US1350895A - Heating device and control therefor - Google Patents

Description

S. THOMSON.

' HEATING DEVICE AND CONTROL THEREFOR.

APPLICATION FILED FEB. 26, 1918.

Patented Aug. 24, 1920.

Stuart, Thcmson,

Invent or UNITED STATES PATENT OFFICE;

STUART THOMSON, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

HEATING DEVICE AND CONTROL THEREFOR.

Specification of Letters Patent.

Patented Aug. 24, 1920.

Application filed February 26, 1918. Serial No. 219,297.

To all whom it may concern Be it known that LISTUART THOMSON, a citizen of the United States, residing at .Washington, District of Columbia, have invented certain new and useful Im rovethe unit with two separate resistance elements which were connected in series or parallel for low or high heats, respectively, medium heat being secured by connecting a single resistance element tothe supply circuit. The two heating units which are required' for such a system of heat control, require four terminals, and are, of course,

more expensive than a single unit and more likely to get out of order.

Another disadvantage of this system of control is that the ratios of the various heats, which are as 12 3:}, are not such as are usually desired in practice. For example, the hot plates used on electric ranges commonly require for medium heat about four or five hundred watts, whereas the maximum desirable is more than twice this amount and may, for example, be 1500 watts, while it may be desirable to operate the unit at half or less than half of the wattage re uired for medium heat.

n accordance with my invention, a single resistance element is used in a heating unit.

My invention relates to an arrangement for varying the temperature of a heating unit or a heating device, comprising a transformer, preferably an auto-transformer, and switch vmechanism associated therewith for varying the number of turns of the secondary of the transformer which are included in circuit with the heating unit or units. In the a way that whenthe heating unit or units are being supplied with full heat, the autotransformer is not called upon to transmit any energy whatever, and does transmit energy only when the unit' or units are operated at a lower heat, as for example medium or low heat, thereby making it possible to use a transformer of moderate size in a heating circuit of high wattage.

In another aspect, my invention relates to a three-wire alternating current system wherein the heating units each have one terminal connected to the neutral with the auto-transformer interposed between the supply circuit and the heating units, toether with an arrangement whereby each heating unit may be connected across a supply conductor and the neutral or across any desired number of turns of the auto-transformer, so that the auto-transformer will be called upon to transmit energy only when one or more of the heating units is connected for a lower heat, and when the heating units are connected for a lower heat all of the coils of the auto-transformer are called upon to transmit energy. The most effective use is thereby made of the auto- ,transformcr, and the temperature of each of the heating units is very nicely condiagrammatically illustrated, and in which Figure 1 is a vlew showing an element of my invention Fig. 2 shows elements of my invention cm odied in a three-wire alternating current system with an auto-transformer interposed between the heating unit, and the supply mains; and Fig; 3 shows an embodiment of my invention in a three-wire alternating current system.

Referring now to the drawings and first to Fig; 1, 10 and 11 are supply conductors across which is connected an auto-transformer 12. One terminal of a heating unit 15 is connected by a conductor 14 to one terminal of the auto-transformer, and the other terminal of the heating unit is connected to a switch 16. This switch cooperates with contacts, here illustrated as three, 18, 19 and 20 which are connected to supply conductor 10, to a tap 21-0n the auto-transformer and to a second tap 22 ioa between the tap 21 and that terminal oil the transformer to which the conductor 11 is connected, respectively.

I ing unit, the switch 16 is connected to the contact 18 andthe heating unit connected directly across the supply circuit. The auto-transformer at this time is not called upon to transmit any power. By connecting the switch to the contact 19, the heating unit will be connected across the portion of the auto-transformer between the tap 21 and the terminal of the auto-transformer to which the conductor 11 is connected, a lower voltage will be impressed on the heating device and the same will accordingly operate at a lower heat, and by connecting the switch to the contact 20, a still lower voltage and lowerheat will be secured. lit will be obvious that by suitably arranging the tape 21 and 22 and by the use of additional taps, it necessary, any desired heat ratios may be secured. I

Tn Fig. 2 l have illustrated elements of my invention embodied in a'threawire al ternating current system, an auto-transformer being interposed-between the. supply circuit and the heating unit or units and the units being so connected tothe autotransformer that the latter will not transmit any energy when the heating unit or units are connected for high heat and will be called upon to transmit energy only when the unit. or units are connected for medium or lowheat. In this figure l have illustrated two heating units 15 and 15*, one terminal of each of which is connected to an intermediate tap 13 on the auto-transformer which divides the same into two sections 12 and 12" by a conductor 14;. The other terminal of the heating unit 15 is connected'through switch 16 and contacts 18-, 19 and 20, either to the conductor 10 or to extra taps 21 and 22 of the auto-transformer in precisely the same manner as the device already described in connection with Fig. 1, while the remaining terminal of the heating unit 15" is conneeted through the switch 16 and contacts 18, 19 and 20 eitherto the conductor 11 or to the extra tape 23 and 24 of the autotransformer in precisely the same manner as the corresponding parts associated with the unit 15.

When used in conjunction with a threewire'system, as illustrated in Fig. 2, in which the neutral is indicated by the reference character 14;, then if either or both of the units are connected for high heat,

plied by the secondary of the'supply transformer (not shown in the drawing), in'a described in connection with Fig. 2.

other two heating units, 73. e. 15 and 15 ea set manner :well understood in the The only time when the auto-transformer will be called upon to transmit energy will be when one or both of the units is connected to'receiv'e less than its maximum energy suppl with the consequence that an autotrans oi'mer of moderate size may be connected in a circuit of high wattage.

In Fig; 8, I have shown an embodiment of my invention in which there aretwo sets of heating units each set comprising two groups of units connected to the respective sections 12 and 12 oi the auto-transformer.

The one set which is shown in the figure as will, of course, be understood that each group may comprise more than a single heatmg unit. The heating units 15 and 15 are connected and operated in precisely the same .manner as the corresponding units have one terminal connected by the conductor 14: to the tap 13 of the auto-transformer. The other terminal of the unit 15 is connected to a switch 16- cooperating with contacts 18, 19 and 20 and the other to a switch 16 cooperating with contacts 18, 19 and 20, respectively. The contacts 18 and 18 are connected to the su ply conductors 10 and 11, respectively and the contacts 19 and 1'9 are connected to the taps 21 and 23 of the auto-transformer. The remaining contacts 20 and 20 are connect ed to taps 25 and 26 of the auto-transformer intermediate between the taps 13 and 21 and the taps 13 and 22, respectively. With this arrangement here shown, it will be apparent'that if all of the heating units are operating at medium heat all of the difcalled upon to perform a part-hf they work and the auto-transformer will, therefore, be more advantageously operated than if a part only of the coils were called upon to transmit all the power. Similarly, if all of the heating units are connected for low heat, the power will be transmitted 'to the heating units by difierent coils of the auto-transformer.

While l have shown an arrangement tor securing three difierent heats in a given heating unit, it will he understood that by suitably varying the nnmher of taps on the auto-transformer, and the relative numher' of turns in the varioussections ofthe autotranstormer, any number otheats and any desired heat'ratios. may be secured in a given heating unit.

. While T have descrihed my invention as The 110 ferent coils of the auto-transformer will be i embodying a concrete structure and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto, since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

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

1. In combination, a supply circuit, an auto-transformer connected thereto, a plurality of sets of heating units connected to different sections of said auto-transformer, means for varying the energy supplied to a given unit, each set comprising two groups of units which are connected to different and connections for varying the number of turns ofthe auto-transformer connected in circuit with each heating unit, whereby when both units are receiving energy allthe turns of the auto-transformer will be used in transmitting power to the heating units.

3. The combination with a three-wire alternatingcurrent supply circuit, of two sets of heating units, the sets being connected on opposite sides of the neutral and having one terminal of each set connected to the neutral, an auto-transformer interposed be tween the heating units and the supply cir- "cuit, and means for connecting each heating unit across its associated supply conductor and the neutral or across any deslred number of turns of the auto-transformer, whereby the auto-transformer transmits no energy unless one or more of the units is connected for a lower heat and when the units are connected for a lower heat all the turns of the auto-transformer are used in transmitting energy to the heating units.

In witness whereof I have hereunto set my hand this 20th da of Februar 1918. ST ART THO SON.

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