Abstract:
A magnetostrictive position transducer and a magnetostrictive sensing element thereof are characterized that a magnetostrictive sensing element is mounted inside an outer tube, the magnetostrictive sensing element has two end mounts respectively mounted on two ends of an insulating and hollow tube and a magnetostrictive wire mounted through the tube, the magnetostrictive wire has two wire adapters respectively mounted on two ends of the magnetostrictive wire and respectively mounted in the end mounts so that the magnetostrictive wire is contactlessly mounted through the tube, a sensing module is mounted in one of wire adapter to sense signal variation on the magnetostrictive wire. With the foregoing structure, the magnetostrictive sensing element does not require devices for applying pre-stress and damping, thereby simplifying structure and ensuring high stability in measurement of the magnetostrictive position transducer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a magnetostrictive position transducer and a magnetostrictive sensing element thereof, and more particularly to a magnetostrictive position transducer specially designed and structurally simplified to have a higher operational stability and having a detachable structure to facilitate mounting and dismounting. 
         [0003]    2. Description of the Related Art 
         [0004]    A magnetostrictive position transducer is basically composed of a magnetostrictive wire, at least one moving magnet, a current pulse generator and a strain pulse detector. Given a magnetic field variation resulting from a strain of one end of the magnetostrictive wire, the strain pulse detector can detect the magnetic field variation through a sensing coil at the other end of the magnetostrictive wire. Besides, strain of a piezoelectric material can be detected and converted into voltage. Such effect is called magnetostrictive effect. When combined with inverse magnetostriction, such effect is called inverse magnetostrictive effect and can detect a variation of a magnetostrictive wire serving as an output signal. The magnetostrictive position transducer is operated to detect a vibration signal of an echo signal using amount of magnetostriction. The entire operation includes the following steps. 
         [0000]    (1) An electric trigger feeds a current pulse signal into a magnetostrictive wire to generate an excited magnetic field to axially propagate along the magnetostrictive wire in light speed.
 
(2) The excited magnetic field collides with a fixed magnetic field of the at least one moving magnet. As the mass of the magnetostrictive wire is far less than that of the moving magnetic, the reaction force arising from collision of the magnetic fields excites a sonic shock wave to propagate along the magnetostrictive wire and toward two ends of the magnetostrictive wire.
 
(3) When received, the shock wave is converted into a voltage pulse signal by a piezoelectric transducer or a sensing coil.
 
(4) Calculate a shock wave speed and a time difference using the current pulse signal and the voltage pulse signal to obtain a distance to a position.
 
         [0005]    As the magnetostrictive position transducer is an industrial position sensor with substantial precision and stability, the structural design thereof should be reliable and the assembly should be as simple as possible. 
         [0006]    As disclosed in U.S. Pat. No. 5,998,991, a magnetostrictive position transducer  40  has an inner tube  44 , an outer tube  54  and a magnetostrictive wire  12  mounted in the inner tube  44 . The magnetostrictive wire  12  is fixed on two ends of the inner tube  44  through a spring  18  so that the spring  18  exerts a pre-stress on the magnetostrictive wire  12 . A first end of the magnetostrictive wire  12  is connected with a damper  20 . Furthermore, the first end of the magnetostrictive wire  12  is connected with an external connector  58 , and a second end is connected with another connector  60  through the inner tube  44  so as to connect to an external sensing circuit. The inner tube  4  is made of a conductive material. To prevent shock wave attenuation caused by the contact between the magnetostrictive wire  12  and an inside wall of the inner tube  44  from affecting the pulse signal transmission, multiple spaced spacers  42  are mounted inside the inner tube  44  to ensure that the inner tube  44  and the magnetostrictive wire  12  are fully isolated. 
         [0007]    The spring  18  in the conventional magnetostrictive position transducer serves to exert a pre-stress to both ends of the magnetostrictive wire  12  so that the magnetostrictive wire  12  can be subjected to a tensile force to maintain good electromgnetic signal and linearity in measurement. However, lengthy operation duration and high-temperature environment make the spring  18  prone to elastic fatigue. As the spring is a critical element in the conventional magnetostrictive position transducer, the elastic fatigue leads to unstable linearity in measurement. Also, the presence of the spring adds complication in parts assembly. 
         [0008]    Furthermore, the damper  20  mounted on the magnetostrictive wire  12  to prevent the interference arising from torsional wave returned along the magnetostrictive wire  12 . If the interference can be removed, the damper  20  is certainly an optional element in design. As the magnetostrictive position transducer  40  is grounded or transmits signal with the inner tube  44 , mounting the spacers  42  in the inner tube to ensure that the magnetostrictive wire  12  is not in contact with the inner tube  44  is also a complicated assembling process. 
       SUMMARY OF THE INVENTION 
       [0009]    A first objective of the present invention is to provide a magnetostrictive sensing element of a magnetostrictive position transducer requiring no pre-stress application or no spring, simplifying a damper design for magnetostrictive wire without trading off internal structural robustness, and employing assembly of multiple insulating and non-conductive combination tubes to prevent shock wave attenuation occurring between the magnetostrictive wire and an inner wall of each of the combination tubes and maintaining signal transmission capability. 
         [0010]    To achieve the foregoing objective, the magnetostrictive sensing element has a tube, a first end mount, a second end mount, a sensing module and a magnetostrictive wire. 
         [0011]    The tube is hollow and has an inner diameter, a first end and a second end. 
         [0012]    The first end mount is mounted around the first end of the tube, is hollow, and has an inner end and an outer end. The inner end has a first wire slot formed therein to communicate with the tube. The outer end has a first mounting slot formed therein to communicate with the first wire slot. 
         [0013]    The second end mount is mounted around the second end of the tube, is hollow, and has an inner end and an outer end. The inner end has a second wire slot formed therein to communicate with the tube. The outer end has a second mounting slot formed therein to communicate with the second wire slot. 
         [0014]    The sensing module is mounted inside the first mounting slot of the first end of the first end mount. 
         [0015]    The magnetostrictive wire is mounted through the tube, has a wire diameter smaller than the inner diameter of the tube, and has two wire adapters respectively mounted on two ends of the magnetostrictive wire. One wire adapter is mounted in the first mounting slot of the first end mount and is mounted through the sensing module. The other wire adapter is mounted in the second mounting slot of the second end mount. The two ends of the magnetostrictive wire are respectively fixed on the first end and the second end of the tube by using the two wire adapters so that the magnetostrictive wire is contactlessly mounted through the tube. 
         [0016]    With the foregoing structure, the magnetostrictive wire is fixed in the first end mount and second end mount at the first end and second end of the tube by using the wire adapters, thereby requiring no spring and effectively simplify the structure and assembling process. 
         [0017]    Moreover, the tube can be assembled with multiple combination tubes and couplers. As the combination tubes and the couplers are both insulating, they are immune to generation of interference to the magnetostrictive wire. Additionally, since each coupler has an inner diameter smaller than that of each of the combination tubes, the magnetostrictive wire is limited not to contact the inner walls of the combination tubes, thereby eliminating generation of shock wave attenuation and maintaining signal transmission capability. 
         [0018]    A second objective of the present invention is to provide a magnetostrictive position transducer facilitating assembly and disassembly thereof. 
         [0019]    To achieve the foregoing objective, the magnetostrictive position transducer has a main body, a magnetostrictive sensing element, a sensing circuit module, an outer tube and at least one moving magnet. 
         [0020]    The magnetostrictive sensing element is the same as the foregoing magnetostrictive sensing element. The tube is combined with one end of the main body. 
         [0021]    The sensing circuit module is mounted in the main body and is electrically connected with the magnetostrictive sensing element. 
         [0022]    The outer tube is detachably mounted around the tube of the magnetostrictive sensing element. 
         [0023]    The at least one moving magnet is movably mounted around the outer tube. Each one of the at least one moving magnet has at least one permanent magnet mounted therein. 
         [0024]    The foregoing structure allows the outer tube and the at least one moving magnet to be detachable, thereby facilitating mounting, maintenance and the need of frequent assembly and disassembly. 
         [0025]    Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a side view in partial division of an embodiment of a magnetostrictive position transducer in accordance with the present invention; 
           [0027]      FIG. 2  is a side view in partial division of a magnetostrictive sensing element of the magnetostrictive position transducer in  FIG. 1 ; 
           [0028]      FIG. 3  is a cross-sectional view of the magnetostrictive sensing element in  FIG. 2 ; 
           [0029]      FIG. 4  is an enlarged side view in partial division of the magnetostrictive sensing element in  FIG. 2 ; 
           [0030]      FIG. 5  is another enlarged side view in partial division of the magnetostrictive sensing element in  FIG. 2 ; 
           [0031]      FIG. 6  is another cross-sectional view of the magnetostrictive sensing element in  FIG. 2 ; and 
           [0032]      FIG. 7  is a side view of another embodiment of a magnetostrictive position transducer in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    With reference to  FIG. 1 , an embodiment of a magnetostrictive position transducer in accordance with the present invention has an outer tube  10 , a magnetostrictive sensing element, a sensing circuit module  11  and a moving magnet  12 . The magnetostrictive sensing element is mounted inside the outer tube  10 . The sensing circuit module  11  is electrically connected with the magnetostrictive sensing element. The moving magnet  12  is movably mounted around the outer tube  10 , slidably aligns with the magnetostrictive sensing element and has a permanent magnet mounted inside the moving magnet  12 . When the moving magnet  12  moves up and down with a liquid level, the permanent magnet induces the magnetostrictive sensing element inside the outer tube  10 . The magnetic induction is detected by the sensing circuit module  11 . The major characteristic of the present invention lies in the magnetostrictive sensing element inside the outer tube  10 . A specific structure of the magnetostrictive sensing element is further introduced in the following. 
         [0034]    With reference to  FIG. 2 , the magnetostrictive sensing element has a tube  20 , a first end mount  30 , a second end mount  40 , a sensing module  50  and a magnetostrictive wire  60 . 
         [0035]    The tube is hollow and has a first end and a second end. The first end is on the left and the second end is on the right in  FIG. 2 . The tube  20  may be a single tube or assembled with multiple combination tubes. In the present embodiment, the tube  20  is assembled with multiple combination tubes  21 , and a hollow coupler  22  is mounted around each two adjacent combination tubes  21 . To facilitate understanding of detailed structure and connection relationship with minimum combination tubes  21  and the hollow couplers  22 , the tube  20  is illustrated by combining two combination tubes  21  and a hollow coupler  22 . The combination tubes  21  and the hollow couplers  22  are made from an insulating material or surface treated to be insulating. The insulating material may be a polymer. 
         [0036]    Each combination tube  21  has an inner diameter and has two open ends to communicate with each other for the corresponding hollow couplers  22  to be mounted therearound, and for the corresponding first end mount  30  and second end mount  40  to be mounted therein. In the present embodiment, the hollow coupler  22  is tubular and has a through hole  221  centrally formed through the hollow coupler  22  for the magnetostrictive wire  60  to pass through. The hollow coupler  22  has two coupling portions  222 . Each coupling portion  222  is formed on one end of the hollow coupler  22  and has a reduced outer diameter matching the inner diameter of the combination tube  21  so as to facilitate coupling. With reference to  FIG. 3 , besides a tight fit, the coupling portion  222  of the hollow coupler  22  engages a combination tube  21  by an engagement structure having two teeth  223  oppositely formed on and protruding from two inner walls of the two coupling portions  222  and two tooth spaces  211  formed through the combination tube  21  and engaging the respective teeth  223  so as to prevent the magnetostrictive wire  60  from being rotated due to the rotation of each combination tube  21 . As the diameter of the through hole  221  of each hollow coupler  22  is smaller than the inner diameter of each combination tube  21 , the magnetostrictive wire  60  passing through each hollow coupler  22  is limited by the hollow couplers  22  and is uneasy to be in touch with an inner wall of any combination tube  21 . Hence, the shock wave attenuation can be avoided. With reference to  FIG. 4 , each hollow coupler  22  has an annular ridge  223  formed on and protruding radially and inwardly from an inner wall of the through hole of the hollow coupler  22  to further limit the magnetostrictive wire  60  having a wire diameter smaller than an inner diameter of the annular ridge  223  and prevent the magnetostrictive wire  60  from being in contact with the inner wall of the combination tube  21 . 
         [0037]    With reference to  FIGS. 2 and 5 , the first end mount  30  is mounted around the first end of the tube  20 , is hollow, and has an inner end and an outer end. The inner end has an insertion portion  31  formed thereon and having a reduced outer diameter. The outer diameter of the insertion portion  31  matches the inner diameter of the combination tubes  21  of the tube  20  so as to facilitate fitting the insertion portion  31  in a corresponding combination tube  21 . Similarly, with reference to  FIG. 6 , the insertion portion  31  of the inner end of the first end mount  30  engages a corresponding combination tube  21  by an engagement mechanism having two teeth  311  oppositely formed on and protruding from an inner wall of the insertion portions  31  and two tooth spaces  211  oppositely formed through the combination tube  21  and engaging the respective teeth  311 . 
         [0038]    The first end mount  30  further has a wire slot  32  and a mounting slot  33 . The wire slot  32  is formed in the inner end of the first end mount  30  to communicate with the tube  20 . The mounting slot  33  is formed in the outer end of the first end mount  30  to communicate with the wire slot  32  and serves for mounting the sensing module  50  therein. The sensing module  50  has an insulating and cylindrical body and a sensing coil (not shown) mounted inside the body. An outer diameter of the body matches an inner diameter of the mounting slot  33  to facilitate the body to be mounted inside the mounting slot  33 . With further reference to  FIG. 5 , the cylindrical body of the sensing module  50  has a through hole  51  formed through two ends of the body for the magnetostrictive wire  60  to pass therethrough. The through hole  51  has an adapter slot  52  formed at an outer end thereof and having an expanded inner diameter for a first wire adapter  61  formed on one end of the magnetostrictive wire  60  to be mounted in the adapter slot  52 . The sensing module  50  may be a piezoelectric material, an electromechanical transducer, an induction coil or a combination of the aforementioned elements. 
         [0039]    With further reference to  FIG. 2 , the second end mount  40  is mounted around the second end of the tube  20 , is structurally similar to the first end mounted  30  in having a hollow form, and has an outer end and an inner end. The inner end has an insertion portion  41  formed thereon and having a reduced outer diameter. The outer diameter of the insertion portion  41  matches the inner diameter of the combination tubes  21  of the tube  20  to facilitate fitting the insertion portion  41  in a corresponding combination tube  21 . Similarly, the insertion portion  41  of the inner end of the second end mount  40  engages a corresponding combination tube  21  by an engagement mechanism identical to that between the insertion portion  31  of the inner end of the first end mount  30  and the combination tube  21 . The second end mount  40  further has a wire slot  42  and a mounting slot  43 . The wire slot  42  is formed in the inner end of the second end mount  40  to communicate with the tube  20  for the magnetostrictive wire  60  to pass therethrough. The mounting slot  43  is formed in the outer end of the second end mount  40  to communicate with the wire slot  42  and serves for mounting a second wire adapter  62  formed on the other end of the magnetostrictive wire  60  in the mounting slot  43 . The magnetostrictive wire  60  is pulled out through the second wire adapter  62 , is extended to the first end mount  30  through a return signal line  63  along a periphery of the tube  20 , and is soldered in the first end mount  30 . 
         [0040]    As mentioned, the magnetostrictive wire  60  penetrates through the combination tubes  21  and the hollow couplers  22  of the tube  20 , and has a first wire adapter  61  and the second wire adapter  62  respectively and securely mounted in both ends of the tube  20 . The first wire adapter  61  is mounted in the mounting slot  33  of the first end mount  30  and is securely mounted in the adapter slot  52  of the sensing module  50 . The second wire adapter  62  is mounted in the mounting slot  43  of the second end mount  40 . The first wire adapter  61  and the second wire adapter  62  serve to tighten both ends of the magnetostrictive wire  60  and respectively fix both ends of the magnetostrictive wire  60  on the first end and the second end of the tube  20 . Accordingly, the magnetostrictive wire  60  can be mounted through the tube  20  without contacting the inner wall of the tube  20 . The magnetostrictive wire  60  may be made of an enameled wire. 
         [0041]    The magnetostrictive wire  60  in the present invention is fixed in the first end and the second end of the tube  20  by using the first wire adapter  61  and the second wire adapter  62 . As a result, the magnetostrictive wire  60  can be contactlessly and firmly mounted inside the tube  20  without using a spring, thereby effectively simplifying the structure and assembling procedures of the present invention. Additionally, if the tube  20  is assembled with the combination tubes  21 , which are connected with the hollow couplers  22 , the hollow couplers  22  have the inner diameter smaller than that of the tube  20 , thereby further limiting the magnetostrictive wire  60  to contact with the inner wall of the tube  20 , prevent the generation of shock wave attenuation, and maintain signal transmission capability. The annular ridge  221  formed on the inner wall of the through hole  221  of the hollow coupler  22  can further securely isolate the magnetostrictive wire  60  from the inner walls of the combination tubes  21 . 
         [0042]    With reference to  FIG. 7 , another embodiment of a magnetostrictive position transducer in accordance with the present invention is shown. The magnetostrictive position transducer is characterized in that the magnetostrictive sensing element employs a mechanical means to be combined with a main body  70 . The mechanical means may be a fastener, a sliding block, a sliding channel, screwing means, welding means and the like. The magnetostrictive position transducer has a sensing circuit module (not shown) mounted in the main body  70  and electrically connected with the magnetostrictive sensing element. In the present embodiment, the tube  20 ′ of the magnetostrictive sensing element has a threaded connector  23  formed on one end thereof adjacent to the main body  70  to serve to be mounted in the outer tube  10 ′. To be screwed with the tube  20 ′, the outer tube  10 ′ has a threaded connector  13  to facilitate mounting of the tube  20 ′ around the outer tube  10 ′ by screwing the threaded connectors  13 ,  23  together. Moreover, at least one moving magnet  12 ′ can be movably mounted around the outer tube  10 ′, and each one of the at least one moving magnet  12 ′ has at least one permanent magnet mounted therein. 
         [0043]    In sum, with the aforementioned structure of the present invention, the present invention can provide the magnetostrictive position transducer with more simplified structure and more stability in measurement. 
         [0044]    Even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.