Means for calibrating pressure switches at extra-low pressure settings

Abstract

A simplified calibration mechanism is provided for a pressure switch using an adjustable, spring-biased plunger arrangement for controlling the trip force and hence the pressure to which the switch responds. The mechanism includes an especially configured lever pivoted at one end, contacting an especially shaped cam as a follower at its other end and the plunger at its mid portion. First calibration means are provided in the lever's pivoted end to adjust the normal low-high pressure settings of the switch. Second calibration means are provided to isolate the lever and cam from the plunger for effecting a precise setting of the pressure switch at extra-low pressures.

What I claim is:  .[.1. A calibration mechanism for a pressure switch of the type having a spring-biased plunger arrangement adjustable to sense different pressures to which said switch responds, said mechanism comprising: 
       means for establishing and calibrating normal "low to high" pressure settings of said switch, said "low to high" pressure setting means including lever means for adjusting said plunger and cam means operatively associated with said lever means to provide a "low to high" range of settings; and 
       means for establishing and calibrating an "extra-low" pressure setting for said switch, said "extra-low" pressure setting means effective to isolate said lever and said cam means from acting on said plunger when said "extra-low" pressure setting means is operative..]. .[.2. The calibration mechanism of claim 1 wherein 
       said lever means includes a lever pivotable at one end to said switch, engaging said cam means at its opposite end as a follower and contacting said plunger about a portion between its ends, 
       said pivotable lever end defined by a follicle therein having a central opening extending through said follicle and a fastener received in threaded engagement with the switch housing and having a head received in said follicle whereby said switch can be calibrated between said low-high pressure settings..]. .[.3. The calibration mechanism of claim 2 wherein 
       said "extra-low" pressure setting means includes an opening extending through said portion of said lever, adjustable stop means suspended above said opening for contacting said plunger, spring means between said lever and the switch housing and longitudinally positioned between said lever portion and said pivotable end for biasing said lever against said cam means and notch means within said cam means for receiving said cam follower end of said lever to raise said lever from contact with said plunger..]. .[.4. The calibration mechanism of claim 3 wherein 
       said lever and said cam means are formed of plastic having a low co-efficient of friction..]. .[.5. The calibration mechanism of claim 3 wherein 
       said plunger arrangement includes said plunger partially received within a bore in the switch housing, said plunger having an exposed top end and a boss extending said top end, said boss extending through said opening in said lever, and 
       said portion of said lever having a pair of arcuate projections extending from the underside surface thereof and spaced on diametrically opposite sides of said opening, said projections straddling said boss of said plunger and contacting said top surface of said plunger when said "low to high" pressure setting means are operable..]. .[.6. The calibration mechanism of claim 3 wherein 
       said cam means includes a rotatable cam having a first stepped profile receiving said follower end of said lever for establishing said "low to high" range and a second stepped profile for establishing said "extra-low" setting, and 
       said notch means including a notch in said second profile, said notch configured similar to said follower end of said lever for relatively locking said cam and said lever in said extra-low range..]. .[.7. The calibration mechanism of claim 6 wherein 
       said extra-low setting is within the range of 3.7 to 5.3 in H 2  O pressure..]. .[.8. In a pressure switch of the type having a plunger arrangement at least partially disposed within a bore formed in a portion of the switch housing and biased by a first spring, the effective force of which determines the pressure at which said switch responds, the improvement comprising: 
       bracket means mounted on said pressure switch housing portion in which said plunger arrangement is formed; 
       1ever means pinned to said housing portion at one end thereof and acting on the plunger to adjust said pressure switch; 
       cam means mounted on said bracket means and acting on said lever means opposite said pinned end to bias said lever means in opposition to said first spring force of said pressure switch over a "low to high" range of settings and movable to an "extra-low" position; 
       first calibrating means at said pinned end of lever means to determine the maximum high setting of said device; and 
       second calibrating means mounted on said bracket means for calibrating said switch to said "extra-low" setting and rendering said cam means ineffective to bias said lever means in opposition to said spring force in said "extra-low" position..]. .[.9. The pressure switch of claim 8 wherein 
       said lever means is defined by a generally channelled shaped lever arm having a follicle at one end with an opening extending therethrough, and 
       said first calibrating means including a fastener received in threaded engagement with said first housing portion, said fastener having a head received within said follicle..]. .[.10. The pressure switch of claim 9 wherein 
       a second spring is compressed between said first housing portion and said lever to exert a bias on said lever in the same direction as said first spring, and 
       said second calibrating means further provides means for rendering ineffective the bearing of said lever on said plunger..]. .[.11. The pressure switch of claim 10 wherein 
       said second calibrating means further includes said cam means relatively locking said lever therewith when said switch is in said extra-low setting..]. .[.12. In a pressure switch of the type having a generally flat housing surface, said housing having a bore therein, an adjustable, spring-biased plunger extending partially within said bore for establishing the effective force which determines the pressure at which said switch responds, calibration means for adjusting the position of said plunger, and electrical terminals on one side of the longitudinal centerline of said housing for receiving field wires to complete switch circuitry, the improvement comprising: 
       a bracket having a base mounted to said generally flat surface; 
       a U-shaped bracket portion extending upwardly from said base; 
       a shaft journalled within said U-shaped bracket portion and a cam secured to said shaft, said cam defining a part of said calibration means; 
       an upwardly extending, sidewall portion of said bracket extending generally parallel to said longitudinal centerline and spaced from said shaft a distance approximately equal to the maximum radius of said cam for preventing fouling of said field wires with said cam..]. .[.13. The pressure switch of claim 12 wherein 
       said housing surface includes an upwardly extending, raised boss portion having first, second, and third bores longitudinally spaced bores formed therein, 
       said plunger extending partially within said bore, 
       said calibration mechanism including a lever having one end engaging said cam, its opposite end pivotable about a fastener, extending therethrough, and a mid-portion thereof adapted to contact said plunger, said fastener received within said second bore, and a spring received partially within said third bore spaced between said first and second bores and compressed against the underside of said lever whereby said raised portion of said housing prevents fouling of said field wires within the lever mechanism..]. .Iadd. 14. A calibration mechanism in a pressure switch of the type having a spring-biased plunger arrangement adjustable to sense different pressures to which said pressure switch responds, said mechanism comprising: 
       (a) means for establishing and calibrating normal "low to high" pressure settings of said pressure switch, said "low to high" pressure setting means including lever means for adjusting said plunger and selectively operative cam means in association with said lever means to provide a "low to high" range of settings, wherein said lever means includes a lever adapted for pivotal movement at only one end thereof with respect to said pressure switch, said lever having the opposite end thereof engaging said cam means, as a follower with portions thereof intermediate said ends contacting said plunger; 
       (b) means biasing said lever in a direction for engaging said cam means; 
       (c) means pivotally mounting said one lever end to said pressure switch, said pivot means including adjustable means operable, upon adjustment, to move the fulcrum of said lever with respect to said plunger for varying the spring biasing of said plunger; and 
       (d) wherein said biasing means acts on said lever intermediate said pivot means and said cam follower and wherein said cam follower, said biasing means and said pivot means are disposed in straight line relationship throughout the range of movement of said lever..Iaddend. .Iadd. 15. The calibration mechanism of claim 14, further including: 
       (a) means for establishing and calibrating an "exta-low" pressure setting for said pressure switch, said "extra-low" pressure setting means including 
       (i) an opening extending through said lever; 
       (ii) adjustable stop means suspended above said opening for contacting said plunger, said "extra-low" pressure setting means effective while said cam means is positioned in said "extra-low" position for directly engaging and limiting the position of said spring biased plunger such that said lever is disengaged from said plunger; 
       (b) said biasing means includes spring means disposed between said lever and said switch and located longitudinally along said lever between said opening and said pivotable end for biasing said lever against said cam means; and 
       (c) latch means within said cam means for receiving said follower end of said lever to raise said lever from contact with said plunger. .Iaddend. .Iadd. 16. The calibration mechanism defined in claim 14, wherein, 
       (a) said adjustable means includes fastener means received through said lever and adjustably engaging said switch, said fastener means including means defining a first surface; and 
       (b) said lever defining a second surface adjacent said one lever end, said biasing means being effective for maintaining said first and second surfaces in self-aligned contact for defining the fulcrum of said lever. .Iaddend. .Iadd. 17. The calibration mechanism defined in claim 14, wherein, 
       said cam means includes notch means operative when said cam means is selectively moved to certain positions to cause said lever to operatively move said plunger. .Iaddend. .Iadd. 18. The calibration mechanism defined in claim 14, wherein said cam means includes a rotatable cam having a stepped profile with said follower end of said lever received thereon for establishing said low-to-high range of pressure settings. .Iaddend. .Iadd. 19. A calibration mechanism in a pressure switch of the type having a spring-biased plunger arrangement adjustable to sense different pressures to which said pressure switch responds, said mechanism comprising: 
       (a) means for establishing and calibrating normal "low to high" pressure settings of said pressure switch, said "low to high" pressure setting means including lever means for adjusting said plunger and selectively operative cam means in association with said lever means to provide a "low to high" range of settings, wherein said lever means includes a lever adapted for pivotal movement at one end thereof with respect to said pressure switch, said lever having the opposite end thereof engaging said cam as a follower, with portions thereof intermediate said ends contacting said plunger; 
       (b) means biasing said lever in a direction for engaging said cam means; 
       (c) means pivotally mounting said one lever end to said pressure switch, said pivot means including adjustable means operable, upon adjustment, to move the fulcrum of said lever with respect to said plunger for varying the spring biasing of said plunger; and 
       (d) means for establishing and calibrating an "extra-low" pressure setting for said pressure switch, said "extra-low" pressure setting means including 
       (i) an opening extending through said lever; 
       (ii) adjustable stop means suspended above said opening for contacting said plunger, said extra-low pressure setting means effective while said cam means is positioned in said "extra-low" position for directly engaging and limiting the position of said spring biased plunger such that said lever is disengaged from said plunger; 
       (e) said biasing means includes spring means disposed between said lever and said switch and located longitudinally along said lever between said opening and said pivotable end for biasing said lever against said cam means; and 
       (f) latch means within said cam means for receiving said follower end of said lever to raise said lever from contact with said plunger. .Iaddend..Iadd. 20. A calibration mechanism in a pressure switch of the type having a spring-biased plunger arrangement mounted in a housing, said spring biased plunger arrangement adjustable to sense different pressure to which said switch responds, said mechanism comprising: 
       (a) said plunger arrangement includes said plunger partially received within a bore in said housing, said plunger having an exposed top end and a boss extending said top end, said boss extending through an opening in said lever, 
       (b) means for establishing and calibrating normal "low to high" pressure settings of said pressure switch, said "low to high" pressure setting means including lever means for adjusting said plunger and selectively operative cam means in association with said lever means to provide a "low to high" range of settings, wherein said lever means includes a lever adapted for pivotal movement at one end thereof with respect to said pressure switch, said lever having the opposite end thereof engaging said cam as a follower, said lever having a pair of spaced projections extending from the underside surface thereof and adjacent said opening, with said boss of said plunger slidably received therebetween and guided thereby, said projections contacting said top surface over said "low to high" range pressure setting; 
       (c) means biasing said lever in a direction for engaging said cam means; 
       (d) means pivotally mounting said one lever end to said pressure switch, said pivot means including adjustable means operable upon adjustment, to move the fulcrum of said lever with respect to said plunger for varying the spring biasing of said plunger; and 
       (e) means for establishing and calibrating an "extra-low" pressure setting for said pressure switch, said "extra-low" pressure setting means effective while said cam means is positioned in said "extra-low" position for directly engaging and limiting the position of said spring biased plunger such that said lever is disengaged from said plunger, thereby isolating and disengaging said cam means and said lever from said plunger during said "extra-low" setting. .Iadd. 21. A calibration mechanism in a pressure switch of the type having a spring-biased plunger arrangement adjustable to sense different pressures to which said switch responds, said mechanism comprising: 
       (a) means for establishing and calibrating normal "low to high" pressure settings of said switch, said "low to high" pressure setting means including lever means for adjusting said plunger and selectively operative cam means in association with said lever means to provide a "low to high" range of settings, wherein said lever means includes a lever adapted for pivotal movement at only one end thereof with respect to said switch, said lever having the opposite end thereof engaging said cam means as a follower with portions thereof intermediate said ends contacting said plunger; 
       (b) means biasing said lever in a direction for engaging said cam means; 
       (c) means pivotally mounting said one lever end to said switch, said pivot means including adjustable means operable, upon adjustment, to move the fulcrum of said lever with respect to said plunger for varying the spring biasing of said plunger, said adjustable means includes fastener means received through said lever and adjustably engaging said switch, said fastener means including means defining a first surface; and 
       (d) said lever defining a second surface adjacant said one lever end, said biasing means being effective for maintaining said first and second surfaces in self-aligned contact for defining the fulcrum of said lever; and 
       (e) wherein said biasing means acts on said lever intermediate said pivot means and said cam follower. .Iaddend.