US1912921A - Thermostatic heater - Google Patents

Description

'June 6, 1933. J. A. SPENCER THERMOSTATIC HEATER Filed Sept. 8, 1930 2 Sheets-Sheet l Patented .lune 6, 1933 UNITED STATES Pa'rla'zla'r OFFICE JOHN A. SPENCER, 0l' NEWTONVILLE, 'HASSACHUBETTB, ASSIGNOB T0 GENERAL LATE COMPANY, 0F ATTLEBORO, MASSACHUSETTS, A CORPORATION 0F KABSACHUBETTS TBERKOSTATIC HEATER Application lled September s, 1930. Serial No. 480,452.

This invention relates to thermostats, and with regard to certain more specific features, to thermostatic heaters.

Among the several objects of the invention may be noted the provision of an im roved form of thermostatic heaters adapte to reduce the la which normally takes place between the time that a medium reaches a predetermined temperature and the time of operation of the thermostat; the provision of a device of the class described which has a more definite and effective thermostatic action under given conditions; the provision of a device ofthe class described which may be used as an only heater or as an auxiliary heater, thus utilizing heat generated within the thermostat; the provision of a device of the class described in which the heat generated in the thermostat and utilized for heating also alters the operating characteristics of the thermostat; and the provision of a device of theclass described which is simple and compact, being adapted to be made portable, and fluid-proof. Other objects will be in art obvious and in part pointed out hereina r.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structure hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which areillustrated several of various possible embodiments of the invention,

Fig. 1 is a longitudinal section taken through a thermostatic heater embodying the invention; l

Fig. 2 is a cross section taken on line 2-2 of Fig. 1;

Fig. 3 is an enlarged cross section of a switch;

Fig. 4 is a plan view of said switch shown on the scale to which the switch is drawn in Fig. 3, or the view may be considered as a cross section on line 1 -4 of Fig. 3;

Fig. 5 is a sectional detail showing an alternative mountingr for certain thermostatic elements;

switch plate 27 held to the base 1.

Fig. 6 is a diagram illustrating applications i The rod 7 carries at its other end a fixed ferrule 9, between which and a shoulder 11 at the other end of the rod is carried a quartz tube 13 or the like. The quartz tube 13 is preferably in spaced relationship with respect to the rod 7 and, for optimum results, additional thermal insulatingl material 15 such as asbestos, is positioned between it and the rod, although this material may be dispensed with and air used as a thermal insulator.

From the above it will be seen that the movement of the inner rod 6 relative to `the base 1 is substantially proportional to the elongation and contraction of the outer tube 3.

Around the quartz. tube 13 is positioned, in the form of a double wire helix, an electrical heating element 19. The double wire helix is referred to as providing one method for obtaining two line contacts for the heating element 19 at the inner end of the tube 13. The quartz tube 13 and the air space between the element 19 and the tube 3 constitute electrical insulating meansdor the element 19 with regard to the rod 7 and thel tube 3, respectively. Thus the heating element 19 may be conveniently connected in series in a circuit 21, said circuit being adapted to be opened and closed by means of a buckling, over-centering switch 23 located in a recess 25 of the base 1.

The switch 23 is shown more particularly in Fi 3 where it is shown as comprising a This plate 27 carries in insulated relationship a series ofthe disc to spring suddenly to the line posicircuit elements 29. The circuit elements 29 are circularly arranged, as shown in Fig. 4, insulation being provided as shown at numeral 31 in Fig. 3. The segmental circuit elements, or terminals 29 are adapted to be bridged to close the circuit 21 by means of terminal engaging elements 33 mounted on a cup-shaped disc or dish 35.

The cupped disc 35 in its nature inherently tends to maintain the full line position shown in Fig. 3, having been formed to the contour there shown. However, if by external force, it is caused to assume a reverse curvature, it will maintain the reverse curved position. This is characteristic of resilient, dished or cupped articles.

When in its solid-line position, the disc 35, as will be seen later, is adapted to hold the terminal engaging elements 33 in enga ement with the line terminals 29 to bridge t e same; and when in its reverse curved position, to hold them out of engagement. Three elements 33 are used in order to obtain a series of breaks. The dotted lines in Fig. 3 indicate rotated positions of certain parts for purposes of clearly demonstrating mechanical action.

Switch action is accomplished by loosely mounting the disc 35 at a central opening 37 between spaced collar 39 of a reciprocable switch controi pin 41. Three studs 43 screwed to the switch piate 27 serve to guide the disc 35, the, heads 112 of said studs 43 providing a reacting ulcrum for purposes to be made clear..

The switch pin 41 is reciprocably mounted within a bushing 4:7 screwed and locked to the switch plate 27 and having a slotted por tion i9 with which co-operates key 51 in the pin el, so that reciprocation of the pin 51 in the bushing 117 is permitted without rotation said pin. At its lower end the pin 41 carries a head 53 against which reacts a compression spring 55.

Permitting or partial compressive action of the spring 55 on the head 53, causes the join L11 to be pushed down, thereby pushing down the disc 35 so that the terminal engaging eiements 33 incipiently increase contact pressure (circuit 21 closed) and then, as a reaction is at the edge of the disc th primary action of the center thereof caused the L11, the disc snaps into recurved position, thereby opening the circuit. ned downward action of the pin is iii .--ed by cri-operation of one of the sh ulders 39 with the bushing 47., thus tion shown in Fig. 3 and again close the circuit.

Control-of the pin 41 is effected by means of the multiplying lever 57 which is fulcrumed at knife edges' 59 against an adjustable head 61 formed on a stud 63, the latter being screwed into said plate 1. The end 17 of the rod 7 bears against the opposite end of the lever 57.

From the above it will be seen that change in temperature of t-he medium in which the thermostat is immersed, or with which it contacts, results ina change in the length of the expansion tube 3, thereby changing the relative positions of the knife edges 59 on the one hand and the contact between the rod 7 and lever 57 on the other hand.

This relative movement relects itself in movement of the lever 57 against pin 41, thus moving the pin and throwing the switch to off and on positions. The motion of the switch is multiplied over that of the knife edges or the rod 7 because of the unequal lengths of movement arms of the lever 57. Expansive movement of the tube 3 opens the switch and `contractive movement of the samecloses the switch. Thus the circuit 21, which energizes the heater 19 is opened and closed.

Several methods of coupling and immersing the device are shown in Fig. 6. In one method the circuit 21 includes the thermostatic heater above described, in series with a simple heater 67. Both the heater and the thermostatic heater may be immersed in the medium 69 which, for example. is to be maintained at or near a predetermined temperature. The operation is as follows:

Assuming that the ambient medium 69 to be at a temperature below the critical one for opening the switch 23, the thermostatic heater as a whole and the heater 67 are immersed, the circuit 21 being connected as shown. The heater 67 may be of the electrical type, for example. With this arrangement, both the heater 67 and the auxiliary heater comprising the element 19 in the thermostat, contribute to raising the temperature of the ambient medium 69, the heat from the element 19 being transferred to the medium through or by way of the relatively goodconductin'g air space surrounding said element in expansion tube 3. Conduction and convection serve to rapidly transfer heat from the tube 3 to the medium so that the temperature dilerence between the two remains practically constant and small as their temperatures rise. The rod 7 however rises in temperature more slowly, because of the heatinsulating qualities of the quartz tube 13 and/or the asbestos 15, so that the difference between its temperature and the temperatures of either the medium or tube increase, thereby, as the critical temperature is reached, thus rapidly increasing the relative displacements between the elements of the thermostatic linkage. This phenomenon is true regardless of the temperature coefficients of eX- 'pansion of the rod and the tube, which may differ as in the exemplary case of Monel and nickel steel recited, or which may be the same, as when the rod and tube are formed of the same metal. The greater difference in tube and rod temperatures than medium and rod temperatures ensures more definite and prompt thermostatic action for a given temperature of medium, especially when `their teinperature coefficients of expansion are unequal.

Another point to be noted is that after the thermostat opens the switch, the tubetemperature quickly drops back to that of the medium, thus shortening the delay until reclosing of the switch and ensuring less drop in the temperature of the medium before re-closing. The difference between the temperature of the tube and the medium upon heatingl may in fact be made great enough so that the lower limit temperature of the tube and rod required for reclosing is reached before the temperature of the medium has dropped any substantial amount.

It will be clear from the above that the invention is operative even though the tube 3 and rod 7 be composed of the same material, the relative movement depending upon their temperature difference. Furthermore, a negative, finite operating temperature differential may be obtained, more readily if the coefiicient of expansion of the inner rod 7 be higher than that of the tube 3. The operating temperature differential is defined as the temperature difference that must exist between the4 thermostat and medium before change of position occurs. Ordinarily, this differential is expressed as a positive value, as representing, say in the cooling phase, the number of degrees the medium must be cooler than the thermostat before the heater is energized to change the system over to the heating phase. A differential of zero is achieved when the change-over occurs when the thermostat and medium are at exactly the same temperature. A negative, finite differ'- ential, as the terms are herein used, is defined as a differential such lthat the change-over might occur while the thermostat, in the cooling phase, is even cooler than the medium.

When the rod 7 is substantially non-expansive and is shielded from the heating effect of the coil 19, the desired effect is enhanced,

because the necessary, though exceedingly small changes in length of this rod, due to temperature changes, are rendered smaller. The following isy pointed out in order to clarify the invention:

Were the heater element 19 not used, but only the heater 67, the thermostat then being only an ordinary rod-and-tube .type thermostat, all temperature difference would be on a gradient descending from the medium to the tube 3, due to transferring heat from the medium 69 to the tube 3. Thus there would be a lag in the operation of the switch 23 in comparison with the medium attaining ,a predetermined temperature.

With the hea-ter 19 operative, the temperature difference grades from the tube 3 to the medium 69 and this results in the switch actually operating at a temperature of the tube 3 which is higher than that of the medium 69. This also permits the thermostatic linkage to operate between wider limits, which is advantageous in the case of a thermostat, providing more powerful, definite and positive action.

It is to be understood that all of the heating of the medium 69 may be accomplished by means of the heater element 19, if desired, and for lthis purpose a disconnection is made at the .point 71 (Fig. 6) and the heater 67 removed. Current is then supplied directly across the terminals of the thermostat. In many cases this is advantageous from the viewpoint of simplicity. It also ensures that the thermostat is operating in the circuit when the heater is operating, thus making a safe structure for heating pur poses.

In Fig. 5 is shown an alternative method for fastening the rod 7 within the tube 3 so that the rod is more effectively insulated therefrom. In this modification a thermal insulating plug 73 composed preferably of porcelain, is placed at the end of the tube 3. The plug 73 supports the rod 7 and a suitable cap 75 is applied.

A modified form of the invention is shown in Fig. 7 which includes the outer expansive tube 3 and inner expansive rod 7. A small heating unit 2 is found in close juxtaposition with the top 3 but electrically insulated therefrom by a thin layer of heat-transmitting material 4. This material 4 may comprise, for instance, a thin sheet of mica. The thermal contact of the heated tube with the rod 7 is poor. The air space between the unit 2 and the rod 7 now assumes the relative rle of a heat insulator, because its heat conductance is lower than that of the mica layer 4. Both mica and air space, of course, are electrical insulators for the unit 2.

If this alternative form is installed in a boiler, preferably near the bottom, as long as there is Watersurrounding the tube there will be little difference in temperature between tube and rod, and the device will hence not operate, no matter what the temperature of the boiler may be. If, however, there be no water present the difference in temperature will be large. This, therefore, could be used as a low water alarm.

It is to be noted that this form presents conditions somewhat different from those above referred to. lt is true difference in temperature between tube and rod depends upon the water temperature to some extent, and in fact this could be used to operate the thermostat as above discussed. The difference in temperature in the entire absence of water will, however, be much greater than the above. Therefore, for the low water alarm the thermostat can be set to operate only at a relatively large temperature difference as compared with the setting when the same device is used for controlling the water temperature.

It is to be understood that the invention herein disclosed may be used in connection with various mechanical and other devices, the tube 3 being suitably mounted so that it may expand and contract while in contact with the medium or material, the temperature of which is to be controlled. The fluid-tight cover 22 for the switch 23 and connected elements is applied over the base 1 where the device is to be totally immersed (Fig. 1).

lt will be seen that the switch herein is ot the snap-acting type, externally operated. lit is to be understood that other snap-acting switches may be used, such as over-centering toggle switches or the like.

rlhis invention is novel in providing a thermostat and a heater such that the heater heats the ambient medium and is in close proximity to one thermostatic element, this iact in itself accounting tor many advantages, as well as the tact that the fluid is heated by way of one element.

ln view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in carrying out the above constructions without departing from the scope of the invention, it is'intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

l claim:

1. A thermostatic heater comprising two concentric elements, said elements comprising a rod and a tube enclosing the rod, said elements being joined at one end, the other ends of said elements being free for relative moveat one end, the other ends of said tube and said rod being free for relative movement, an electrical heating element between said rod and said tube, electrical insulating means between said element and said tube constituting a relatively good conductor o heat, and electrical insulating means between said element and said rod constituting effective heat insulating means as well.

3. A thermostatic heater comprising a thermally responsive tube and a rod surrounded thereby, said tube and said rod being oined at one end, the other ends of said tube and said rod being free for relative movement, an electrical heating element between said rod and said tube, an air space between said element and said tube electrically insulating said element from said tube but permiltting relatively free flow of heat from said element to said tube, and a quartz tube electrically insulating said element from said rod, and in addition presenting an effective heit insulation between said element and said ro 4. In combination, .a thermostatic heater immersed in a body of medium, the temperature of which it is desired to control, said thermostat comprising a thermally responsive tube and a .rod surrounded thereby, said tube and said rod being joined at one end, the other ends of said tube and said rod being free for relative movement, an electric switch operated by the relative movement of said free ends, an electrical heating element between said rod and said tube, said heating element being connected in series with said electric switch, electrical insulating means between said element and said tube constituting a relatively good conduction of heat, and electrical insulating means between said element and said rod constiiting eilective heat insulating means as we En testimony whereof, I have signed my name to this specification this 7th day of August, 1930.

JOHN A. SPENCER.

ment, an electrical lheating means between said elements, electrical insulating means between said heating means and one of said elements constituting a relatively good conductor of heat, and additional electrical insulating means between said heating means and the other of said elements constituting elective heat insulating means as well.

2. A thermostatic heater comprising a thermally responsive tube and a rod surrounded thereby, said tube and said rod being joined

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