US2448289A - Temperature control apparatus - Google Patents

Description

g- 31, 1948- c. E. ANDERSON 2,448,289

TEMPERATURE CONTROL APPARATUS Filed June 5, 1946 IN VEN TOR.

C/eopfias 2?? 14/20 6150]? .4 TTORNEYJ Patented Aug. 31, 1948 UNITED STATES PATENT OFFICE TEIVIPERATURE CONTROL APPARATUS Cleophas E. Anderson, Dubuque, Iowa, assignor to Thermo Electric Manufacturing Company,

Duhuque, Iowa, a corporation of Illinois Application June 5, 1946, Serial No. 674,607

2 Claims. 1

This invention relates to temperature control apparatus and more particularly to temperature control apparatus for electrically heated units wherein control is effected by an auxiliary heating circuit which may be positioned remotely from the main heating circuit or load.

It is an object of my invention to provide temperature control apparatus especially adapted for use in conjunction with units which operate at high temperatures such as, for example, electric 'furnaces, but which may also be adapted for use with relatively low temperature apparatus, such as hot plates, domestic ovens, melting apots and the like.

In the usual electrically heated units heretofo-re known, variations in the line voltage supplied thereto resulted in variations in the temperature of the working chamber of the unit because the heating element therein when operating on various voltages emitted different quantities of heat and no control was afforded to compensate for such variation. It is an object of (my invention to overcome this objection by associating a temperature control device with the prim-ary heating unit in such a manner that variations in the line voltage efiect a similar variation in the voltage of the control circuit to thereby automatically compensate for the. variation in the line voltage as applied to the main heating element by either shortening o-r prolonging the period during which the greater or lesser amount of current, respectively, flows through the main heating element, depending upon whether the line voltage rises or lowers. Hence, it will be seen that when my apparatus is in use, if the line voltage drops, thus causing reduced current flow through the main heating element with a resultant lowering of the quantity of heat :put out by the main heating element per unit of time, the control circuit will cause the reduced current to flow through the main heating element a greater proportion of the time; and if. on the other hand, the line voltage rises the control circuit will cause the increased current to flow through the main heating element a smaller proportion of the time. It will thus be seen that with this control the temperature of the working chamber, which the main heating element is employed to heat, may be kept constant within relatively narrow limits even though the line voltage may vary considerably.

It is a further obj-cot of my invention to construot a temperature control apparatus wherein a fixed main load may be used, the only adjustably variable load, associated therewith, being 2 in the control circuit which is in parallel with the main load.

Another object of my invention is to associate a temperature control unit with a main heating element in such a manner that the control circuit may be used at a place remote from the working chamber within which the main heating element is used so that the control unit is not efiected by radiated heat from too main heating element or other sources other than the heating element of the temperature control unit itself.

It is a further object of my invention to construct a control circuit which when utilized in a heating circuit draws a very small percentage of the total current demand required by the entire circuit.

Another object of my invention is to construct a temperature control unit operated by an auxiliary heating unit wherein the auxiliary heating unit and switches used in the temperature control unit device may be small and therefore are much more sensitive and quicker acting than the thermostat elements commonly used interiorly of electric furnaces, or the like, where in the latter must be of relatively heavy construe" tion to withstand the high temperatures to which they are subjected and are, therefore, relatively sluggish in their action.

Yet another object of my invention is to cors-truc-t a temperature control operated by an auxiliary heating unit where the elements of the control unit are associated in such a manner that proper operation of the control unit is assured even though the ambient temperature may vary considerably.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawing which, by way of illustration, shows a preferred embodiment and the principle thereof and what I now consider to be the best mode in which I have contemplated applying that principle. Other embodiments of the invention embodying the same or equivalent principle may be used and structural changes may he made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

In the drawing:

Fig. 1 constitutes a diagnarnmatic illustration of the preferred form of my invention; and

2 constitutes a, diagrammatic illustration of a modified form of my invention.

In Fig. l of the drawing, my novel temperature control apparatus is illustrated. as embodying a main heating element ID which may be the heating element used to heat the interior of an electric furnace, or to heat an oven, melting pot, electric grill or the like. One end of the heating element Iii is connected to a main power line H by means of a connecting line I2, and the other end of the main heating element In is connected through a line I3, a line I4, and a normally closed switch IE to the other main power line it. The switch It is preferably a snap action switch such as, for example, what is known to the trade as a microswitch, having a push button H, a stationary contact I9 and a movable contact 20.

A control circuit 2: is connected across the power lines I i and E6 in parallel to the main heating element ill and comprises a variable resistance such as a rheostat 22, one end of which is connected to the power line I I by a line 23, and the movable contact 2d of the rheostat 22 is connected through a line 25, an auxiliary heating element or control unit heating element 26 and a line 2? to the junction of the lines I3 and I t and, thus, to the other power line IS. The control unit heating element 28 is preferably wrapped around a bimetallic element 28 and forms a heating coil therefor as will be presently explained.

The switch I5 has a bracket 29 projecting upwardly therefrom adjacent to the push-button ll, and a switch arm 30 has one end portion 3i pivotall attached to the bracket 29 by means of a pin 32. The free end portion of the switch arm 30 comprises a lei-metallic arm or element 33 one end of which is fastened to the free end of the end portion 3I by any suitable means such as a rivet 3t and the other end of which has an upstanding lug or ear 35 provided thereon. A helical spring 35 is positioned between the top wall of the switch I 5 and the point of juncture between the end portion 3! and the bimetallic element 33 of the switch arm so, and yieldingly urges the free end of the switch arm 30 upwardly. A limit stop 3? is provided on the top wall of the switch I5, adjacent to the bracket 29, and limits the rotation of the switch arm to in a counterclockwise direction (Fig. 1).

The switch arm 3i! underlies the bimetallic element 28 and is substantially parallel thereto, and

preferably is insulated therefrom in an suitable manner such as, for example, by positioning a sheet of insulating material therebetween through which the ear 35 projects and is free to move.

The switch arm so also overlies the push button I! and it is, of course, apparent that rotation of the switch arm 32] a predetermined amount in a clockwise (Fig. 1) direction will cause the push button I! to be depressed and, therefore, the movable contact 25] to move downwardly out of engagement with the fixed contact I9.

In the operation of my device, the main heating element I is positioned within the working chamber of the electric furnace, or the like, which it is desired to heat and the control circuit 2I is positioned outside of the working chamber at some point where it is not subject to the heat of the working chamber. Line voltage is provided across the lines II and I6 and when the contacts I9 and 20 of the switch I are closed the current flow through the main heating element It is from the main power line II through line I2, the main heating element It, line I3, line I4, the switch contact I9, and the switch contact 2!] to the other main power line it. Also it will be noted that when the contacts I9 and 20 of the switch arm 38.

switch I5 are closed, the current also flows from the main line I I through the line 23, the variable resistance 22, line 25, the control unit heating element 26, line 21, line I4, contact I9 and contact 20 to the main line I6. However, it will be noted that when current flows through the control unit 2| the control unit heating element 26 is caused to be heated and thereby heats the bimetallic element 28, which, upon being heated sufiiciently, is caused thereby to deflect downwardl into engagement with the lug 35 of the Continued downward deflection of the heating element 28 will then cause the switch arm 30 to rotate about the pin 32 and thereby press the push button I 1 down to deflect the movable contact 2o downwardly and thereby break the circuit through the main heating element In and the control unit 2|. When the circuit is broken by the opening of the switch I 5, the heating element 26 is, of course, no longer caused to be heated and, therefore, the heating element 26 and the bimetallic element 28 cool, and when the bimetallic element 28 has cooled sufficiently, it again straightens out and moves out of engagement with the switch arm at, which, therefore rotates in a counter-clockwise direction under the urging of the spring 36. The counterclockwise rotation of the switch arm 30 releases the push button I1 and the movable contact 20 to again close the switch I5 and reestablish the circuits through the main heating element I0 and the control device 2|.

It will be apparent that although when the heating coil 26 is energized and the bi-metallic element 28 is thereby heatedit is caused to defiect relative to the bi-metallic arm 33, changes in ambient temperatures adjacent the control circuit 2i causes an equal deflection of the bimetallic element 28 and the bi-metallic arm 33 and, therefore, change in the ambient temperature does not change their relative position or affect the operation of the unit.

From the foregoing it will be seen that regulation of the heat output of the main heating element It is elfected by controlling the proportion of the time that the heating element Iii is on. Thus if a high temperature is desired within the working chamber of the electric furnace, or the like, it is necessar that the heating element It] be on for a relatively great proportion of the time, and this is accomplished by adjusting the variable resistance 22 to impose a relatively great resistance in the control circuit 2! so that a relatively small current flows through the auxiliary heating element 26 and, therefore, it takes a relatively great length of time for the heating element 26 to heat the bimetallic arm 28 sufliciently to cause it to open the switch I5 as compared to the time that it takes, after the switch I 5 has been opened, for the arm 28 to cool sufficiently to again permit switch I5 to close. If, on the other hand, it is desired to maintain a relatively low temperature within the working chamber of the electric furnace or the like, the variable resistance is adjusted to impose a relatively low resistance in the control circuit 2I so that th current flow through the auxiliary heating element 28 is relatively great and, therefore, each time the switch I5 is closed the heating element 26 relatively quickly heats the bimetallic arm 23 to again open the switch 28.

From the foregoing it will be noted that current intermittently flows and stops flowing through the main heating element In in accordance with the closing and opening, respectively,

of the switch I5; and the temperature of the working chamber, which is heated by the main heating unit I is controlled by regulating the proportionate time that the switch I is closed and current ilows through the main heating element I0, which regulation is accomplished by the control device 2I.

Also, it will be noted that with my apparatus, it is unnecessary to put control devices in series with the main heating element I0 as was heretofore common in the art and, therefore, the main load remains relatively constant as distinguished from the widely varying loads imposed by controlled heating apparatus heretofore known to the art. All the controls that are necessary in my apparatus are incorporated in the control device, the circuit for which is in parallel with the main heating element circuit, and the load imposed thereby is relatively small, and is preferably maintained below of the entire load of the whole circuit.

Also it will be noted that when once set my control unit is efiective to maintain the same temperature in a working chamber, within very narrow limits, although the line voltage may vary considerably.

In addition, it will be noted that, with my apparatus, regulation of temperature within a working chamber may be effectively remotely controlled.

The modification shown in Fig. 2 embodies a somewhat different control unit which is primarily adapted for use in places where the ambient temperature which surrounds the control unit is substantially constant. Only enough of the circuit is shown to clearly illustrate how it would be embodied in a complete circuit such as that illustrated in Fig. 1 and identical elements are indicated by the same reference numerals with the prefix "1 added thereto.

The principal diiference between the modification shown in Fig. 2 and the preferred form of my invention illustrated in Fig. 1 is that the switch arm 30 is eliminated in the modified form and the bi-metallic element I 28 actuates the push-button II'I directly.

The auxiliary heating unit I26 may be placed adjacent to, or wound around, the bi-metallic element I28.

It will be apparent that in the operation of the modified form of my invention, when the switch elements II 9 and I are closed current flows from one power line (not shown) through the movable contact I24, line I25, the heating unit I26, line I21, line III, the switch Hi to the other power line H6, and upon the heating unit I26 heating the bi-metallic element I28 sufficiently, the latter is caused to deflect sufilciently to depress the push button I I1 and thereby open the switch contacts IIS and I20. Opening of the switch contacts II9 and I20 breaks the circuit through the heating unit I26 as well as the main heating unit (not shown), and the bi-metallic element I28 then begins to cool and when it has cooled sufllciently it straightens out to thereby release the push-button III and permit the contacts H9 and I20 to again close and re-establish the circuits through the control heating unit I26 and the main heating unit (not shown).

It will be noted that the modified form of my invention may be economically constructed and is especially well adapted for use in places where the ambient temperatures around it are substantially constant.

Thus, while I have illustrated and described the preferred embodiment of my invention, it is to be understood that this is capable of variation and modification and I therefore do not wish to be limited to the precise details set forth, but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. Temperature control apparatus for an elec tric furnace or the like and comprising in combination, an electrical heating element, a switch connected in series with said electrical heating element, a bi-metallic arm pivotally mounted on said switch and operable upon rotation in one direction to open said switch, a bi-metallic element adjacent to and substantially parallel to said bi-metallic arm, a second electrical heating element wrapped around said bi-metallic element in heat exchange relationship thereto, a variable resistance, said resistance and said second heating element being connected in series with each other and with said switch, and being connected in parallel with said first mentioned electrical heating element, said bi-metallic element being adapted to be deflected into operative engagement with said bi-metallic arm and to rotate said arm in said one direction to thereby open said switch upon application of a suflicient quantity of heat to said bi-metallic element by said second heating element.

2. Temperature control apparatus comprising an electrical heating element, a switch connected in series with said electrical heating element, a bi-metallic arm mounted on said switch and operable upon the application of a predetermined pressure thereon in one direction to open said switch, a bi-metal1ic element normally positioned adjacent to and substantially parallel to said bi-metallic arm, a second electrical heating element wrapped around said bi-metallic element in heat exchange relationship thereto, a variable resistance, said resistance and said second heating element being connected in series with each other and with said switch, and being connected in parallel with said first-mentioned electrical heating element, said bi-metallic element being adapted to be deflected into operative engagement with said bi-metallic arm and to press against said arm with said predetermined pressure in said one direction to thereby open said switch upon the application of a sufficient quantity of heat to said bi-metallic element by said second heating element.

CLEOPHAS E. ANDERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,873,421 Kanter Aug. 23, 1932 1,908,676 Appelberg May 16, 1933 2,009,601 Anderson July 30, 1935 2,125,110 Harty July 26, 1988 2,196,380 Biebe1 Apr. 9, 1940 2,400,735 Bradford May 21, 1946 FOREIGN PATENTS Number Country Date 221,480 Great Britain Feb. 19, 1925

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