Patent Publication Number: US-2023162933-A1

Title: Sensor Assemblies

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/487,713, filed Sep. 28, 2021, entitled “SENSOR ASSEMBLIES,” which claims priority to GB2101771.0, filed Feb. 9, 2021, the entire contents of which are incorporated by reference herein. 
    
    
     TECHNOLOGICAL FIELD 
     Examples of the disclosure relate to sensor assemblies, and particularly magnetic proximity sensor assemblies. 
     BACKGROUND 
     Magnetic proximity sensor assemblies for monitoring the position of magnetic or ferromagnetic targets are known. 
     A typical magnetic proximity sensor assembly comprises a switch assembly received in a blind bore of a body tube. The switch assembly comprises a magnetic assembly moveable in the blind bore. The switch assembly also comprises and an operator which extends from the magnetic assembly and serves as a drive for a moving contact positioned between a first contact and a second contact. 
     When a target, such as a magnet or ferrous object, is within the sensing range of the magnetic proximity sensor assembly, the magnetic assembly moves in the blind bore from a magnetically biased position towards the target. In this position of the magnetic assembly, the moving contact is urged by the operator into contact with the first contact to complete a first electrical circuit. 
     In the absence of a target within a sensing range, the magnetic assembly adopts the magnetically biased position in the blind bore. In the magnetically biased position of the magnetic assembly, the moving contact is urged by the operator into contact with the second contact to complete a second electrical circuit. 
     In use, a controller is configured to continuously supply an electrical input signal to the magnetic proximity sensor assembly, and to monitor the electrical output signal. The electrical output signal is different for the first and second electrical circuits. Accordingly, by monitoring the electrical output signal it can be determined whether or not the target is within the sensing range of the magnetic proximity sensor assembly. 
     The switch assembly must be precisely positioned in the blind bore to facilitate the in-use movement of the magnetic assembly. Typically, the blind bore is provided with a varying diameter to provide a shoulder on which the switch assembly is seated at the required position in the blind bore. However, this is both challenging to achieve and difficult to detect from a quality control perspective. 
     BRIEF SUMMARY 
     According to various, but not necessarily all, examples of the disclosure there is provided a magnetic proximity sensor assembly, the magnetic proximity sensor assembly comprising a switch assembly received in a blind bore of a body tube, wherein the switch assembly comprises a magnetic assembly moveable in the blind bore, wherein the switch assembly comprises an operator which extends from the magnetic assembly and serves as a drive for a moving contact positioned between a first contact and a second contact, wherein the magnetic assembly comprises a primary magnet and a biasing magnet, wherein the switch assembly comprises a center magnet interposed between the primary magnet and the biasing magnet, wherein the blind bore has a uniform bore diameter, wherein the magnetic proximity sensor assembly comprises a sleeve in the blind bore contacting the closed end of the blind bore, wherein the switch assembly is seated on the sleeve such that the primary magnet of the magnetic assembly is surrounded by the sleeve. 
     Possibly, the sleeve is configured such that in use movement of the magnetic assembly in the blind bore causes the primary magnet to move only within an area of the blind bore defined by the sleeve. 
     Possibly, the distance between the closed end of the blind bore and the primary magnet is defined by the length of the sleeve. Possibly, the sleeve is configured to space apart the primary magnet and the closed end. 
     The blind bore may be a cylindrical blind bore. 
     Possibly, the switch assembly is seated on a rim of the sleeve. Possibly, the center magnet is comprised in a center housing molding of the switch assembly, wherein the center housing molding is seated on the sleeve. The sleeve may be cylindrical. 
     Possibly, the magnetic proximity sensor assembly comprises a flux sleeve, wherein the switch assembly is seated on the sleeve such that the flux sleeve is also surrounded by the sleeve. 
     Possibly, the first contact is a normally open contact and the second contact is a normally closed contact. 
     The sleeve may comprise Mu-metal. 
     According to various, but not necessarily all, examples of the disclosure there is provided a method of manufacturing a magnetic proximity sensor assembly according to the preceding paragraphs, wherein the method comprises:
         providing a body tube comprising a blind bore, wherein the blind bore has a uniform bore diameter;   inserting a sleeve into the blind bore such that the sleeve contacts the closed end of the blind bore;   inserting a switch assembly into the blind bore;   seating the switch assembly on the sleeve such that the primary magnet of the magnetic assembly is surrounded by the sleeve.       

     The method comprises forming the blind bore by a drilling operation. 
     According to various, but not necessarily all, examples of the disclosure there may be provided examples as claimed in the appended claims. 
    
    
     
       BRIEF DESCRIPTION 
       For a better understanding of various examples that are useful for understanding the detailed description, reference will now be made by way of example only to the accompanying drawings in which: 
         FIG.  1    illustrates a part cross sectional view of a magnetic proximity sensor assembly accordingly to examples of the disclosure; 
         FIG.  2    illustrates an exploded view of the magnetic proximity sensor assembly of  FIG.  1   ; 
         FIG.  3    illustrates a cross sectional view of a part of the magnetic proximity sensor assembly of  FIG.  1    in a first condition; 
         FIG.  4    illustrates a magnification of a part of the part of the magnetic proximity sensor assembly of  FIG.  3   ; 
         FIG.  5    illustrates a cross sectional view of the part of the magnetic proximity sensor assembly of  FIG.  1    in a second condition; 
         FIG.  6    illustrates a magnification of a part of the part of the magnetic proximity sensor assembly of  FIG.  5   ; 
         FIG.  7    illustrates a cross sectional view of another part of the magnetic proximity sensor assembly of  FIG.  1   ; 
         FIG.  8 A  illustrates two of the elements of the magnetic proximity sensor assembly of  FIG.  1    in part cross sectional view; 
         FIG.  8 B  illustrates the two elements of  FIG.  7 A  in an assembled condition; and 
         FIG.  9    illustrates a part cross sectional view of a magnetic proximity sensor assembly of  FIG.  1    but also showing the magnetic field. 
     
    
    
     DETAILED DESCRIPTION 
     The figures illustrate a magnetic proximity sensor assembly  10  and a method of manufacturing the magnetic proximity sensor assembly  10 . 
     The magnetic proximity sensor assembly  10  comprises a switch assembly  12 . The switch assembly  12  is received in a blind bore  14  of a body tube  16 . The blind bore  14  has a uniform bore diameter. Accordingly, the blind bore  14  has straight sides. The blind bore  14  may be a cylindrical blind bore. The blind bore  14  is an inner blind bore. 
     The switch assembly  12  comprises a magnetic assembly  18  moveable in the blind bore  14 . The magnetic assembly  18  comprises a primary magnet  20  and a biasing magnet  22  (see  FIGS.  3  and  5   ). The primary magnet  20  is comprised in a primary magnet holder  24 . The switch assembly  12  comprises a center magnet  26  interposed between the primary magnet  20  and the biasing magnet  22 . The center magnet  26  is comprised in a center housing molding  27  of the switch assembly  12 . The switch assembly  12  is a cartridge. The switch assembly  12  may also be referred to as a sensor element. 
     The magnetic proximity sensor assembly  10  comprises a sleeve  28  in the blind bore  14 . The sleeve  28  may be referred to as a shim. According, the sleeve  28  is received in the blind bore  14 . The sleeve  28  contacts the closed end  30  of the blind bore  14 . The switch assembly  12  is seated on the sleeve  28  such that the primary magnet  20  of the magnetic assembly  18  is surrounded by the sleeve  28 . Accordingly, the primary magnet  20  is received in the sleeve  28 . The primary magnet  20  is inside the sleeve  28 . 
     The sleeve  28  is configured such that movement of the magnetic assembly  18  in the blind bore  14  is unhindered by the sleeve  28 . The sleeve  28  is configured such that in use movement of the magnetic assembly  18  in the blind bore  14  causes the primary magnet  20  to move only within an area of the blind bore  14  defined by the sleeve  28 . 
     In the illustrated example, the sleeve  28  is cylindrical. The switch assembly  12  is seated on a rim  32  of the sleeve  28 , which can be an annular rim  32 . The rim  32  is an outer edge of the sleeve  28 . Accordingly, the sleeve  28  provides an annular rim  32  in the blind bore  14 . The switch assembly  12  contacts the rim  32 . The rim  32  defines a shoulder on which the switch assembly  12  is seated, which may be a stepped shoulder. In the illustrated example, the center housing molding  27  of the switch assembly  12  is seated on the sleeve  28 . 
     The switch assembly  12  is precisely positioned in the blind bore  14  by being seated on the sleeve  28 , i.e., by contacting the rim  32 . 
     Accordingly, the distance between the closed end  30  of the blind bore  14  and the primary magnet  20  is defined by the length of the sleeve  28 . Accordingly, the sleeve  28  acts as a positioning device. This distance is critical because in use the magnetic assembly  18  moves to a limited extent in the blind bore  14 , as described in detail below. The length of the sleeve  28  is selected such that in use the magnetic assembly  18  may move in the blind bore  14  without the primary magnet  20  contacting the closed end  30  of the blind bore  14 . Accordingly, the sleeve  28  is configured such that the primary magnet  20  does not contact the closed end  30  of the blind bore  14 . The sleeve  28  is configured to space apart the primary magnet  20  and the closed end  30 . 
     In examples of the disclosure, the length of the sleeve  28  can be precisely controlled and easily checked. Accordingly, the distance between the closed end  30  of the blind bore  14  and the primary magnet  20  can also be precisely controlled and easily checked. 
     The blind bore  14  extends from the closed end  30  to an open end  34  (see  FIGS.  3 ,  5  and  7   ). The open end  34  connects with a body tube cavity  36 , as illustrated in  FIG.  7   . The body tube cavity  36  extends to an open end  38  of the body tube  16 . The body tube cavity  36  has a diameter larger than the diameter of the blind bore  14 . The body tube cavity  36  has a non-uniform diameter. The diameter of the body tube cavity  36  increases towards the open end  38  of the body tube  16 . The body tube cavity  36  is provided within an enlarged area  37  of the body tube  16 . The enlarged area  37  has the form of a bolt head, such as a standard hex-head bolt head. Accordingly, the body tube  16  is an elongate hollow tubular member comprising the blind bore  14  and the body tube cavity  36 . 
     The biasing magnet  22  is spaced apart from the primary magnet  20 , for instance, on a coupling member  40 , for example, a shaft. The magnetic assembly  18  may be referred to as a floating shaft. 
     Accordingly, the center magnet  26  is separated from the primary magnet  20  and the biasing magnet  22 . An air gap separates the center magnet  26  from the primary magnet  20 , and an air gap separates the center magnet  26  from the biasing magnet  22 . 
     The center magnet  26  is within the magnetic flux zone of the primary magnet  20 . The center magnet  26  is within the magnetic flux zone of the biasing magnet  22 . The primary magnet  20 , center magnet  26  and biasing magnet  22  may be permanent magnets. 
     The primary magnet  20  and the center magnet  26  are magnetically biased to be attracted to each other. The biasing magnet  22  and the center magnet  26  are magnetically biased to be repelled away from each other. This arrangement causes an internal magnetic bias which causes the magnetic assembly  18  to adopt the magnetically biased position in the blind bore  14  of the body tube  16 . Accordingly, the primary magnet  20  and the center magnet  26  have opposite poles facing each other, i.e., north to south or south to north, in order to be magnetically biased to be attracted to each other. The respective opposite poles are proximal. The biasing magnet  22  and the center magnet  26  have the same poles facing each other, i.e., north-to-north or south-to-south, in order to be magnetically biased to be repelled away from each other. The respective same poles are proximal. 
     As illustrated in  FIGS.  3  to  6   , the switch assembly  12  also comprises an operator  42  which extends from the magnetic assembly  18  and serves as a drive for a moving contact  44  positioned between a first contact  46  and a second contact  48 . In some examples, the first contact  46  is a normally open contact and the second contact  48  is a normally closed contact. 
     When a target, such as a magnet or ferrous object, is within a sensing range of the magnetic proximity sensor assembly  10 , the magnetic assembly moves  18  in the blind bore  14  of the body tube  16  from a magnetically biased position towards the target. Accordingly, the magnetic attraction between the primary magnet  20  and the target overcomes (i.e., overpowers) the internal magnetic bias. The internal magnetic bias is caused by the magnetic repulsion between the biasing magnet  22  and the center magnet  26  and the magnetic attraction between the primary magnet  20  and the center magnet  26 . In this position of the magnetic assembly  18 , the moving contact  44  is urged by the operator  42  into contact with the first contact  46  to complete a first electrical circuit. In examples in which the first contact  46  is a normally open contact, this may be referred to as the open position of the switch assembly  12 . This condition of the magnetic proximity sensor assembly  10  is illustrated in  FIGS.  3  and  4   , in which the moving contact  44  is contacting the first contact  46  and not contacting the second contact  48 . Accordingly, the moving contact  44  is spaced from the second contact  48 . 
     In some examples there is a 0.3 mm or 0.4 mm air gap between the primary magnet  20  and the closed end  30  of the blind bore  14  in this condition of the magnetic proximity sensor assembly  10 . The volume of the air gap is defined by the length of the sleeve  28 . 
     In the absence of the target within the sensing range, the magnetic assembly  18  adopts the magnetically biased position in the blind bore  14  of the body tube  16 . The magnetically biased position is adopted because of the internal magnetic bias, as described above. In this position of the magnetic assembly  18 , the moving contact  44  is urged by the operator  42  into contact with the second contact  48  to complete a second electrical circuit. This condition of the magnetic proximity sensor assembly  10  is illustrated in  FIGS.  5  and  6   , in which the moving contact  44  is contacting the second contact  48  and not contacting the first contact  46 . Accordingly, the moving contact  44  is spaced from the first contact  46 . In examples in which the second contact  48  is a normally closed contact, this may be referred to as the closed position of the switch assembly  12 . 
     As illustrated in  FIGS.  3 ,  5  and  7   , the switch assembly  12  also comprises a contact molding  50  with first, second and third contact pins  52 ,  54 ,  56  extending therefrom, and a seal plug  57 . As is conventional, the contact pins  52 ,  54 ,  56  are electrically coupled to the moving contact  44 , first contact  46  and/or second contact  48 . 
       FIG.  7    illustrates a cross sectional view of the enlarged area  37  of the body tube  16  of the magnetic proximity sensor assembly  10 . In an installed condition, electrical wires extend from the first, second and/or third contact pins  52 ,  54 ,  56 . The electrical wires may be combined in a single cable  66 , or may be separate cables  66 . The electrical wires are arranged for being connected with control and/or sensing circuits elsewhere for completing the first electrical circuit and second electrical circuit. The electrical wires extend through the body tube cavity  36  and out of the open end  38  of the body tube  16 . 
     In use, a controller (not illustrated) is configured to continuously supply an electrical input signal to the magnetic proximity sensor assembly  10 , and to monitor the electrical output signal using the control and/or sensing circuits. The electrical output signal is different for the first and second electrical circuits. Accordingly, by monitoring the electrical output signal it can be determined whether or not the target is within the sensing range of the magnetic proximity sensor assembly  10 . 
     In one none limiting example, the opening and closing of a valve causes the target to move in and out of the sensing range. Thus, by monitoring the electrical output signal it can be determined whether the valve is open or closed. 
     In the illustrated example, the magnetic proximity sensor assembly  10  also comprises a flux sleeve  62  located on a flux sleeve holder  58 . The switch assembly  12  is seated on the sleeve  28  such that the flux sleeve  62  is also surrounded by the sleeve  28 . Accordingly, in such examples the switch assembly  12  is seated on the sleeve  28  such that the primary magnet  20  and the flux sleeve  62  are surrounded by the sleeve  28 . In some examples of the disclosure, the magnetic proximity sensor assembly  10  may be provided without a flux sleeve  62 . 
     In some examples, the sleeve  28  comprises mu-metal. The sleeve  28  may consist of mu-metal. The sleeve may be formed from mu-metal. Mu-metal is a soft magnetic alloy with exceptionally high magnetic permeability. The high permeability of mu-metal provides a low reluctance path for magnetic flux. Accordingly, the sleeve  28 , which surrounds the primary magnet  20  of the magnetic assembly  18 , acts as a magnetic shield against magnetic fields from the primary magnet  20  in the area surrounded. 
     As illustrated in  FIG.  9   , the mu-metal sleeve  28  works by providing a path for the magnetic field lines  68  around the shielded area, thus focusing the magnetic field from the primary magnet  20  out of the end  60  of the magnetic proximity sensor assembly  10  towards the target, thus optimizing sensing distance. 
     Magnetic proximity sensor assemblies  10  according to examples of the disclosure may be mounted adjacent to or surrounded by ferrous metals without affecting the sensing distance because the mu-metal sleeve  28  prevents magnetic field from the primary magnet  20  being lost to the adjacent or surrounding ferrous metal. Accordingly, the mu-metal sleeve  28  stops surrounding ferrous metal from robbing flux and reducing the sensing range. 
     In examples where the sleeve  28  is mu-metal, an advantage of the flux sleeve  62  being surrounded by the mu-metal sleeve  28  is that the flux sleeve&#39;s  62  attraction to both the primary magnet  20  and center magnet  26  is shielded from outside interference. 
     In hazardous environments, electrical contacts  44 ,  46 ,  48  have to be shielded from exposure to potentially hazardous atmospheres. As illustrated in  FIG.  7   , and as is conventional, the switch assembly  12  is hermetically sealed within the body tube  16  using an epoxy resin to provide an end seal assembly  64 , i.e., potting. Alternatively, a glass hermetic seal and potting compound may be provided as an end seal assembly  64 . The potting fixes and seals internal components. The potting substantially fills the body tube cavity  36 . 
     A method of manufacturing a magnetic proximity sensor assembly  10  according to examples of the disclosure is also provided. 
     As illustrated in  FIG.  8 A , the method comprises providing a body tube  16  comprising a blind bore  14 , wherein the blind bore  14  has a uniform bore diameter. 
     As illustrated in  FIG.  8 B , the method comprises inserting a sleeve  28  into the blind bore  14  such that the sleeve  28  contacts the closed end  30  of the blind bore  14 . The sleeve  28  is a separately manufactured part. 
     The method comprises inserting a switch assembly  12  into the blind bore  14 . The method comprises seating the switch assembly  12  on the sleeve  28  such that the primary magnet  20  of the magnetic assembly  18  is surrounded by the sleeve  28 , for instance, as illustrated in  FIG.  1     
     The method may comprise providing a body tube  16  comprising a blind bore  14 , wherein the blind bore  14  has a uniform bore diameter by a drilling operation. Accordingly, the method comprises forming the blind bore  14  by a drilling operation. 
     The method may also comprise providing a body tube  16  comprising a body tube cavity  36  by a drilling operation. Accordingly, the method comprises forming a body tube cavity  36  by a drilling operation. 
     There is thus described a magnetic proximity sensor assembly  10  and a method of manufacture with a number of advantages as described above. 
     Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. 
     Features described in the preceding description may be used in combinations other than the combinations explicitly described. 
     Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. 
     Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not. 
     The term “comprise” is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use “comprise” with an exclusive meaning then it will be made clear in the context by referring to “comprising only one . . . ” or by using “consisting”. 
     In this brief description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term “example” or “for example” or “may” in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus “example”, “for example” or “may” refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that comprise some but not all of the instances in the class. It is therefore implicitly disclosed that features described with reference to one example but not with reference to another example, can where possible be used in that other example but does not necessarily have to be used in that other example. 
     Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.