46 to a second contact 47, and then to a third contact 48.

The bimetal 42 is provided with a heating element or resistor 50 which is voltage responsive and is connected between the first contact 46 and the line wire 38. The other line wire 36 is connected to the stationary or mounted end of the bimetal 42. A resistor 52 is connected between the second contact 47 and the line wire 38. The third contact 48 is connected to the lead 30 which extends to the conductive coating 28. The other lead 32 is connected to the line wire 38.

Initially, the contactor 44 on the bimetal 42 engages the contact 46. When power is supplied to the line 34, current flows from the line wire 36 through the bimetal 42 and the contactor 44 to the contact 46, and then through the resistor 50 to the line wire 38. Considerable heat is thus generated in the resistor 50. It will be understood that the resistor 50 is closely adjacent the bimetal 42, so that the heat is quickly transmitted from the resistor to the bimetal. As a result, the bimetal 42 is caused to curl, so that the contactor 44 engages the contact 47, and then the contact 48. The circuit through the resistor 50 is broken as soon as the contactor 44 moves away from the contact 46, but the contactor 44 does not return to the contact 46, but rather overshoots past the contact 47 to the contact 48. This overshooting action is due to the rapid heating of the resistor 50, in conjunc- 4 tion with the somewhat delayed transmission of heat to the bimetal 42.

When the contactor 44 engages the contact 48, the main power circuit is established through the bimetal 42 and the conductive coating 28 on the electrically heated glass 12. The resulting current through the bimetal 42 is quite great, so that the bimetal is heated to a considerable extent by direct resistance heating. The bimetal 42 is heated to such an extent that it maintains its curl so that the contactor 44 continues to engage the contact 48.

This condition prevails as long as the glass panel 12 is unbroken so that it draws its normal current from the power line 34. If the glass panel is broken due to some accident, the heating current through the bimetal 42 is interrupted. As a result, the bimetal 42 loses some of its curl so that the contactor 44 returns to the contact 47. In this position, a circuit is established through the bimetal 42 and the resistor 52, between the

line wires

36 and 38. The resulting current through the resistor 52 is less than the normal load, but is sufiicient to maintain the temperature of the bimetal so that the contactor 44 continues to engage the contact 47. Thus, the electrical power is supplied to the resistor 52, rather than to the glass panel 12, so that the power is completely disconnected from the glass panel 12. It will be noted that the line wire 38 is grounded, while the line wire 36 is ungrounded. Thus, the disconnection of the glass panel 12 from the line wire 36 is suflicient to obviate any electric shock hazard.

If the electric power is disconnected from the line 34, the control device 10 is de-energized, so that the bimetal 42 returns to its initial position, in which the contactor 44 engages the contact 46. The glass panel 12 may then be replaced with a new unit, so that the system will be ready to go into normal operation.

FIG. 2 illustrates a modified control device which is adapted to diminish the supply of electric power to a harmless level, if the glass panel 12 is broken. In FIG. 2 and the subsequent figures, the conductive coating or heating element 28, constituting the normal resistive load, is shown symbolically. In the control device 60 of FIG. 2, the heating element 28 is adapted to be connected across the

line wires

36 and 38 through a resistor 62, a bimetal 64, and a pair of

contacts

66 and 68. The resistors 62 is of a small value and is connected between the line wire 36 and the stationary or mounted end of the bimetal 64. The contact 66 is carried on the free or movable end of the bimetal 64. The contact 68 is adapted to be engaged by the contact 66 and is connected to the ungrounded lead 30 running to the heating element 28. The bimetal 64 is adapted to be heated by a resistor which is connected between the contact 68 and the stationary end of the bimetal 64. The resistor 62 is also adapted to heat the bimetal 64. It will be noted that the resistor 62 is effectively in series with the

contacts

66 and 68, while the resistor 70 is effectively connected across the contacts.

Before power is applied to the line 34, the bimetal 64 is in the position shown in FIG. 2, so that the contact 66 is out of engagement with the contact 68. When power is applied to the line 34, current flows through the series circuit comprising the

resistors

62 and 70 and the heating element 28. The resistor 70 is of a relatively high value, so that considerable heat is generated therein by the application of the line voltage. As a result, the bimetal 64 is heated so that it curls in such a direction that the contact 66 engages the contact 68. The normal heating circuit is thus completed through the resistor 62, the bimetal 64, the

contacts

66 and 68, and the heating element 28. The resistor 70 is bypassed or short-circuited by the bimetal 64 and the

contacts

66 and 68, so that the resistor 70 is no longer heated to any substantial extent. However, the resistor 62 is heated sufficiently by the normal load current through the heating element 28, with the result that the bimetal 64 is maintained in a curled position, so that the

contacts

66 and 68 are held closed.

If the glass heating element 28 is broken due to some accident, the load current is interrupted so that the resistor 62 is no longer heated. Thus, the contact 66 is moved out of engagement with the contact 68. As a result, the resistor 70 is switched into the circuit between the ungrounded power line 36 and the ungrounded lead 30 to the heating element 28. The resistor 70 is of a sufficiently high value to obviate any shock hazard at the ungrounded side of the heating element 28. Thus, the resistor 70 so diminishes the supply of power to the broken heating element 28 that the power may be considered to have been etfectively disconnected. If anyone should happen to touch the broken heating element 28, he will not receive a hazardous shock.

The control devices described thus far utilize thermal control relays, but other types of relays or switching devices may be employed, including magnetic relays and electronic switching devices. Thus, FIG. 3 illustrates a modified control device 80 utilizing a magnetic relay 82. It will be seen that the relay 82 comprises two

coils

84 and 86, both of which are adapted to operate a movable armature 88, so as to close a pair of switching

contacts

90 and 92. In the illustrated control devices 80, the coil 84 has a large number of turns and a high electrical resistance and impedance, while the coil 86 has a relatively small number of turns and a low electrical resistance and impedance. The coil 84 is voltage responsive and connected between the ungrounded line wire 36 and the ungrounded lead 30 running to the heating element 28. The coil 86 is current responsive and is connected in a series circuit with the

contacts

90 and 92 between the ungrounded line wire 36 and the ungrounded lead 30.

When voltage is supplied to the line 34, voltage develops across the

open contacts

90 and 92 so that current flows through the series circuit comprising the coil 84 and the heating element 28. As a result, the armature 88 is actuated so as to close the

contacts

90 and 92. The normal load current then flows through the series circuit comprising the coil 86, the

contacts

90 and 92, and the heating element 28. The high resistance coil 84 is effectively bypassed by the series circuit comprising the low resistance coil 86 and the

contacts

90 and 92. The energization of the coil 86 holds the

contacts

90 and 92 closed.

If the heating element 28 is broken due to some accident, the normal load current is interrupted. Thus, the coil 86 is de-energized so that the relay 82 drops out. As a result, the

contacts

90 and 92 are opened. The coil 84 is of such a high resistance that only an insignificant and harmless amount of power is supplied to the ungrounded lead 30. Accordingly, the shock hazard is obviated and the broken heating element 28 is effectively disconnected from the power line 34.

- FIG. 4 illustrates another modified control device 100 which is similar to that illustrated in FIG. 2, except that the separate series resistor 62 is not needed, because the bimetal 64 is heated sufficiently by direct resistance heating. Thus, the line wire 36 is connected directly to the stationary or mounted end of the bimetal 64.

In the control device 100, the

contacts

66 and 68 are initially open. When power' is applied to the line 34, a small current flows through the resistor 70 and the heating element 28. The resistor 70 is rapidly heated so that the adjacent bimetal 64 is caused to curl. As a result, the contact 66 engages the contact 68. This closes the normal heating circuit, so that the normal load current flows through the bimetal 64 and the

contacts

66 and 68 to the heating element 28. The load current causes heating of the bimetal 64 due to its own resistance. This heating is suflicient to maintain the bimetal 64 in a curled position, so that the

contacts

66 and 68 remain closed.

If the heating element 28 is broken, the normal load current no longer flows through the bimetal 64 so that it cools off and causes the

contacts

66 and 68 to open. The high value resistor 70 is thus introduced into the circuit between the ungrounded line wire 36 and the ungrounded lead 30. The resistor 70 is of such a high value that no shock hazard exists at the ungrounded lead 30.

FIG. 5 illustrates another modified anti-shock control device which is similar to that illustrated in FIG. 4, except that the device of FIG. 5 is compensated for variations in the ambient or atmospheric temperature. The device 110 of FIG. 5 is adapted to operate in a consistent manner over a wide range of ambient temperature varia tions.

It will be seen that the control device 110 of FIG. 5 employs the bimetal 64, the

contacts

66 and 68 and the resistor 70, as previously described. However, the contact 68 is mounted on a compensating bimetal 112, rather than on a stationary support. The compensating bimetal 112 is adapted to curl with changes in the ambient temperature, so as to maintain the relationship between the

contacts

66 and 68 unchanged, despite the ambient temperature variations. Thus, the compensating bimetal 112 moves the contact 68 with changes in the ambient temperature, to follow the similar movements of the contact 66, due to the effects of ambient temperature variations upon the bimetal 64.

It will be seen that the compensating bimetal 112 is remote from the heating resistor 70, which is adjacent the main bimetal 64. Moreover, the load current does not pass through the bimetal 112. Thus, aside from the compensating action of the bimetal 112, the operation of the control device 110 of FIG. 5 is the same as described in connection with FIG. 4. Initially, the resistor 70 heats the bimetal 64 so that the

contacts

66 and 68 are closed. Thereafter, the load current heats the bimetal 64 by direct resistance heating. If the heating element 28 is broken, the interruption of the load current causes the bimetal 64 to cool so that the

contacts

66 and 68 are opened.

FIG. 6 illustrates another modified anti-shock device which is the same as that illustrated in FIG. 1, except that the resistor 52 is replaced with a resistor 122 which is connected between the

contacts

46 and 47. The resistor 122 may be of a higher value than the resistor 52.

The operation of the control device 120 is the same as described in connection with FIG. 1, except for the manner in which the contactor 44 is maintained in engagement with the contact 47 when the glass heating element 28 is broken. The breakage of the heating element 28 interrupts the load current, with the result that the bimetal 42 cools oif and starts to move back toward its initial position. When the contactor 44 engages the contact point 47, a circuit is established between the

line wires

36 and 38, through the bimetal 42, the contactor 44, the contact 47, the resistor 122 and the resistor 50. The current in this circuit heats the bimetal 42 to such an extent that the contactor 44 is maintained in engagement with the contact 47. Because of the high value of the resistor 50, only a small current is needed in this circuit. Thus, the resistor 122 may also be of a high value. If desired, the resistor 122 may be located near the bimetal 42 so that the bimetal is also heated by the heat generated in the resistor 122. The heat generated in the

resistors

50 and 112 is insufficient to cause the contactor 44 to move against the contact 48. Thus, the broken heating element 128 remains disconnected from the un grounded power line 36.

By way of example, FIGS. 7 and 8 illustrate a mechanical construction which may be employed for the antishock control device 100 as shown in FIG. 4. It will be seen that the bimetal 64 is in the form of a helical ribbon 124 which is coiled around the resistor 70. As shown, the resistor 70 comprises a generally cylindrical body 126 having end leads 128 and 130 extending axially from the opposite ends thereof. One end of the helical ribbon 124 is soldered, welded or otherwise secured to the lead 128 to form a joint 132. The movable contact 66 is soldered, welded or otherwise secured to the free end of the helical coil 124. It will be seen that the fixed contact 68 is mounted on a strip or other support 134, which is soldered, welded or otherwise secured to the lead 130, to form a joint 136.

When the resistor 70 heats the helical bimetallic strip 124, it curls in a counter-clockwise direction, as seen in FIG. 8, so that the contact 66 moves against the contact 68. During normal operation, the load current passes along the helical bimetallic strip 124 and heats it to such an extent that the

contacts

66 and 68 are kept closed.

FIG. 9 illustrates a mechanical construction for the compensated control device as shown in FIG. 5. It will be seen that the compensating bimetal 112 takes the form of a helical bimetallic strip 142 which is coiled around the end lead 130 of the resistor 70. One end of the helical strip 142 is soldered, welded or otherwise secured to the lead 130 to form a joint 144. The contact 68 is mounted on the free end of the bimetallic strip 142, adjacent the contact 66. To prevent the bimetallic strip 142 from carrying the full load current, a flexible pig-tail lead 146 is connected between the contact 68 and the end lead 130.

In the construction of FIG. 9, the bimetallic strip 142 is arranged to curl in such a direction as to compensate for the curling of the main bimetallic strip 124 due to ambient temperature variations. With increasing ambient temperature, the main bimetallic strip 124 becomes curled more tightly, while the compensating bimetallic strip 142 becomes curled less tightly. Thus, the relationship between the

contacts

66 and 68 is kept substantially the same. The main bimetallic strip 124 is wound with the more expansive metal on the outside, while the compensating bimetallic strip 142 is wound with the more expansive metal on the inside.

The initial current through the resistor 70 heats the main bimetallic strip 124 and causes it to become wound more tightly so that the contact 66 engages the contact 68. The compensating bimetallic strip 142 is remote from the resistor 70 and thus is heated very little by the resistor. After the

contacts

66 and 68 are closed, the resistor 70 is no longer heated, but the bimetallic strip 124 is heated by the load current. Very little of the load current passes along the compensating lbimetallic strip 142, because most of the load current is carried by the flexible lead 146. When the load current is interrupted, the main bimetallic strip 124 cools off and is effective to open the

contacts

66 and 68. The resistor 70 is of such a high value that it eliminates the shock hazard at the broken glass heating element.

It will be recognized that the present invention provides efiective means for obviating the shock hazard when electrically heated glass is broken. The control devices of the present invention are eifective to disconnect the electrical power from the glass, or to diminish the supply of power to such an extent that the shock hazard is eliminated. While the anti-shock control devices of the present invention are effective in operation, they are extremely low in cost and easy to manufacture.

Various other modifications, alternative constructions, and equivalents may be employed without departing from the true spirit and scope of the invention, as exemplified in the foregoing description and defined in the following claims.

We claim:

1. Fully automatic electrical heating apparatus,

comprising the combination of a plural pane glass pane1 having an inaccessible surface with a heating element mounted thereon,

a power line for receiving electric power,

switching means connected between said power line and said heating element,

first electrically operable automatic means for efiectively closing said switching means in response to the application of power to said power line,

the closure of said switching means being effective to supply normal load current to said heating element from said power line,

and second means responsive to the interruption of the normal load current to cause the opening of said switching means,

so as to obviate any shock hazard in the event of breakage of said glass panel.

2. Apparatus according to claim 1,

in which said switching means comprise a pair of normally open relay contacts,

said first means comprising a voltage responsive element connected between said power line and said heating element for causing closure of said contacts,

said second means comprising a current responsive element connected to carry the normal load current to said heating element for maintaining the closure of said contacts,

whereby said contacts will open in response to interruption of the normal load current,

said voltage responsive element having a high impedance in relation to the applied voltage such that the current through said voltage responsive element when said switching means are open is limited to a value which does not present a shock hazard to human health.

3. Apparatus according to claim 1,

in which said switching means comprise a pair of contacts connected between said power line and said heating element,

and a bimetal for carrying one of said contacts,

said first means comprising a first heater adjacent said bimetal and effectively connected across said contacts for causing said bimetal to close said contacts,

said second means comprising a second heater connected to carry said normal load current for heating said bimetal to maintain closure of said contacts,

whereby the breakage of said heating element is effective to de-energize said second heater while preventing energization of said first heater,

said first heater having a high resistance in relation to the applied voltage such that the current through said first heater is limited to a value which does not present a shock hazard to human health.

4. Apparatus according to claim 1,

in which said switching means comprise a pair of normally open contacts connected between said power line and said heating element,

and a bimetal for carrying one of said contacts,

said first means comprising a first resistance adjacent said bimetal and eifectively connected across said contacts for heating said bimetal to cause closure of said contacts,

said second means comprising a second resistance for carrying the normal load current to heat said bimetal and maintain the closure of said contacts,

the breakage of said heating element being etfective to de-energize said second resistance while preventing energization of said first resistance,

said first resistance having a high value in relation to the applied voltage such that the current through said first resistance is limited to a value which does not present a shock hazard to human health.

5. Apparatus according to claim 4,

in which said second resistance comprises the selfcontained resistance of said bimetal.

6. Apparatus according to claim 1,

in which said switching means comprise a pair of normally open contacts connected between said power line and said heating element for supplying the normal load current to said heating element,

and a bimetal for carrying one of said contacts,

said first means comprising a resistance heater adjacent said bimetal and eifectively connected across said contacts for causing said bimetal to close said concontacts,

said second means comprising means for causing said load current to fiow along said bimetal whereby said bimetal is heated by said load current to maintain the closure of said contacts,

the breakage of said glass panel being efiective to interrupt the load current along said bimetal while preventing the energization of said resistance heater,

/ said resistance heater having a high resistance in relation to the applied voltage such that the current through said resistance heater is limited to a value which does not present a shock hazard to human health.

7. Apparatus according to claim 6,

in which said bimetal is in the form of a generally helical member,

said resistance heater being'mounted within said helical member.

8. Apparatus according to claim 6,

in which said bimetal is in the form of a helical member, I

said resistance heater being disposed within said helical member,

said resistance heater having a first end lead supporting one end of said helical member,

one of said contacts being supported by the other end of said helical member,

said resistance heater having a second end lead supporting the other contact.

9. Apparatus according to claim 1,

in which said switching means comprises a pair of normally open contacts effectively connected between said power line and said heating element,

said first means comprising a relatively high impedance coil eflectively connected across said contacts for closing said contacts,

said second means comprising a relatively low impedance coil effectively connected in series with said contacts for maintaining the closure of said contacts,

whereby the interruption of the normal load current through said-low impedancecoil will cause the opening of said contacts, i

said high impedance coil being effective to obviate any shock hazard at said heating element.

10. Apparatus according to. claim 1,

in which said switching means comprises a' series of three contacts,

a contactor movable successively to said contacts,

and a bimetal carrying said contactor,

said first means comprising a first resistance heater adjacent said bimetal and having an energizing circuit connected to the first of said contacts for initially heating said bimetal and causing said bimetal to move said contactor to the second and third of said contacts,

said second means comprising means for causing the normal load current to flow through said bimetal and said contactor to said third contact for heating said bimetal and thereby maintaining said contactor against said third contact,

and a holding resistance having an energizing circuit connected to said second contact for heating said bimetal to hold said contactor against said second contact upon the return of said contactor when the normal load current is interrupted.

11. Apparatus according to claim 10,

in which said holding resistance is connected from said second contact to said first contact and thus to said first resistance heater.

12. Apparatus according to claim 1,

in which said switching means comprises first, second and third contacts,

a contactor initially engaging said first contact and movable to said second and third contacts,

and a bimetal for moving said contactor,

said first means compressing a first resistance heater adjacent said bimetal and having an energizing circuit connected to said first contact for initially heating said bimetal to move said contactor to said second and third contact,

said contactor and said third contact being effective to carry the normal load current,

said second means comprising means for causing the normal load current to heat said bimetal for maintaining said contactor against said third contact while causing said contactor to return to said second contact upon interruption of the load current,

and a second resistance having an energizing circuit connected to said second contact for heating the bimetal to maintain the contactor against said second contact.

13. Apparatus according to claim 12,

in which said second resistance is connected from said second contact to said first contact and thus to said first resistance heater.

14. Apparatus according to claim 12,

in which said means comprises circuit connections for causing the normal load current to flow along said bimetal to heat said bimetal.

15. Electrical heating apparatus,

comprising the combination of a glass panel having an inaccessible surface with a heating element mounted thereon,

a power line for receiving electric power,

switching means connected between said power line and said heating element,

first electrically operable means for effectively closing said switching means in response to the application of power to said power line,

the closure of said switching means being elfective to supply normal load current to said heating element from said power line,

second means responsive to the interruption of the normal load current to cause the opening of said switching means, so as to obviate any shock hazard in the event of breakage of said glass panel,

said switching means comprising a pair of contacts connected between said power line and said heating element for carrying the normal load current,

a bimetal for carrying one of said contacts,

' said first means comprising a' resistance heater effectively connected across said contacts for heating said bimetal to close said contacts,

said second means comprising means for causing said normal load current to heat said bimetal to maintain the closure of said contacts,

and a compensating bimetal for carrying the other contact to compensate for the etfects of ambient temperature variations on said first mentioned bimetal,

said resistance heater having a high resistance in relation to the applied voltage such that the current through said resistance heater is limited to a value which does not present a shock hazard to human health.

16. An anti-shock control device for electrically heated glass or the like,

comprising the combination of a pair of normally open contacts to carry the normal load current,

a bimetal carrying one of said contacts,

a resistance heater effectively connected across said contacts for heating said bimetal and thereby causing the closure of said contacts,

means for causing the normal heating current through said contacts to heat said bimetal and thereby maintain the closure of said contacts,

whereby the interruption of the normal load current causes the opening of said contacts,

said resistance heater having a high value in relation to the applied voltage such that the current through said resistance heater when said contacts are open is limited to a value which does not present a shock hazard to human health,

and a compensating bimetal for carrying the other contact to compensate for the efiects of ambient temperature variations on said first-mentioned bimetal.

17. A control device according to claim 16,

said means comprising circuit connections for causing the normal load current to flow along said firstmentioned bimetal while avoiding the flow of the load current along said compensating bimetal.

18. A control device according to claim 7,

in which said first mentioned bimetal is in the form of a first helical member,

said resistance heater being disposed within said first helical member,

said resistance heater having a first end lead supporting one end of said first helical member,

said one contact being mounted on the other end of said first helical member,

said compensating bimetal being in the form of a second helical member having one end supporting the other contact,

said resistance heater having a second end lead extending within said second helical member and supporting the other end thereof,

said compensating bimetal being effective to compensate for the effects of ambient temperature variations on said first-mentioned bimetal.

19. Fully automatic electrical heating apparatus,

comprising the combination of a plural pane glass panel having an inaccessible surface with a heating element mounted thereon,

a power line for receiving electric power,

normally open switching means connected between said power line and said heating element,

first electrically operable automatic means responsive to the development of substantial voltage across said switching mean for closing said switching means to cause said switching means to carry the normal load current to said heating element,

and second means for causing the normal load current to maintain the closure of said switching means while causing the opening of said switching means in response to the interruption of said load current,

said switching means being arranged to inactivate said first electrically operable means in response to closure of said switching means.

20. A control device according to claim 19,

in which said switching means comprises a pair of contacts and a bimetal for closing said contacts,

said first means comprising a first resistance heater for heating said bimetal to close said contacts,

said second means comprising a heating circuit for causing the load current through said contacts to heat said bimetal,

said first resistance heater having a high value in relation to the applied voltage such that the current through said first resistance heater is limited to a value which does not present a shock hazard to human health.

21. A control device according to claim 19,

in which said switching means comprises a pair of normally open relay contacts,

said first means comprising a high impedance coil elfectively connected across said contacts for closing said contacts,

and a low impedance coil elfectively connected in series with said contacts for maintaining the closure thereof,

said high impedance coil having an impedance which is high in relation to the applied voltage such that the current through said high impedance coil is limited to a value which does not present a shock hazard to human health.

References Cited UNITED STATES PATENTS 2,403,803 7/1946 Kearsley 219-511 X 2,417,778 3/ 1947 Osterheld 219-512 X 2,448,289 8/1948 Anderson 219-511 2,499,906 3/1950 Crise 219-511 2,756,382 7/ 1956 Wuerth 323-68 2,806,118 9/1957 Peterson 21 9-203 2,914,637 11/1959 Wuerth 200-122 2,945,933 7/1960 Girolano et al. 200-122 3,330,942 7 1967 Whitson 219-522 2,557,905 6/1951 Burton et a1. 219-522 X 2,898,433 8/1959 Felt 219-202 X 3,379,859 4/1967 Marriott 219-522 3,449,551 6/ 1969 Aisanich 219-522 X VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R.

Patent No. ,753 Dated Sept. 1, 1970 Inventor(s) D. J. Aisanich et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 43, change "resistors" to "resistor."

Column 11, line 9, change "7" to "16." Column 11, line 36, change "mean" to "means."

SiGNED AND QEALED 6EAL) Amen:

EdwardMFIctchcr, Ir. mm E. SGHUYIER, m-

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