US2704803A - Control circuits for electric blankets - Google Patents

Description

March 1955 G. c. CROWLEY ETAL CONTROL CIRCUITS FOR ELECTRIC BLANKETS 2 Sheets-Sheet 1 Filed July 11, 1951 Inventors. George C. Crowleg,

Rober'fIG Holmes,

Paul A.Cheok,

Their- Attorney.

March 22, 1955 a c CROWLEY ETAL CONTROL CIRCUITS FOR ELECTRIC BLANKETS 2 Sheets-Sheet 2 Filed July 11, 1951 Inventors: Gecrge C. Crowley,

Robert G. Holmes,

Paul A.Check,

I 8 Their Attorney.

United States Patent 2,704,803 CONTROL CIRCUITS FOR ELECTRIC BLANKETS Application July 11, 1951, Serial No. 236,268 9 Claims. (Cl. 219-24)) This invention relates to electrically-heated blankets and more particularly to the control means used to regulate the current flow to the heaters for such blankets.

Heretofore, there have been available two types of double-bed electric blankets, namely, the single-control type and the dual-control type. In the single-control type, the same temperature is maintained throughout the entire blanket, but in the dual-control type, a different temperature may be maintained in one half of the blanket than in the other half. The obvious advantage of the dual-control blanket over the single-control blanket is, of course, that when two persons are using the dual-control blanket, each person may then set the temperature of his half of the blanket to his own liking. However, the dual-control blanket possesses a disadvantage in that it is more expensive than the single-control blanket. The difference in cost between the two types is caused by the fact that the dualcontrol blanket requires two thermal control devices, such as bimetallic cycling controls, while the single-control blanket requires only one such thermal control device.

Due to this price differential, persons many times purchase the single-control blanket without considering seriously whether it will satisfy their wants. When, as oftentimes happens, they subsequently find that for them a dual-control blanket is almost a necessity, their only recourse is to sell the single-control blanket, often at a loss, and buy a dual-control blanket. Although at present this inconvenience and accompanying monetary loss is unavoidable, it could be averted if there were only some way of converting the single-control blanket to a dual-control blanket. The provision of such conversion means would also be desirable from the manufacturing point of view, since the manufacturers would then need to make only a single-control blanket and a conversion unit to change it to a dual-controlblanket, rather than making two types of blankets as they now do. i

it is an object of this invention to provide an electric blanket which may be simply and easily converted from a single-control unit to a dual-controlunit.

It is a further object of this invention to provide a conversion unit for converting a single-control electric blanket into a dual-control blanket.

It is another object of this invention to provide a singlecontrol blanket circuit having terminals adapted to receive a quick plug-in type conversion unit whereby the conversion unit and single-control circuit act together as a dual-control blanket circuit.

The features of this invention be novel are pointed out with pended claims. The invention to organization and mode of further objects and advantages derstood by reference to the be taken in conjunction with ings in which:

Fig. l is a schematic diagram of one form of this invention as embodied in a singlet-control blanket circuit and a conversion unit for converting, the circuit to a dualcontrol circuit;

Fig. 2 is a schematic diagram of an alternate for'm of this invention as embodied in a single-control blanket circuit which is adapted to be converted into a dualcontrol circuit;

Fig. 3 is a schematic diagram including the circuit of Fig. 2 in block form but showing it converted to a dual-control circuit by a conversion unit;

Fig. 4 is a view of a single-control electric blanket together with its control unit and aconversion unit for converting it into a dual-control blanket, the control which are believed to particularity in the apitself, however, both as operation, together with thereof, maybe best unfollowing description to the accompanying draw unit and conversion unit embodying a preferred form of this invention;

Fig. 5 is a schematic circuit diagram of the preferred form of this invention shown in Fig. 4; and

Fig. 6 is a view of the quick detachable means used to connect together the single-control and conversion units of Figs. 4 and 5.

Referring to Fig. l, therein is shown a double-bed electric blanket 1 in which there is arranged, in any of the patterns well known to the art, a combined heating and thermosensitive element 2 such as is disclosed and claimed in the copending application of Spooner et a1., Serial No. 91,396 for Thermo-Sensitive Devices and Apparatus Incorporating the Same filed May 4, 1949, now Patent 2,581,212, and owned by the General Electrio Company, the assignee of the. present invention. This invention is illustrated and will be described with respect to blankets incorporating such a combined heating and thermosensitive element, since an element of that sort provides the most convenient and reliable means for actuating the over-temperature protection circuit customarily included in blanket control circuits. However, the invention is not limited to such an element, for as will become increasingly obvious, it may be employed with any sort of resistance heater and blanket temperature sensing element. As shown, the preferred combined heating and thermosensitive element 2 comprises a first conductor or heater resistor 3 separated from a second conductor or signal wire 4 by a thin layer 5 of one of the organic materials disclosed in the aforementioned Spooner et al., Patent 2,581,212, nylon being preferable. The thin layer 5 is essentially an insulator at normal operation temperatures of the blanket and is a conductor of electricity at predetermined higher temperatures. I

Otuside the blanket, element 2 is connected to a multiterminal' plug 6 having contacts 6a, 6b, 6c, 6d and 6e. Signal wire 4 is connected across terminals 6b and 6d, and resistor 3 is connected across terminals 6a and 62. The remaining terminal 6c is connected to a tap 7 provided at the midpoint of resistor 3. Moreover, the sections of resistor 3 lying respectively between midtap 7 and terminals 6a and 6e are arranged on opposite halves or sides of blanket 1, so that when the blanket is used to cover two persons, the blanket area over each person is heated by a diiferent section of the resistor. An obvious modification of this circuit, of course, would be to use a separate heating and thermosensitive element in each half of the blanket and then connect the two elements together so that the same actual circuit exists with two elements as is illustrated using only one element. Thus, for example, if two elements were used, their heater resistors would each have an end terminal common to both and each would have a separate end terminal. No matter which is used, the one midtapped heater, or two heaters connected at their one end to a common terminal, each of the heater sections preferably should have a resistance in the order of 135 ohms, if the blanket is to be used with the conventional volt 60 cycle A. C. domestic supply circuit and such control units as are described hereinafter.

Plug 6 is adzpted to cooperate either with a multiterminal plug-in type receptacle or socket 8, which has female terminals 8a, 8b, 8c, 8d, 32, and 8 or with a combination plug-and-socket receptacle member 9, which includes four combination terminals fin, 9b, 9c, and 9d, each consisting of a female terminal jumpered to a male contact, a separate female terminal 9e, and a separate male contact 9f. Plug 6 may be inserted directly in socket 8 or may be joined thereto through plug 9.

Socket 8 forms the terminus for a blanket control circuit which is housed in a control box 10 and is energized by a plug 11 from any conventional domestic supply circuit. This control circuit both regulates the current to the blanket heating circuit, i. e., heater resistor 3, and also serves to de-energize the blanket upon the overheating of any portion thereof. This overt-emperature protection is provided by a circuit such as is disclosed and claimed in the copending application of George C. Crowley for Temperature Responsive Control Circuit, Serial No. 91,402, filed May 4, 1949, now Patent 2,565,478, and also owned by the General Electric Company, the assignee of the present invention. Specifically, the overtemperature protection is provided by a relay 12 whose normally open contacts 13 are connected serially in the blanket heating circuit; and in accordance with the aforesaid Crowley Patent 2,565,478, the operating coil' 14 of relay 12 is connected to be energized across opposite output terminals of an impedance bridge, two legs of which consists of a voltage divider "circuit comprising the serially connected 12,000 ohm resistors 15 and 16 and the other two legs of which'consist of a series resonant circuit comprising in serial relationship a 0.1 mfd. capacitor 17, signal wire 4, and a 75-henry choke coil 18, the resistance of signal wire 4 being preferably less than 400 ohms.

In order to provide means for connecting signal wire 4 into the resonant circuit, the ends of capacitor 17 and choke 18 associated therewith are brought out respec tively to terminals 8d and 8b of plug 8. Thus, no matter whether plug 6 is joined directly to plug 8 or is joined thereto through plug 9, signal wire 4 is still connected in the same position in the resonant circuit. The plug connection used then has no effect on the voltage supplied to coil 14 and thereby has no effect on the operation of relay 12. For proper operation of the control circuit, the impedance of coil 14 should be approximately 90,000 ohms with the relay armature closed, and relay 12 should pick up with about 130 volts applied to coil 14 and should drop out at approximately 75 volts.

The control circuit may be energized by momentarily closing a switch 19 which is biased to the open position and manually operable to the closed position. The closing of switch 19 energizes the resonant circuit directly and energizes resistors 15 and 16 through a 12,000 ohm current limiting resistor 20. The resistors act as voltage dividers and thus the voltage available at one output terminal of the impedance bridge is approximately line voltage. However, due to the series resonant effect of the resonant circuit, the voltage available at the other output terminal of the bridge, i. e., the voltage across choke 18, rises considerably above line voltage. In fact, with a source voltage of 115 volts, the closing of switch 19 results in a voltage of about 150 volts being applied to coil 14. This causes relay 12 to pick up, closing contacts 13 and energizing the heating circuit.

Once relay 12 closes, switch 19 may the impedance bridge is then energized through contacts 13. The voltage applied to coil 14 is not as great, however, when the bridge is energized through contacts 13 as it is when the bridge is energized through switch 19, because of an automatic shift in position of resistor 20 from the voltage divider circuit to the resonant circuit. But under normal operating conditions of the bridge, the

voltage does not fall off enough to allow relay 12 to .drop

out. The fact that the control circuit is energized is indicated by a neon glow lamp 21, which is energized across the voltage divider circuit through a 200,000 ohm current limiting resistor 22.

As previously mentioned, the closing of contacts 13 serves to energize the blanket heating circuit. According to this invention, however, the thermal control device 23 included in the control circuit may be used, depending upon whether or not plug 9 is inserted between plugs 6 and 8, to control the heating of both sides of the blanket or to control the heating of only one side of the blanket. First, assuming plugs 6 and 8 to be direct connected so that terminals 6a, 6b, 6c, 6d and 6e mesh respectively with terminals 30, Sb, 8c, 8d, and 82, the heating of both sections of heater resistor 3 is then regulated by control device 23. Although various thermal control devices may be employed, the preferred control is of the roomtemperature responsive type described and claimed in the U. S. patent to William K. Kearsley, 2,195,958, April 2, 1940. The temperature regulation is accomplished through a bimetallic cyling switch member 24, which alternately carries a movable contact 25 into and out of engagement with a fixed contact 26 in response to the heat supplied from a 1.35 ohm heater resistor 27 and the surrounding atmosphere. An external control knob 28 is provided to act on switch member 24 in order that the control may be adjusted to produce various operating temperatures of the blanket.

Contacts 25 and 26 form a serial part of the heating circuit, contact 25'being connected to one side of the be released, since heating of opposite halves of the blanket.

power supply line, and contact 26 being connected to the blanket heater terminals 8a and 86 of plug 3. Specifically, contact 26 is connected directly to terminal 8e but is connected to terminal 8a through heater 27.

The third blanket heater terminal 3c of socket 8 is connected in the control circuit to contacts 13. Since the associated terminals 6a, 6e and 6c of plug 6 are connected respectively to opposite ends or" resistor 3 and to its midtap 7, the insertion of plug 6 into socket 8 thus connects the two sections of heater resistor 3 in parallel between contact 26 and contacts 13. Assuming control 23 to be calling for heat, i. e., contacts 25 and 26 being in engagement, the closing of contacts 13 then places the two sections of resistor 3 across the power supply.

Since the resistance of both sections of heater resistor 3 is approximately one-hundred'times the resistance of resistor 27, the addition of resistor 27 between one heater section and contact 26 does not cause an appreciable difierence in the current flowing in that section as opposed to the current flowing in the section connected directly to contact 26. Thus, as switch arm 24 cycles to open contacts 25 and 26 in response to the heat from resistor 27, an essentially even temperature is maintained in both sides of the blanket. In other words, the temperatures on both sides of the blanket are regulated by control device 23.

The blanket continues to operate subject to the cycling of switch arm 24 until it is tie-energized by the opening of contacts 13. These contacts may be opened at the discretion of the blanket users by means of'a normallyopen switch 29, which is connected in parallel with capacitor 17 and signal wire 4, or they may be opened automatically by the action of the control circuit upon an overheat condition of a predetermined magnitude occurring in the blanket. Both the manual shut-oft and the automatic shut-off are accomplished by disturbing the resonance of the resonant circuit, so that the voltage across choke 18 and thus across coil 14 falls 011 to a value insufiicient to keep relay 12 locked in.

Thus, the closing of switch 29 disturbs the circuit resonance by shorting out capacitor 17, while an overheat condition of the blanket disturbs the resonance by changing the impedance presented by nylon layer 5. At normal operating temperatures of the blanket, layer 5 is essentially an insulator, but if the blanket overheats to a predetermined cut-otf temperature, as fully explained in the aforementioned patent of Spooner et al., No. 2,581,212, the impedance of layer 5 decreases sufficiently in magnitude that appreciable current passes from resistor 3 to signal wire 4. These current paths formed between the resistor and the signal wire efiectively complete parallel circuits around capacitor 17 and choke 1S and thereby disturb the resonance of the resonant circuit. As mentioned above, this causes the voltage to decrease across coil 14 so that relay 12 drops out and opens the circuit. When the blanket, and thus control layer 5, has cooled sufficiently that there are no longer any parallel circuits between resistor 3 and signal wire 4 effective to disturb the circuit resonance, the closing of switch 19 will again restore the blanket to normal operation.

The action of the impedance bridge is exactly the same when plug 9 is inserted between plug 6 and socket 8 because signal wire 4 is still connected in the circuit in exactly the same manner. However, the insertion of plug 9 converts the blanket from a single-temperature control blanket to a dual-temperature control blanket, i. e., it provides means for independently controlling the For that purpose, in control box 10, terminal 8 of socket S is connected to the line side of switch 23, while in plug 9 a room-temperature responsive cycling control 30 is connected between terminals 9 and 9e. In other words. when plug 9 is placed in the circuit, terminals 641. 6b, 6c and 6d of'plug 6 are connected in the blanket circuit exactly the same'as before, but terminal 6e is connected to the line through control device 30, rather than through control device 23. Thus, the heating of one section of resistor 3 is still controlled by device 23 but the heating of the other section is controlled by device 30. Device 30, like device 23, is preferably of the type disclosed in.

the aforementioned Kearsley Patent 2,195,958 and has a bimetallic switch arm 31 which carries a contact 32 into and 91 1 of engagement with a fixed contact 33, in response to the heat supplied from a 1.35 ohm heater resistor 34 and the surrounding atmosphere. Resistor 34 is serially connected with contacts 32 and 33 and the heating circuit of the associated side of blanket 1, so that the. cycling of switch arm 31 controls the temperature of that side of the blanket. The control device is housed in a separate box and an external adjusting knob 36 is provided to act on switch arm 31 to supply means for adjusting the switch arm to open the contacts at various blanket temperatures.

Thus, in this first form, the invention provides means whereby an electric blanket may be converted from a single-control blanket to a dual-control blanket merely by the insertion of a special plug between the plug and socket ordinarily used to join the blanket to the singlecontrol device.

An alternate form of this invention, as embodied in a single-control electric blanket and a conversion unit therefor, is illustrated in Figs. 2 and 3 of the diagram. The same blanket heating element and the same overtemperature protection circuit are used in this form of the invention as were employed in the form shown in Fig. l, and hence identical members in the two forms are labeled with identical numbers. Thus, in Fig. 2, a combined heating and thermosensitive element 2 is arranged in a blanket 1 in the same manner as in Fig. 1, so that the heater resistor 3 is divided by midtap 7 into two sections disposed on opposite sides of the blanket. Outside the blanket, element 2 is connected to a S-terminal plug having male contacts 411a, 40b, 40c, 40d and 402, signal wire 4- being connected across terminals 400 and 402, resistor 3 being connected across terminals 40a and 49b, and midtap 7 being connected to terminal 4003. Adapted to receive plug 411 is a 7-terminal plug-in type receptacle or socket 41, having terminals 41a, 41b, 41c, 41d, 41a, 41], and 41g, the five terminals of plug 40 being inserted respectively in the upper five terminals 41a through 41e of socket 41 when the blanket is operated as a single control unit. As above, the control circuit includes a relay 12 whose coil 14 is energized across an impedance bridge, two legs of which comprise matched resistors 15 and 16, and the other two legs of which comprise a resonant circuit including capacitors 17, choke 18, and signal wire 4. Terminals 41c and 41e are connected respectively to choke 18 and capacitor 17 so that the joining of plug 40 and socket 41 completes the resonant circuit. The blanket heating circuit is likewise completed through plug 44) and socket 41, midtap 7 of resistor 3 being joined to one side of the power source through 1 terminal 41d and contacts 13 of relay 12, and the ends of resistor 3 being joined to the other side of the line through terminals 41a and 41b respectively and a room temperature responsive control device 42.

Device 42 is preferably of the type control device disclosed in the aforesaid Kearsley Patent 2,195,958, and here includes a bimetallic switch arm 43 which carries a movable contact 44 into and out of engagement with a fixed contact 45 in response to the total heat supplied from a 0.34 ohm heater resistor 46, a 1.01 ohm heater resistor 47 and the surrounding atmosphere. An external control knob 48 is provided to adjust the control to supply different blanket temperatures. Resistor 46 is connected alone between contact 45 and terminals 41a and 41b and is connected in series with resistor 47 between contact 45 and terminal 41 Contact 44 is joined to the opposite side of the power source from contacts 13 and also to socket terminal 41g. A plug 11 is provided to connect the control circuit to the conventional domestic power source, and an operation indicating circuit including neon glow lamp 21 and current limiting resistor 22 is provided for indicating when the blanket is energized.

As above, the blanket is energized by the closing of the switch 1% and may be de-energized either manually through the closing of a switch 27', or automatically through a change in the impedance of layer 5 upon an overheat condition occurring in the blanket. Switch 27 is connected in a different position in the circuit than was switch 27, being connected directly across coil 14. However, switch 27 accomplishes the same result as switch 27 Since when it is closed it shorts out the relay coil and causes relay 12 to drop out.

When plug 40 is connected in socket 41, as indicated in Fig. 2, control device 42 operates to control the temperature of both sides of the blanket, as both sections of the blanket heating circuit are then connected in series with contacts 44 and 45 of heater 46. Since heater 47 is not connected in the circuit, switch arm 43 cycles in response to the heat supplied from resistor 46 due to the sum of the currents in both sections of resistor 3 flowmg therein. Thus, the control circuit housed in control box 10 permits operation of the blanket as a singlecontrol unit.

However, if it is desired to operate the blanket as a dual-control unit, such a conversion may be made, as is illustrated in Fig. 3, by inserting one side of a combination plug-and-socket member 50 having four combination terminals 50a, 50b, 50c, and 59d, each consisting of a male contact jumpered to a female terminal, a male contact 562, and a female contact 50 into the lower five terminals 410 through 41g of socket 41, and then inserting plug 41) into the opposite side of member 50. The circuit inside control box 10 in Fig. 3 is identical with that inside the control box in Fig. 2, and in order to obtain the correct blanket connections with this form of the invention, the respectively jumpered male and female terminals of member 50 are displaced in numerical position from one side of member 50 to the other side, as shown. Thus, when member 50 is placed in the circuit, terminal 41c of socket 41 is connected to terminal 400 of plug 40, terminal 41d to terminal 40d, terminal 41c to terminal 40c, and terminal 41 to terminal 40a. Terminal 41g, however, is connected to terminal 40b through a temperature responsive control device 30, like that of Fig. 2, connected between terminals 50e and 50; of member 50 and housed in a control box 35.

Thus, although signal wire 4 is still connected in the same position in the resonant circuit, and midtap 7 is still connected through contacts 13 to one side of the power source, the connections to the ends of resistor 3 have been altered. The one end of resistor 3 is now connected to contact 45 through both resistors 46 and 47, and the other side of resistor 3 is now completely disconnected from contact 45, being connected through control device 30 to the same side of the line as contact 44. The two heater sections of resistor 3 are essentially in parallel across the power source, but the heating of each is controlled by a separate ambient temperature responsive control device, the temperature of one section being controlled by device 42 and the temperature of the other section being controlled by device 30.

In other words, exactly the same result may be accomplished with this form of the invention as with the firstdescribed form. Specifically, an electric blanket may be easily and quickly converted from a single-control blanket to a dual-control blanket by inserting a single plug-andsocket member in the proper position between the control box and the blanket itself. As above, equally as good results are obtained whether the blanket is operated as a single-control unit or as a dual-control unit.

The preferred form of this invention, however, is illustrated in Figs. 4, 5 and 6. Once again, the same heating and thermosensitive element 2 is arranged in a blanket 1 so that the heater resistor 3 is divided into two sections disposed on opposite sides or halves of the blanket. The various leads of element 2 are brought out of the blanket and are run through a multi-conductor cord 60 into a control box 61, wherein is housed a blanket control circuit. If so desired, cord 60 may be severed at some point and a plug-and-socket arrangement mounted on the free ends to provide means for disconnecting the blanket from the control box. Inside the control box, much of the circuit system is identical with that in control box 10, and the members in box 61 which are identical in construction and function to those in box 10 are numbered identically. For example, housed in box 61 except for signal wire 4 is an impedance bridge, two legs of which comprise matched resistors 15 and 15 and two legs of which comprise a resonant circuit including in serial relationship a capacitor 17, signal wire 4, and choke 18. The coil 14 of an electromagnetic relay is connected to be energized across the output terminals of the bridge, and the normally-open contacts 13 are connected serially in the blanket heating circuit. Relay 12 is actuated in exactly the same manner as in the other two forms of the invention and, as above, drops out to clear the circuit when switch 27 is closed or when an overheat condition '7 occurs in the blanket. The operation indicating circuit is also identical with that housed in control box 10.

The blanket heating connections, however, are somewhat difierent in this form of the invention. Thus, the lead from one end of resistor 3 is connected to an electrically conducting spring arm 62, which is mounted in a plug-in type receptacle or two terminal jack 63, and is normally in engagement with a contact 64. Contact 64 is in turn connected to contact 26 of thermostatic control device 23. Also connected to contact 26, but through heater 27, is the opposite end of resistor 3. Thus, both ends of the resistor are connected to one side of the line through the contacts of control device 23, while the midtap 7 of the resistor is connected, as before, to the other side of the line through contacts 13.

The blanket may then be operated as a single-control blanket with substantially identical heating in both sides of the blanket. The cycling of the bimetallic switch arm 24 is actually, however, responsive to the current in only one side of the blanket since its actuating heater 27 is connected in the circuit. of only one of the two sections of resistor 3. However, since the resistance of heater 27 is negligible compared with that of the sections of resistor 3, its connection in one section and not in the other does not cause any appreciable difference in the heating of the two sides of the blanket.

In order that the blanket may be operated as a dualcontrol unit, a connection is provided between the side of the power source associated with contact and a spring arm which is mounted in jack 63. As 18 more clearly shown in Fig. 6, jack 63 includes a pair of electrically insulating sockets 66 and 67, which are adapted to receive the male terminals 68 and 69 of a plug 70. The rounded ends of spring arms 62 and 65 extend respectively into sockets 67 and 66 through apertures provided in the socket walls, and are forced out of the sockets as plug is inserted therein. A circumferential groove is provided on each of the terminals 68 and 69 and upon plug 70 being fully inserted into jack 63 the rounded ends of spring arms 62 and 65 move into these grooves to retain the plug in the jack. The inserhon of plug 70 removes spring arm 62 from engagement with contact 64 and places the section of resistor 3 connected to contact 62 in series with a control device 71, which is mounted in a separate box 72 and is connected across terminals 68 and 69 by a two-conductor cord 73. S1nce spring arm 65 is joined directly to one side of the line, device 71 and the associatedsection of resistor 3 are thereby connected directly across the power source through midtap 7 and contacts 13.

Control device 71 is preferably of the room temperature responsive type control disclosed in the aforesa d Kearsley Patent 2,195,958 and includes a brmetalllc switch arm 74 which carries a movable contact 75 into and out of engagement with a fixed contact 76, in response to heat supplied from a heater resistor 77 and the surrounding atmosphere. An external control knob 78 is provided whereby the control may be adjusted to operate at different temperatures. Control device '71 is thus similar to the other thermostatic control devices described herein and serves to regulate the heating of the associated side of the blanket. 1

Although the insertion of plug 7 0 Into ack 63 cnanges the connections of one section of resistor 3, it does not change the connections of the other section which was originally energized from contact 26 through resistor 27. Therefore, that section of resistor 3 is still controlled by control device 23 and thereby an independent control is provided for each side of the blanket, device 71 controlling one side and device 23 controlling the other. The blanket may thus be converted from a single-control blanket to a double-control blanket merely by the insertion of plug 71 into the jacket 63, one particular advantage of this form of the invention being that only a two-conductor plug-and-jack system is required rather than a 5 to 7 conductor system as in the other forms illustrated.

Although the various circuits produce satisfactory results using the values stated for the various circu t components, these values are meant to be merely illustrative. Obviously, numerous modifications and alterations may be made by those skilled in the art without actually departing from the invention, and it is therefore aimed in the appended claims to cover all such equivalent variations as fall within the true spirit and scope of this invention.

.What we claim as new and desire to secure by Letters Patent of the United States is:

1. In combination with a blanket, a pair of heaters disposed in opposite sides of said blanket, a power supply for said heaters, connections between said heaters and said power supply comprising a first thermal control means for both heaters, said means including a multi-terminal socket and a multi-terminal plug receivable in said socket, a second thermal control means including a combination plug-and-socket member adapted to be inserted between said plug and said socket, said combination member being so arranged as to disconnect said first control means from operative relationship with one of said heaters upon being inserted between said plug and said socket, said combination member being further arranged to connect said second control means to control only said one of said heaters.

2. in combination with a blanket, first and second heaters disposed in opposite sides of said blanket, each of said heaters having an end terminal common to both and each having a separate end terminal, a pair of power supply terminals for said heaters, a multi-terminal socket and a multi-terminal plug adapted to be received in said socket, a connection between one of said supply terminals and said common terminal including said socket and said plug, a first thermal control device, connections between said separate end terminals and the other of said supply terminals including said plug, said socket, and said first thermal control device to cause said device to control both heaters, a combination plug and socket adapted to be inserted between said plug and said socket and adapted upon insertion therebetween to break the connection between the separate end terminal of said second heater and said first control device to cause said first control device to control said first heater only, a second thermal control device connected to said combination member to complete a circuit between said separate end terminal of said second heater and said other supply terminal on the insertion of said combination member between said plug and said socket, said second control device thereupon to control said second heater.

3. In combination with a blanket, a pair of heaters disposed in opposite sides of said blanket, each of said heaters having an end terminal common to both and each having a separate end terminal, an overtemperature signal wire disposed in said blanket, a S-contact plug having separate contacts connected respectively to each of said separate end terminals, said common terminal and each of the ends of said signal wire, a first thermal control device, a six-terminal socket adapted to receive said plug contacts in a predetermined 5 terminals thereof. the terminal of said socket connected through said plug to said common terminal being connected to one of said supply terminals, the terminals of saidsocket connected through said plug to said separate end terminals being connected to the other of said supply terminals through said first control device to cause said first control device to control both heaters, and the odd terminal of said socket not engaged by said plug being connected directly to said other supply terminal, a second thermal control device, a combination plug and socket member having four plug contacts jumpered respectively to four socket terminals, a separate plug contact and a separate socket terminal, said second thermal control device being connected between said separate socket terminal and separate said plug contact, said combination member adapted to be inserted between said plug and said socket member to engage the contacts of said plug and a pre-arranged 5 terminals of said socket including said odd socket terminal, the insertion of said combination member being effective to disconnect one of said separate end terminals from said first terminal device and to connect said terminal through said second thermal control device to said other supply terminal, said first control device thereupon controlling one heater only and said second control device controlling the other heater.

4. In combination with a blanket, a pair of heaters disposed in opposite sides of said blanket, each of said heaters having an end terminal common to both and each having a separate end terminal, an overternperature signal wire disposed in said blanket, a S-contact plug having separate contacts connected respectively to each of said separate end terminals, said common terminal and each of the ends of said signal wire, a first thermal control device, a 7-terminal socket adapted to receive said plug contacts in a predetermined terminals thereof, the terminal of said socket connected through said plug to said common terminal being connected to one of said supply terminals, the terminals of said socket connected through said plug to said separate end terminals being connected to the other of said supply terminals through said first control device to cause said first control device to control both heaters, one of the odd terminals of said socket not engaged by said plug being connected directly to said other power supply terminal, and the other of said odd terminals being connected to said other power supply terminal through said first control device, a second thermal control device, a combination plug and socket member having four plug contacts jumpered respectively to four socket terminals, a separate plug contact and a separate socket terminal, said second thermal control device being connected between said separate socket terminal and said separate plug contact, said combination member adapted to be inserted between said plug and said socket member to engage the contacts of said plug and a prearranged 5 terminals of said socket including said odd socket terminals, the insertion of said combination member being effective to disconnect one of said separate end terminals from said first control device and to connect said separate end terminal through said second thermal control device to said other supply terminal, said first control device thereupon controlling one heater only and said second control device controlling the other heater.

5. In combination with a blanket, a pair of heaters disposed in opposite sides of said blanket, each of said heaters having an end terminal common to both and each having a separate end terminal, a pair of power supply terminals, a two-t rminal jack having a pair of spring arms and a fixed contact normally engaged by one of said spring arms, a plug having contacts receivable in said jack and adapted to contact said spring arms and remove said one spring arm from engagement with said fixed contact, a pair of power supply terminals, a first thermal control device, a second thermal control device connected across the contacts of said plug, a circuit connecting said common terminal of said heaters to one of said supply terminals, a circuit connecting one of said separate end terminals to the other of said supply terminals through said first thermal control device, a circuit connecting the other of said separate end terminals to said supply terminals through said fixed contact and said one spring arm of said jack and said first control device to cause said first control device to control both heaters when said plug is removed from said jack, and a circuit connecting the other of said spring arms to said power supply terminal whereby said second control device controls one of said heaters when said plug is inserted in said jack.

6. In an electrically heated blanket, a first heater disposed in the blanket for heating one part thereof, a second heater disposed in the blanket for heating another part thereof, a pair of power supply terminals, a cycling switch having a thermostat member, an adjustable temperature setting member, a pair of contacts, and a heating coil for the thermostat member, a first heater circuit connecting the power supply terminals to the first heater in series with said pair of contacts and said heating coil, a second heater circuit connecting the second heater to said cycling switch in parallel with the first heater whereby both heaters are regulated by the temperature setting of said cycling switch, a plug receptacle having contacts in said second heater circuit, a second cycling switch having a thermostat member, an adjustable temperature setting member, a pair of contacts, and a heating coil for the thermostat member, and a plug connected thereto having contacts which when connected with said plug receptacle disconnects said second heating circuit from said first named cycling switch and connects it in series with the contacts and heating coil of the second cycling switch whereby when said plug is connected to said plug receptacle the first heater is regulated by the temperature setting member of the first named cycling switch and the second heater is regulated by the temperature setting member of the second named cycling switch.

7. In an electrically heated blanket, a first heater disposed in the blanket for heating one part thereof, a second heater disposed in the blanket for heating another part thereof, a pair of power supply terminals, a cycling switch having a thermostat member, an adjustable temperature setting member, a pair of contacts, and a heating coil for the thermostat member, a first heater circuit connecting the power supply terminals to the first heater in series with said pair or contacts and said heating coil, a second heater circuit connecting the power supply terminals to the second heater in series with said pair of contacts but in shunt to said heating coil whereby said second heater is connected in parallel with the first heater through said pair of contacts and both heater circuits are regulated by the temperature setting member of the cycling switch for the one blanket part, a plug receptacle having contacts in said second heating circuit, a second cycling switch having a thermostat member, an adjustable temperature setting member, a pair of contacts, and a heating coil for the thermostat member, and a plug connected thereto having contacts which when connected with said plug receptacle contacts disconnects said second heating circuit from the contacts of said first named cycling switch and connects it in series with the contacts and heating coil of the second cycling switch whereby when said plug is connected to said plug receptacle the first heater is regulated by the temperature setting member of the first named cycling switch and the second heater is regulated by the temperature setting member of the second named cycling switch.

8. The combination defined by claim 7 wherein said plug receptacle comprises a pair of normally closed contacts in the second heater circuit and a contact connected to such second heater circuit in shunt to the contacts of said first named cycling switch, and said plug has two terminals one of which separates said normally closed contacts to disconnect the second heater circuit from said first named cycling switch and connect one side of it to one side of the second named cycling switch and the other of. which connects the other side of the second heater circuit to the other side of the second named cycling switch.

9. In an electrically heated blanket, a first heater disposed in the blanket for heating one part thereof, a second heater disposed in the blanket for heating another part thereof, a pair of power supply terminals, a cycling switch having a thermostat member, an adjustable temperature setting member, a pair of contacts, and a heating coil for the thermostat member, a first heater circuit connecting the power supply terminals in series with said pair of contacts and said heating coil, a second heater circuit connecting the power supply terminals in series with said pair of contacts but in shunt to said heating coil, a plug receptacle and a plug connecting the first heater circuit to the first heater and the second heater circuit to the second heater whereby said second heater is connected in parallel with the first heater through said pair of contacts and both heating circuits are regulated by the temperature setting member of the cycling switch for the one blanket part, a second cycling switch having a thermostat member, a pair of contacts, and a heating coil for the thermostat member, and a plug connected thereto having contacts which when interposed between said first named plug and plug receptacle disconnects said second heating circuit from the contacts of said first named cycling switch and connects it in series with the contacts and heating coil of the second cycling switch whereby when said plug is thus interposed the first heater is controlled by the temperature setting member of the first named cycling switch and the second heater is controlled by the temperature setting member of the second named cycling switch.

References Cited in the file of this patent UNITED STATES PATENTS 2,138,745 Pecker Nov. 29, 1938 2,163,297 Waage June 20, 1939 2,190,225 Vollmer Feb. 13, 1940 2,367,014 Finlayson Ian. 9, 1945 2,467,349 Van Daarn Apr. 12, 1949 2,480,827 Armstrong Sept. 6, 1949 2,565,478 Crowley Aug. 28, 1951 2,581,212 Spooner et al. Ian. 1, 1952 FOREIGN PATENTS 117,224 Germany Jan. 29, 1901 651,733 Great Britain Apr. 11, 1951

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