US2425164A - Temperature compensated switch - Google Patents

Description

wg. 5, 1947. E. c. THOMSQN 2,42%64- TEMPERATURE COMPENSATED SWITCH med Jan; 15,- 1944 i l ma u .if i

da O Patented Aug. 5, 1947v UNITED leirrlalv'lV OFFICE TEMErwrUar; coMPENsa'rEn lswrrcuy EllhuCraigThomaom Boston, Mass., assignor to Combustion. Control Corporation, Cambridge, Mass., acorportlon ofiMassachusetts i 'Appueanqn January 13,y 19,44, serial No. 518,130

1 This-invention relates to electric switches and particularly to switcheswhich are controlled or i tion by actuating elements depend for positive and certain operationuponhdenite corelationof somma. (cileno-122) switch spring position and actuator deection, es-

pecially if one actuatcr is. supposed to yoperate several* contact springs ,in` Va given sequence. While it is possible denitelytocorelate the-switch operation to a given actuator deection, the latter ling the genus of the invention. The description refers toa drawing in which e' Figs. 1 to 3 are elevations of a switch accordingto the invention, with the actuator, contact,

and stop elements in various operative positions; Fig. 4 .is a detail view ofy a bimetallic switch spring according to the invention, and

" Fig. 5 a fragmentary elevation of a second em- I bodiment of the invention.

Referring to Figs. 1 to 3, a suitable housing or frame, for example a U-shaped strip I (which may have aninsulating portion la), having tapped holes 2, 3 for mounting the switch on an itself may depend not only uponfthecoritrolling ef'lect purposely applied thereto butalso upon the ambient temperature which, under' unfavorable conditions may even causev undesired. switch op eration without intended A,d'eiiectionpfl the actua-l tor.

plied thereto by a heating elementsince such actuators will respond to changes' ofambient`temperature just as much as to the intended temperature changes of theheating element.

Itis one of the principal objects of the present invention tqprovide a switch actuatedby a; device whose deiiection depends on its temperature, and the operation of whichhswitch is independentof ambienttemperature conditions. Other Vobjects are to provide a switch ofthe type v`described inl Patent No. 2,358,372, dated September 19, 1944,l

which operates reliably, in. response ito, a; certain temperature vchange applied by. a heating` element, regardless of ambienttem'peratureconditions; to providea thermally operated switch ha'v ing two Iswitcnelements which .establish contact.

consecutively in predetermined sequence regardless of ambient temperature conditions; antigen-v erally to provide. a switch o f Ithis type which Vis simple, rugged, inexpensive andyetvery accuraie.V

`These and v other objectsl yand `aspects will bel more fully apparent from4 thefollowingdescriptionjof several practical embodiments illustrat- This undesirable veiiect is especially ,apt to occur when the actuator is puIDOsely designed to deflect in response vto temperature changes apt appropriate' support 4, holds between its arms by means of screw bolts 5, 6 a series of blocks I and a 'block 8 of insulating material. Betweeny these blocks and insulated from the bolts are clamped switch spring strips I5, I6, II, IB constituting switch contact elements, and an actuating switch stripv I9. Screwed to end block 8 is a .bimetallic actuator strip 22 which can move only in a plane normal to the plane in which strips I5 to I9 are operating,

Strips I9 and 22 are provided with heating resistors C and D, respectively. In normal, un-

heated condition, thesel thermal strips I9, 22 assume the positions shown in Fig.v 1, Whereas when heated they bend as indicated in Figs. 2 and 3. Suitable means may be .provided for adjusting the movement of the thermal strips I9 and 22.

Stops'25, 26 may be providedinf order t limit the movement of springs Il, I8 when they follow fiexure. of actuator I9 towards the right-hand side of the iigures, assuring sudden breaking and closing of Contact at points CI and C2, with springs., I1, I8, ISat a definitely predeterminable relative position.

The actuating contact strip I9, the contact springsll and I8 and stops 25, 26 are made of bimetallic material for the purpose to be described below.

Y Theiree ends of switch springs t1, I8 are bent over and downwardly in inverted U-shape With the more distant spring I'I reaching with lateral portion I'Ia over'the similar portion IBa of spring Iii-and the descending portions E'Ib and I8b being arranged to contact spring I9 in unhcated position..

The switch springs I5 to I9 are provided with contactpoints constituting switches CI, C2 and D2; under-normal conditions, with bimetal strips I9 and` ZZ-Kunheated, strip I9 retains contacts CI and C2 closed (Fig. 1) and insulating finger 24 of strip 22, constituting a stop element, closes switch D2,v The lower ends of the switch springs are extended into tails for connection with lead wires, as indicated at I I.

A resetting mechanism may consist of a cylindi'lcal block or bar 55 of insulating material which has two control faces or shoulders I, 52 and slides in two openings 53, 55 of frame I. Opening 53 is wide enongh to -permlt insertion of block 30, but screw' 55, if placed as indicated in Figs. 1 to 3. after insertion of the block 35 retains the latter in the frame without, however, hindering its sliding movement in openings 53, 55. A spring 55 inserted between frame I and shoulder 51 of block Il urges the block out of contact with springs I5, I5.

'I'he control faces 5 I, 52 are preferably so spaced that their distance is greater than the distance of the stop faces of switch springs I5, I5 in open position. Therefore, pushing in of block III by means of resetting push button extension 55 will not close switch D, whereas release of the button will permit such closing, if the actuator 22 is in the position indicated in Figs. 1 and 3; with element 22 in the position of Fig. 2, switch D2 is open with spring I5 retaining actuator 22 in denected pition.

The heater coils C and D may be supplied with current through tailed lead strips 5I, 52, 53 and insulated connectors 54, 55.

Asmentioned before, and shown in Ilig. 1. all three switches CI, C2, D2 are closed when the thermal strips I9, 22 are cold. When strip I9 deflects, switchesCI and C2 are permitted to open, with switch CI opening ilrst as shown in Fig. 3, and switch C2 opening thereafter as shown in Fig. 2. If resistor D heats strip 22, the latter bends laterally (forward in Figs. l to 3) and permits switch D2 to open as likewise shown in Fig. 2. Flexure back into the position shown in Fig. l will cause reclosing of switches CI and C2, the contacts being so arranged that switch C2 closes before switch CI.

The operation of switch elements 22, i5, I5 Iis explained in detail in the above-mentioned patents and not described in detail herein since this aspect of the switch is not part of the present invention and merely shown as belonging to the switch unit chosen for description by way of a well-tested embodiment of the invention.

Switches of the above-described type operate as follows.

When heater C does not carry current, actuator spring I9 contacts springs I1 and I5 and establlshes contact at CI and C2. Birnetallic springs I1 and I5 are so mounted and dimensioned that, with changing temperature, they deiiect in the same sense as actuator I9, so that contact at CI, C2, and the general mechanically effective relative location of the three elements is maintained regardless of prevailing ambient temperature.

When current is for control purposes supplied to heater C, actuator strip I9 vbegins to bend ,away from strips I1 and I5 which follow the actuator, retaining CI and C2 closed, until strip I1 strikes stop 25 whereupon C I opens as shown in Fig. 3. As actuator I9 deflects further,A strip I5 strikes stop 25 and C2 also opens.

The eifectlve positions of bimetal stops 25 and 25 likewise change with temperature so that, with proper arrangement which of course depends upon the particular shape and dimension of every individual switch design, the mechanically effective position of contact springs such as I1 and I8, and stop elements such as 25 and 25 can be rendered independent of ambient temperature.

When heater C is supply, actuator I5 deflects in opposite direction, first contacting spring I5 at C2 (Fig. 3) and then spring I1 at CI (Fig. 1).

It should be noted that the construction shown in Figs. l to 3 is especially advantageous to secure opening of one contact, as at CI, before that of another, as C2, for the following reason. Bimetal spring I1 which is to open contact first at CI, is located furthest from heater element C,so that any possible heat transfer from C to I1 is less than from C to Il.V Hence, deflection due to such transfer, of I1 and 25 towards l5 is less than of I8 and 25 towards I5, which insures that the tendency of Ci to open first is enhanced rather than diminished, due to the expedient of extending the contact point I1b effective for switching at C I, over contact point 15b effective with regard to switch C2 that depends for operation upon the strip nearer to heater C and is required to open after switch CI.

The principle of the invention can be applied to different switch constructions as for example that of the abve-identined patent shown in Fig. 5. In this figure, I is the supporting frame, II1, II5 and Il! three bimetallic springs forming switch contacts vCI and C2, and 2l a non-conducting actuator strip carrying an insulating button 23 and a heater element C. The'strips H1, Ill, Il! and 2| are so arranged that theydeilect in the samesense with varying temperature. so that their mechanically elective relative position is not aliected by changes in ambient temperature, in the manner described ebove. Deiiection of 2| towards the right of Fig. if),v upon heating by means of coil C, will cause opening of CI and C2, if desired in a predetermined sequence, "and deflection of 2| in opposite direction will analoously cause closing of CI and C2.

It will be understood that. although advantageously applicable to switcheswith temperature sensitive elements actuated by any desirable means, the principle of the invention is especially advantageous if one of these elements is purposely made temperaturey responsive and provided with controlling heater means. as herein described.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

I claim: Y

l. A switch system comprising a switch base, an actuating element adapted to deflect with changing temperature vmounted on said base, means for deflecting said actuating element. a switch spring element tending to contact said actuating element, and a stop element limiting lsaid tendency of said switch spring. said switch spring and said stop element being likewise adapted to deflect Iwith changing temperature, and said actuator element and said switch spring being so arranged and mounted on said base that flexure of said actuating element may cause mechanical actuation oi' said switch element whereas temperature changes of actuating element, switch element and stop element leave the mechanically effective relative location thereof substantially unaffected.

2. A switch system comprising a switch base, an actuating switch element adapted to deflect with changing temperature mounted on said base, means for heating said switch element. a first switch spring element and a second switch spring element likewise adapted to. denect with changing disconnected from current temperature, said switch elements being so arranged and mounted on said base that flexure of said actuating switch element through temperature change of said heating means may cause contact of said actuating switch element first with one of said switch spring element and thereafter with the other switch spring element through mechanical contact therewith whereas temperature changes of actuating and both switch spring elements leave the mechanically effective relative location of the three elements substantially unafIected.

3. A switch system comprising a switch base, an actuating bimetallic switch strip mounted on said base, a heating coil wound on said switch strip, a first bimetallic switch spring strip and a second himetallio switch spring strip, said strips being mounted on said base for coplanar deflection with said second spring strip arranged between said actuating strip and said rst spring strip, the ends of said spring strips forming contacts extending towards the end of said actuating strip so that flexure of said actuating strip through temperature changes of said coil may cause disengagement of said end of said actuat- REFERENCES CITED The following references are of record in the Yille of this patent:

UNITED STATES PATENTS Number Name Date 2,035,426 Field Mar. 24, 1936 2,116,858 Winckler May 10, 1,938 2,274,399 Cook Feb. 24, 1942 2,358,372 Wolfner 2nd Sept. 19, 1944 1,562,932 Walker Nov. 24, 1925 2,329,119 Jacobs Sept. '7, 1943 2,129,477 Parks Sept. 6. 1938 1,783,904 Carter et al. Dec. 2, 1930

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