US1804367A - Thermostat - Google Patents

Description

.'Inlllll N. T. BRANCHE THERMOSTAT Filed May 9, 1928 Imi. .H l

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' the casting and .is secured at its upper and Patented May l93ll UNM NELSON BRANCHE, OF TOLEJO, GEIQ, ASSIGNOR T0 SURFACE COMBUSTX'SBN COB'QR- TION, I0F TOLEDO, (EH10, A CORPORATIN 0F NEW 'YORK THERMOSTAT Application led May 9,

rlhis invention relates to thermostats-and more particularly to a thermostat having a thermal member adapted for positioning within a heating chamber of a heat treating furnace.

lt is an object of the invention to provide an instrument of the character indicated which shall be provided with means for damping the operation of the instrument in order to prevent immediate actuation of the instrumentalities under the control of the thermostat upon the opening or closing of a circuit within the thermostat in order to prevent hunting of said thermostatically'con# trolled instrumentalities under relatively small variation in temperatures.

Another object is to provide a thermostat of the character indicated which shall be rugged in construction, relatively inexpensive to manufacture, and which shall be capable of some adjustment in the hands of 'the ordinary operator. t

rlhe single figure ofthe dra-wing illustrates the preferred embodiment of the invention, the circuit wires being laid out diagrammatically and some parts being broken away and in section to more clearly illustrate the various constructional features.

ln the drawing l0 indicates the main body casting or support to which most of the other parts of the instrument are secured. The

lower end,12 of the casting is round in plan.

and the upper en ,d thereof is of ring like form having a cutaway portion 16 for the convenience in placing the circuit wires.. A tubular -casing 18 is telescopically positioned over lower end by securing screws 20 which screw into the upper and lower parts 14 and 12 respectively of the casting. y i

rllhe expansible thermal element is a relatively long tube 22 which is threadedly secured in the lower part 12 of the main body casting. Positioned within the tube 22 and restingon the bottoni thereof is a cylindrical rod 24 having a negligible cociiicicnt of eX- pansion such as a quartz rod. Also positioncd within the tube/*22 and resting on the top of the quartzrod24 is a push rod 26 of any suitable material having a relatively 1928., Serial No. 276,301.

small coefficient of expansion. rllhe quartz rod 24 and the rod 26 are of such diameter as to be capable of easy sliding fric-tion within the tube 22 as will be readily understood.

Threadedly secured in the upper end of the push rod 26 is a post 28 having a head between whicli and the top of the rod 26 is confined a relatively strong coil spring 30. rEelcscoped over the head ofthe post 28 is a cap 32 the top of which is pointed to serve as a point abutment bearing.

Appropriately fulcrumed on the casting l() above the cap 32 is an elbow lever 34. r-lfhis lever is fulcrumed at the outer extremity of one of its arms as indicated at 36, this arm being extremely short as compared with the other arm of the lever. The pointed end of the cap 32 is adapted to engage with the lever at one side of its fulcrum in order to rock the lever about its fulcrum as will be readily understood. As shown, the point where the cap engages with the leveris provided with a hard steel insert 38 to minimize wear, the top of the cap 32 being preferably also hardened. lt will be noted that the longarm of the lever is disposed longitudinally of the casting.

Projecting laterally from the body of the casting and disposed in the path of movement of the upper end of the lever 34 is a lug 40 in which is positioned a switch contact point 42. Positioned'in the upper end of the lever 34 is a contact point 44, these two points constituting the two lements of a switch which is normally closed when the thermal tube 22 is cold.

Secured to the casting near its top as by a securing bolt or bolts 46 is aA porcelain body extensions 50 and 52. Secured to the lower lug 52 by az brass securing bolt y53 is a relatively long bimetal blade 54, the securing means and blade being in the electrical connection with the switch contact point 42 as by a wire 56. Projecting laterally through the lug 50` are two brass bolts 58 and 60. The end of the bolt 58 facing the upper end of the blade 54 constitutes a switch Contact point for the blade.

Trapped around the blade 54 are many turns of fine Wire which constitute a heating 48 having twolongitudinally.spaced lateral over a thin asbestos sheath which serves the double purpose of an insulator and a. means for tempering the heat from the heating element as will be readily understood. A part of the blade above the securing point is not covered by the asbestos sheath and about this exposed part a sufiicient number of turns of wire are wound to establish proper electrical connection with the securing bolt 53. The wire at the upper end of the blade is continued over and appropriately connected with the bolt below the bolt 5 8. When the blade 54 becomes heated it bends and makes contact with its switch point constituted by the end of the bolt 58.

Secured tothe top ofthe casing 18 is a hard `rubber cap 64 in vwhich are mounted three electrical terminals 66, 68, 70. Terminal 66 is wired to connect with the switch contact point 44 at the upper end of the lever 34. Terminal 68 is wired to connect with the bolt 60 with which the heating element 62 is also connected, and terminal 70 is wired to connect with the bolt 58 which, it will berecalled, is oneelement of the switch which includes the blade 54.

Projecting laterally from the casting 10 is a pin 72 which serves as a stop for coniining the lever 34 within a limited range of movement. Secured to the lug 40 opposite the top of the lever is a linger spring 74 which presses against the lever 34 and which tends to open the lever switch.

Adjustably mounted on the thermal tube 22 is a collar 76. The primary purpose of the collar 76 .is to abut against the 4furnace wall when the thermal. tube is inserted through an openingl in the wall for projection into a heating chamber whose temperature is to be controlled.

As previously stated the terminal tube 22 is y adjustably mounted in the lower part 12 of the casting 10. A set screw 78 serves to sccure the tube in its adjusted position. By screwing the tube into or out of the body 12 of thecasting such adjustment as may be necessary to calibrate the instrument is effected. When the tube 22 is turned the cap 32 willvbe longitudinally*adjusted with respect to its abutment at the bottom of the lever34 as will be readily understood aud consequently a lesser or greater expansion as the case may be must take place in the tube 22 before the lever 34 is operated to open or close its switch as will be readily appreciated. To facilitate turning of the tube 22 I prefer tolsecure tothe tube at its upper end a collar 80 from which projects a handle 82. By grasping the handle 82 and after loosening the set screw 78 turning` the tube 22, the instrument may be readily adjusted within limits Without dismantling the iiistruinent as will now be readily understood. In order that the weight of the arm 34 may not cause an appreciable variation in the operation of the instrument when the instrument is horizontally disposed, I provide a suitable external pointer or the like, not shown, to enable the operator to place the instrument in such position that the lever 34 will swing about a vertical axis.

Terminals 66 and 68 will be connectedwith a power line A and terminals 7() and 68 will constitute the terminals of a circuit B which leads to a suitable instrumentality, as for example, an electrically operated valve for controlling the flow of gas or other heating agent, for regulating the heat input to the furnace whose .temperature is to be controlled.

The operation of the instrument-may be briefly described as follows: When the thermal element 22 is inserted in the heating chamber it will expand under the iniiuence of the heat therein. This expansion will cause the push rod cap 32 to recede with respect to the Ai'fulcrum 36 of the lever 34. Spring 74 tends to open the lever switch. When the thermostat circuit is open the exterior circuit B is open and consequently the condition of the instrumentality controlled by the circuit j B will be changed and such instrumentality allowed to control the How of fuel or the heat input to the heating chamber. When the temperature within the heating chamber drops the tube 22v will contract and when it has contracted suiciently the lever switch will again close and current iiow through the blade heating element 62. When the blade has become suliciently heated it swings over and makes contact with its contact point or bolt 58 closing the blade switch and the exterior circuit B. Some current will s till continue to flow through the blade heating element 62 but since the switch is closed the main circuit will now be through the blade as a conductor, as will be readily understood. In other words reading from the power line A the current will flow by way of the terminal 66through the contacting switch ele ments 44 and 42 constituting the lever switch, through the blade 54, the bolt 58. terminal 70, that lead of power lirfe B which connects with terminal 70, then through the instrumentality connected with the circuit B, then throughthe other lead of the .circuit B to terminal 68 andinally to the power lineA. As stated some current. continues to flow through the heating element 62 even though the blade switch is closed, the heating'element being in circuit with the lever switch. The primary purpose of providing the biios metal blade switch is to render the instruwords the blade switch introduces a time lag' between the openings and closings of the lever switch and the corresponding openings and closings of the external circuit B to prevent the instrumentality connected with the circuit B from hunting as will now be readily understood.

Although I have shown an operative device, still it will kbe obvious that various changes may be made in size, shape, or arrangement o the parts without departing materially from the spirit of the invention.

What is claimed is:

1. In a thermostat, the combination of a tubular casing, an elongated member removably positioned within said casing, a bell crank lever pivoted on said member and having arms of unequal length, the longer arm of said lever extending longitudinally in said casing and the shorter arm of said lever ex-` tending transversely in said casing, a pair of contacts, one of said contacts being held by the elongated member, the other of said oontacts attached to the longer arm of said lever for movement to and from its fellow contact by said lever, thermally controlled means carried by said elongated member and extending from one end of said casing for actuating said lever, said means being longitudinally adjustable with respect to said member. and means inserted between said lever and said thermally controlled means for absorbing the differential of the movement of said lever and said thermally controlled means.

2. In a thermostat, the combination of a tubular casing, an elongated member removably positioned within said casing, a fixed4 contact carried by said member intermediate its ends, elongated thermally controlled means projecting longitudinally from and axially adjustable with respect to said member, a bell crank lever pivoted on said member and having arms of unequal length, the longer arm extending longitudinally of said casing and the shorter arm extending transversely of said casing, a movable contact fixed to the longer arm and adapted to swing to and from engagement with the iiXe-d contact, means inserted between the shorter arm of said lever `and said thermally controlled means for absorbing the differential of the movement of said lever and said thermally controlled means, and means tending to keepy said contacts in open relation.

3. In a thermostat, the combination of a tubular casing, an elongated member removably positionedvwithin said casing, a fixed contact carried by said member intermediate the top and bottom thereof, a bell crank lever pivoted on said member and having arms of unequal length. the longer arm of said lever extending longitu-linally in said casing and the shorter arm extending transversely in said casing, a movable contact fixed to the longer arml of the lever and arranged to swin laterally into and out of contact with the xed contact, thermally controlled means

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