Patent Publication Number: US-3875800-A

Title: Temperature responsive electrical switch

Description:
United States Patent Stockton Apr. 8, 1975 [76] Inventor: Harold E. Stockton, 700 Ashley Dr.,  
 Moore, Okla. 73160 [22] Filed: May 16, I973 [21] Appl. No: 360,68l  
  Related US. Application Data [63] Continuation&#39;in-part of Ser. No. 326.516, Jan. 24.  
 [52] US. Cl 73/368.6; ZOO/81.8 [51] Int. Cl. ..G01k 5/36 [58] Field of Search 73/3686, 389, 411; ZOO/81.8, 56 R; 340/229 [56] References Cited UNITED STATES PATENTS 670,999 4/1901 Purinton et a1. ZOO/81.8 1,290,928 1/1919 Denison ZOO/81.8 1.504.848 /1924 Trova 73/368!) Primary E.\&#39;aminerDonald O. Woodiel Attorney, Agent, or FirmLaney, Dougherty, Hessin &amp; Fish [57] ABSTRACT A temperature responsive electrical switch which includes a temperature calibrated pressure gauge employing a gas-filled sealed temperature sensing assembly comprising a bourdon tube connected to a thermal bulb by means of a tubular conduit. Enclosed within the housing of the temperature responsive electrical switch is electrical switch means which makes or breaks contact in response to variations in temperature at the thermal bulb which in turn causes motion of the bourdon tube. Means are disclosed for mechanically linking the bourdon tube to the electrical switch means to open or close the contacts of the switch means in response to temperature variations. Means are also disclosed for adjusting the electrical switch means so that the electrical switch means will open or close at a precise temperature which is visually displayed on the temperature responsive electrical switch.  
 8 Claims, 11 Drawing Figures TEMPERATURE RESPONSIVE ELECTRICAL SWITCH CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of co-pending application Ser. No. 326.516. filed Jan. 24. 1973.  
 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to electrical switches and. more particluarly, but not by way of limitation. to temperature controlled electrical switches.  
 2. Description of the Prior Art It has been found in the refrigeration and food processing industries, among other. that it is often necessary to monitor the temperature in a particular mrdium so that if the temperature reaches a dangerously high or low level corrective action can be taken. For this reason it is most important to monitor such temperatures with a highly reliable and accurate temperature gauge. However. it is also important that when such dangerous I or undesirable temperatures are experienced action is immediately taken to correct the improper conditions.  
  The prior art contains varios teachings of temperature responsive electrical switches involving the use of bi-metallic springs and switches, but these devices have not proved accurate and reliable enough for many applications. Also. the range of temperature adjustment for bi-metallic temperature switches is somewhat limited.  
  While pressure gauges utilizing bourdontubes are considered to be highly reliable and accurate. such devices in combination with electrical switches are not currently found to be available.  
 SUMMARY OF THE INVENTION The present invention contemplates a temperature responsive electrical switch comprising a frame, and a gas-filled sealed temperature sensing assembly comprising a bourbon tube mounted on the frame, a conduit having opposite ends and communicating at one end thereof with the bourbon tube, and a thermal bulb communicating with the opposite end of the conduit. The switch also inlcudes a temperature calibrated planar dial carried by the frame. an indicator shaft journally supported by the frame normal to the dial with one end thereof extending through the dial, and pointer means fixedly secured to the one end of the indicator shaft for rotating with the shaft in a plane parallel to the plane of the dial to indicate a temperature on the dial. The pinion gear is fixedly secured to the indicator shaft for rotation therewith.  
  A lever arm is pivotally secured to the frame intermediate the first and second end portions thereof and includes a gear sector formed on the first end portion thereof in meshing engagement with the pinion gear. The switch further includes rigid link means pivotally secured at one end thereof to the second end portion of the lever arm and pivotally secured to the opposite end thereof to the bourdon tube for transferring motion from the bourdon tube the lever arm.  
  Also included are electrical switch means carried by the frame for alternatley opening and closing an electrical circuit, together with actuator means responsive to the motion of the lever arm for actuating the electrical switch means to alternately open and close the elcetrical circuit.  
  The temperature responsive electrical switch further includes adjusting means operatively connected to the electrical switch means for selectively adjusting the switch means to alternately open and close the switch means at a predetermined temperature. and indicator means operatively engaging the adjusting means for visually indicating the predetermined temperature at which the switch means is adjusted to alternately open and close.  
  An object of the present invention is to provide a temperature responsive electrical switch which is accurate and reliable.  
  Another object of the present invention is to provide a temperature responsive electrical switch which may be precisely set to open or close an electrical switch at a predetermined temperature.  
  A further object of the present invention is to provide a temperature responsive electrical switch which is simple in design, inexpensive to manufacture. rugged in construction, easy to use and efficient in operation.  
  Other objects and advantages of the present invention will be evident from the following detailed description when read in conjunction with accompanying drawings.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view of one form of the present invention with a portion thereof broken away to illustrate details of the interior construction.  
  FIG. 2 is a side elevation view of the apparatus of FIG. 1 with portions of the housing broken away to illustrate the internal construction of the apparatus.  
  FIG. 3 is an enlarged cross-sectional view taken along line 33 of FIG. 1.  
  FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2.  
  FIG. 5 is a front elevation view of another form of the present invention with a portion thereof broken away to more clearly illustrate the internal construction thereof.  
  FIG. 6. is an enlarged partial front elevation view of the apparatus of FIG. 5.  
  FIG. 7 is a front elevation view of another form of the present invention with a portion thereof broken away to more clearly illustrate the details of the interior construction thereof. I  
  FIG. 8 is a side-elevation view of the apparatus of FIG. 7 with portions of the housing broken away to more clearly illustrate the details of the interior construction thereof.  
  FIG. 9 is a partial rear elevation view of the apparauts of FIG. 7 to more clearly illustrate the adjusting means thereof.  
  FIG. 10 is a front elevation view of another form of the present invention with a portion thereof broken away to more clearly illustrate the details of the internal construction thereof.  
  FIG. 11 is a partial front elevation view of the apparatus of FIG. 10 more clearly illustrating the adjusting means thereof.  
 DESCRIPTION OF THE EMBODIMENT OF FIGS. 1, 2, 3 AND 4 Referring now to the drawings, and to FIGS. 1, 2, 3 and 4 in particular, the temperature responsive electrical switch of the present invention is generally designated by the reference character 10. The switch comprises a main support frame 12 which supports a sealed temperature sensing assembly 14.  
  The temperature sensing assembly 14 comprises a C- shaped closed bourdon tube 16 mounted on the main support frame 12, a tubular conduit 18 having opposite ends and communicating at one end thereof with the bourdon tube 16 through a passageway (not shown) formed in the main support frame 12, and a thermal bulb 20 which communicates with the opposite end of the tubular conduit 18. The bourdon tube 16, tubular conduit 18, and thermal bulb 20 form a sealed envelope in which a suitable gas is contained such that variations in temperature applied to the thermal bulb 20 will result in movement of the bourdon tube 16 in a conventional, well-known manner. The temperature sensing assembly 14 may suitably contain a number of different gases, e.g., mercury, argon, freon, etc.. depending upon the desired temperature range. The operative range may be selected from the cryogenics temperatures up through 1000F.  
  A temperature calibrated planar dial 22 is rigidly mounted on the front portion of the main support frame 12. An indicator shaft 24 is journally supported at one end 26 thereof in the rear portion of the main support frame 12 by means of suitable bearings 28. The axis of the indicator shaft 24 is aligned normal to the plane of the dial 22 and the outer end 30 of the shaft 24 extends through an aperture 32 formed in the dial 22. A temperature indicating pointer 34 is rigidly secured to the outer end 30 of the shaft 24 and is adapted to rotate with the shaft 24.  
  A pinion gear 36 is nonrotatably secured to the shaft 24 and is separated from the rear portion of the main support frame 12 by a suitable spacer 38. A second pinion gear 40 is coaxially journally supported on the indicator shaft 24 and is free to rotate thereon. The pinion gear 40 is separated from the pinion gear 36 by means of a suitable spacer 42. A tubular extension 44 is integrally formed on the pinion gear 40 and is coaxially aligned with the shaft 24. The tubular extension 44 extends through the previously mentioned aperture 32 in the dial 22. An indicator pointer 46 is rigidly secured to the tubular extension 44 intermediate the planar dial 22 and the temperature indicating pointer 34.  
  A lever arm 48 is pivotally secured to the main support frame 12 intermediate the first and second end portions SO-and 52 thereof. A gear sector 54 is formed on the first end portion of the lever arm 48 and meshingly engages the pinion gear 36. A rigid link 56 is pivotally secured at one end 58 thereof to the second end portion 52 of the lever arm 48. The opposite end 60 of the link 56 is pivotally secured to the outer end 62 of the bourdon tube 16.  
  A fan gear 64 is pivotally secured at its medial portion 66 to the main support frame 12 by means ofa fan gear support shaft 68 which is fixedly secured at one end 70 thereof to the main support frame 12. The fan gear 64 is spaced from the main support frame 12 by means of a suitable spacer 72. The fan gear support shaft 68 is aligned substantially parallel to the indicator shaft 24.  
  An adjusting shaft 74 is journally supported at one end 76 .thereof by the main support frame 12. The opposite end portion 78 extends through an aperture 80 formed in the dial 22. A pinion gear 82 is nonrotatingly secured to the adjusting shaft 72 intermediate the dial 22 and the main support frame 12.  
  An upper gear sector 84 if formed on the fan gear 64 and meshingly engages the previously mentioned pinion gear 40. A lower gear sector 86 is also formed on the fan gear 64 and meshingly engages the pinion gear 82. An arm 88 is formed on the fan gear 64 proximate to the upper gear sector 84 and extends outwardly therefrom.  
  A first electrical contact 90 is fixedly secured to the second end portion 52 of the lever arm 48. The first electrical contact 90 is electrically insulated from the lever arm 48. A second electrical contact 92 is mounted on the outer end portion 94 of the arm 88 by means of a flat spiral overtravel spring 96 and a rigid pin member 98 which interconnects one end of the spring 96 and the outer end portion 94 of the arm 88. The second electrical contact 92 is electrically insulated from the spring 96 and the arm 88.  
  A housing 100 encloses the structure thus far described, with the exception of the conduit 18 and the thermal bulb 20. The housing 100 includes a transparent dial window 102 and a window retaining ring 104 which secures the dial window 102 in place adjacent to the dial 22 to facilitate visual recognition of the temperature values being indicated on the dial 22. The end portion 78 of the adjusting shaft 74 extends through an aperture 106 formed in the transparent dial window 102. An adjusting knob 108 is nonrotatingly secured to the end portion 78 of the adjusting shaft 74 to provide means for manually adjusting the temperature responsive electrical switch 10 without entry into the housing 100. The housing 100 is suitably secured to the frame 12 by means of threaded screws 110 or other suitable means.  
  The first and second electrical contacts 90 and 92 are electrically connected to electrical conductors 112 and 114, respectively. which conductors extend therefrom through a suitably insulated port 116 in the housing 100 where they may be connected at their opposite ends to a suitable electrical circuit external to the housing 100.  
 OPERATION OF THE EMBODIMENT OF FIGS. 1, 2, 3 AND 4 During operation of the temperature responsive electrical switch 10, the thermal bulb 20 is placed in the particular medium the temperature of which is to be monitored. An increase in the temperature of the par-- ticular medium causes an expansion of the gas contained in the sealed temperature sensing assembly 14 thereby causing the outer end 62 of the bourdon tube 16 to move outwardly relative to the frame 12. This movement of the bourdon tube is transmitted through the rigid link 56 to the second end portion 52 of the lever arm 48 causing counterclockwise motion of the lever arm 48 about its pivotal connection with the main support frame 12 as viewed in FIG. 1. The temperature indicating pointer 34 is thereby driven in a clockwise direction as viewed in FIG. 1 through the action of the gear sector 54 driving the pinion gear 36 and the indicator shaft 24. It will be readily apparent that a lowering of the temperature of the medium will cause the outer end 62 of the bourdon tube 16 to move inwardly thereby causing the pointer 34 to move in a counterclockwise direction through the action of the previously mentioned elements.  
  The temperature at which the switch contacts 90 and 92 will engage one another may be readily adjusted by turning the adjusting knob 108 thereby rotating the fan gear 64 on the shaft 68 by means of the pinion gear 82 on the adjusting shaft 74. By turning the adjusting knob 108 in a counterclockwise direction, as viewed in FIG. 1, it will beseen that the electrical contacts 90 and 92 will be moved relatively toward another thereby allowing them to make contact at a lower medium temperature. Conversely, turning of the adjusting knob 108 in a clockwise direction moves the electrical contacts 90 and 92 further apart thereby requiring a higher medium temperature before the contacts 90 and 92 will engage one another. The inherent resiliance of the overtravel spring 96 permits the switch to continue to indicate higher temperature after the contacts 90 and 92 have closed.  
 Adjustment of the adjusting knob 108 simultaneously causes movement of the indicator pointer 46 relative to the dial 22. This movementof the indicator pointer 46 is occasioned by the rotation of the pinion gear 40 by the fan gear 64 in response to rotation of the adjusting knob 108.  
 Thus, it will be seen that the temperature responsive electrical switch 10 permits the precise selection of a medium termperature at which point the electrical contacts 90 and 92 will engage one another thereby completing a connection between the electrical conductors 112 and 114, and provides a clear visual indication of the particular temperature at which the electrical contacts 90 and 92 are to close.  
 DESCRIPTIONCF THE EMBODIMENT OF FIGS. 5 AND6 opposite ends and communicating at one end thereof with the bourdon&#39; tube 126 through a passageway (not shown) formed in the main support frame 122, and a thermal bulb (not shown), substantially identical to the thermal bulb described above, which communicates with the opposite end of the tubular conduit 128. The boundon tube 126, tubular conduit 128, and theremal bulb form a sealed envelopein whch a suitable gas is contained as described above for the sealed temperature sensing assembly 14.  
  A temperature calibrated planar dial 130 is rigidly mounted on the front portion of the. main support frame 122. An indicator shaft 132 is journally supported at one end&#39;thereof in the rear portion of the main support frame 122 by means of suitable bearings. The axis of the indicator shaft 132 is aligned normal to theplane of the dial 130 and the outer end of the shaft 132 extends through an aperture formed in thedial 130. A temperature indicating pointer 134 is rigidlysecured tothe &#39;outer end of he indicatorshaft 132 and is adapted to rotate with shaft .l32.-A pinion gear l36&#39;is nonrotatably secured to the shaft-132. Y A  
  A lever arm 138 is pivotally secured to the main support frame 122 intermediate the first and second end portions 140 and 142 thereof. A gear sector 144 is formed on the first end portion 140 of the lever arm 138 and meshingly engages the pinion gear 136. A rigid link 146v is pivotally secured secured at one end 148 thereof to the second end portion 142 of the lever arm 138. The opposite end 150 of the link 146 is pivotally secured to the outer end 152 of the bourdon tube 126.  
  A switch adjusting member 154 is pivotally secured at one end 156 thereof to the main support frame 122. A gear sector 158 is formed on the opposite end 160 of the switch adjusting member 154.  
  A contact support arm 162 is pivotally secured at the inner end 164 thereof to the lever arm 138. A first electrical contact 166 is secured to the outer end 168 offthe contact support arm 162 and is electrically insulated therefrom. A tension coil overtravel spring 170 extends between the second end portion 142 of the lever arm 138 and the contact support arm 162 intermediate the inner and outer ends 164 and 168 thereof. A second electrical contact 172 is secured to the opposite end 160 of the switch adjusting member 154 and is electrically insulated therefrom.  
  A housing 174 encloses the structure thus far described, with the exception of the conduit 128 and the thermal bulb,(not shown). The housing 174 includes a transparent dial window 176 and a window retaining ring 178 which secures the dial window 176 in place adjacent to the dial 130 to facitlitate visual recognition of the temperature values being indicated on the dial 130.  
  An adjusting shaft 180 is journally supported in the housing 174 with one end thereof extending through suitable apertures formed in the dial 130 and the dial window 176. A pinion gear 182 is nonrotatingly secured to the adjusting shaft 180 and meshingly engages the gear sector 158 on the switch adjusting member 154. An indicator pointer 184 is nonrotatingly secured to the adjusting shaft 180 intermediate the dial 130 and the dial window 176. An adjusting knob 186 is nonrotatingly secured to the adjusting shaft 180 just outside the dial windor 176 where it may be onveniently grasped.  
  It will be seen in FIG. 5 that temperature indications are displayed on the dial 130 which may be indicated by the temperature indicating pointer 134. It will also be seen in FIG. 6 that additional temperature indications are displayed on the dial 130 which may be inidicated by the indicator pointer 184.  
  The first and second electrical contacts 166 and 172 are electrically connected to electrical conductors 188 and 190, respectively, which conductors extend therefrom through a suitably insulated port 192 in the housing 174 where they may be connected at their opposite ends to a suitable electrical circuit external to the housing 174.  
 OPERATION OF THE EMBODIMENT OF- FIGS. 5  
 AND 6 I Operationof the temperature responsive electrical however, that the temperature at which the switch contact 166 and 172 will engage one another may be readily-adjusted by turning the adjusting knob 186 thereby &#34;rotating the switch adjusting member 154 about its pivotal connection to the support frame 122 by&#39;means of the pinion gear 182 on the adjusting shaft 180. By turning the adjusting knob 186 in a counterclockwise direction as viewed in FIG. 6, it will be seen that the electrical contacts 166 and 172 will be moved relatively toward one another thereby allowing them to make contact at &#39;a lower medium temperature. Conversely, turning of the adjusting know 186 in a clockwise direction moves the electrical contacts 166 and 172 furtherapart thereby requiring a higher medium temperature before the contacts 166 and 172 will engage one another. The inherent resiliance of the overtravel spring 170 permits the switch 120 to continue to indicate higher temperatures after the contacts 166 and 172 have closed.  
 Adjustment of the adjusting knob 186 simultaneously causes movement of the indicator pointer 184 relative to the dial 130. This movement of the indicator pointer 184 is directly responsive to the movement of the adjusting knob 186.  
  Thus, it will be seen that the temperature responsive electrical switch 120 permits the precise selectin of a medium temperature at which point the electrical contacts 166 and 172 will engage one another thereby completing a connection between the electrical conductors 188 and 190, andiprovides a clear visual indication of the particular temperature at which the electrical contacts 166 and 172 are to close.  
 DESCRIPTION OF THE EMBODIMENT OF FIGS. 7, 8 AND 9 FIGS. 7, 8 and 9 illustrate yet another form of temperature responsive electrical switch which will be generally designated by the reference character 200. The switch 200 is especially adapted for high explosion areas and comprises a main support frame 202 which supports a sealed temperature sensing assembly 204.  
  The temperature sensing assembly 204 comprises a C-shaped, closes bourdon tube 206 mounted on the main support frame 202, a tubular conduit 208 having opposite ends and communicating at one end thereof with the bourdon tube 206 through a passageway (not shown) formed in the main support frame 202, and a thermal bulb (not shown), substantially identical to the thermal bulb described above, which communicates with the opposite end of the tubular conduit 208. The bourdon tube 206, tubular conduit 208, and thermal bulb form a sealed envelope in which a suitable gas is contained as described above for the sealed temperature assembly 14.  
  A temperature calibrated planar dial 210 is rigidly mounted on the front portion of the main support frame 202. An indicator shaft 212 is journally supported by the main support frame 202 and is aligned substantially normal to the plane of the dial 210. The outer end 214 of the shaft 212 extends through an aperture 216 formed in the dial 210. A temperature indicating pointer 218 is rigidly secured to the outer end 214 of the indicator shaft 212 and is adapted to rotate with the shaft 212. A pinion gear 220 is nonrotatably secured to the shaft 212.  
  A lever arm 222 is pivotally secured to the main support frame 202 intermediate the first and second end portions 224 and 226 thereof. A gear sector 228 is formed on the first end portion 224 of the lever arm 222 and meshingly engages the pinion gear 220. A rigid ;202 and extends generally downwardly therefrom. A  
 I conventional mercury switch 242 is secured to the lower end portion 244 of the switch mounting member 238. The mercury switch 242 is preferably of the type comprising a glass envelope of generally elongated shape having a pair of contacts enclosed within the envelope which are alternately electrically connected and disconnected by means of a small amount of mercury contained in the envelope in response to movement of the switch envelope.  
  An adjusting shaft 246 is journaled in the enlarged medial portion 248 of the switch mounting member 238. A cam 250 having an eccentric cam surface is nonrotatably secured to the inner end portion 252 of the adjusting shaft 246. The cam 250 engages the second end portion 226 of the lever arm 22. This engagement is maintained by means of a tension coil spring 254 interconnecting the lower end portion 244 of the switch mounting member 238 and the main support frame 202, which spring constantly biases the cam 250 into contact with the second end portion 226 of the lever arm 22.  
  An indicator pointer 256 is nonrotatably secured to the adjusting shaft 246 adjacent to the rear surface of the enlarged medial portion 248 of the switch mounting member 238. It will be seen in FIG. 9 that suitable temperature indications are displayed on the rear surface of the enlarged medial portion 248 of the switch mounting member 238 which may be indicated by the indicator pointer 256. These temperature indications correspond to the temperature indications displayed on the dial 210 as illustrated in H6. 7.  
  A sealed housing 258 encloses the structure thus far described with the exception of the conduit 208 and the thermal bulb (not shown), and so enables safe usage in explosion incident areas. The housing 258 includes a transparent dial window 260 and a window retaining ring 262 which secures the dial window 260 in place adjacent to the dial 210 to facilitate the visual recognition of the temperature values displayed on the dial 210. An aperture 264 is formed in the rear portion of the housing 258 through which the outer end portion 266 of the adjusting shaft 246 extends. The aperture 264 is sufficiently large to readily permit the visual inspection of the position of the indicator pointer 256 relative to the temperatures displayed on the medial portion 248 of the switching mounting member 238.  
  An adjusting knob 268 is nonrotatably secured to the outer end portion 266 of the adjusting shaft 246 just to the rear of the housing 258. The position of the adjusting knob 268 provides a convenient point of grasp for the adjusting of the temperature responsive electrical switch 200.  
 First and second electrical conductors 270 and 272 are connected to the respective contacts of the mercury switch 242 and extend through the housing 258 in v a manner substantially identical to that described in detail above for the switch 10 to a suitable electrical circuit external to the housing 258.  
 OPERATION OF THE EMBODIMENT OF FIGS. 7, 8 AND 9 Operation of the temperature responsive electrical switch 200 is substantially identical to the operation previously described for the electrical switch 10 and need not be described again in detail. It should be noted however that the temperature at which the mercury switch 242 will close may be readily adjusted by turning the adjusting knob 268 thereby rotating the cam 250 about the axis of the adjusting shaft 246 thereby rotating the switch mounting member 238 about its pivotal connection to the support frame 202. The cam 250 is so positioned on the adjusting shaft 246 relative to the position of the indicator pointer 256 that rotation of the adjusting knob 268 in a counterclockwise direction as viewed in FIGv 9 will adjust the position of the mercury switch 242 such that it will close at a higher medium temperature. Conversely, turning the adjusting knob 268 in a clockwise direction will cause the mercury switch 242 to close at a lower medium temperature.  
  Adjustment of the adjusting knob 268 causes simultaneous movement of the indicator pointer 256 relative to the enlarged medial portion 248 of the switch mounting member 238. This movement of the indicator point 256 is directly responsive to the movement of the adjusting knob 268.  
  Thus, it will be seen that the temperature responsive electrical switch 200 permits the precise selection of a medium temperature at which point the mercury switch 242 willclose thereby completing a connection between the electrical conductors 270 and 272, and provides a clear visual indication of the particular temperature at which the mercury switch 242 is to close.  
 DESCRIPTION OF THE EMVODIMENT OF FIGS. 10 AND 11 FIGS. 10 and 11 illustrate another form of temperature responsive electrical switch which will be generally designated by the reference character 280. The switch 280 comprises a main support frame 282 which supports a sealed temperature sensing assembly 284.  
  The temperature sensing assembly 284 comprises a C-shaped, closed bourdon tube 286 mounted on the main support frame 282, a tubular conduit 288 having opposite ends and communicating at one end thereof with the bourdon tube 286 through a passageway (not shown) formed in the main support frame 282, and a thermal bulb (not shown), substantially identical to the thermal bulb described above, which communicates with the opposite end of the tubular conduit 288. The bourdon tube 286, tubular conduit 288 and and thermal buld form a sealed envelope in which a suitable gas is contained as described above for the sealed temperature sensing assembly 14.  
  A temperature calibrated planar dial 290 is rigidly mounted on the front portion of the main support frame 282. An indicator shaft 292 is journally supported at one end thereof in the rear portion of the main support frame 282 by means ofa suitable bearing. The axis of the indicator shaft 292 is aligned normal to the plane of the dial 290 and the outer end of the shaft 292 extends through an aperture formed in the dial 290. A temperature indicating pointer 294 is rigidly secured to the outer end of the indicator shaft 292 and is adapted to rotate with the shaft 292. A pinion gear 296 is nonrotatably secured to the shaft 292.  
  A lever arm 298 is pivotally secured to the main support frame 282 intermediate the first and second end portions 300 and 302 thereof. A gear sector 304 is formed on the first end portion 300 of the lever arm 298 and meshingly engages the pinion gear 296. A rigid link 306 is pivotally secured at one end 308 thereof to the second end portion 302 of the lever arm 298. The opposite end 310 of the link 306 is pivotally secured to the outer end 312 of the bourdon tube 286.  
  A switch adjusting member 314 is pivotally secured at the medial portion 316 thereof to the main support frame 282. A gear sector 318 is formed on the lower end 320 of the switch adusting member 314.  
  A conventional snap-action switch 322 is rigidly secured to the upper end portion 324 of the switch adjusting member 314. A switch-actuating cam follower 326 is mounted on the snap-switch 322. The cam follower 326 includes a cam-contacting surface 328 supported by a leaf spring 330 extending between the camcontacting surface 328 and the snap-switch 322. A suitable snap-switch for the use in this application is manufactured and sold under the trademark Microswitch.  
  The cam-contacting surface 328 of the snap-switch 322 is engaged by a cam surface 332 formed on the first end portion 300 of the lever arm 298 adjacent to the gear sector 304. An adjusting shaft 334 is journally supported by the support frame 282 and is aligned substantially parallel to the indicator shaft 292. The adjusting shaft 334 extends through an aperture formed in the dial 290. A pinion 336 is nonrotatably secured to the adjusting shaft 334 and meshingly engages the gear sector 318 formed on the switch adjusting member 314.  
  A housing 338 encloses the structure thus far described, with the exception of the conduit 288 and the thermal bulb (not shown). The housing 338 includes a transparent dial window 340 and a window retaining ring 342 which secures the dial window 340 in place adjacent to the dial 290.  
 An indicator pointer 344 is nonrotatably secured to the adjusting shaft 334 intermediate the dial 290 and the dial window 340. An adjusting knob 346 is nonrotatably secured to the adjusting shaft 334 just outside the dial window 340 through which the adjusting shaft 334 extends.  
  It will be seen in FIG. 10 that temperature indications are displayed on the dial 290 which may be indicated by the temperature indicating pointer 294. It will also be seen in FIG. 11 that additional temperature indications are displayed on the dial 290 which may be indicated by the indicator pointer 344.  
  First and second electrical conductors 348 and 350 are connected to the terminals of the snap-switch 322 and extend therefrom through a suitable insulated port (not shown) in the housing 338 in a manner as described in detail above for the temperature responsive electrical switch 10. The conductors 348 and 350 may be connected at their opposite ends to a suitable electrical circuit external to the housing 338.  
 OPERATION OF THE EMBODIMENT OF FIGS. 10 AND 11 Operation of the temperature responsive electrical switch 280 is substantially identical to the operation previously described for the electrical switch 10 and need not be described in detail again. It should be noted, however, that the temperature at which the snap-switch 322 will close may be readily adjusted by turning the adjusting knob 346 thereby rotating the switch adjusting member 314 about its pivotal connec tion to the support frame 282 by means of the pinion gear 336 engaging the gear sector 318. By turning the adjusting knob 346 in a counterclockwise direction, as viewed in FIG. 11, it will be seen that the camcontacting surface 328 will be moved relatively away from the cam surfaces 332 thereby requiring a higher medium temperature before the switch 322 is closed by the action of the cam surface 332 acting through the cam follower 326. Conversely, turning the adjusting knob 346 in a clockwise direction moves the camcontacting surface 328 relatively toward the cam surface 332 thereby allowing the switch 322 to close at a lower medium temperature. The inherent resiliance of the leaf spring 330 of the cam follower 326 permits the temperature responsive electrical switch 280 to continue to indicate higher temperatures after the switch 322 closes.  
  Adjustment of the adjusting knob 346 simultaneously causes movement of the indicator pointer 344 relative to the dial 290. This movement of the indicator pointer 344 is directly responsive to the movement of the adjusting knob 346. Thus, it will be seen that the temperature responsive electrical switch 280 permits the precise selection of a medium temperature at which point the snap-switch 322 will close thereby completing a connection between the electrical conductors 348 and 350, and provides a clear visual indication of the particular temperature at which the snap-switch 322 is to close.  
  it will be readily apparent to those skilled in the art that the various embodiments of the present invention described above can be readily adapted and adjusted to open or close the electrical switch contacts at a precise predetermined temperature as the medium tempera ture is either increasing or decreasing in value. The opening or closing of such electrical switch contacts may be utilized to control some form of audible or visual alarm system or a refrigeration system on or off. It will also be apparent that the present invention readily fulfills the stated objects set forth above.  
  The present invention has been described generally in relation to the more usual temperature control applications, but it should be understood that similar types of switchgauges may be employed in diverse industrial applications ranging from freight and warehousing usage through highly exacting employ in such fields as Cryogenics. biomedics, chemical industries, etc.  
  Changes may be &#39;made in the combination and arrangement of the parts or elements as heretofore set forth in the specification and shown in the drawings without departing from the spirit and scope of the invention.  
 What is claimed is:  
  l. A temperature responsive electrical switch comprising:  
 a frame;  
 a sealed hollow temperature casing assembly comprising a bourdon tube mounted on the frame, a conduit having opposite ends and communicating at one end thereof with said bourdon tube, and a thermal bulb communicating with the opposite end of said conduit;  
 a temperature calibrated planar dial carried by said frame;  
 an indicator shaft journally supported by said frame normal to said dial with one end thereof extending through said dial;  
 pointer means fixedly secured to the one end of said indicator shaft for rotating with said shaft in a plane parallel to the plane of said dial to indicate a temperature on said dial;  
 a pinion gear fixedly secured to said indicator shaft for rotation therewith;  
 a lever arm pivotally secured to said frame intermediate the first and second end portions thereof and having a gear sector formed on the first end portion thereof in meshing engagement with said pinion gear;  
 rigid link means pivotally secured at one end thereof to the second end portion of said lever arm and pivotally secured at the opposite end thereof to said bourdon tube for transferring motion from said bourdon tube to said lever arm;  
 electrical switch means carried by said frame for alternately opening and closing an electrical circuit, said switch means consisting of a first electrical contact mounted on the second end portion of said lever arm and a second electrical contact privotally supported on said frame and operatively connected to said adjusting means;  
 - actuator means responsive to the motion of said lever arm for actuating said electrical switch means to alternately open and close the electrical circuit;  
 adjusting means operatively connected to said electrical switch means for selectively adjusting said switch means to alternately open and close said switch means at a predetermined temperature; and  
 indicator means operatively engaging said adjusting means for visually indicating the predetermined temperature at which said switch means is adjusted to alternately open and close.  
  2. The temperature responsive electrical switch as defined in claim 1 characterized further to include:  
 a housing substantially enclosing said frame, said bourdon tube, said temperature calibrated dial, said indicator shaft. said pointer means, said pinion gear, said lever arm, said rigid link means, said electrical switch means, said actuator means, said adjusting means, and said indicator means, said housing including a transparent dial window adjacent to said temperature calibrated dial;  
 a control knob disposed outside said housing;  
 means extending through said housing and interconnecting said control knob and said adjusting means for transmitting motion from said control knob to said adjusting means; and  
 electrical conductor means connected to said electrical switch means and extending therefrom through said housing for electrically connecting said electrical switch means to an electrical circuit external to said housing.  
  3. In combination with a temperature indicator of the type which includes a housing supporting a bourdon tube which is in communication with a gas-filled temperature sensing bulb and connected by mechanical linkage to impart rotary motion to a temperature indicator, an electrical control device comprising:  
 first contact means secured insulatively for movement in response to movement of said mechanical linkage, said first contact means consisting of an arm means having first and second ends and being pivotally mounted within said housing, with one end connected to said mechanical linkage and the other end reciprocally moved in response thereto. and an electrical Contact means resiliently secured to said arm means one end;  
 second contact means secured insulatively and intermittently movably within said housing, said second contact means being aligned for electrically conductive contact with said first contact means at a preselected temperature; and  
 first and second conductor means leading from respective first and second contact means for external connection.  
 4. An electrical control device as set forth in claim 3 wherein said first contact means comprises:  
 lever means centrally pivotally secured in said housing with one end connected to said mechanical linkage and having an insulatively secured contact mounted thereon, and with the other end connected to provide rotary motion to said temperature indicator. 5. An electrical control device as set forth in claim 3 wherein:  
 said indicator is secured to an indicator shaft and pinion gear journally supported within said housing; and said lever arm means other end is formed as a sector gear in mesh with said pinion gear. 6. An electrical control device as set forth in claim 3 wherein:  
 said second contact means is intermittently movable by adjustment control to pre-select a temperature at which said first and second contact means make conductive contact. 7. An electrical contact device as set forth in claim 6 which is further characterized to include:  
 second indicator means actuated by said second contact means adjustment control to indicate continually said pre-selected temperature. 8. An electrical control device as set forth in claim 3 wherein said second contact means comprises:  
 arm means pivotally mounted and intermittently movable within said housing to extend a support arm; spring means secured to said support arm; and electrical contact means securely supported by said spring means in alignment for contact with said first contact means.  
 mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3, 875,800 Dated April 8, 1975 Inventor(s) Harold E. Stockton It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:  
 &#39; Column 1, line 16 change &#34;mrdium&#34; to -medium-; 1  
 Column 1, line 26, change &#34;varios&#34; to various-; Column 1, line 46, change &#34;inlcudes&#34; to -inclu des;  
 Column 1, line 66, change &#39;alternatley&#34; to alternately;  
 Column 2, line 53, change &#34;apparauts&#34; to apparatus-;  
 Column 4, line 3, change &#34;if&#34; to -is; 0  
 Column 5, line 10, after &#34;toward&#34; insert -one--;  
 Column 5, line 52, change &#34;theremal&#34; to thermal--;  
 Column 5, line 65, change &#34;he&#34; to -the; Column 6, line 6, delete one of the words &#34;secured&#34; Column 6, line 30, change &#34;facitlitate&#34; to --facilitate;  
 Column 6, line 44&#39;, change &#34;windor&#34; to window and change &#34;onveniently&#34; to conveniently;  
 Column 6, lines 49-50, change &#34;inidicated&#34; to -indicated-;  
 Column 7, line 9, change &#34;know&#34; to -knob-;  
 Column 7, line 23, change &#34;select in&#34; to --&#39;sel,ection--;  
 Column 7, line 40, change &#34;closes&#34; to closed-;  
 Column 7, line 51, after &#34;ture&#34; insert sensing--;  
  Page 2 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,11%&#34;? Da ed April 8, 1975 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:  
 Column 8, line 55, change &#34;switching&#34; to -switch--;  
 Column 9, line 37 change &#34;EMVODIMENT&#34; to EMBODIMENT;  
 &#34;Tolumn 9, line 55, change &#34;buld&#34; to -bulb-;  
 Column 10, line 32, after &#34;pinion&#34; insert -gear-; Column 11, line 10, change &#34;surfaces&#34; to&#39;-surface-- Column 12, line 26, change &#34;privotally&#34; to --pivotally-;  
 Column 14, line 3, delete &#34;lever&#34;.  
 Signed and Scaled this twenty-second Day Of July 1975 [SEAL] Arrest:  
 RUTH C MASON (f. MARSHALL DANN Arresting Officer Commissioner of Parents and Trademarks