Abstract:
A sensor used to sense the position of an attached movable object. The sensor can be mounted to a pneumatic actuator. The sensor includes a housing that has a pair of cavities or pockets separated by a wall. A magnet carrier is positioned within one of the cavities and a magnet is coupled to the magnet carrier. The magnet carrier is coupled to the moveable object. A magnetic sensor is positioned in the other of the cavities. The magnetic sensor generates an electrical signal that is indicative of a position of the movable object.

Description:
CROSS-REFERENCE TO RELATED AND CO-PENDING APPLICATIONS 
     This application is a continuation application which claims the benefit of U.S. patent application Ser. No. 12/592,170 filed on Nov. 20, 2009, now U.S. Pat. No. 8,400,142 issued on Mar. 19, 2013, entitled Linear Position Sensor with Anti-Rotation Device, the disclosure of which is explicitly incoporated herein by reference, as are all references cited therein, which claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 61/200,244 filed on Nov. 26, 2008, the contents of which are explicitly incorporated by reference, as are all references cited therein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to linear position sensors and, more specifically, to devices to prevent the rotation of the magnet used in a non-contacting linear position sensor. 
     BACKGROUND OF THE INVENTION 
     Position sensing is used to electronically monitor the position or movement of a mechanical component. The position sensor produces an electrical signal that varies as the position of the component in question varies. Electrical position sensors are included in many products. For example, position sensors allow the status of various automotive components to be monitored and controlled electronically. 
     A position sensor needs to be accurate, in that it must give an appropriate electrical signal based upon the position measured. If inaccurate, a position sensor may hinder the proper evaluation and control of the position of the component being monitored. 
     Typically, it is also a requirement that a position sensor be adequately precise in its measurement. However, the precision needed in measuring a position will obviously vary depending upon the particular circumstances of use. For some purposes, only a rough indication of position is necessary; for instance, an indication of whether a valve is mostly open or mostly closed. In other applications, more precise indication of position may be needed. 
     A position sensor should also be sufficiently durable for the environment in which it is placed. For example, a position sensor used on an automotive valve may experience almost constant movement while the automobile is in operation. Such a position sensor should be constructed of mechanical and electrical components adequate to allow the sensor to remain sufficiently accurate and precise during its projected lifetime, despite considerable mechanical vibrations and thermal extremes and gradients. 
     In the past, position sensors were typically of the “contact” variety. A contacting position sensor requires physical contact to produce the electrical signal. Contacting position sensors typically consist of potentiometers that produce electrical signals which vary as a function of the component&#39;s position. Contacting position sensors are generally accurate and precise. Unfortunately, the wear due to contact during movement has limited their durability. Also, the friction resulting from the contact can degrade the operation of the component. Further, water intrusion into a potentiometric sensor can disable the sensor. 
     One advancement in sensor technology has been the development of non-contacting position sensors. A non-contacting position sensor (“NPS”) does not require physical contact between the signal generator and the sensing element. Instead, an NPS utilizes magnets to generate magnetic fields that vary as a function of position, and devices to detect varying magnetic fields to measure the position of the component to be monitored. Often, a Hall effect device is used to produce an electrical signal that is dependent upon the magnitude and polarity of the magnetic flux incident upon the device. The Hall effect device may be physically attached to the component to be monitored and thus moves relative to the stationary magnet(s) as the component moves. Conversely, the Hall effect device may be stationary with the magnet(s) affixed to the component to be monitored. In either case, the position of the component to be monitored can be determined by the electrical signal produced by the Hall effect device. 
     The use of an NPS presents several distinct advantages over the use of a contacting position sensor. Because an NPS does not require physical contact between the signal generator and the sensing element, there is less physical wear during operation, resulting in greater sensor durability. The use of an NPS is also advantageous because the lack of any physical contact between the items being monitored and the sensor itself results in reduced drag. 
     While the use of an NPS presents several advantages, there are also several disadvantages that must be overcome in order for an NPS to be a satisfactory position sensor for many applications. Irregularities or imperfections in the magnet can compromise the precision and accuracy of an NPS. The accuracy and precision of an NPS can also be affected by the mechanical vibrations and perturbations likely to be experienced by the sensor which, in turn, can cause the magnet or magnet carrier to rotate. Because there is no physical contact between the item to be monitored and the sensor, it is possible for the magnet or magnet carrier to be knocked out of alignment as a result of such vibrations and perturbations. A misalignment or rotation of the magnet relative to the sensor can result in the measured magnetic field at any particular location not being what it would be in the original alignment. Because the measured magnetic field can be different than that when properly aligned, the perceived position can be inaccurate. Linearity of magnetic field strength and the resulting signal is also a concern. 
     SUMMARY OF THE INVENTION 
     The present invention is directed broadly to a linear position sensor which comprises a housing, a magnet carrier located in the housing, a magnet located in the magnet carrier, and several different embodiments of anti-rotation means or devices associated with the magnet carrier for preventing the rotation of the magnet outside of allowable variations in rotational movement and eliminating the risk of undesired magnetic field measurements and incorrect sensor signal outputs. 
     More specifically, in one embodiment, the magnet carrier includes a base having at least one receptacle defined therein and the anti-rotation means comprises an anti-rotation plate which is coupled to the housing and the magnet carrier and the magnet carrier includes at least one finger which extends into the receptacle in the base of the magnet carrier to prevent the rotation of the magnet carrier and thus the rotation of the magnet. 
     In one embodiment, the base of the magnet carrier includes a peripheral edge and the receptacle is defined by a groove formed in the peripheral edge of the magnet carrier. 
     In another embodiment, the base of the magnet carrier includes a lower surface and the receptacle is defined by a groove formed in the lower surface of the magnet carrier. The groove may be a circumferentially extending slot formed in the lower surface of the magnet carrier. 
     In a further embodiment, the base of the magnet carrier includes opposed upper and lower surfaces and the receptacle is defined by a through-hole which extends between the upper and lower surfaces of the magnet carrier. 
     In yet another embodiment, the anti-rotation plate includes at least one interior slot formed therein which defines the finger and the finger is adapted to abut and exert a force against the lower surface of the base of the magnet carrier. 
     In yet a further embodiment, the magnet carrier includes a magnet housing having an interior surface with a key defined by a projection and the anti-rotation means comprises a groove in the magnet. The projection in the magnet carrier extends into the groove in the magnet to prevent the rotation of the magnet. The projection may be formed in an interior side surface of the magnet housing and the groove may be defined in an exterior side surface of the magnet. Alternatively, the projection may be formed in an interior base surface of the magnet housing and the groove may be defined in an exterior bottom surface of the magnet. Still further, the magnet housing may include at least one prong extending from a peripheral top edge thereof and another groove may be defined in an exterior top surface of the magnet and the prong extends into the groove in the exterior top surface of the magnet. 
     There are other advantages and features of this invention which will be more readily apparent from the following detailed description of the embodiments of the invention, the drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the invention can best be understood by the following description of the accompanying drawings as follows: 
         FIG. 1  is a part vertical cross-sectional view, part perspective view of a linear position sensor with a first embodiment of a magnet carrier/anti-rotation plate combination or device in accordance with the present invention; 
         FIG. 2  is an enlarged perspective view of the magnet carrier/anti-rotation plate combination shown in  FIG. 1 ; 
         FIG. 3  is an enlarged exploded perspective view of the magnet carrier and anti-rotation plate shown in  FIGS. 1 and 2 ; 
         FIG. 4  is an enlarged broken perspective view of a second embodiment of a magnet carrier/anti-rotation plate combination in accordance with the present invention; 
         FIG. 5  is an enlarged vertical cross-sectional view of the magnet carrier/anti-rotation plate embodiment of  FIG. 4  coupled to the base in the interior of a linear position sensor as shown in  FIG. 1 ; 
         FIG. 6  is an enlarged exploded perspective view of the magnet carrier and anti-rotation plate combination shown in  FIGS. 4 and 5 ; 
         FIG. 7  is an enlarged broken part vertical cross-sectional view, part perspective view of a third embodiment of a magnet carrier/anti-rotation plate combination in accordance with the present invention coupled to the base in the interior of a linear position sensor as shown in  FIG. 1 ; 
         FIG. 8  is an enlarged exploded perspective view of the magnet carrier and anti-rotation plate shown in  FIG. 7 ; 
         FIG. 9  is an enlarged bottom perspective view of the magnet carrier/anti-rotation plate combination shown in  FIGS. 7 and 8 : 
         FIG. 10  is an enlarged top broken perspective view of another embodiment of a magnet carrier/anti-rotation plate combination in accordance with the present invention coupled to the base in the interior of a linear position sensor as shown in  FIG. 1 ; 
         FIG. 11  is an enlarged vertical cross-sectional view of the magnet carrier/anti-rotation plate combination of  FIG. 10 ; 
         FIG. 12  is a broken exploded perspective view of the magnet carrier and anti-rotation plate combination of  FIG. 10 ; 
         FIG. 13  is an enlarged perspective view of yet another magnet carrier/anti-rotation plate combination in accordance with the present invention; 
         FIG. 14  is an enlarged broken vertical cross-sectional view of the magnet carrier/anti-rotation plate combination of  FIG. 13  coupled to the base in the interior of a linear position sensor as shown in  FIG. 1 ; 
         FIG. 15  is an enlarged exploded perspective view of the magnet carrier and anti-rotation plate combination shown in  FIGS. 13 and 14 ; 
         FIG. 16  is an enlarged exploded perspective view of a magnet carrier/anti-rotation magnet combination in accordance with the present invention; 
         FIG. 17  is an enlarged horizontal cross-sectional view of the magnet carrier/anti-rotation magnet combination of  FIG. 16  with the anti-rotation magnet secured in the magnet carrier; 
         FIG. 18  is an enlarged vertical cross-sectional view of another embodiment of a magnet carrier/anti-rotation magnet combination in accordance with the present invention; and 
         FIG. 19  is an enlarged broken top perspective view of the magnet carrier/anti-rotation magnet combination of  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     A first embodiment of an anti-rotation magnet carrier/anti-rotation plate assembly or device or combination  25  in accordance with the present invention is shown in  FIGS. 1-3  which comprises an anti-rotation disc or plate  27  and a magnet carrier  29 . 
     Anti-rotation disc or plate  27  has a circular solid base  28 , an outer circumferentially extending peripheral edge  31 , a central through-hole or aperture  33 , and a plurality of tabs or fingers  35  and  37  projecting outwardly and upwardly away from the peripheral edge  31  and extending around the base  28  in a spaced-apart, equidistant, and alternating relationship. Anti-rotation disc or plate  27  can be stamped from sheet metal. The tabs or fingers  35  are wider and shorter than the tabs or fingers  37 . 
     Magnet carrier  29  has a generally circular base  41  with a circumferentially extending outer peripheral edge  43 ; a vertical, hollow magnet tube or housing  45  extending generally normally upwardly from a central portion of the base  41 ; and a plurality of receptacles in the form of recesses, grooves, notches, or slots  47  which are formed in the peripheral edge  43  and extend around the base  41  in a spaced-apart, equidistant relationship. Magnet carrier  29  may be made from any suitable thermoplastic material. 
     As shown in  FIG. 1 , anti-rotation disc or plate  27  is seated flat against the base plate  80  of a cup  82  located in the interior of linear position sensor  10  in a relationship wherein the central aperture  33  in anti-rotation plate  27  is in alignment with a central aperture  85  defined in the base plate  80  of cup  82  of linear position sensor  10 . Linear position sensor  10  additionally comprises an elongate, generally cylindrically-shaped shaft  84  which extends through the aligned apertures  33  and  85  in the plate  27  and base  80  respectively. The shaft  84  includes a head  86  having a width greater than the diameter of the shaft  84  and a circumferential recess or groove defined in the outer surface on the shaft  84  below the head  86  which defines a shoulder  90  spaced from the head  86 . The anti-rotation plate  27  and base  80  together with a portion of a membrane  87  located below the base  80  and another plate  89  located below the membrane  87  are sandwiched between the head  86  and the shoulder  90  of shaft  84  to clamp the plate  27  to the base  80  of the cup  82  and keep the plate  27  from moving or rotating relative to the cup  82 . 
     As shown in  FIGS. 1 and 2 , magnet carrier  29  is seated over the anti-rotation plate  27  in a relationship wherein the lower face of the base  41  of magnet carrier  29  is seated in abutting relationship against the upper face of the base  28  of anti-rotation plate  27 ; the peripheral edge  43  of the base  41  of magnet carrier  29  is abutted against the interior face of each of the tabs  35  on the base  28  of anti-rotation plate  27 ; and fingers  37  are aligned with the notches  47 . The fingers  37  are bent inwardly from their  FIG. 3  positions to their crimped  FIGS. 1 and 2  positions in which the fingers  37  are located in the respective notches  47  and abutted against surface  41  of magnet carrier  29  to prevent the magnet carrier  29  from rotating relative to the plate  27  which, in turn, prevents the magnet  100  ( FIG. 1 ) in magnet carrier  29  from rotating relative to the sensor  102  ( FIG. 1 ) outside of allowable variations of rotational movement to eliminate the risk of unacceptable deviations in the signal generated by the sensor  102 . This, of course, is important inasmuch as any deviations in the rotational movement of magnet  100  from the magnet&#39;s original programmed state can induce undesired magnetic field variations and cause incorrect signal outputs. 
     Another embodiment of anti-rotation assembly  125  in accordance with the present invention is shown in  FIGS. 4-6 . 
     Anti-rotation assembly  125  comprises an anti-rotation disc or plate  127  and a magnet carrier  129 . Anti-rotation disc or plate  127  has a circular solid base or plate  128 , an outer circumferentially extending edge  131 , a central aperture  133 , and a plurality of tabs  137  projecting outwardly and upwardly from the edge  131  of plate  127  and extending around the base  128  in equidistant, spaced-apart relationship. The base  128  additionally defines a plurality of interior spaced-apart, equidistant, generally U-shaped slots  130  defining a plurality of circumferentially extending interior raised pre-stressed prongs, tabs, or fingers  132 . Anti-rotation disc or plate  129  can be stamped from sheet metal. 
     Magnet carrier  129 , which may be made from any suitable thermoplastic material, includes a generally circular base  141  having an outer circumferentially extending peripheral edge  143  and a central generally cylindrical, hollow magnet tube or housing  145  extending upwardly from the center of the base  141 . 
     As shown in  FIG. 5 , anti-rotation disc or plate  127  is seated on the base  80  of the cup  82  in the interior of linear position sensor  10  and the shaft  84  secures the plate  127  against rotational movement relative to the base  80  in the same manner as the plate  27  of anti-rotation assembly  25 , and thus the earlier description with reference to the attachment of the plate  27  of assembly  25  to the base  80  is incorporated herein by reference. 
     As shown in  FIGS. 4 and 5 , the bottom face or surface of the base  141  of magnet carrier  129  is seated against the upper face or surface of the base  128  of plate  127  in a relationship wherein the prongs  132  in the base  128  of plate  127  abut against the bottom surface of the base  141  of magnet carrier  129 . Tabs  137  on the base  141  of magnet carrier  129  are bent and crimped inwardly into abutting relationship with the top face or surface of the base  141  to secure the base  141  and thus the magnet carrier  129  to the plate  127 , thus preventing the rotation of the magnet carrier  129  relative to the plate  127  and the rotation of magnet  100  ( FIG. 1 ) relative to the sensor  102  ( FIG. 1 ) outside of allowable variations in rotational movement to eliminate the risk of undesired magnetic field measurements and incorrect sensor signal outputs. 
     According to this embodiment, the crimp force exerted by the tabs  137  on the base  141  exerts a downward force against the base  141  which, in turn, causes the raised pre-stressed prongs or tabs  137  on plate  127  to flatten out. The pre-stress prongs  137 , however, are also adapted to flex with the thermoplastic material of the base  141  as a result of thermal exposure to reduce the effects of creep and eliminate the rotation of the magnet carrier  129 . 
     Another embodiment of an anti-rotation assembly  225  in accordance with the present invention is shown in  FIGS. 7-9 . Anti-rotation assembly  225  comprises an anti-rotation disc or plate  227  and a magnet carrier  229 . 
     Anti-rotation disc or plate  227  has a circular base  228 , an outer circumferential peripheral edge  231 , a central aperture  233 , and a plurality of prongs  237  extending outwardly and generally normally upwardly from the peripheral edge  231 . In the embodiment shown, prongs  237  extend around the base  228  in an equidistant, spaced-apart relationship. Each of the prongs  237  has a pair of sharp points  238  that extend generally normally inwardly from opposed sides of each of the prongs  237 . Anti-rotation disc or plate  227  may be stamped from sheet metal. 
     Magnet carrier  229 , which may be made from any suitable thermoplastic material, has a generally circular base  241  with an outer circumferentially extending peripheral edge  243 ; a vertical, cylindrical, hollow magnet or housing tube  245  extending generally upwardly from a central portion of the top surface or face of the base  241 ; and an annular circumferentially extending interior receptacle in the form of a slot  244  formed and extending into the bottom surface or face of base  241 . 
     As shown in  FIG. 7 , the plate  227  of anti-rotation assembly  225  is seated on the base  80  of the cup  82  in linear position sensor  10  and is rigidly connected to the shaft  84  of linear position sensor  10  in the same manner as the plate  27  of anti-rotation assembly  25  and thus the earlier description with reference to assembly  25  is incorporated herein by reference. 
     As shown in  FIGS. 7 and 9 , the bottom face or surface of the base  241  of magnet carrier  229  is seated against the upper face or surface of the base  228  of the plate  227  in a relationship wherein the prongs  237  on plate  227  are aligned with and extend into respective portions of the slot  244  in the bottom face or surface of the base  241  of magnet carrier  229 . The sharp points  238  on each of the prongs  237  have a length which is greater than the width of the slot  244  so that the points  238  wedge into the material of the base  241  upon insertion of the prongs  237  in base  241  to secure the magnet carrier  229  to the plate  227  and prevent the rotation of the magnet carrier  229  relative to the plate  227  which, in turn, prevents the rotation of the magnet  100  ( FIG. 1 ) relative to the sensor  102  ( FIG. 1 ) outside of allowable variations in rotational movement to eliminate the risk of undesired magnetic field measurements and incorrect sensor signal outputs. 
       FIGS. 10-12  depict a further embodiment of an anti-rotation assembly  325  in accordance with the present invention which comprises an anti-rotation disc or plate  327  and a magnet carrier  329 . 
     Anti-rotation disc or plate  327  has a circular base  328 , an outer peripheral circumferential edge  331 , a central aperture  333 , and a plurality of fingers  337  projecting outwardly and generally normally upwardly from the peripheral edge  331  and extending around the base  328  in an equidistant, spaced-apart relationship. Anti-rotation disc or plate  327  may be stamped from sheet metal. 
     Magnet carrier  329 , which may be made from any suitable thermoplastic material has a generally circular base  341  with an outer peripheral circumferential edge  343 ; a vertical, hollow, cylindrical magnet tube or housing  345  extending normally upwardly from the center of the top surface of the base  341 ; at least one receptacle in the form of a recess, groove, notch, or slot  344  formed in the peripheral edge  343  of base  341 ; and a plurality of interior receptacles in the form of through-holes or openings  346  defined in the base  341  and extending between the top and bottom surfaces thereof. Through-holes  346  extend around the base  341  in an equidistant, spaced-apart relationship. 
     As shown in  FIG. 11 , anti-rotation disc or plate  327  is seated on the base  80  of the cup  82  in linear position sensor  10  and the shaft  84  of linear position sensor  10  couples and secures the plate  327  to the cup  82  in the same manner as described earlier with respect to the plate  27  of anti-rotation assembly  25 , and thus the earlier description with reference to plate  27  is incorporated herein by reference. 
     As shown in  FIGS. 10 and 11 , magnet carrier  329  is located and seated in the interior of the cup  82  of linear position sensor  10  in a relationship wherein the bottom face or surface of the base  341  of magnet carrier  329  is seated against the upper face or surface of the base  328  of the plate  327  in a relationship wherein the fingers  337  on plate  327  are aligned with and extend through respective ones of the through-holes  346  defined in the base  329  of magnet carrier  341  to prevent the rotation of the magnet carrier  329  relative to the plate  327  and thus prevent the rotation of magnet  100  ( FIG. 1 ) relative to the sensor  102  ( FIG. 1 ) outside of allowable variations in rotational measurement to eliminate the risk of undesired magnetic field measurements and incorrect sensor signal outputs. 
     As also shown in  FIGS. 10-12 , linear position sensor  10  additionally comprises an annular outer ring  390  including a tab  392  which extends generally normally outwardly and downwardly from an interior peripheral circumferential edge  394  of ring  390 . 
     Ring  390  is seated in the cup  82  of linear position sensor  10  in a relationship surrounding and abutting against the top surface of the peripheral circumferential edge  343  of the base  341  of magnet carrier  329  with the tab  392  seated in the groove  344  defined in the edge  342  of the base  341  of magnet carrier  329  to prevent the rotation of the ring  390  relative to the magnet carrier  329  and the cup  82 . 
       FIGS. 13-15  depict yet a further embodiment of an anti-rotation assembly  425  in accordance with the present invention which comprises an anti-rotation disc or plate  427  and a magnet carrier  429 . 
     Anti-rotation disc or plate  427  has a circular base  428 , an outer peripheral circumferential edge  431 , a central aperture  433 , a plurality of crimp tabs  437  projecting outwardly and upwardly from the peripheral edge  431 , and a plurality of elongate legs  439  also extending outwardly from the peripheral edge  431 . The fingers  437  and legs  439  extend around the base  428  in a spaced-apart and alternating equidistant relationship. The tabs  437  are shown in  FIG. 15  in their uncrimped position and orientation generally normal to the base  428  of plate  427 . The legs  439  extend outwardly from the peripheral edge  431  of plate  427  in a relationship generally co-planar with the base  429 . Each of the legs  439  includes a distal upturned ear  440  extending generally normally upwardly from the distal end of each of the legs  439 . 
     Magnet carrier  429  has a generally circular base  441  with an outer peripheral circumferential edge  443 , and a vertical, hollow, cylindrical magnet tube or housing  445  extending generally normally upwardly from the center of the base  441 . 
     As shown in  FIG. 14 , the plate  427  is seated and secured to the base  80  of the cup  82  in the interior of linear position sensor  10  and the shaft  84  couples and secures the plate  427  to the cup  82  in the same manner as described earlier with respect to the plate  27  of anti-rotation assembly  25  and thus the earlier description with reference to the plate  27  and assembly  25  is incorporated herein by reference. 
     As additionally shown in  FIG. 14 , the exterior face of each of the ears  440  of the legs  439  of the plate  427  is positioned in abutting relationship with and against the interior face of one of the coils  497  of helical spring  495  which is also located in the interior of the linear position sensor  10  and seated on the base  80  of the cup  82  in linear position sensor  10  to provide for the concentric positioning and compression of the spring  495  in linear position sensor  10  and eliminate the risk of collision and controlling axial force compression in the interior of linear position sensor  10 . 
     As shown in  FIG. 14 , magnet carrier  429  is located and seated in the interior of linear position sensor  10  in a relationship wherein the lower face or surface of the base  441  of magnet carrier  429  is seated against the upper face or surface of the base  428  of plate  427 ; the tube  445  is co-linearly aligned with the shaft  84 ; and the peripheral edge  443  of the base  441  of magnet carrier  429  is abutted against the inside face of respective crimp tabs  437  on plate  427 . The tabs  437  are bent inwardly and crimped into abutting relationship with the top surface or face of the base  429  of magnet carrier  429  to secure the magnet carrier  429  to the plate  427 , thus preventing the rotation of the magnet carrier  429  and the rotation of the magnet  100  ( FIG. 1 ) relative to the sensor  102  ( FIG. 1 ) outside of allowable variations in rotational movement to eliminate the risk of undesired magnetic field and signal variations as described above. 
     Although not shown in any of the FIGURES, it is understood that a compression o-ring may be sandwiched between the lower surface of the base  441  of the magnet carrier  429  and the upper surface of the base  428  of the plate  427  to enhance the crimp action and connection between the plate  427  and magnet carrier  429 . 
       FIGS. 16 and 17  depict an anti-rotation assembly  525  in accordance with the present invention which comprises a magnet carrier  529  and an anti-rotation magnet  590 . 
     Magnet carrier  529  has a generally circular base  541  with an outer peripheral circumferential edge  543  and a vertical, hollow, cylindrical magnet tube or housing  545  extending generally normally upwardly from the center of the base  541 . In the embodiment of  FIGS. 16 and 17 , the peripheral edge  543  of magnet carrier  529  additionally includes a pair of diametrically opposed straight segments  593  and  595  defining a pair of keying features for automated feeding of the magnet carrier  529  during assembly. Tube  545  includes an interior cylindrical surface  544  having a key defined by an elongate projection or bump  546  protruding outwardly therefrom and extending the length of the tube  545  in an orientation generally normal to the base  541 . The interior cylindrical surface  544  of the tube  545  additionally includes a plurality of elongate, spaced-apart, parallel crush ribs  548  projecting outwardly therefrom and extending around the circumference of the interior surface  544  in a relationship spaced from and parallel to the elongate key  546 . 
     The magnet  590  is in the form of an elongate solid cylinder which includes respective top and bottom surfaces  592  and  594  and a side exterior longitudinal surface  596  having an elongate groove or recess  598  defined therein and extending generally between the top and bottom surfaces  592  and  594 . 
     As shown in  FIG. 17 , magnet  590  is slid into and secured in the interior of the tube  545  in a relationship wherein the key  546  in tube  545  is aligned with and extends and protrudes into the groove  598 . The diameter of the tube  545  and the diameter of magnet  590  are such that the ribs  548  in the tube  545  are crushed when magnet  590  is slid into the tube  545 , thus providing for a friction fit between magnet  590  and tube  545 . The combination of the key  546  in tube  545  and groove  598  in magnet  590  eliminates the risk of any rotation of the magnet  590  relative to the tube  545  outside of allowable variations of rotational movement to eliminate the risk of undesired magnetic field measurements and thus incorrect signal variations as described above. 
       FIGS. 18 and 19  depict another anti-rotation assembly  625  in accordance with the present invention which comprises a magnet carrier  629  and an anti-rotation magnet  690 . 
     Magnet carrier  629  has a generally circular base  641  with an outer peripheral circumferential edge  643  and a vertical, hollow, cylindrical magnet tube or housing  645  extending generally normally upwardly from the center of the base  641 . Tube  645  includes an interior cylindrical surface  644  and an interior lower or bottom horizontal base or surface  648  with a key defined by a projection or bump  646  protruding outwardly therefrom. 
     Magnet  690  is in the form of an elongate solid cylinder which includes respective top and bottom surfaces  692  and  694  and a side exterior longitudinal surface  696 . Each of the top and bottom surfaces  692  and  694  includes an elongate groove  697  and  698  formed therein. 
     As shown in  FIG. 18 , magnet  690  is slid into and secured in the interior of tube  645  in a relationship wherein the bottom surface  694  of magnet  690  is abutted against the bottom interior surface or base  648  of the tube  645  and the key  646  extends and protrudes into the groove  698  defined in the bottom surface  694  of magnet  690 . 
     As shown in  FIG. 19 , the magnet carrier  629  and, more specifically, the tube  645  thereof includes a plurality of prongs  672  extending outwardly and inwardly from a top peripheral edge  674  thereof. Two of the prongs  672  are opposed to each other and are positioned and extend into the groove  697  formed in the top surface  692  of the magnet  690 . 
     Thus, according to the invention, the use of a key  646 /groove  698  combination and prong  672 /groove  697  combination eliminates the risk of rotation of the magnet  690  relative to the tube  645  outside of allowable rotational variations to again eliminate the risk of undesired magnetic field and signal variations as described above. 
     While the invention has been taught with specific reference to the embodiments shown, it is understood that a person of ordinary skill in the art will recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.