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Publication numberUS3205323 A
Publication typeGrant
Publication dateSep 7, 1965
Filing dateFeb 16, 1962
Priority dateFeb 16, 1962
Publication numberUS 3205323 A, US 3205323A, US-A-3205323, US3205323 A, US3205323A
InventorsDeshautreaux Jr Emile C
Original AssigneeDeshautreaux Jr Emile C
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Magnetic reed proximity switch
US 3205323 A
Abstract  available in
Images(2)
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Claims  available in
Description  (OCR text may contain errors)

l sept. 7, 1965 E. C. DESHAUTREAUX, JR

MAGNETIC REED PROXIMITY SWITCH Filed Feb. 16, 1962 Byr 2 Sheets-Sheet 1 #MMM A T TORNE YS Sept. 7, 1965 E. c. DESHAUTREAUX, JR 3,205,323

MAGNETIC REED PROXIMITY SWITCH Fied Feb. 16, 1962 2 sheets-sheet 2 United States Patent O 3,205,323 MAGNETIC REED PROXIMITY SWITCH Emile C. Deshautreaux, Jr., 2121 4th St., Kenner, La. Filed Feb. 16, 1962, Ser. No. 173,678 9 Claims. (Cl. 200-87) This invention relates to a new and improved proximity switch, and more particularly, to one utilizing two pairs of unlike magnetic poles for creating a magnetic eld used in actuating switch contacts.

Industrial applications of limit and analogous switches involve their use for machine control, counting of objects, alarms, signals, and other such functions where the approach or passage of a material body must be detected. In Wide use today is the mechanical type of switch which requires physical contact between a cam, or other actuating deivce, and a lever arm of push pin which protrudes through the switch case. However, in these type of switches the external levers and push-buttons are very often subject to abuse in all but the simplest environments, Furthermore, the external lever pivots are open to corrosive and abrasive attack at the point where they extend from the case. Since more and more corrosive and abrasive materials are being used in industry, the switch may fail to function properly after but a short period of use.

On the other hand, a proximity type switch requires no physical contact with the material object in order to be actuated. Many of the proximity switches available today employ magnetic sensing such that when an object of magnetic material is brought into the vicinity of the switch sensing area, a change in the flux pattern within the switch causes the contacts to either open or close. Some of these prior -art switches, however, require amplitiers using vacuum tubes and/ or transistors or other delicate components that are subject to damage due to vibration and shock. This variety also requires a certain amount of external energy in order to make the device operative. Other prior art proximity switches are constructed using permanent magnets, but some of these are too large and heavy for certain applications and others do not have the sensitivity required in many environments.

The primary object of my present invention is to provide an improved proximity switch that can be actuated by the introduction of objects of magnetic material in the vicinity of the sensing area. The main components of the Switch are a set of contacts of magnetic material and a magnetic assembly having at least two pairs of magnetic poles. The contacts are placed such that if one is subjected to the eld of a north seeking magnetic pole of One pair and the other subjected to the iield of the south seeking magnetic pole of the same pair, there will be a magnetic force tending to close the contacts. Alternatively, only one contact may be exposed to the iield between the poles. In the magnetic assembly, the preferred arrangement is such that the rst pair of unlike poles is weaker than a second pair of unlike poles. The sensing area is in the vicinity of the iield of the second pair. Although the magnetic poles of the assembly may be created by electro-magnets, the preferred embodiment utilizes permanent magnets so that no burden load is required. The magnetic assembly and associated switch contacts can be completely encapsulated for maximum ruggedness, and the entire switch can be produced at a reasonable price making it practical for the average control problems found in the normal industrial process.

Therefore, one object of the invention is to provide an improved proximity switch for sensing objects of magnetic material brought into the sensing area.

Another object of the present invention is to provide a ICC switch that can be completely sealed with no moving parts external to the encapsulation.

A further object of the present invention is to provide a switch utilizing two pairs of unlike magnetic poles which is completely independent of any external power source.

Another object of the present invention is to provide a proximity switch that has high reliability and excellent sensitivity, as well as a fast operating speed.

These and other objects of the invention will become apparent during the course of the vfollowing description, which is to be read in conjunction with the drawings, in which:

FIGURES la and 1b illustrate the basic theory of operation ofthe present invention;

FIGURE 2 is a perspective view of -a preferred embodiment of the magnetic assembly showing the two pairs of poles;

FIGURE 3 illustrates how the poles may be formed on the assembly of FIGURE 2;

FIGURES 4a and 4b illustrate the use of the assembly with a pair of switch contacts;

FIGURE 5 shows how the assembly may be modified to obtain the desired operation by placing a magnetic shunt across one pair of the poles;

FIGURE 6 shows the invention with an addition of a biasing magnet used to aid the field from the magnetic assembly;

FIGURE 7 shows an embodiment wherein electro-magnet means is provided for opening the switch contacts when they have once been closed;

FIGURE 8 illustrates a normally closed embodiment of the switch utilizing a biasing magnet;

FIGURE 9 is a different embodiment of the invention similar to FIGURE 8 but utilizing an external signal for initially closing the contacts;

FIGURE l0 shows still another embodiment utilizing an external signal in conjunction with the magnetic assembly of the present invention for opening the switch contacts;

FIGURE ll shows one way in which the switch might be encapsulated for commercial use; and

FIGURE 12 shows a slightly alternative embodiment for encapsulating the switch.

FIGURES la and 1b illustrate the basic theory of operation of the present invention. Two magnets 10 and 11, each of length b and each having north and south poles at the ends thereof, are placed parallel to one another and spaced apart a distance a. Magnet 10 is turned degrees with respect to magnet 11 when considering their poles, such that lines of force, 4or flux lines, link the north pole N of magnet 11 and the south pole S of magnet 10, and magnetic lines of force link the north pole N' of magnet 1t! with the south pole S of magnet 11. Other flux lines link the north and south poles common to the same magnet, i.e., S and N of magnet 10, as well as N and S' of magnet 11.

If the distances a and b are varied, the relative strength of the various flux linkages changes in the following manner. If the distance a is mad-c greater while the distance b is made smaller, more of the flux will link with poles of the same magnet. In other words, the flux lines from the north pole N' of magnet 10 links more with the south pole S of magnet 10 than with the south pole S' of magnet 11. Consequently, the magnetic eld intensity between N and S' decreases, while that surrounding magnet 10 increases. In similar fashion more flux from the north pole N of magnet 11 links with its south pole SV than with the south pole S of magnet 10 in event that ldistance a increases. Consequently, the magnetic attraction between north and south poles of different magnets decreases as the distance between `the magnets increases and/ or the distance between the poles of the same magnet decreases. This phenomenon is due generally to the change in reluctance of the magnetic circuit, said reluctance being directly proportional to the length of the path between unlike poles, and inversely proportional both to the permeability of the material comprising said path and also to its cross-sectional area.

If there is a decrease in the permeability of the magnetic path between poles S and N, or between poles N and S', then the flux density between the poles in either of these pairs becomes greater, since the magnetic resistance of the path decreases. Assuming that the magnets 10 and 11 in FIGURE la are separated by the medium air, the path between poles S and N may be decreased in reluctance by placing a bar 9 of magnetic material close to these poles so that most of the flux therefrom links via the medium of said bar. However, this increased liux linkage between poles S and N consequently reduces the amount of flux available to be linked between unlike poles of the same magnet. For example, since most of the llux from pole S of magnet 10 now links with pole N of magnet 11, there is very little ux left available to link poles S and N of magnet 10, or N and S' of magnet 11. Therefore, the flux from the N and S poles must link said poles together in the manner shown in FIG- URE lb so as to increase the magnetircveld intensity in the airpath between said primed poles ofltlrese magnets. If magnetic bar 9 is removed from the vicinity of poles S and N, then the llux pattern reverts to that shown in FIG- URE la, with there being only few lines of flux linking unlike poles of the different magnets. In essence, then, the distances a and b between the various poles may be adjusted relative to one another so that in the absence of a magnetic shunt between poles N and S, most of the flux from poles N and S is short circuited to poles S and N, respectively.

The phenomenon described in connection with FIG- URES 1a and lb is the basis for the novel proximity switch lof the present invention. The same effect described above can be achieved by using two electro-magnets. However, this would cause a burden load requiring a source of energy to establish magnetic elds. In preference to the use of two separate magnets as shown in FIG- URE la, or two electro-magnets, the preferred means for providing two pairs of unlike poles is shown in FIGURE 2. This comprises a ceramic type wafer magnet formed generally in the shape of a thin bar by pressing ceramic powder material in a fashion well known in the art. Additionally, an aperture 13 is provided in the wafer 12. A ceramic wafer magnet of the type disclosed may be permanently magnetized so as to form a pair of unlike poles on each of its two major parallel faces or surfaces between which aperture 13 extends. The arrangement for magnetizing the wafer in this manner is shown in FIGURE 3, wherein an electro-magnet 7 provided with a source of energy 8 sets up a flux pattern as indicated which links with the pressed wafer 12 so that the lines of flux enter one surface of wafer 12 on one side of aperture 13 and emerge from the same surface but on the other side of aperture 13 as shown. The llux from the north pole of electro-mag-net 7 causes a south pole S to be formed on the portion of the surface entered by said flux lines, whereas a north pole N is formed on the portion `of the surface from which said lines exit which in turn return to the south pole lof the electro-magnet. The relative positions of these poles S and N are better shown in FIGURE 2, where they are seen to be on the same major surface of the wafer, but on either side of aperture 13.

The ux pattern set up in wafer 12 by the arrangement of FIGURE 3 also forms two auxiliary poles N' and S' on the other major surface of wafer 12, said surface being parallel to the surface in which the poles S and N have been formed. The formation of these auxiliary poles is believed to be due to the following reasons. First, the type of ceramic wafer magnet under consideration has a natural tendency to magnetize in the direction of pressing, which may be in the direction of arrow c in FIG- URE 2. Second, some of the flux lines entering wafer 12 from the north pole of magnet 7 emerge from the opposite major surface and travel through a path in the environment before entering the major surface on the other side of aperture 13 and recombining with those flux lines which remain in wafer 12. The strength of the auxiliary poles N and S is normally less than the strength of the main poles S and N formed on the opposite major surface of the wafer. This is so, since the flux density used to form the main poles is greater than the flux density associated with the auxiliary poles. Consequently, a magnet of this type will show strong magnetic attraction from the major poles, but practically no magnetic attraction from the auxiliary poles. Furthermore, the major portion of the flux from the secondary or auxiliary poles N and S is short-circuited to the unlike main poles as shown in FIGURE 4a. Thus, most of the flux from auxiliary pole N links or is short-circuited with the unlike main pole S which is in the corresponding pole area cn the opposite major surface. In similar fashion, the flux from main pole N primarily links with the auxiliary pole S. Very little flux, if any, links main poles N and S, or auxiliary poles N and S. However, if a piece of magnetic material is placed close to the major poles N and S of the wafer magnet 12, the flux linkages between the major poles and the auxiliary poles are broken so that the ux of the auxiliary poles N and S is free to attract or link with objects of magnetic material placed sufficiently close to said auxiliary poles.

A pre-magnetized ceramic wafer magnet assembly particularly suitable for use in the present invention is made from a non-oriented barium ferrite material which is pressed into the shape -of a thin wafer having a center hole. The dimensions in inches of this wafer are: length, 1.00; width, 0.75; thickness, 0.177; hole diameter, 0.18'7. However, as emphasized above, the novel features of the present invention do not necessarily depend upon the particular magnetic assembly shown and/ or described which is but an example of a preferred embodiment.

In FIGURE 4a, a pair of reed contacts 14 and 15 are provided each being made of semi-exible or spring ternper magnetic material. In the embodiment of the invention shown in FIGURE 4, contacts 14 and 15 are normally open when there is little or no flux linkage between N :and S' of wafer 12. However, in FIGURE 4b the magnetic material 16 to be detected is shown adjacent to the main poles S and N so that t-he flux linkages between the unlike auxiliary and main poles is broken because of the phenomenon discussed in connection with FIGURE 1b. The increased number of ilux lines from pole N to pole S' will link both contacts 14 and 15 since these contacts provide a magnetic path of lower resistance than the surrounding environment. Consequently, contact 14 actually becomes a north seeking pole whereas contact 15 becomes a south seeking pole. The increased strength of the magnetic field linking contacts 14 and 15 is calculated to provide an attractive force sufiicient to overcome the spring biased normally open positions of these contacts which thus draws them together. When the magnetic material 16 is removed from the vicinity of main poles S and N, then the flux pattern of the poles on wafer 12 reverts to that shown in FIGURE 4a. Contacts 14 and 15 thereupon open due to their spring-like nature since the strength of poles N and S has been reduced, at least as far as regards the effect that these poles have upon the magnetic attraction between contacts 14 and 15.

It will therefore be appreciated from the above that the novelty of the present invention lies essentially in the provision of two pairs of unlike magnetic poles so arranged that the ux linkages between unlike poles of one pair can only be increased by the increase in ux linkages between unlike poles of the other pair, said latter increase tension exerted to keep these contacts open.

occurring due to the proximity of magnetic material which lowers the resistance of the magnetic path between the unlike poles of said other pair. By providing magnetic contact material to respond to the increased flux linkages between the unlike poles of said first pair, a switch is provided for making or breaking an electrical circuit according to t-he proximity of material in the eld of the poles of said other pair. Although the preferred basic embodiment of the invention utilizes pairs of poles that have different strengths and which are found on faces of the same body, it is not necessary that such be the case. FIGURE la shows that the invention may be constructed wherein unlike poles of a pair need not physically be on the same magnet. Furthermore, electro-magnetic poles may be utilized if a burden load on a source of energy is deemed satisfactory.

If the auxiliary poles N and S have strengths great enough to normally force contacts 14 and 15 closed even in the absence of material 16, then it may be necessary to provide a magnetic shunt 17 between said poles in order that the flux actually linking contacts 14 and 15 be reduced to a point where these contacts normally remain open. This shunt 17 in FIGURE 5 is made of magnetic material of such cross-sectional area that it is substantially saturated by the flux linking N and S even during the absence of material 16. In this case, little or no flux will link contacts 14 and 15 since the environment path between the auxiliary poles and these contacts is of greater resistance than the path provided by shunt 17. However, upon material 16 being moved in proximity with the main poles S and N, the increased llux linkages between N and S must take the environment path via contacts 14 and 15 due to the saturation of shunt 17. Consequently, this modification of the basic circuit of FIGURE 4 may be necessary in the event of magnets of large size or those that have been magnetized in a stronger field than is necessary to get proper action of the switch. Hence, the incorporation of shunt 17 provides a very convenient way to get proper operation of the switch without requiring a high degree of precision in the formation of the auxiliary poles N and S. This shunt arrangement may also be utilized with success when two different magnets, such as shown in FIGURE 1a, are employed, since very often in this case the poles all have the same strengths.

If the auxiliary poles N and S' have insuflicient strength to close contacts 14 and 15 even during the presence of material 16, then it may be necessary to provide a biasing larrangement as shown in FIGURE 6. In this modification of the basic switch arrangement, a biasing permanent magnet 18 is placed in such a manner that the ux from its north seeking pole N links with contact 14, while the flux from the south pole S of the magnet links with contact 15. The flux field of magnet 18 by itself is insuicient to provide an attracting force between contacts 14 and 15 large enough to overcome the spring However, upon bringing a piece of material into proximity with the main piles S and N of wafer 12, the flux contributed by auxiliary poles N' and S and added to the ux from magnet 18 is suflicient to set up a force closing the contacts 14 and 15. It will be appreciated that the liux pattern contributed by auxiliary poles N and S in FIGURE 6 is the same flux pattern shown in FIGURE 4b, so that summation of the lines of force from magnet 18 and wafer 12 occurs within the material comprising contacts 14 and 15. However, it should be appreciated that the field strength necessary to keep contacts 14 and 15 closed after they have once been forced together is normally less than the value necessary to move them from their normally open position to their closed position. Therefore, if the switch operation is to be such that contacts 14 and 15 are forced open whenever there is no material in proximity with main poles S and N, the strength of 6 the field contributed by magnet 18 should be less than the field necessary to maintain contact.

The provision of a biasing magnet 18 provides a simple way for changing the mode of operation of the basic switch in a manner illustrated in FIGURE 7.` In FIG- URE 7, the field strength provided by the poles of magnet 18 is by itself insufficient to initiate closing of contacts 14 and 15. However, magnet 18 field strength is suflicient by itself to maintain contacts 14 and 15 in their closed position until a reset electro-magnet 19 is energized. The energization of magnet 19 causes the formation of north and south poles in the position shown which set up flux lines within contacts 14 and 15 in a direction calculated to cancel the effect of the flux from magnet 18. Consequently, the operation of FIGURE 7 is as follows: Assuming that contacts 14 and 15 are normally biased to an open position due to the spring-like nature of the contact material, a bar 16 must be placed in proximity with main poles S and N of wafer 12 in order that these contacts can be closed in the manner described in connection with FIGURE 6. When once the material 16 has been withdrawn from the sensing area adjacent main poles S and N, the field contributed by magnet 18 is sufficient to maintain contacts 14 and 15 closed until the subsequent energization of magnet 19. It may be noted in connection with both FIGURES 6 and 7 that the field strength of biasing magnet 18 can be controlled by changing the size of said magnet and/or by changing the distance between the magnet and the positions of contacts 14 and 15.

A further modification of the basic switch is that shown in FIGURE 8 wherein the biasing-magnet 18 is reversed so that its north pole N links with contact 15 and its south pole S links with contact 14. Wafer magnet 12 is still retained in the position shown in the preceding figures, in that its auxiliary north pole N links with contact 14 while its auxiliary south pole S' links with contact 15. In this embodiment, the field st-rength of magnet 18 by itself is sufficient to overcome the normally open tendency of the spring contact members 14 and 15 and so maintains them closed in the absence of material 16. However, upon such material 16 being sensed by poles S and N, the lines of force now contributed by auxiliary poles S and N is such as to oppose and efectually cancel the lines of force from magnet 18. In this case, the net amount of flux linking contacts 14 and 15 is reduced below the level necessary to provide the minimum attracting force necessary to keep t-hem closed. Consequently, contacts 14 and 15 are forced open as long as material 16 remains in the sensing are'a of magnet 12. Upon removal of this material, the flux from the auxiliary poles N and S is once again short-circuited to their main poles so as to again allow the field from magnet 18 to attract and hold closed contacts 14 and 15. FIGURE 8 therefore discloses 'a normally closed switch which is only opened by the proximity of material in the sensing area adjacent to main poles S and N.

Reference is now made to FIGURE 9 which shows a slight modification of the embodiment in FIGURE 8. If the flux from the biasing magnet 18 by itself is not suficient to attract contacts 14 and 15, but is only sufficient to maintain them closed when once attracted, then the provision of a magnet 19 with north and south poles as shown accomplishes the following. If contacts 14 and 15 are open, then current of correct polarity into magnet 19v forms north and south poles which generate flux to aid the flux from magnet 18 in linking contacts 14 and 15. This additional fiux from magnet 19 thereupon provides sufiicient force between contacts 14 and 15 so that they close. If magnet 19 is now de-energized, the field contributed by magnet 18 is suflicient by itself to maintain contacts 14 and 15 in their closed position until material 16 is brought within the sensing area of magnet 12 so that the llux from auxiliary poles N' and S now cancels the magnet 18 flux in the manner described in connection with FIGURE 8. Thereupon, contacts 14 and 15 open. After the material 16 has been removed from the sensing area of magnet 12, a subsequent energization of magnet 19 is required before contacts 14 and 1S can again be closed.

FIGURE 10 is still another embodiment of the inven- Ytion which utilizes a biasing magnet 18I having its poles in `the position shown, as well as an electro-magnet 19 which, when energized, forms poles as illustrated. In this ernbodiment, which is similar to that shown in FIGURE 8, the field contributed by magnet 1S is by itself sufficient `to force contacts 14 and 15 into their closed position and maintain them there until its field is cancelled. Cancellation of the field from magnet 18 is caused by the concurrent energization of magnet 19 as well as the proximity of magnetic material 16 in the sensing area of magnet 12 adjacent main poles N and S. Unless both of these latter conditions occur at the same time, there is insufii cient cancellation of the magnet 18 field to cause contacts 14 and 15 to open. For example, assume that magnet 19 is de-energized at the time that material 16 is brought into the sensing area of magnet 12. Although the flux from the auxiliary poles N and S increases and effectually cancels a portion of the magnet 18 liux, this cancellation is not suficient to allow contacts 14 and 15 to spring open. On the other hand, if only magnet 19 is energized and without magnet 12 sensing the proximity of material 16, then the magnet 19 field strength is again insufficient to cancel enough of the magnet 18 field intensity so as to allow contacts 14 and 15 to open. However, when both magnet 19 and the auxiliary .poles of magnet 12 contribute flux, then the addition of said flux in a direction opposing the flux from magnet 1S is sutlicient to reduce the attractive force between contacts 14 and 15 below that necessary to maintain them in a closed position. In effect then, the switch arrangement of FIGURE 10 requires that a conditioning signal be applied to electro-magnet 19 of proper polarity in order that proximity of magnet material in the sensing area of magnet 12 will cause the contacts to open. Upon cessation of one or both of the fields from magnets 19 and magnets 12, magnet 18y again forces contacts 14 and 15 to close in the manner shown.

In all of the preceding FIGURES 6 through l0, biasing magnet v18 can just as well be electro-magnetic in nature instead of permanent. Furthermore, electro-magnet 19 in FIGURES 7, 9, and l0 might well be replaced with a magnetic assembly similar to unit 12 so that the switch would have two separate sensing areas each detecting the proximity of the same or different magnetic bodies thereto. In such an embodiment along the lines of FIG- URE 7, for example, the proximity of one magnetic body to one sensing area would close contacts 14 and 15, while the proximity of a different magnetic body to the other sensing area, at a subsequent time, would open these contacts.

Although all of the previous figures show two spring reed contacts 14 and 15 each capable of motion toward and away from one another, other contact arrangements may be provided. For example, a single moving armature may be pivoted at one end in the nature of a singlepole single-throw switch so that its free end moves toward and away from a fixed contact depending upon the magnitude of the field linking it with the auxiliary poles N and S of a magnet 12. It would also be possible with a single armature type of switch to use biasing magnets and/ or solenoids in the manner shown in FIGURES 6 through 10. Therefore, the basic novel principle of operation of the present invention may be adapted for use in a variety of environments.

FIGURES 11 and 12 of the drawings show two ways in which the novel switch of the present invention may be fabricated for commercial uses. In FIGURE l1, a switch `having a mode of operation described in connection with FIGURES 4a and 4b is shown. Contacts 14 and 15 are located in a glass enclosure 20 which is hermetically sealed with glas-s to metal seals at the points where the contacts emerge from the glass wall. The glass enclosure 20 itself is filled with a non-conducting gas so that no current liows when the contacts are open and an impressed across the contacts. Conductors 21 and 22 are mechanically and electrically connected to their respective contacts 14 and 15 and extend through the hollow interior of a mounting conduit 23 in order to provide access to the external electrical circuit that they are controlling. Conduit 23 has external threads and is placed in a plastic potting compound 24 prior to the setting of the compound after it has been poured. The plastic compound 24 actually provides a case for the glass closure 20 with the latter being potted therein. A lock nut 25 may be provided having internal threads that are engaged to the external threads of conduit 25. This lock nut may have flats to accommodate a wrench to facilitate the connection of conduit 23 to an external supporting object. The lower face of lock nut 25 is in contact with the plastic potting material 24, which greatly improves the mechanical bond between the conduit 23 and compound 24. Magnet 12 is a ceramic type wafer magnet of the type described and so magnetized to form two main poles on the surface .adjacent the exterior of potting compound 24. In addition, two auxiliary .poles are formed on the surface of the wafer 12 which is adjacent the glass container 20. The lower face of magnet 12, which is that containing the main poles, may be fiush with the lowerrnost edge of the plastic compound 24 in the manner shown in FIG- URE 11.

FIGURE 12 shows another embodiment of switch mounting means, said switch also having the mode of operation described in connection with FIGURES 4a and 4b. This embodiment is very much like that shown in FIGURE l1 in that the -switch contacts 14 and 15 are hermetically sealed in a glass envelope 2f) which in turn is encased by a potting compound 24. External conductors for contacts 14 and 15 are provided by threaded rods 26 and 27 which are secured both mechanically and electrically to their associated contacts 14 and 15. Portions of the threaded rods 26 and 27 are also encased in the potting compound 24 but extend therethrough via internal threaded pieces 28 and 29 which in turn are partly submerged in the plastic potting compound which affords resistance to the turning of the threaded rods as nuts 3f) and 31 are tightened. The potted switch is mounted on a plate 32 that is designed to serve as the cover for a standard conduit fitting 33. Conduit fitting 33 has an internal threaded hub 34 designed to be `supported by an external conduit screwed therein. The conduit 34 is also used to house wires from the external electrical circuit to threaded rods 26 and 27. Gaskets 35 are used to pro vide a water and dust tight seal between the cover plate 32 and the conduit fitting 33 to which it is attached by means of screws 35. Cover plate 32 should be made of non-magnetic material since it is adjacent the sensing area located opposite the main poles of the ceramic wafer 12.

Although only the basic switch in FIGURE 4 has been shown mounted in the manner of FIGURES 11 and l2, it is obvious that modifications of this basic switch as show n in FIGURES 5 through 10 may also be mounted in a similar fashion. Thus, while preferred embodiments of the invention have been shown and illustrated in de tail, it is obvious that many modifications may be made thereto by persons skilled in the art without departing from the spirit of the invention as defined in the appended claims.

I claim:

1. A switching device which comprises:

(a) a first pair of unlike magnetic pole surfaces, and

means to support said first pair pole surfaces in generally a same first plane so that both said first pair pole surfaces face in generally a same first direction, said last named means further supporting said first pair pole surfaces in a spaced apart relationship such that a first fiux path is formed therebetween which lies therefrom in said first direction and whose reluctance is inversely proportional to the degree of proximity of magnetic material thereto;

(b) a second pair of unlike magnetic pole surfaces, and means to support said second pair pole surfaces in generally a same second plane parallel to said first plane so that both said second pair pole surfaces face in generally a same second direction opposite to said first direction, said last named means further supporting said second pair pole surfaces in a spaced apart relationship such that a second iux path is formed therebetween which lies therefrom in said second direction and with each said second pair pole surface being in line with an unlike pole surface of said first pair so as to form other linx paths between the unlike pole surfaces in difierent pairs, whereby the value of fiux in said second fiux path varies inversely with the reluctance of said first flux path;

(c) switch apparatus responsive to a particular fiux value, and means positioning said switch apparatus adjacent to said second pair pole surfaces in said second direction therefrom so as to be within said second flux path; and

(d) magnetic shunt material positioned in said second fiux path and parallel with said switch apparatus to provide a shunt therearound, said magnetic shunt material being sufficiently saturated by iiux in said second flux path such that said predetermined flux value in said switch apparatus is absent or present for the absence or presence, respectively, of magnetic material in said first flux path.

2. A switching device according to claim 1 wherein said switch apparatus comprises electrical contact means normally biased open for fiux values other than said particular value, but which close for said particular value of fiux.

3. A switching device according to claim 1 wherein said switch apparatus comprises electrical contact means normally biased closed for fiux values other than said particular value, but which open for said particular value of fiux.

4. A switching device which comprises:

(a) a thin wafer of magnetizable material less thick than wide and long, whose thickness dimension is boundediby opposed parallel first and second major faces, and having a first pair of spaced apart unlike permanent magnetic pole areas on said first major face and a second pair of spaced apart unlike permanent magnetic pole areas on said second major face which are arranged so that the north and south pole areas of said first pair are respectively opposite the south and north pole areas of said second pair, with Said first major face being a sensing region for magnetic material brought into proximity with the magnetic field of said first pole pair such that the magnetic field of said second pole pair increases with an increase inthe magnetic field of said first pole pair;

(b) switch apparatus responsive to a particular flux value which is positioned externally to said wafer and adjacent said second major face in the magnetic field of said second pole pair; and

(c) magnetic shunt material located externally to said Wafer in the magnetic field of said second pole pair and between said second major face and said switch apparatus to-provide a shunt therearound, said magnetic shunt material being sufficiently saturated by flux between said second pole pair such that said predetermined fiux value in said switch apparatus is absent or present for the absence or presence, respectively, of magnetic material in proximity with the magnetic field of said first pole pair.

5. A switching device according to claim 4 wherein said switch apparatus comprises a pair of cooperating electrical contacts normally open for fiux values less than said predetermined flux value.

6. A switching device according to claim 4 wherein said switch apparatus comprises a pair of cooperating normally open electrical contacts, and means located adjacent to said contacts for generating a magnetic field in said contacts to bias them closed, said last named magnetic field having a direction opposed to the direction of the magnetic field of said second pole pair.

7. A switching device according to claim 4 wherein said switch apparatus comprises a pair of cooperating electrical contacts normally open for fiux values less than said predetermined flux value, means located adjacent to said contacts for generating a first magnetic field in said contacts to maintain them closed when once they have been closed, said first magnetic field having the same direction as the direction of the magnetic field of said second pole pair, and means located adjacent said contacts and selectively operable to generate a second magnetic field in a direction and of a strength to cancel said first magnetic field.

8. A switching device according to claim 4 wherein said switch apparatus comprises a pair of cooperating electrical contacts normally open for fiux values less than said predetermined fiux value, means located adjacent to said contacts for generating a first magnetic field in said contacts to maintain them closed when once they have been closed, said first magnetic field having a direction opposed to the direction of the magnetic field of said second pole pair, and means located adjacent to said contacts and selectively operable to generate a second magnetic field in said contacts in the same direction as said first magnetic field for closing said contacts.

9. A switching device-according to claim 4 wherein said switch apparatus comprises a pair of cooperating electrical contacts normally open for fiux values less than said predetermined flux value, means located adjacent to said contacts for generating a rst magnetic field in said contacts to bias them closed, said first magnetic field having a direction opposed to the direction of the magnetic field of said second pole pair, and means located adjacent to said contacts and selectively operable to generate a second magnetic field in said contacts in opposition to said first magnetic field.

References Cited by the Examiner UNITED STATES PATENTS 1,891,568 12/32 Morris et al. 200-87 2,180,701 11/39 Wilson 20D-122 2,231,105 2/ 41 Block et al. 200-87 2,431,319 11/ 47 Ellwood 200-87 2,877,361 3/59 Chase 340-274 2,896,043 7/59 Andrews 200-87 2,973,414 2/ 61 Bossemeyer 200-87 3,009,033 11/ 61 Werts 200-87 3,011,036 11/ 61 LaRocca 200-87 3,022,398 2/ 62 Abel 200-87 3,040,143 6/ 62 Peay et al. 200-87 3,043,931 7/ 62 Gruber 200-87 3,056,000 9/ 62 Lucas 200-87 3,114,020 12/ 63 Hall 200-87 BERNARD A. GILHEANY, Primary Examiner.

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Classifications
U.S. Classification335/207, 324/228, 335/153
International ClassificationH01H36/00
Cooperative ClassificationH01H36/002
European ClassificationH01H36/00B2B