US2611057A - Thermally actuated mercury switch - Google Patents

Description

lrxvefitov John L. Slonneger',

- @042 vwm Hi5 Attorney J. L. SLONNEGER THERMALLY ACTUATED MERCURY SWITCH Filed Dec. 29, 1949 Sept. 16, 1952 Patented Sept. 16, 1952 THERMALLY ACTUATED MERCURY SWITCH John L. Slonneger, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application December 29, 1949, Serial No. 135,753 1 Claim. (01. 200-140) My invention relates to electric switching devices and, more particularly, to switching devices which are responsive to temperature changes, either increases or decreases, without regard to the exact temperature at which such changes occur.

Switching devices of the type mentioned are frequently employed in control apparatus for oil burning furnaces and the like to indicate whether or not combustion is established therein. In such a switch a slip-clutch" action is generally employed. For example, the switch may be actuated in response to a relatively small initial increase in temperature. Following actuation, the switch remains in the actuated condition during continuing temperature increases and at steadystate temperatures established during or following the increase. Subsequently, at an increased temperature the switch may be actuated in the reverse direction in response to a relatively small initial decrease in temperature. Following actuation of the switch the temperature may continue to be decreased without further action of switching element which requires relatively little force for the actuation thereof. In response to a relatively small change in temperature in one direction, as for example an increase, actuation of the switch is eifected, following which the switching element is mechanically stopped from Additional actuating force further motion. which may be provided by further change in temperature of the actuating element is spent in slipping the clutch without moving the switch element. However, should the temperature switch element is immediately actuated in the opposite direction following which slipping of the clutch again occurs.

It is a principal object of the present inven- .40 change slightly in the reverse direction the tion to provide a new and improved switching device which is responsive to relatively small changes in temperature and in which an overtravel action similar to such slip-clutch action is included.

In practisin my invention I utilize an expandin which positions fixed electrodes are contacted in various combinations by the liquid to effect switching operations. Slip-clutch or overtravel action is obtained by effecting transfer of the liquid in response to a relatively small initial change in gas pressure, following which further change in gas pressure in the same direction results only in bubbling of the gas through the liquid. However, a change in gas pressure in the opposite direction immediately results in a transfer of the liquid to its original position with subsequent bubbling resulting from further change in gas temperature and pressure.

My invention will be better understood from a consideration of the following description taken in connection with the figures of the accompanying drawing, and its scope will be pointed out in the appended claim. In the drawing, Fig. 1 is a cross-section of a switching device embodying my invention; Fig. 2 shows the device of Fig. 1 following actuation due to an increase of tem perature; and Fig. 3 is a cross-section of a modi fication of the arrangement shown in Fig. 1.

Referring now to Fig. 1, there is shown a switching device I comprising principally a temperature sensing element 2, a switching element 3 and a capillary tube 4 interconnecting elements 2 and 3. Temperature-sensing element 2 may conveniently be a metal bulb of a type commonly used in thermostatic apparatus. Bulb 2 is completely sealed except for a gas-tight connection 5 to capillary tube 4. Tube 4, which may likewise be metal, may be relatively long to permit remote location of sensing bulb 2 relative to switching element 3. Switching element 3 is provided with a housing 6 which is a generally U-shaped member having end portions or legs I and 8 forming the side members of the U, and an intermediate bight portion 9 connecting end portions 1 and 8 and forming the lower portion of the U. v i

A plurality of switching electrodes H), II and I2 are positioned at predetermined points in housing 6. More particularly, electrodes l0 and [2 are positioned in legs I and 8 in the vicinity of their junctions with bight portion 9, while electrode H is positioned at the lower extremity of bight 9. In this arrangement of electrodes 10, H and 12, a single-pole, double-throw switch is provided, electrode H being the common electrode. It is, of course, necessary for electrodes [0, H and [2 to be insulated from one another. In case housing 6 is made of metal, therefore, it is necessary for electrodes l0 and 12 to be insulated from housing 6 by the use of suitable insulating bushings. However, housing, 6 :may

conveniently be made of glass, which has the advantage of permitting the internal conditions of switch element 3 to be viewed. In Fig. 1 housing 6 is shown as made of glass or other insulating material and accordingly no insulating bushings are shown.

Capillary tube 4 ,is-inserted in the outer or free extremity of end portion I and is fixed thereto at a gas-tight joint I3. The free or outer extremity of end portion 8 is provided with a .bulblike portion l4 having a predetermined volume and integrally formed with end portion 8. A predetermined quantity of a conducting liquid I5,

preferably mercury, is placed in the lower or bight portion 9 of housing 6. The volume of the liquid is such that when the liquid surface in either end leg I or 8 is at the level of the top wall N5 of the bight 9, the other leg is only partially filled with liquid. The volume of liquid requiredis such thatwhenliquid l5 stands at equal levels. in legs 8 and 'I ,of' housing, 6, contact isnot made with electrodes lil'and l 2. How- .ever under this condition the levelof liquid stands appreciably, above. the top wallfllfi of bight portion 9 between legs 1 and 8. A porous filter plugfll'l; which may he made of a ceramic material,.is.,positioned in end portion I between the ,end.of capillary tube 4 and electrode I9 and is preferably fixed; to the innersurface of end portion .1. ...Plug.. IT is not essential to the opera- .tion of the switch butv may be. included if desired to prevent liquid. I5 from entering capillary tube land bulb 2 when the apparatus is. inverted, as for: exampleduring shipment.

Bulbaz, tube 4 andlthe. space in housing 6 not otherwise occupied are charged. with a gas. I8 which is inertrelative to theliquid and the vari- .ous. materials employed in constructing the elevNo further actuation of switch element 3 may occur under such conditions.

When the temperature of bulb 2 ceases to rise, steady-state conditions are achieved and no further transfer of gas from bulb 2 to bulb I4 occurs. Liquid I5 thus remains in the position shown in Fig. 2 and theswitch remains in the actuated condition shown therein. Under this condition the pressure provided by the gas in bulb I4 and column I9 equals the pressure in bulb 2. Re-

'ments-ofthe switch. The pressure ofgas. I8

under charging conditions may conveniently be approximately one atmosphere since such a pressure is'readily obtainable. Following chargin of theswitch, the entire switching device is sealed .to prevent escape of the. gas when the pressure 'thereof'isincreased due to heating.

I In. operation, liquid I5 is first made to assume the positionshown in Fig. 1 wherein a. column .I9. ;of liquid I5 is established'in leg I causing contact ofliquid. I5 with electrode Ill. Column. I3 is.-establishedi by tilting switchelement 3 in the direction ofleg I. In the tilted. position liquid l5 provides asealbetween the portion of gas. [8a inthe space enclosed by bulb 2, tube 4 and leg 1, andtheportion of gas l8b in the space enclosed by leg 8- and bulb |4.. For convenience these spacesa are referredto hereinafter as bulbs 2 and [4, respectively.- When element 6 is returned to theupright position liquid l5 movesto theposition shown in Fig. 1 causing a slightreduction in the pressure of gas |8a.- and an increase in the pressure of gas I822, the difference in these; pressures being sufficient; to maintain column .1 9.

-.-eAsbulb 2. isheated gas I8a therein expands throu h capillary tube 4 and filter plug I1 and "frbmesliquid l5v from the position. shown in Fig. 1 to thepositionshown in Fig. 2. It willbe 'seen thatthe; position of Fig. 2 is substantially reversed fromthe. position of Fig. 1 anda column trodes. Ill and His interrupted and a conducting'patlrisestablished between electrodes II and gardless of the final temperature of bulb 2 and the gas I8a therein, when gas I So is cooled a relatively few degrees contraction thereof occurs, with accompanying reduced pressure, and liquid I5 is transferred to its-original position as shown in Fig. 1. Further reduction of temperature of the gas in bulb 2 results in bubbling'of the gas through liquid 15 without further effect on the position of liquid I5. Depending on their direction, changes in the temperature of bulb I l and gas I 8?) may assist or oppose normal actuation of theswitch in response to temperature changes of bulb 2,as described. It is desirable, therefore, in

the operation of the switch, thatthe temperature of. bulb, I4 remain substantially constant to prevent spurious actuation of the switch.

Itwill be seen that an overtravel or slip-clutch action is. provided by switch element 3. Liquid I5 may be transferred in either direction by a relatively small change in the temperature of gas [8a in bulb 2 but further change of temperature in ,the same direction results in slipping which is in the. form of bubbling of gas I8 through liquid Iiwithout eifect on the position of the latter. To efiect actuation of the switch in response to a relatively small change or differential in temperature it is desirable that the volume of bulb 2 be relatively large with respect to the total, volume of the space containing gas l8a, this space com.- prising bulb 2, tube 4 and leg 1.. Thus thevolumes of tube 4 and leg I are preferably made small relative to the volume of bulb 2. The. volume of the. space enclosed by leg 8 and bulb I4 is preferably approximately one-half of the volume of bulb 2; The exact proportionsof the various elements of the switch may readily be determined in actual practice .to obtain desired operating characteristics. f

Attention is now directed to Fig. 3 in which thereis shown a modification of the embodiment of my invention previously described. There is shown a. switching device I provided with atemperature-sen'sing bulb 2' and a capillary tube .4 which are generally similar tocorrespondingelements in Fig. 1. Housing 6'. of switchin element 3', however, differs in construction from housing 6 of switch element 3 inFig. 1. Housing 6' is a generally U-shaped member provided with a pair of vertically disposed end portions or legs I and 8. having gas chambers therein and a bight portionS. 'The latter comprises a relatively heavy- Walled capillary tube 2i interconnecting. the chambers in legs 7' and 8'. Bight portion 9. terminates in generally tapered extremities. 22, the larger portions of which are sealed at gas tight joints .23 to legs 'I' andB. The reducedportions 25 of tapered extremities 22 extend into. the chambers in legs I and i3. as'shownin Fig. 3. .Thus the-extremities 25 of capillary tube 2| are positioned above joints 23, thereby providing reservoir spaces 26 between tapered portions 24 and the inner surfaces of legs l" and 8, respectively.

As in the device previously described a predetermined quantity of a conducting liquid 15', preferably mercury, is introduced in housing 6, and the space in the system not otherwise cccupied is charged with an inert gas it. Capillary tube 4 preferably extends a substantial distance into leg to minimize the possibility of liquid !5' entering capillary tube 4 and bulb 2' when switch I is inverted. The portion of gas [8' in bulb 2, tube l and leg '2" is designated as i812, while the portion of gas in leg 8 is designated as I82). Housing b is again shown as being made of an insulating material such as glass, and accordingly insulating bushings are not employed in connection with the switch electrodes. A pair of electrodes is and 52' are positioned in leg 1" and 3 respectively as in Fig. 1. However, in the arrangement of Fig. 3 a pair of electrodes 21 and 28, rather than a single electrode, such as electrode H, are provided to act cooperatively with electrodes iii and i2, respectively. Electrodes 27 and 28 are positioned in legs 1 and 3' so as to extend into reservoirs 23 and are provided with a common connection 25. It will be seen that regardless of the position of liquid [5, that is, whether the bulk of liquid i5 is in leg 1' or leg 8', portions of liquid it remain permanently in reservoirs 26 since the sole outlets of legs I and 8 are through extremities 25 of capillary tube 22 which are at the upper levels of reservoirs 28. Thus electrodes 21 and 28 are in continuous contact with the portions of liquid l5 in reservoirs 26.

Operation of switch I is generally similar to the operation of switch I in that liquid #5 is forced in response to pressure changes in gas i811. through capillary tube 2! between legs l" and 8. When liquid 55' is in leg 7 as shown in Fig. 3 a conducting path is formed between electrodes l and 2'! thus completing the circuit therebetween. Under this condition the circuit between electrodes l2 and 28 is open. When, on the other hand, liquid i is transferred to leg 8' the reverse is true and a circuit is completed between electrodes l2 and 28 and the circuit between electrodes l0 and 21 is open.

The arrangement of Fig. 3 which makes use of a capillary tube 2| to interconnect legs 1' and 8' is particularly useful to prevent surging of liquid l5 due to relatively rapid changes in the pressure of gas Ida. In general liquid I5 is forced completely out of tube 2|, as shown in Fig. 3. Regardless of the rate of change of pressure, tube 2| acts as a dampening medium to enable gas IE to pass through liquid i5 without undue agitation and violence. While the volume of the chamber containing gas l8b is shown as comprisin only leg 8' without a bulb portion similar to bulb l4 in Fig. 1 at the extremity thereof, it will be obvious that it is only necessary to provide the desired volume therein and that the particular configuration employed in the construction of housing 6 is principally a matter of convenience. It will be further obvious that by sealing the end of leg 1' and by suitably increasing the volume thereof, leg I may be employed as the temperature-sensing element of switch I without the use of bulb 2 and tube 4. In this case it is necessary to provide thermal insulation between legs '1' and 8', as by lengthening intermediate portion 8' and capillary tube 2|, to permit changes in the temperature of leg 7 without appreciably aii'ecting the temperature of leg 8'.

While I have shown and described a preferred embodiment of my invention, it will be understood that my invention may well take other forms and I, therefore, aim in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

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

An electric switch responsive to temperature changes comprising, a U-shaped housing positioned with the leg portions thereof vertically disposed and with its bight portion at the bottom, a pair of gas chambers forming parts respectively of said leg portions, a capillary conduit in the said bight portion interconnecting said chambers, a pair of reservoirs within said chambers forming respectively portions thereof with each reservoir located adjacent the connection between said conduit and the chamber in which it is located, a quantity of electrically conductive liquid only partially filling said housing but of sufiicient volume to more than fill both said reservoirs, an inert gas filling said housing above said liquid, a pair of electrodes extending through said housing respectively into said reservoirs, a second pair of electrodes extending through said housing above said reservoirs respectively in said two chambers, whereby an upper and a lower electrode are provided in each chamber, a predetermined increase in the pressure of the gas in a first of said chambers relative to the pressure of the gas in the second chamber produced by a change in the temperature of the gas in one of said chambers causing said liquid to flow through said capillary conduit from said first chamber to said second chamber whereby to raise the level of the liquid in said second chamber sufficiently to produce an electrical connection through said liquid between the upper and lower electrodes in said second chamber, and a predetermined inverse change in said relative pressure produced by an oppositely effective temperature change causing said liquid to flow from said second chamber to said first chamber whereby to raise the liquid level in said first chamber sufficiently to produce an electrical connection through said liquid between the electrodes in said first chamber, said chambers and the reservoirs therein being so constructed and arranged that all Of the liquid in one chamber except that remaining in the reservoir may flow through said conduit from said one chamber to the other chamber and that upon such an occurrence gas flows from said one chamber through said conduit to the other chamber until the gas pressure in said one chamber is substantially equal to the gas pressure plus liquid head pressure in said other chamber.

JOHN L. SLONNEGER.

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

UNITED STATES PATENTS Number Name Date 1,691,016 McCabe et a1 Nov. 6, 1928 FOREIGN PATENTS Number Country Date 277,344 Great Britain Dec. 7, 1928 407,861 Great Britain Mar. 29, 1934 501,592 Great Britain Feb. 27, 1939

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