US1983077A - Adjustable thermostatic switch - Google Patents

Description

Dc. 4, 1934. I B. E. GETCHELL 1,983,077

ADJUSTABLE THERMOSTATIC SWITCH Filed Jan. 6, 1934 4 INVENTOR BENJAMIN E. GETCHELL 5thumb.piece;or.other adjusting device.

Patented Dec. 4, 1934 1,983,077 PATENT OFFICE ADJUS TABL E THERMOSTATIC SWITCH Benjamin E. Getchell, Plainville, Conn., assignor toThe Trumbull Electric Manufacturing Company, Plainville, Conn.,

Connecticut a corporation of Application January 6, 1934, Serial No. 705,491

7 Claims.

My invention relates particularly to a combination of electric heater and switch provided with means of adjustment to vary the temperature at which the switch will operate.

One object is to provide a compact, enclosed type of thermostatic switch provided with external means to permit adjustment.

Another object is to provide an enclosed snap action thermostatic switch which may be readily ;adjusted to operate at different temperatures.

Another object is to, provide a switch of the foregoing character in which the initial adjustments can be effected at the factory to remain fixed.

Another object-is to provide a heat actuated thermostatic switch which can be made economi cally and which is reliable in its operation.

Another object is to provide a simple compact type:.of heat actuated switch which can be readily ,;adjusted over a wide range of temperatures.

.*Another object is to provide an adjustable thermostatic switch inwhich can be readily embodied withoutchange of construction, an auxiliary heateL-for the purpose of compensating for the differential of temperature between the on and off? movements of the switch.

in .carrying .out the invention I preferably mount an. operating mechanism inside of a casing which is sealed and is provided with an external The thermosta'tic' switch includes a bendable element which supportsthe bi-metallic strip in such a manner that both may be'adjusted to vary the action of theswitch.

If it is desirable to reduce the differential in temperature betweengthe ,on and off movementsofg-the switch; the bendable element supportingthe lei-metallic strip may be made of an electrical resistance material.

.Fig- 1 is a longitudinal sectional view of one form of device embodying my invention, showing the parts of the switch in the open circuit position.

Fig. 2 isa side view of the switch mechanism removed from the casing.

Fig. 3 is a plan view of the same showing the parts of the switch in the closed circuit position.

Fig.4 is a bottom view of the support for the 5(} switch with the adjusting mechanism.

6 action thiscontact 12 may be carried by an arm 14 hinged to the end of the strip 13 as set forth in application Ser. No. 701,714 filed December 9, 1933 by Benjamin E. Getchell.

A washer 15 is supported by a knife edge like tip of the strip 13 and a spring 16 is interposed between the washer 15 and a shoulder on the switch member so as to produce a toggle like action.

The arm 17 is preferably formed of bendable resistance metal and so as to serve as a support for one end of strip 13. Arm 17 may be formed of resistance material to serve as a heater to compensate for differential. One end of this arm 17 is supported by a post-like member or members 18 which are secured to the support 8. The other end of the arm 17 is secured to one end of the thermostatic strip 13 by rivets 19 with insulating pieces 20, 20 on opposite sides. A back piece 21 may also be provided to afford a seat for the adjusting screw 22 which passes through the strip 13 and the arm 1'7 so that by tightening or loosening the screw 22 the relative position of the strip 13 with respect to the arm 17 may be adjusted.

The shaft 23 is supported in bearings 24 and has an eccentric pin 25 at its inner end located between the spaced apart ends of the insulating pieces 20, 20. A finger piece 26 is provided on the outer end of the shaft 23 for rotating the shaft and thereby adjusting the heater arm 1'7 and the thermostatic strip 13.

To hold the shaft 23 and associated parts in adjusted position I provide a disc 27 on the shaft 23 which coacts with a spring finger 28 carried by the support 9. The edge of the disc 27 is notched to provide definite positions for the engagement of the spring finger 28.

p The finger piece 26 is preferably provided with an indicating pointer or mark 29 which is adapted to coact with the stationary scale 30 to show the adjusted position of the parts.

A stationary stop 31 is provided opposite the post-like member 18 to limit the movement of the thermostatic strip awayfrom the heater arm. An abutment member 32 opposite the contact 10 limits the movement of the switch member away from the contact 10.

The electrical parts are preferably housed in a casing made up of the two parts 33 and 34 which are suitably connected and one of which is provided with an outlet 35 for the electric conductors. In order to provide a water tight joint between the shaft 23 and the casing I may provide a soft rubber washer 36 and a metal washer 37.

When the parts are in the position shown in Fig. 3 electric current passes successively through the parts 11, 10, 12, 14, 13. 17 and 18. When the temperature changes so as to warp the thermostatic strip 13 from the position shown in Fig. 3 toward the position shown in Fig. 1, the switch parts snap to the open circuit position, and vice versa, and when the temperature conditions change in the other direction, the parts will move from the positions shown in Fig. 1 to the positions shown in Fig. 3.

' The temperatures at which these changes occur will depend upon the position of the supporting arm 17. This position can be readily adjusted by simply rotating the finger piece 26 with the shaft 23 and the crank pin 25. The scale 30 may be calibrated to indicate temperature'points at which the changes take place, such calibration being in accordance Wtih any suitable code or thermometric standard. The primary adjustment for raising or lowering the adjustable range is efiected by means of the screw 22 which adjustment, of course becomes fixed for a given instrument if the parts are sealed in the casing.

When this supporting arm 17 is also used as a heater, it is not for the purpose of moving the bi-metallic strip to produce action of the contacts. t is for the purpose .of moving the strip just enough to compensate for the difierential between the normalopening and closing temperatures of the thermostat so that a slight further change in external temperature will cause switch action.

-compensation-with a setting of 60 degrees, the

' thermostat would snap on at 60 degrees and off at '72 degrees, a diiferential of 12 degrees.

When the thermostat is controlling a fixed load, it is possible to make arm 17 of resistance metal of just the right resistance to add a pre-determined amount of heat to the thermostat, independent of outside temperature. For instance, if this resistance added 11 degrees of heat to the thermostat, an outside temperature increase of 1 degree would be sufiicient to cause it to trip Thus the differential would be reduced to 1 degree instead of 12 degrees, making it possible to more closely regulate the heating of hotbeds, etc.

This construction has the added advantage over the ordinary enclosed thermostatic switch in that it can be actuated manually to open and close the circuit independently of changes in temperature. For instance, if the parts are normally in the open circuit position of Fig. 1, the switch can be manually actuated to the position of Fig. 3 by simply turning the finger piece 26 and without waiting for the temperature change;

I claim:

l. A thermostatic switch including a bendable arm supported at one end and free at the'-other end, a bi-metallic strip having one end secured to and movable with the free end of said arm, a

switch contact carried by the opposite end of said i 1 strip, means for adjusting the position of the strip with respect to the arm to vary the action of the strip with respect to, the arm, and means for adjusting the free end of said arm and the attached end of said strip to vary the moment of action of the switch.

2. In a thermostatic switch a heater element, a bi-metallic strip supported thereby, 39%!!5 Or relative thereto.

adjusting said strip with respect to said heater element, and means for adjusting one part of said heater element with said strip.

3. In a thermostatic switch, a stationary contact, a bi-metallic strip movable across a predetermined point under the influence of changes in temperature, a contact member carried by said strip and being adapted to move into engagement with the stationary contact under snap action upon the movement of the strip across said point, a heater arm for heating said strip and manual means for variably adjusting the position of said arm and strip relative to said point, said means including a crank shaft operatively connected to 'said arm and strip and a finger piece for actu ating said shaft. j

4. In a thermostatic switch, a stationary contact, abi-metallic strip movable across a predetermined point under the influence of change of temperature, a contact member carried by said strip .and being. adapted to move .into engagement with the stationary contact under snap action upon the movement of the strip across said point, a heater arm for heatingsaid strip and manual means for initially adjusting the position of said arm and strip relative to said point, and means to indicate the positions of said arm and strip relative to said point, said means including a crank shaft, a dial and a pointer carried by-the crank shaft.

5. In a thermostatic switch, a stationary contact, a bi-metallic strip movable across a predetermined point under the influence of heat, a contact member carried by said strip and being adapted to move into engagement with the sta-' tionary contact under snap action upon the movement of the strip across, said point, a heater arm for heating said strip, manual means for initially adjusting the position of said arm and strip relative to. said point, said means including a crank shaft having a member engaging the heater arm to move the same and means for holding the crank shaft in adjusted positions.

6. In a thermostatic switch, a stationary contact, a bi-metallic strip movable across a predetermined point under the influence of changes in temperature, a contact member carried by said strip and being adapted to move into or out of engagement with the stationary contact under snap action upon the movement of the strip across said point, a heater arm for heating said strip, means for initially adjusting the position 'of saidstrip relative to said arm', means for variably adjusting the position of said arm and strip relative to said point, said latter means including a crank shaft havinga portion connected to the heater arm and a manually operable member for rotating the crank shaft and means to indicate the said predetermined point and the adjusted position of the arms and strip '7. A thermostatic switch including a casing, an insulating support therein, a stationary contact on said support, a bi-metallic strip movable across a predetermined point on said support, a contact member carried by said strip and being adapted to move into or out of engagement with the stationary contact under snap action upon the movement of the strip across said point, a heater arm for heating said strip and means positioned exteriorally of the casing for readily adjusting the position of the arm and strip relative to said point.

BENJAMIN E. GETCHELL.

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