US3516279A - Method for adjusting a pressure operated switch utilizing the nonlinear properties of a biasing means - Google Patents

Description

United States Patent 3,516,279 METHOD FOR ADJUSTING A PRESSURE OPERATED SWITCH UTILIZING THE NONLINEAR PROPERTIES OF A BIASING MEANS Robert J. Maziarka, Niles, Ill., assignor to Alphamatic Corporation, a corporation of Illinois Filed Feb. 23, 1967, Ser. No. 617,961 Int. Cl. C011 27/00; H01h 35/34, 35/38 US. Cl. 734 5 Claims ABSTRACT OF THE DISCLOSURE A fluid pressure electric switch having means for varying the pressure at which the switch closes and the pressure at which it opens with a variably biased pressure sensing plunger providing adjustable closing pressure and an adjustable support for an electric switch activated by the plunger to provide adjustable opening pressure.

BACKGROUND OF THE INVENTION The differential pressure in a pressure switch is the difference in pressure between the pressure at which the switch senses a first condition (e.g. turns the switch on) and when the switch senses a subsequent second condition (e.g. turns the switch off). In some applications for pressure switches it is desirable to have this pressure differential as small as possible, while in other applications it is desirable to have a fairly wide range of differential pressures and it is particularly advantageous that this differential be variable.

An example of the latter described application is in an air compressor where it is desirable to initiate operation of the compressor when the tank pressure drops to say 100 p.s.i., and to maintain the compressor running until the tank pressure reaches 150 p.s.i. where it is desired that the compressor be turned off. A pressure switch for this application should have a fifty p.s.i. pressure differential.

One prior known pressure switch for this general purpose includes a spring biased pressure sensing piston connected to actuate a microswitch. By varying the bias on the pressure sensing piston, one of the two sensed pressures can be selected with the other being determined by the inherent mechanical differential of the microswitch.

The mechanical differential of a microswitch may be defined as that linear movement of the switch plunger when returning towards its normal position necessary to break the set contacts and return the switch arm to the normal position or contacts. In many microswitches manufactured today, this mechanical differential distance is constant. Therefore, for a given pressure selected in the prior switch described above there will result a predetermined pressure differential, and this differential would not be adjustable or variable even if so desired. Thus, in pressure switches of this type it is necessary to combine in almost custom fashion a. particular microswitch and actuator to give both the desired set pressure and pressure differential.

Still another type of pressure switch includes a spring biased pressure sensing device connected to actuate a microswitch with the position of an actuating plunger being adjustable with respect to the microswitch to vary the make or set pressure as desired. However, for a given make pressure, there will be a corresponding break pressure, and the pressure differential thus is constant for all desired make or set pressures. The present pressure switch obviates the flexibility limitations of the pressure switches described above by providin-g a switch in which a wide range of sensed make or set pressures is possible with the pressure differential at each make pressure being variable over a substantial range if desired. While the pressure differential in pressure switches has been variable in prior known switches the adjustments therefor have been made internally in the microswitch itself such as by changing the position of one of the contacts.

SUMMARY OF THE INVENTION In the present device no such change in the internal portions of the microswitch is necessary, and conventional mass produced non-adjustable microswitches may be employed in the present pressure switch.

In accordance with the present invention a spring biased pressure sensing piston is provided arranged so that the piston assumes a position proportional to the sensed pressure. By varying the bias on the piston, the sensitivity thereof may be varied so that the piston will assume a desired position at a predetermined pressure. A plunger driven by the piston drives the switch plunger in a microswitch. By varying the bias on the piston the pressure at which the microswitch will activate or make may be selected as desired. This will result in a certain break or deactuate pressure. However, there is also provided a means for positioning the switch plunger with respect to the actuator plunger to effectively vary the actuator plunger movement necessary to actuate the switch. To vary the differential pressure the position of the switch with respect to the plunger is changed which effectively varies the differential pressure in that it requires a readjustment of the spring bias on the actuator to the desired make pressure.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal section of the present pressure switch;

FIGS. 2 and 3 are cross sections of a microswitch in its normal position and make position, respectively; and

FIGS. 4 to 7 are schematic illustrations of the actuator and microswitch in their various positions of adjustment.

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail an embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated. The scope of the invention will be pointed out in the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, a pressure switch assembly 10 is seen to consist generally of a pressure sensor and switch actuator 11 responsive to pressure in line 12,

3 a microswitch 14, and a switch support assembly for supporting the switch on the actuator 11.

To appreciate the interrelationship between the switch 14 and the actuator and sensor 11 it is necessary to have a complete understanding of the construction of microswitch 14, although this switch may be of purely conventional design such as Honeywell microswitch 115M401 (1966).

As seen in FIGS. 2 and 3 the switch 14 includes a frame member 16 supporting a flexible elongated pole member 17 having contacts 18 and 19 on the distal end thereof. Also supported on frame member 16 are stationary contacts 21 and 22 flanking the distal end of pole member 17 and positioned to selectively engage the contacts 18 and 19, respectively. Contacts 18 and 19 are electrically connected to terminals 24 and 25 projecting from one side of frame 16, while pole 17 is electrically connected to a similar terminal 26. For moving the switch from the normal contact 21 a plunger 64 is provided engageable with the flexible pole 17 and slidable in switch cover member 28. A U-shaped spring 29 is provided for normally maintaining the contact 18 in engagement with contact 21 and for providing the snap action of pole member 17 from contact 18 to contact 19 when displaced a suflicient distance by plunger 64. Spring 29 has one projecting end seated in a groove in a stationary support 30 and the other projecting end engaging the side of an enlarged opening in pole member 17. In operation when plunger 64 is depressed from the zero or reference position shown in FIG. 4 the portion of the member 17 ad jacent the plunger will be displaced downwardly against the upward bias of spring 29 which tends to maintain contact 18 in engagement with contact 21. The result of this is a flexure or bending of member 17. When plunger 64 moves the adjacent portion of member 17 downwardly sufliciently so that it passes below the point of engagement of spring 29 with member 30 a toggle action occurs snapping the right end of pole 17 downwardly causing engagement of contact 19 with contact 22. The distance plunger 64 travels from its normal or rest position shown in FIG. 2 to a position where the switch transfer occurs from contact 21 to contact 22 is referred to as the pretravel of the switch. This latter position is referred to as the operating point or make point of the switch. Of course, the plunger may overtravel somewhat from this position without damaging the switch. When the switch reaches the operating point it assumes the position shown in FIG. 3 where spring 29 assists in holding contact 19 in engagement with contact 22 although it cannot do so alone. As plunger 64 is moved in the opposite direction, toward rest, member 17 will move above the point of engagement of spring 29 with support 30 permitting the snap action of pole 17 from contact 22 back to contact 21. The return distance plunger 64 must move from the operating point to effect the breaking of contacts 19 and 22 is referred to as the mechanical differential of the switch and the position of plunger 64 when this occurs is the reset position.

In a great number of commercially available switches the ditferential of the switch is constant. Therefore, if the switch is used in a pressure switch of conventional construction the pressure ditferential of the pressure switch (pressure sensor and actuator and electric switch combined) is fixed for any given make pressure setting. The pressure differential of a pressure switch may be defined as that reduction in pressure from a pressure necessary to move plunger 64 from its operating point to its reset or break point. If the pressure sensing switch actuating parts have a constant sensitivity, then the pressure dilferential Will remain constant. The present device permits the sensitivity of the actuator or sensor to be varied as desired at each pressure setting.

The sensor and actuator assembly 11 has two generally cylindrical housing members 36 and 37 fastened together by suitable threaded fasteners 38. A central bore 40 in member 36 defines a pressure chamber which communicates with line 12 through suitable fitting 41.

Seated within a counterbore 43 in one end of member 36 is a circular diaphragm 44 made of rubber or other elastomeric material. An annular shoulder 45 on the end of cylindrical member 37 engages one side of the diaphragm 44 forcing it into engagement with the bottom of counterbore 43 thereby sealing the chamber 40. This is efiected by turning the counterbore 43 to a depth less than the sum of the width of diaphragm 44 and projection 45. Upon the application of pressure in chamber 40 the central portion of diaphragm member 44 bends to the right in FIG. 1.

Seated Within a counterbore 46 in member 37 is a piston 48 having an enlarged portion 49 closely slidable in counterbore 46 and a central cylindrical projection 50 slidable in a central through bore 52 in member 37.

The depth of counterbore 46 is selected somewhat greater than the maximum desired movement of piston 48 and defines a positive means for limiting movement of the piston. In this manner the diaphragm 44 may not be damaged by extrusion caused by pressure surges in chamber 40.

Also slidable in the bore 52 is a plunger 55 which may be constructed of a non-metallic material such as a nylon.

Plunger 55 has a cylindrical portion 56 which engages the end of piston projection 50. Formed integrally with plunger 55 is an enlarged spring seat 57 which receives one end of a spring 58 for biasing the piston 48 toward the no-pressure position shown where it holds the diaphragm 44 against the bottom of counterbore 43.

The other end of spring 58 is seated on a suitable seating shoulder '60 in adjustment cap 61 which also slidably supports end 62. of plunger 55. Cap 61 has a threaded portion 63 interengaging mating threads on member 37 and provides a wide range of compression on spring 58.

The distal end of plunger 55 engages switch plunger 64 and drives the switch.

The sensitivity of pressure sensing piston 48 varies over its range of axial movement. That is, if the sensitivity he defined as the incremental pressure (or pressure change) necessary to move the plunger a given incremental distance, the piston is more sensitive as it moves from its rest or normal position shown in FIG. 1 toward the right. It is more sensitive the further it moves from rest in that a lesser incremental pressure (or pressure change) in chamber 40 is required to move the piston the incremental distance. While the spring rate of spring 58 is theoretically constant, the above non-linearity in the sensitivity of the piston 48 appears to result from variations in the etfective area of diaphragm 44 with movement of the piston, non-linearities in spring 58 and possibly other effects.

For supporting the microswitch 14 adjacent the end of plunger 55 the bracket assembly 15 is provided including a U-shaped strap member 65 having the ends thereof fixed by suitable fasteners 66 to the member 37 in recesses 68. A flexible support arm 69, generally L- shaped, is fixed to the inside of bracket '15 at 70 by suitable means, such as welding. A portion 69a of arm 69 forms a flexible detent engaging the cap 61 to provide an indexing adjustment for the cap. The flexible depending portion of support arm 69 supports and carries the switch 14. Switch plunger 64 extends through a suitable opening 71 in support arm 69.

A vernier adjustment means 73 is provided for varying the pressure differential of the switch 10 by axially moving microswitch 14 with respect to plunger 62. Toward this end, a vernier adjustment screw 74 is threadedly mounted in a boss 75 fixed to strap 65 and has a tool receiving slot 76 for the reception of a suitable tool. The other end of screw 74 is axially fixed in boss 77 fixed to the distal or free end of flexible member 69', but rotational movement of the screw 74 with respect to the boss 77 is permitted. Suitable graduations may be provided on boss 75 for the purpose of indicating the pressure diiferential that the switch is adjusted for.

The method of operation of the present pressure switch is as follows. Assume firstly that it is desired that the set or make contacts 19, 22 of switch 14 be closed at an initial rise in pressure to fifteen p.s.i. and that these contacts remain closed until the pressure in chamber 40 drops to below nine p.s.i. Thus, the desired pressure differential in this case is six p.s.i. Firstly, fluid under pressure from a suitable source is connected to line 12 and regulated to fifteen p.s.i. with the cap 61 completely threaded in member 37 so that the maximum spring force is exerted against piston 48 and the plunger 55 remains in its zero displacement position shown. Then the screw adjustment cap 61 is backed off reducing the precompression of spring 58 thereby reducing the biasing force on piston 48 until the piston 48 moves just far enough to actuate switch 14. This means that plunger 55- has moved a distance at least equal to the pretravel of the switch and plunger 64 has moved to the operating point. This movement of plunger 55 is illustrated in FIGS. 4 and 5 (where this pretravel distance is indicated by the letter P. Pressure in chamber 40 is then reduced. Note that a predetermined pressure drop in chamber 40 will be required before the plunger '55 permits switch plunger 64 to move the mechanical differential distance d of switch 14 breaking the make contacts and closing the normally closed contacts 18, 21 of the switch. This may be, for example, on the order of two pounds so that the switch 14 resets itself When the pressure in chamber 40 drops to thirteen pounds.

However, this pressure differential is less than the six p.s.i. we have assumed in this example. The pressure in chamber 40 is then reduced to atmosphere. To increase the pressure difierential of the present switch, screw 74 is rotated in a direction to pivot switch 14 clockwise from the position shown in FIGS. 1 and 5 (with plunger 55 in its rest position) to the position shown in FIG. 6 causing a depression of switch plunger 64 by actuator plunger 55. This has the effect of reducing the necessary pretravel of valve plunger 64 from P to P as shown in FIG. 7. However, it is important to note that this adjustment does not vary the mechanical differential of the switch. But it does vary the axial positions of the piston 48 and plunger 55 at the operating point and the reset point. More specifically, it moves these positions closer to the rest positions of piston and plunger shown in FIG. 1.

Since the pretravel of switch plunger 64 has been shortened, the switch 14 now will make at a pressure below fifteen p.s.i. To correct for this, a regulated pressure of fifteen p.s.i. is again applied to chamber 40 and adjustment cap 61 is threaded all the way into member 37 and then backed out therefrom until switch 14 again just makes at the fifteen p.s.i. pressure at chamber 40'. This, of course, will result in a greater precompression of spring 58 by cap 61 than was required for the initial fifteen p.s.i. setting. The pressure differential of the switch has thus been increased from two to six by shifting the positions of plunger 55 at the operating point and the reset point so that the piston 48 is in a less sensitive range in that a greater incremental pressure in chamber 40 is required to move the piston an incremental distance as described in detail above which means a greater pressure drop will be required in chamber 40 topermit plunger 64 to traverse the mechanical differential of the switch. With the proper adjustment of control 73 the pressure differential can be increased to the six p.s.i., desired, so that the switch will set at fifteen p.s.i. and reset at nine p.s.i., if so desired.

If on the other hand a less than two p.s.i. differential is desired, the control 73 may be adjusted to move switch plunger 64 away from the actuator plunger 55 (rather than toward it) after the initial adjustment of spring cap 61. This has the effect of increasing the travel of plunger 55 necessary to actuate switch 14 and to compensate for this the end cap 61 must be unthreaded to reduce the compression of spring 58 to maintain the fifteen p.s.i. make switch pressure. This shifts the position of piston 48 at the operating point and reset point further from the rest position shown in FIG. 1 and this as described above is a more sensitive range so that lesser pressure drop than two p.s.i. is required to permit movement of lunger 64 through the mechanical differential of the switch.

I claim:

1. A method of selecting the pressure settings of a pressure switch including a microswitch having a movable switch member adjacent an actuator that has a variably biased pressure sensing means with a non-linear forceposition character engageable without a variable lost motion connection with said movable switch member for actuation thereof, comprising the steps of applying a relatively high bias to said pressure sensing means, applying a fluid pressure equal to the desired switch actuation pressure to said pressure sensing means, reducing the bias on said pressure sensing means until said switch member moves to a position actuating said switch, moving said microswitch with respect to said pressure sensing device to vary the switch deactuation pressure as desired, again varying the bias on said pressure sensing means to again effect switch actuation at said switch actuation pressure.

2. A method of selecting the pressure settings of a pressure switch as defined in claim 1, wherein said microswitch is moved closer to said pressure sensing means to increase the pressure differential between said actuation pressure and said deactuation pressure, thereafter increasing the biasing force on said pressure sensing means, and then reducing the biasing force with said actuation pressure applied until the switch actuates.

3. A method of selecting the pressure settings of a pressure switch as defined in claim 1, wherein said microswitch is moved further from said pressure sensing means to decrease the pressure differential between the actuation pressure and the deactuation pressure, thereafter reducing the biasing force on said pressure sensing device with the actuation pressure applied until the switch actuates.

4. A method of selecting the pressure settings of a pressure switch including a microswitch having a movable switch member adjacent a non-linear actuator including a variably biased pressure sensing means engageable with said movable switch member for actuation thereof, comprising the steps of adjusting the position of the microswitch to vary the pressure differential between switch actuation and switch deactuation, and varying the biasing force to vary the switch actuation pressure.

5. A method of selecting the pressure settings of a pressure switch including a microswitch having contacts with open and closed states and a member movable from a first position to a second position to place the contacts in one of said states and movable from a second position to a third position for placing the contacts in the other of said states, the movement of the movable switch member from the second to the third position defining the mechanical differential travel of the microswitch, sensing means movable from a first position in response to a predetermined first pressure and movable to a second position in response to a predetermined second pressure, with adjustable biasing means for said sensing means for varying the first and second positions with respect to said first and second sensed pressures, said sensing means being non-linear in force-position relations, with separate means for said movable switch member, and means for adjusting the position of the microswitch with respect to said sensing means to move said switch movable member toward and away from said movable sensing means, comprising the steps of applying a relatively high bias to said pressure sensing means, applying a fluid pressure equal to the desired switch actuation pressure to said pressure sensing means, reducing the bias on said pressure sensing means until said switch member moves to a position 8 actuating said switch, moving said microswitch with re- 3,393,282 7/ 1968 Peter et a1. s spect to said pressure sensing device to vary the switch 3,256,393 6/1966 Snider 200 231 deactuation pressure as deslred, agaln varylng the hlas FOREIGN PATENTS on said pressure sensing means to agaln effect switch actuation at said switch actuation pressure. 7751882 5 1957 Great Bntaln- 5 762,363 11/1956 Great Britain. References Cited UNITED STATES PATENTS I ROBERT K. SCHAEFER, Primary Examiner 1, 75, 11 /1923 r m 2 0.4 K V N Y Assistant i r 2,800,549 7/1957 Guthrie ZOO-83.91 10 2,953,929 9/1960 Koutz 73 4 US. Cl. X.R. 3,363,072 11/1968 Moody. 200 s2, 83, 166

3,370,336 2/1968 Otto 734 X

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