Патент USA US2120938код для вставки
June Carl GKronmíller June 14, 1938. C. G, KRONMlLLER THI.«*.RMOSTA'1‘V Filed Nov. 19, 1934 2,120,938* 2 Sheets-Sheet 2 ì 50 47 gwoentoc Carl GKI'Onmiller Patented June 14, 1938 UNITED STATES PATENT OFFICE 2,120,938 THERMOSTAT Carl G. Kronmiller, Minneapolis, Minn., assigner to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application November 19, 1934, Serial No. '353,589 14 Claims. This invention relates to thermostats and par ticularly to thermostats utilizing a volatile fiuid thermal responsive element for operating a novel switching mechanism. Due to present day transportation require ments, it is necessary to maintain even tempera ture conditions in moving vehicles such as air planes, railway cars and busses. Thermostats including temperature responsive fluid actuated 10 elements for operating switching mechanisms have been installed in such vehicles to control the temperature conditions therein but they have not proved satisfactory due to the operation of such vehicles through various altitudes with conse quent changes in barometric pressure acting on the thermostats to render their calibrations in accurate and also due to severe jolting, jarring and vibrating of the thermostats caused by the motion of the vehicles which renders the switch ing action thereof unreliable by causing vibra tions to be set up in the movable contact arms of the switching mechanisms. Therefore, the prime object of this invention is to provide a thermostat comprising a tempera ture responsive ñuid actuated element for operat ing a switching mechanism according to changes in temperature which is suitable for regulating the temperature of moving vehicles and which is not effected by changes in barometric pressure or by jolting and jarring of the vehicle. Thermostats of this general character, using temperature responsive fluid actuated elements, are very accurate and maintain their initial cal ibraticn as long as they are subjected to the same atmospheric or barometric pressure condition as when they are initially calibrated. However, a thermostat of this .general character, when cali brated at sea level, would not be accurate when used at high altitudes and vice versa. Further, ki (i local changes in barometric pressure caused by changing weather conditions also have some ef fect‘on the calibration of a thermostat of this type to render it inaccurate. Since a thermostat „of this general ,type may be used in places hav ' ing different barometric pressure than that where the instrument is calibrated and since the instru ment may be subjected to varying barometric pressure by reason of its use in moving vehicles or by reason of changing barometric conditions caused by changing weather conditions, it is also contemplated to` provide a thermostat of general utility which is not subject to these changes in barometric pressure. Consequently, it is an object of this invention to provide a temperature responsive fluid pres sure-operated device or a pressure 'responsive de vice, generally, that is not rendered inaccurate by changes in atmospheric or barometric pressure acting thereon. More specifically, an object of this invention is to provide a volatile fluid thermostat or pressure responsive device embodying a double bellows construction whereby the eiiect of changes in atmospheric or barometric pressure acting there on is reduced to a practical minimum. Another object of this invention is to provide a thermostat or pressure responsive device that may be adjusted to and locked in an “oil” position” whereby changes in temperature or pressure act ing thereon will not operate the thermostat or 15 pressure responsive device. A further object is to provide a novel adjust ing and indicating means in a thermostat of the class described. / A still further object is to provide a novel ad justing and indicating means in combination with a locking means `whereby a thermostat or pres-, sure responsive device may be adjusted or locked in an “off‘position” by a single control means. Another object is to provide a switching mech anism that is positively moved from one position to another by a novel snap action means whereby jarring and jolting of the switching mechanism will not aiîect the operation of the switching mechanism. A further object is to provide a snap action switching mechanism with means to insure move ment of the switch arm in case the switch arm should be stuck or held in one of its shifted posi tions by failure of the snap action means. Other objects and advantages will become ap parent to those skilled in the art by reference to the accompanying description and drawings in which: Fig. 1 is a vertical side elevational view of the 40 thermostat looking from the left in Fig. 2.but showing the cover and the electric switch mecha nism in section; Fig. 2 is a front elevational view with the cor ner remo-ved and the temperature responsive 45 means shown in section; Fig. 3 is a top plan view with the cover removed; Fig. 4 is a side elevational view looking from the right in Fig. 2 with the cover removed and showing the temperature adjusting means and a modification of the temperature responsive means in section; Fig. 5 is a side elevational view looking from the right in Fig. 2; . Figs. 6, 7, 8, and 9 are plan views of a portion 55 E aisance or“ the adjusting mechanism showing the parts located in different positions oi adjustment. it) designates a base made of insulating ma terial such as “Bakelite” to which the various' parts are secured and by which the instrument may be secured to a wall or like structure. A support ci' insulating material is shown at l i and supports a plate l2. The plate l2 and support il are secured to the base l@ by means of screws i3 which screws also act as electrical conducting means from the plate l2 to suitable binding posts located on the bacia of the base lli, lli designates another plate similar to the plate i2 but spaced rearwardly therefrom. The plates l2 and i@ sup port, respectively, magnets l@ and l5. The plate M and magnet i5 are secured to the base l@ by means of a screw il and the magnet it is se cured to the plate l2 by mea is oí a screw l@ coop erating with a nut The screws il' and i8 20 have abutments l5 and 2@ respectively located at the inner ends thereof. Screw'll‘ aiîords an elec trical connection between the plate id and a suitable binding post located on the back of the 25 base iii. Secured to the plates löl and l2 by means of rivets 2t are spring arms 22 and respectively. rl‘hese spring arms 22 and 23 have contacts 25 and 2t and upwardly extending portions to en gage the abutments l@ and 2li to limit the in ward movement thereof. Located between spring arms 22 and 23 is a conducting spring switch arm 2l, having abutments 28 engageable alter« nately with the abutments i@ and 2@ and contacts andengageable liti of the spring alternately arms 22 with andthe contacts Abutment 35 2e levers lili and lll are provided in spaced relation on either side of the spring switch arm 2l', the abutment levers and ¿il and the spring switch arm 2l being secured to an actuator block 33, made of insulating material, by means oi screws 32. An electrical connection is made between by the means flexibleofswitch a flexible arm 2l lead andwire a binding 36 being post con nected to one screw 32 and the binding post The forward plate l2 has a forwardly extending ilange 3i? to which is riveted an insulating shield 38 by means oi rivets 3l. 39 designates a knife edge supporting member secured to the base ill by means oi screws il@ 50 and having downwardly extending knife edges di. lever in a counter-clockwise direction against the top of the slot ¿it as viewed in Fig. l. Assum ing that the temperature acting upon the tem perature responsive means is relatively high, thc lever ¿it is maintained in a counter~clockwise di« rection against the tension of the spring ii2 as seen in Fig. l to urge the movable contact 2@ oi the switch arm 2l against the contact 25 and the movable abutment against the abutment itl to complete an electric circuit from the screw il, through plate spring arm contact 25, con tact switch arm screws and lead wire to binding post dii. Current is also carried from screw lil to switch arm 2l through the abut ments lil and 'When the temperature decreases, the tension spring 52 overcomes the force oi the temperature responsive means tid and moves the lever «lil in a clockwise direction from that position shown in Fig. l. to move the contact 29 away from the con tact and the abutment 28 away from the abut ment lil. However, the switch arm 2l is located in the magnetic heid of the magnet l5 and this movement is retarded until sufficient spring force has been built up in the spring switch arm 2l Ji to overcome this magnetic holding eiîect of the magnet i5. When this magnetic effect is so overcome, the tension in the switch arm 2l caused by clockwise movement of lever @il will snap the contact 2Q and the abutment il@ into engagement 30 with the contact and the abutment 2li com pleting a circuit from the screws i?) through plate l2, spring arm 2S, contact 2G, contact 2t?, switch arm 2li, screw and wire il@ to binding post Here again, current is conducted from plate l2 to the switch arm 2l' by means of the screw l@ and abutments and 2li. Due to the fact that the switch arm 2l is magnetically held in one position until suñicient torce has been built up to move it to another position, jolting and jarring 40 of the thermostat will not cause the switch arm to vibrate between its contacts. if, for any reason, the contact should become stuck to the contact Z5 or the abutment 22 become stuck to the contact lil or the magnetic lields or" the magnets iii and iti be too powerful so as to prevent the above normal movement of the con tact 29 and the abutment 2d to the right, iur ther movement oi the lever «i3 in the clockwise A lever 43 is provided with concavo~conveis por direction will cause abutment arm 30 to engage switch arm 2l to positively move contact 2S into tions ¿32 to be engaged by the knife edges Gi and an upwardly extending ñange @nl to which the engagement with contact 26 the abutment 2li into Contact with the abutment 20. This in~ actuator block 33 is secured by means of screws 45. On the lower side of the lever ¿13 there is suitably secured an abutment :il adapted to rc~ sures positive movement of the switch arm 21 to make and breal; the contacts. "Ji Ui Upon an increase in temperature, the tempera ture responsive means 5E will overcome the ten sion in the spring 52 to move the contact 29 into engagement with the contact 25 and the abut~ ment 2li into engagement with the contact i9 in - ceive a knife edge t8 which is held in place by a bolt head ¿i9 of an upwardly extending bolt Sill. The bolt 5U is screw-threaded into a grooved nut 60 5l which is secured to the lower end of a tension spring 52 and the upper end oi’ the tension spring 52 is secured to a temœrature adjusting means generally indicated at 53. Also, on the lower side of the lever 43 is a con ' cave portion :'i?l adapted to receive a plunger point 55 of a temperature responsive means gen erally designated at The forward portion or" the supporting member Sii is provided with a slot 4E through which the lever cli-3 extends to provide stops to limit the movement ci” the lever 43. » From the above, it will be seen that the tension spring 52 urges the lever 43 in a clockwise direc~ tion against the bottom of the slot 46 and that the temperature responsive means 56 urges the the exact reverse manner as pointed out above and a complete description of this reverse opera tion is therefore not considered necessary. A vital feature of this invention is the pro vision of a novel temperature responsive means 56 A which is not affected by changes in barometric pressure and which comprises a volatile fluid containing chamber 5l which is secured by means of bent over ñanges 58 to a plate 559 which is se» cured by means of a screw G0 to the forward end of the knife edge supporting member and by means of screws 6i to the base lû. Soldered to the inside of the chamber iì'l' adjacent the top thereof is an annular plate 62 and soldered to the underside of this annular plate 62 is the up-` 3 2,120,938 per end of a bellows 63. Soldered -to the inner periphery of the annular plate 62 is another an nular plate 64, having adownwardlyextending an nular shoulder 65 to which is soldered atubular guide and stop member 66. At the inner portion of the plate 64Á is soldered the upper end of a bel lows 61 of much smaller diameter than the bel lows 63. Soldered to the lower ends of the bel lows 63 and 61 is a movable plate 68 which is 10 riveted and soldered to a vertical plunger 69. _The spaces enclosed by the casing 51 and the bel lows 63v and by- the bellows 63 and 61 are, there fore, hermetically sealed. 'I'he vertical plunger 69 has a longitudinally extending bore 10- which is 15 normally closed by means of a screw-threaded plug 1 I. Secured over the up er end of the plung er 69 so as to enclose the plug I is a cap 18 which has formed. integral therewith the plunger point 55. 20 i . By removing the plug 1|, a charge of volatile fluid may be inserted through the bore 1l) into a chamber formed by the volatile fluid containing' chamber 51, the annular plate 62, the bellows 63ì and the movable plate 68. After the required 25 amount of volatile ñuid has been inserted in this chamber, the chamber is hermetically sealed by inserting the plug 1I to close the passage 10. An increase in temperature of the air surrounding the' volatile fluid containing chamber 51 causes 30 the fluid contained therein to expand and act volatile fluid is volatilized in the bulb 82 and the pressure is transmitted therefrom to the chamber 51 by means of the capillary tube 80. f Although I have disclosed a volatile iiuid tem perature responsive device, it is within the con- 5 cept oi' `this invention to include a pressure-actu ated devíce wherein changes in pressure from some pressure device may be transmitted into the casing 51 by means of suitable connections. The means 53 for adjusting the spring 52 to 10 de‘ermine at which temperature the thermo stat will become operative is supported by means of a support 85 which is secured to the base lil by means of screws 8‘6. This support 85 extends forwardly and supports the upper end. of a col umn, 8l which is secured at its lower end into the knife edge supporting member 39. „as seen in Fig. mounted in an opening in. t? support 85 is a shaft 88, having a. shoulder 89 abutting relation. with the support 85, a c 9.n‘ gated por-« tion 9U, e. screw-threaded portion 9i a squared 92. Mounted against rotation on the ‘» ed portion 98 of the shaft 88 a cam 93 ‘held in place by means of a n t 99 screw on the screw-threaded po on 9i of 25 88. Secured to the shalt beneath ‘t 85 by means of a pin 95 a helix which' cooperates with a helix nut. 91, ii which the bottom is attached of the the helix 'u ‘out’ E. against the movable plate 68 to move the plunger 69 upwardly to actuate the switching mech anism as pointed out above. If the bellows 61 were not present, atmospheric ~35 or barometric pressure would exert a downward force on the upper side of the movable plate *58 The helix nut @l porting member 85. ‘ ri By t ` . will "i the rotate shaft therewith 88 is rotated, by reason „l since the heiix nut @l is bei... A.elia nut 91 will move „ec'tio „ »carrying with 'and tween area fected would isthe bysubstantially the be bellows effective volatile 63 the fluid and uponsame the and theplunger annular changes as the 69. area in barc 99 and 40 f . ‘ ‘the same time 40 metric pressure would counteract the action ci >the increase volatile in fluid barometric contained pressure in the would chamber retard 51. the movement of the plate 68 by the expansion of 45 the volatile thermostat fluidWhile and destroy a decrease the in calibration barometric pressure would hasten the action of the volatiie ñuid also to render the calibration of the thermo stat inaccurate. g adjacent iiange @l5 is an downwar „ M2 which e ad is plvoted to forward ‘dit of the supporting member S5 y mf M13. The pin I0! ci the c ‘wnw ».g ñange §95 engages a i" le *o the 'G62 so that upward and downward " ` extend ` 50 theBydevice inserting as above the relatively described,small changes bellows in baro 61 slideable member S9 causes os metric pressure will affect the movabie plate 68 ` ment ci' lthe arm |02 about its pivot only on the annular area defined by the bellows ~ 455 "cated dial |05 is secured to 'the ici 61 and the the plunger 69 since the space between the ai i M2 by means of‘screws ttc and i" ‘" the bellows 63 and 61 is hermetically sealed from the atmosphere. This area is extremely small as G01 in. compared to the area subject tothe pressure of the volatile fluid whereby any changes in baro--A 55 graduated dial I05 cooperates with le cover lill! ‘to indicate in` 'tensio ture i the spring 52 or directly .. tempera- . which the thermostat will bec e opera metric pressure acting upon this extremely small » tive to move the switch arm 21. Rotating move 60 annular area ll be practically negligible and will not affect the calibration or operation of the thermostat. ‘ ' In Fig. 4 I have illustrated ay modi ed form of temperature responsive device wherein I use a ‘ remote control system. - The bellows structure is the same as described above but the volatile fluid containing chamber 51 has'an opening made in the bottom thereof and a plug 19 is riveted and soldered in this opening. The plug 19 is adapted to receive in a‘gas-tight mannerk a. capillary tub-c 80; which is secured to a remote control bulb 82 and the plug 19 is also adapted to receive a protective covering 8| for the capillary tube 88. . The operation of this modification is the same as the one pointed out above except that the ment to adjust the adjusting mechanism 53 is 60 imparted to the shaft 88 by means of a key i09 engageable with the squared. portion 92 of the shaft 88. - y v A’ latch arm i Il is pivotally mounted on the upper end of the column 81 and is held in place by means of a nut H0. This latch arm ill is urged in a clockwise direction as shown in Fig. 3 by means of a spring I l2 which engages the latch arm iii and the supporting member 85. On the f outer end of the latch arm Ill is a proâection H3 70 which engages at various adjustments in notches ' H4, H5, H6, and H1 in the cam 93. These notches are annularly spaced to correspond to the graduations of- the dial |05 and in the ex empliñcation shown, the latch projection H3 en 75 aiadose gages in the notch `i id when the vgraduation. “Wi” respond directly with the graduations “Sii”, “Gd” the thermostat, that moves the switch with a positive snap action, that insu the novernent of the switch in case the swi" h should become stuck or held in any one oi its shii’ted positions and; “off”. and that provides a novel means 4¿or adjusting appears in the opening lill oi the cover itil. En like manner, the notches lliliö, M6, and Si? cor , 'By referring to Figs. 6, 7, S, and 9, it is seen that notches Sie and liti have 'tapered sides and that notches iid have their sides nearesil to the notches liti and lil@ tapered and their adjacent sides not so ta ered so clockwise movement of the cam as seen in d is prevented and counter~clocl§wise movement of the cam S3 as seen in Fig. 9 is prevented. Therefore, these notches Ilifl and i determine the amount of rotation of the cam and consequently the range of ad justment of the adjusting means 53. The 'tapered sides of 'the notches eject the latch projection i i3 therefrom upon rotation of the cam ‘5 andindicating the adjustment of the thermostat. While the apparatus herein described consti tutes a preferred-embodiment of the invention, it is to be understood that the invention is not limited to the preferred apparatus and that changes may be made therein without depa dg from the scope oí the invention which is defined in the appended claims. claim: i. ïn a device of the character described, comeV prising in combination, a casing having an aper ture therethrough, a movable wall in said casing, an actuating member associated with said wall shows the parts in position for operation at 74°, Fig. 7 at 68°, -Fig. 8 6d" and Fig. 9 at “orf”. and extending through said aperture into the surrounding atmosphere, a bellows surrounding 20 it is obvious to anyone skilled in the art that the number of notches the cam Q3 and the number of graduations on the scale iiih may he increased or decreased at will according to the said aperture and sealed to said wall whereby said casing, wall, and bellows form a pressure chamber, variations in pressure therein serving to move said wall, and a seal adjacent said aper desired adjustment of the instrument. ture to preclude contact of atmospheric pressure The arm lil?? extends downwardly and has an abutment i2@ which engages a pin i2!! located on with at least a portion of said wall. 2. En a device of the character described, com~ When the upwardly the adjusting extending means ilange 53 has ¿id so oi been the lever adjust prising in combination, a casing having an aper ture therethrough, a movable wall in said casing, an actuating member associated with said wall 30 d@ ed to move it to “on” position, the abutment iliiii engages pin. 02H as shown in Fig. 5 which pre-> vents counter-clockwise movement of the lever G3 as viewed in Fig. 5 so that when the tempera~ ture aiîecting the temperature responsive means 55 decreases, the spring 52 cannot become op erative to move the switching mechanism. A brief description of the operation of the de vice is as follows: Assume that the thermostat is hooked up to a heating device in such n‘lanner that when the contact 29 oi the switch arm 2li and extending through said aperture into the surrounding atmosphere, a bellows surrounding said Aaperture and sealed to said wall whereby said casing, wall, and bellows form a pressure chamber, variations in pressure therein serving to move said wall, and sealing means surrounding said aperture and associated with said wall to preclude contact or" atmospheric pressure with at least a portion of said wall. 3. Zin a device or" the character described, com engages the contact 25, the heating device will be " prising in combination, a casing having an aper» shut oit and that 'when the contact 2@ engages the ture therethrough, a movable wall in said casing, contact it the heating device will be turned on. an actuating member associated with said wall With the parts in the position shown in Fig. "i, and extending through said aperture into the the .device is adjusted to respond to a 'tempera surrounding atmosphere, a bellows surrounding ture o‘i 68° and the temperature acting on the said aperture and sealed to said wall whereby temperature responsive means 5h is greater than said casing, wall, and bellows form a pressure 68°, therefore the heating device is shut ofi. When chamber, variations in pressure therein serving the temperature falls below 68°, the tension spring to move said wall, and a second bellows surround E2 overcomes the temperature responsive device ing said aperture and sealed to said wall but 56 and moves contact 29 of the switch arm 2li into positioned interiorly of said first mentioned bel~ engagement with contact 25 to complete a circuit lows with respect to said aperture whereby to to turn on the heating device to restore the tem perature to 68°. Lilre operation will occur when the device is set for 741° and for 60°, the 74° posi tion being shown in Fig. 4. When. the adjusting means 53 is adjusted to “off” position, the abutment i263 engages the pin ¿2i which prevents counter-clockwise movement of lever 39 as viewed in Fig. 5 or prevents clock wise movement of lever 43 as viewed in Fig. l.. Since this movement of the lever 39 is prevented by means of the abutment §20, the contact 29 cannot move to the right to engage the contact 26 as viewed in Fig. i to close the circuit for turn ing on the heating device. Therefore, when the thermostat is adjusted to “oiï” position, it can not become operative to call for heat regardless of how low the temperature may fall. From the above, it is seen‘ that I have invented 70 a novel thermostat that ls not rendered yinaccu rate by` changes in atmospheric or barometric pressure acting thereon', that may be adjusted and locked in an “off” position whereby changes 75 in temperature acting thereon will not operate 40 form a seal to preclude contact of atmospheric pressure with a portion or said wall. in a device ofthe character described, com prising in combination, a casing having an aper~ ture therethrough, a movable wall in said casing, an actuating member sealed to said wall and ex~ tending through said aperture into the surround ing atmosphere, a bellows surrounding said aper-- 60 ture and hence said actuating member and sealed to said wall whereby said casing, wall, and bel lows form a pressure chamber, variations in pres sure therein serving to move said wall and- hence said actuating member, a second bellows sealed to said wall and to said casing adjacent and sur rounding said aperture to form a hermetically sealed chamber co-axial with and interiorily po sitioned with respect to said pressure chamber whereby to preclude contact of atmospheric pres~ 70 sure with a portion of said wall, said second men tioned bellows being spaced from said actuating member whereby said actuating member may move in accordance with the movement of said wall in a substantially friction free manner. 5 2,120,938 5. A pressure operated switch adapted for use under varying external pressure conditions and subject to‘jolting and jarring comprising', a pres member tol engage said resiliently mounted con tacts, adjusting means for determining the sure actuated device having a member that is Gi movable according to changes in pressure acting thereon, means associated with said pressure change in the condition required to move said resilient member from one abutment to the other and means associated with said adjusting means to lock said resilient .member against one of said device to prevent the varying external pressure conditions from affecting the movement oi said movable member, said means comprising a seal ing member to Vpreclude contact of atmospheric pressure with at least a portion of said pressure actuated device, a resilient switch arm operated by said movable member, contacts to be engaged by said resilient switch arm, magnetic means for resisting movement of said resilient switch arm until said resilient switch arm is suillciently flexed by said movable member to completely move said resilient switch arm with a 'snap action whereby jolting and jarring of the switch will 20 not cause said switch arm to vibrate. 6. In a switching mechanism of the class de scribed, opposed abutments, opposed magnets adjacent said abutments, opposed resiliently mounted contacts adjacent said abutments, means for varying the position of at least one of said contacts and its associated abutment simul taneously, a spring switch arm between said abut~ ments adapted to be moved from one abutment to the other and held in shifted position by said magnets until suillcient energy has been built up in said spring switch arm to insure its movement from one abutment to the other and contacts abutments. 10. An adjusting and indicating means for an instrument operated in response to changes in a condition comprising, a rotatable screw and nut for determining the change in the condition re quired to operate the instrument, a cam rotated by said screw and having notches therein, means cooperating with said notches for determining the value of adjustment and a graduated indi eating dial moved by said nut to visually indi cate the value of adjustment, said notches and said graduations corresponding in value with each other. 11. A combined adjusting, indicating and lock 20 ing means for an instrument operated in re sponse to a condition, means for adjusting the instrument for determining the change in the condition required to operate the instrument, means operated by said adjusting means for lock ing the instrument whereby the instrument con 25 not be operated by changes in the condition, means for indicating the value _of adjustment» and the locking of the instrument and detênt means for maintaining said adjusting means in any one 30 of its adjusted positions. ' 12. A combined adjusting, indicating and lock on said spring switch arm to alternately engage . ing means for an instrument operated in response said opposed contacts. ' 7. In a switching mechanism of the class de scribed, opposed abutments, a magnet adjacent - each abutment, a resiliently mounted contact ad jacent each abutment, means for varying the position of at least one' of said contacts and its associated abutment simultaneously, a resilient member movable alternately between said abut ments and adapted to be held against said abut ments by said magnets, means i'or ilexing said resilient member to overcome the ei'iect of said magnets -to snap said resilient member from one abutment to the other and contacts on said re silient member to engage said resiliently mounted contacts. 8. In a switching mechanism of the class de 50 55 scribed, opposed abutments, a magnet adjacent each abutment, a resiliently mounted contact ad jacent each abutment, a resilient member’mov able alternately between said abutments and adapted to be held against said abutments by said magnets, means for flexing said resilient member to overcome the eiïect of said magnets to snap said resilient member from one abutment to the other, and means to move said resilient member from one abutment to the other in case 80 said first means fails to move said resilient member. ' 9. In a switching mechanism of the class de to changes in a condition comprising, a rotatable screw and nut for determining the change in the condition required to operate the instrument, a member rotated by said screw having a plurality of detents therein, means cooperatingwith said detents for determining the value of adjustment and limiting the range of adjustment, a gradu 40 ated indicating dial moved by said nut and means operated by said nut at one limit of the range of adjustment to lock said instrument whereby said instrument cannot be operated by changes in the condition, said graduaticns of the dial corre 45 sponding to the detents of the member to indi cate the value of the adjustment and the locking of the instrument. _ 13. In a device of the character described, a casing, an element _to be moved, means to move 50 said element in response to pressure changes in said casing, means associated with said element to preclude external atmospheric pressure from ail’ecting said element, adjusting means movable 55 through a given range of adjustment for de termining the change in pressure required to move said element, and detent means associated with said adjusting means for maintaining said adjusting means in any one of a plurality of 60 » adjusted positions. 14. In a mechanism of the class described, op posed contacts, a magnet adjacent each contact, scribed, opposed abutments opposed magnets a resilient member movable alternately between adjacent said abutments, opposed resilientlyY said contacts andadapted to be held against said 65 mounted contacts adjacent said abutments, a resilient member movable alternately between said abutments and adapted to be held against said abutments by said magnets, means respon sive to changes in a condition for flexing said 70 resilient member to overcome the effect of said magnets to snap the resilient member from one abutment to the other, contacts _on said resilient contacts by said magnets, means ior flexing said resilient member to overcome the eiiect of said magnets to snap said resilient member from one contact to the other, and means to move said resilient member from one contact to the other in case said first means fails to move said resilient member. CARL G. KRONMIILER.