Patent Document

CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/921,757, entitled “Magnetoelastic Tension Sensor,” filed Dec. 30, 2013, and U.S. Provisional Application No. 61/925,509 entitled “Magnetoelastic Tension Sensor,” filed Jan. 9, 2014, the contents of which applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a magnetoelastic sensor and, more specifically, to a magnetoelastic sensor for sensing tension or compression. 
         [0004]    2. Description of Related Art 
         [0005]    Conventional tension and compression sensors use strain gauges to produce electrical signals which indicate the tension or compression present. Illustrated in  FIG. 13  is a conventional strain gauge, generally designated as  1300 . The strain gauge  1300  comprises an input  1310  and an output  1320  connected by a plurality of windings  1330 . The input  1310 , output  1320 , and plurality of windings  1330  are formed from a thin-film conductor  1340 , such as a metal foil. The input  1310 , output  1320 , and plurality of windings  1330  are disposed on an insulative substrate  1350 . 
         [0006]    The insulative substrate  1350  is adhered to a surface for which strain is desired to be measured. Strain is measured by sensing a resistance of the thin-film conductor  1340  as the strain gauge  1300  is deformed when under tension or compression. When stretched in a direction indicated by A or B in  FIG. 13 , the resistance of the thin-film conductor  1340  increases. Thus, by measuring the increase in resistance, the tension of the surface to which the strain gauge  1300  is attached may be inferred. When compressed in a direction opposite to that indicated by A or B in  FIG. 13 , the resistance of the thin-film conductor  1340  decreases. Thus, by measuring the decrease in resistance, the compression of the surface to which the strain gauge  1300  is attached may be inferred. 
         [0007]    S-shaped tension or compression sensors, also known as load cells, typically incorporate one or more conventional strain gauges  1300  to sense tension or compression. Illustrated in  FIG. 14  is a conventional S-shaped load cell, generally designated as  1400 . The load cell  1400  comprises a first arm  1410 , a second arm  1420 , and a body  1430 . Disposed on the body is a plurality of strain gauges  1440 A through  1440 D. Each strain gauge  1440  may be a strain gauge  1300 . 
         [0008]    The load cell  1400  detects an amount of force applied in directions generally designed as C in  FIG. 14 . When the force is applied in the directions C, the strain gauges  1440 A and  1440 D undergo compression, and the strain gauges  1440 B and  1440 D undergo tension. By measuring the tension and compression, the size of the force can be calculated. 
         [0009]    Conventional tension sensors using magnetoelastic effects are described in U.S. Pat. Nos. 5,195,377 to Garshelis, and U.S. Pat. No. 6,220,105 to Cripe. A conventional Villari effect tension sensor is described in U.S. Pat. No. 5,905,210 to O&#39;Boyle et al. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    In accordance with an aspect of the present invention, there is provided a tension sensor comprising a plate comprising a magnetoelastic region. The tension sensor further comprises at least one pair of sensors disposed above the magnetoelastic region. The at least one pair of sensors are configured to sense a change in a magnetic field produced by the magnetoelastic region in response to a strain in the plate imposed by a tension on the plate. 
         [0011]    In accordance with another aspect of the present invention, there is provided a compression sensor comprising a plate comprising a magnetoelastic region. The compression sensor further comprises at least one pair of sensors disposed above the magnetoelastic region. The at least one pair of sensors are configured to sense a change in a magnetic field produced by the magnetoelastic region in response to a strain in the plate imposed by a compression on the plate. 
         [0012]    In accordance with yet another aspect of the present invention, there is provided method of manufacturing a magnetoelastic sensor. The method comprises steps of forming a plate from an austenitic non-magnetic stainless steel alloy, cold-working an area of the plate to convert the austenitic non-magnetic stainless steel alloy in the area of the plate to martensite, rotating the plate, bringing a magnet near a surface of the plate and near the area of the plate converted to martensite to magnetize the area, and mounting at least one pair of magnetic field sensor assemblies above the surface of the plate near the magnetized area. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    For the purpose of illustration, there are shown in the drawings certain embodiments of the present invention. In the drawings, like numerals indicate like elements throughout. It should be understood that the invention is not limited to the precise arrangements, dimensions, and instruments shown. In the drawings: 
           [0014]      FIG. 1  is top view of a magnetoelastic tension sensor comprising a plate and a plurality of sensor assemblies, in accordance with an exemplary embodiment of the present invention; 
           [0015]      FIG. 2A  is a first cross-sectional view of the magnetoelastic tension sensor of  FIG. 1 , in accordance with an exemplary embodiment of the present invention; 
           [0016]      FIG. 2B  is a second cross-sectional view of the magnetoelastic tension sensor of  FIG. 1 , in accordance with an exemplary embodiment of the present invention; 
           [0017]      FIG. 3  illustrates a detailed view of a region of the plate of the magnetoelastic tension sensor of  FIG. 1 , in accordance with an exemplary embodiment of the present invention; 
           [0018]      FIG. 4  illustrates another detailed view of a region of the plate of the magnetoelastic tension sensor of  FIG. 1 , in accordance with an exemplary embodiment of the present invention; 
           [0019]      FIG. 5  illustrates another view of the magnetoelastic tension sensor of  FIG. 1 , in accordance with an exemplary embodiment of the present invention; 
           [0020]      FIG. 6  illustrates various directions of changes in magnetic fields produced at the sensor assemblies of the magnetoelastic tension sensor of  FIG. 1 , in accordance with an exemplary embodiment of the present invention; 
           [0021]      FIG. 7  illustrates an exemplary alternative embodiment of the magnetoelastic tension sensor of  FIG. 1 , in accordance with an exemplary embodiment of the present invention; 
           [0022]      FIG. 8A  illustrates a first cross-sectional view the magnetoelastic tension sensor of  FIG. 7 , in accordance with an exemplary embodiment of the present invention; 
           [0023]      FIG. 8B  illustrates a second cross-sectional view the magnetoelastic tension sensor of  FIG. 7 , in accordance with an exemplary embodiment of the present invention; 
           [0024]      FIG. 8  illustrate an exemplary alternative embodiment of the magnetoelastic tension sensor of  FIG. 1 , in accordance with an exemplary embodiment of the present invention; 
           [0025]      FIG. 9  illustrates an exemplary alternative embodiment of the magnetoelastic tension sensor of  FIG. 7 , in accordance with an exemplary embodiment of the present invention; 
           [0026]      FIG. 10A  is a first cross-sectional view of the magnetoelastic tension sensor of  FIG. 9 , in accordance with an exemplary embodiment of the present invention; 
           [0027]      FIG. 10B  is a second cross-sectional view of the magnetoelastic tension sensor of  FIG. 9 , in accordance with an exemplary embodiment of the present invention; 
           [0028]      FIG. 11  illustrates a sensor assembly comprising the magnetoelastic tension sensor of  FIG. 1 ,  7 , or  9 , in accordance with an exemplary embodiment of the present invention; 
           [0029]      FIG. 12  illustrates a graph of data from a test of an exemplary implementation of the magnetoelastic tension sensor of  FIG. 1 , in accordance with an exemplary embodiment of the present invention; 
           [0030]      FIG. 13  illustrates a conventional strain gauge; and 
           [0031]      FIG. 14  illustrates a conventional load cell. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Reference to the drawings illustrating various views of exemplary embodiments of the present invention is now made. In the drawings and the description of the drawings herein, certain terminology is used for convenience only and is not to be taken as limiting the embodiments of the present invention. Furthermore, in the drawings and the description below, like numerals indicate like elements throughout. 
         [0033]    Illustrated in  FIG. 1  is a top view of an exemplary embodiment of a magnetoelastic sensor, generally designated as  100 , in accordance with an exemplary embodiment of the present invention.  FIG. 2A  illustrates a right-side view along a cross-section of the magnetoelastic sensor  100  at a section line  180 , and  FIG. 2B  illustrates a left-side view along a cross-section of the magnetoelastic sensor  100  taken at a section line  170 . 
         [0034]    Referring to  FIGS. 1 ,  2 A, and  2 B, the magnetoelastic sensor  100  comprises a plate  110 , a first distribution bar  120  connected to the plate  110  at a first end  111  of the plate  110 , and a second distribution bar  130  connected to the plate  110  at a second end  112  of the plate  110 . Disposed in the plate  110  is a magnetic band  140 . In the exemplary embodiment of the magnetic band  140  illustrated in  FIG. 1 , the magnetic band  140  is an annulus. In other exemplary embodiments of the magnetic band  140 , different shapes of the magnetic band  140  are contemplated. For example, the magnetic band  140  may be diamond shaped. It is to be understood that the plate  110  may have various dimensions, may not be perfectly planar on either surface, and may not have a perfectly uniform thickness across its entire length. 
         [0035]    Disposed above the magnetic band  140  are a plurality of sensor assemblies  150 A,  150 B,  150 C, and  150 D. Each of the sensor assemblies  150 A,  150 B,  150 C, and  150 D comprises, respectively, a sensor platform  152 A,  152 B,  152 C, and  152 D on which a respective sensor  154 A,  154 B,  154 C, and  154 D is disposed. The sensors  154 A and  154 C are disposed along the section line  170  (also referred to herein as “centerline  170 ”). The sensors  154 B and  154 D are disposed along the section line  180  (also referred to herein as “centerline  180 ”). The centerline  170  longitudinally bisects the sensor assemblies  150 A and  150 C and their respective sensors  154 A and  154 C. The center line  170  longitudinally bisects the sensor assemblies  150 B and  150 D and their respective sensors  154 B and  154 D. The sensors  154 A,  154 B,  154 C, and  154 D are disposed symmetrically about a center point  165  of the plate  110 , which center point  165  is also the center point of the magnetic band  140 . The sensors  154 A,  154 B,  154 C, and  154 D are disposed over the magnetic band  140  such that a centerline  145  of the magnetic band  140  laterally bisects the sensors  154 A,  154 B,  154 C, and  154 D. 
         [0036]    The sensor assemblies  150 A,  150 B,  150 C, and  150 D are disposed on the magnetic band  140  each at a respective angle, −α, α, −α, and α, relative to a longitudinal axis  160  of the plate  110 . The angles, α and −α, are chosen so that the centerlines  170  and  180  are neither parallel to the longitudinal axis  160  nor perpendicular thereto. 
         [0037]    In an exemplary embodiment, the angles, α and −α, are chosen so that the centerlines  170  and  180  intersect the magnetized band  140  perpendicularly to a tangent of the centerline  145  of the magnetic band  140 , and where the magnetic field produced by the magnetic band  140  at the points of intersection is neither parallel nor perpendicular to the centerline  160  of the plate  110 . 
         [0038]    In another exemplary embodiment, the magnitude of angle, α, −α, is chosen to be greater than or equal to 30° and less than or equal to 60°. 
         [0039]    In yet another exemplary embodiment, the magnitude of angle, α, −α, is chosen to be greater than or equal to 40° and less than or equal to 50°. 
         [0040]    In still another exemplary embodiment, the magnitude of angle, α, −α, is 45°. 
         [0041]    The magnetic field sensors  154 A,  154 B,  154 C, and  154 D each produce an output signal that changes when a magnetic field produced by the magnetized band  140  in a direction parallel to the centerlines  170  and  180  changes. The magnetic field sensors  154 A and  154 C have high sensitivity to magnetic fields parallel to the centerline  170 , and the magnetic field sensors  154 B and  154 D have high sensitivity to magnetic fields parallel to the centerline  180 . 
         [0042]    The first and second distribution bars  120 ,  130  at the top  111  and the bottom  112  of the plate  110  are thicker than the plate  110 . Thus, as forces, F 1  and F 2 , are applied to the distribution bars  120 ,  130 , respectively, an even amount of strain or compression is produced in the plate  110 , rather than a large amount of strain or compression along the center line  160  of the plate  110  and less elsewhere. 
         [0043]    In an alternative exemplary embodiment of the magnetoelastic sensor  100 , the first and second distribution bars  120 ,  130  are formed integrally with the plate  110  and are areas of the plate that are thicker than the portion of the plate  110  in which the magnetized band  140  is disposed. In such embodiment, as forces, F 1  and F 2 , are applied to the distribution bars  120 ,  130 , respectively, an even amount of strain or compression is produced in the plate  110 , rather than a large amount of strain along the center line  160  of the plate  110  and less elsewhere. 
         [0044]    In the exemplary embodiment of the magnetoelastic sensor  100  described above, the magnetic band  140  is formed within the plate  110 . In such embodiment, the magnetic band  140  may be formed from a magnetized band that is molded within a nonmagnetized or nonmagnetizable, e.g., non-ferromagnetic, plate  110 . 
         [0045]    In another exemplary embodiment of the magnetoelastic sensor  100 , the magnetic band  140  may be a magnetized region of the plate  110 , in which case the plate  110  is formed entirely from a ferromagnetic material. It is to be understood that other exemplary embodiments of the magnetoelastic sensor  100  in which the magnetic band  140  is disposed above or on a top surface  113  of the plate  110  are contemplated. In such other embodiments, the plate  110  is not magnetized and may be formed from a material that is not capable of being magnetized. 
         [0046]    In yet another exemplary embodiment of the magnetoelastic sensor  100 , the plate  110  is made from a non-magnetic material where the region  140  can be subjected to a process to change its metallurgical phase. A type of austenitic non-magnetic stainless steel alloy is selected to form the plate  110 . The area corresponding to the region  140  is cold-worked to convert it to martensite, which is ferromagnetic. The plate  110  is rotated around an axis perpendicular to the center point  165  of the plate  110 , and then while it is rotating, a permanent magnet is brought close to the surface  113  of the plate  110  near the area of the plate  110  corresponding to the region  140  for a large number of revolutions. The permanent magnet is removed after a magnetization direction has been imparted in the region  140 . This approach is beneficial because forming the plate  110  from a homogeneously ferromagnetic material could lead to problems, and molding or attaching the region  140  could be problematic because of the extremely high interface shear stresses in the plate  110  in certain applications. Sensor assemblies in accordance with the exemplary embodiments described herein are then mounted above the surface  113  of the plate  110 . 
         [0047]    In an exemplary embodiment in which the plate  110  is formed from a ferromagnetic material, the magnetized band  140  having a circumferential magnetization direction indicated by the arrowed centerline  145  in  FIG. 1  is produced by rotating the plate  110  around an axis perpendicular to the center point  165  of the plate  110 , and then while it is rotating, bringing a permanent magnet close to the surface  113  of the plate  110  for a large number of revolutions. The permanent magnet is removed after a magnetization direction has been imparted in the magnetic band  140 , which is a magnetized region of the plate  110 . In this exemplary embodiment, the plate  110  is formed from a ferromagnetic material. It is to be understood that reference number  145  also refers to the magnetic field produced by the magnetic band  140 . Sensor assemblies in accordance with the exemplary embodiments described herein are then mounted above the surface  113  of the plate  110 . 
         [0048]    Although  FIG. 1  illustrates a single magnetic band  140 , it is to be understood that other exemplary embodiments in which a plurality of permanent magnets placed at various azimuthal locations in the plate  110  can also be used. In other exemplary embodiments, more than one magnetic band may be formed in or on the plate  110 , in which case the magnetoelastic sensor comprises four sensor assemblies for each ring. In still other exemplary embodiments, instead of a permanent magnet forming the magnetic band  140 , an electromagnet is used to produce the magnetized band  140 . 
         [0049]      FIG. 2A  illustrates the relative positions of the sensor assemblies  150 B and  150 D and the plate  110 .  FIG. 2B  illustrates the relative positions of the sensor assemblies  150 A and  150 C and the plate  110 . 
         [0050]    As illustrated in  FIGS. 2A and 2B , the sensor platforms  152 A,  152 B,  152 C, and  152 D comprise, respectively, inside surfaces  151 A,  151 B,  151 C, and  151 D on which the sensors  154 A,  154 B,  154 C, and  154 D are respectively disposed. The sensor platforms  152 A,  152 B,  152 C, and  152 D further comprise, respectively, outside surfaces  153 A,  153 B,  153 C, and  153 D. The inside surfaces  151 A,  151 B,  151 C, and  151 D face the magnetic band  140  such that the sensors  154 A,  154 B,  154 C, and  154 D, as disposed on the respective inside surfaces  151 A,  151 B,  151 C, and  151 D, are between the magnetic band  140  and the respective sensor platforms  152 A,  152 B,  152 C, and  152 D. 
         [0051]      FIG. 3  illustrates a detailed view of a region  300  of the plate  110  under the sensor assembly  150 C and specifically a region  300  of the magnetic band  140  under the sensor assembly  150 C, in accordance with an exemplary embodiment of the present invention. Inside this region  300 , there are illustrated a tension axis (also referred to as a “magnetoelastic anisotropy axis”)  310 , a first effective anisotropy axis  320 , and a second effective anisotropy axis  330 . 
         [0052]    The first effective anisotropy axis  320  is the direction of the magnetic field  145  produced by the magnetic band  140  when the forces, F 1  and F 2 , are not present. The second effective anisotropy axis  330  is the direction of the magnetic field  145  produced by the magnetic band  140  when the forces, F 1  and F 2 , are present. The second effective anisotropy axis  330  is a result of the combination of the tension axis  310  and the first effective anisotropy axis  320  and is proportional to the strength of the forces, F 1  and F 2 . The first effective anisotropy axis  320  is offset from the second effective anisotropy axis  330  by an angle β, which changes as the magnitude of the forces, F 1  and F 2 , change. The angle, β, increases as the magnitude of the forces, F 1  and F 2 , increase and decreases at the magnitude of the forces, F 1  and F 2 , decrease. 
         [0053]      FIG. 4  illustrates another detailed view of the region  300  of the plate  110 , in accordance with an exemplary embodiment of the present invention. The view of the region  300  in  FIG. 4  illustrates an effect of the tension caused by the forces, F 1  and F 2 . The magnetic field  145  in the magnetic band  140  is represented in  FIG. 4  by a vector  410 . As the direction of the effective first anisotropy axis  320  changes to the direction of the second anisotropy axis  330 , the magnetic field  410  inside the magnetic band  145  changes direction to a direction represented by a vector  420 . The change in magnetic field is represented by a vector  430 , which is perpendicular to the vector  410 , the sum of the vectors  410  and  430  being the vector  420 . 
         [0054]    The change of the magnetic field, i.e., the magnetic field component  430 , produces a change in the magnetic field outside the plate  110  in the region  300 . The sensor  154 C is positioned to detect the change in the magnetic field  430  outside the plate  140 . The sensor  154 C is positioned to be especially sensitive to magnetic fields in an outwardly radial direction, i.e., in a direction parallel to the centerline  170 . Thus, the sensor  154 C is positioned to sense the component of the magnetic field outside the plate  140  caused by the magnetic field component  430 . The sensor  154 C is configured to output a signal indicative of the magnetic field  430  when the tension caused by the forces, F 1  and F 2 , is present. 
         [0055]    The sensors  154 A,  154 B, and  154 D are positioned similarly to the sensor  154 C. Thus, the sensor  154 A is positioned to be especially sensitive to magnetic fields in an outwardly radial direction, i.e., in a direction parallel to the centerline  170 . The sensors  154 B and  154 D are positioned to be especially sensitive to magnetic fields in a direction parallel to the centerline  180 . The sensors  154 A,  154 B, and  154 D are positioned to sense a component of the magnetic field outside the plate  140  caused by a change of the magnetic field outside of the plate  110  because of tension in the plate  110 . 
         [0056]    Although  FIGS. 3 and 4  are described with reference to a tension in the plate  110 , it is to be understood that such description is applicable to an instance in which the forces, F 1  and F 2 , cause compression in the plate  110 . Under compression, however, the changes in the anisotropy axis and the magnetic fields are opposite to the changes described with reference to  FIGS. 3 and 4  when tension is present. 
         [0057]    Referring now to  FIG. 5 , there is illustrated the magnetoelastic tension sensor  100  of  FIG. 1  annotated to show strain axes  510  and  520 , in accordance with an exemplary embodiment of the present invention. The strain axis  510  passes through a center point of the sensor  154 C and the center point of the sensor  154 B. The strain axis  520  passes through a center point of the sensor  154 D, and the center point of the sensor  154 A. 
         [0058]    The sensor assembly  150 A is positioned to sense a portion  145 A of the magnetic field  145 ; sensor assembly  150 B is positioned to sense a portion  145 B of the magnetic field  145 ; sensor assembly  150 C is positioned to sense a portion  145 C of the magnetic field  145 ; and sensor assembly  150 D is positioned to sense a portion  145 D of the magnetic field  145 . The sensors  154 A through  154 D produce respective signals indicative of the magnetic fields that they sense. 
         [0059]    Each sensor signal produced by the sensors  154 A through  154 D comprises a first component resulting from the tension or compression in the plate  110  caused by the forces, F 1  and F 2 , and a second component resulting from environmental magnetic field(s). When connected correctly to electronic circuitry (described below with reference to  FIG. 11 ), the first components of the sensor signals provided by the magnetic field sensors  154 A,  154 B,  154 C, and  154 D in response to the tension or compression created by the forces, F 1  and F 2 , add constructively. The second component of the sensor signals provided by the magnetic field sensors  154 A,  154 B,  154 C, and  154 D in response to environmental magnetic fields largely add destructively. Thus, the final sensor output (described below with reference to  FIG. 11 ) is mostly insensitive to environmental magnetic fields. 
         [0060]    Referring now to  FIG. 6 , there are illustrated various directions of the changes in the magnetic fields produced at the locations of the sensor assemblies  150 A,  150 B,  150 C, and  150 D as a result of tension in the plate  110 , in accordance with an exemplary embodiment of the present invention. When the plate  110  is placed under tension, the magnetic field  145 A under the sensor assembly  150 A changes, as represented by a vector  650 A; the magnetic field  145 B under the sensor assembly  150 B changes, as represented by a vector  650 B; the magnetic field  145 C under the sensor assembly  150 C changes, as represented by a vector  650 C; and the magnetic field  145 D under the sensor assembly  150 D changes, as represented by a vector  650 D. 
         [0061]    The angles of the vectors  650 A,  650 B,  650 C, and  650 D are −α, α, α, and −α relative to the centerline  160  of the plate  110  (illustrated in  FIG. 1 ). Providing for the magnetic field sensors  154 A,  154 B,  154 C, and  154 D to have identical polarity of sensitivity to the changes  650 A,  650 B,  650 C, and  650 D in the magnetic field  145  produced by the magnetized band  140  causes the sensitivity of the final sensor output to the tension to be high. Note that the direction of the vector  650 C is the same as the vector  430 . 
         [0062]    In one exemplary embodiment, the magnetic field sensors  154 A,  154 B,  154 C are fluxgate magnetometers. In another exemplary embodiment, the magnetic field sensors  154 A,  154 B,  154 C are Hall sensors. 
         [0063]    The various embodiments of the magnetoelastic sensor  100  described herein are advantageous in that the magnetic field sensors  154 A,  154 B,  154 C, and  154 D sense very little magnetic field when the tension or compression is not present. This is the result of the magnetic band  140  being ring shaped or generally symmetrical about the center point  165 . Thus, the magnetoelastic sensor  100  ideally has no unpaired magnetic poles where the sensor assemblies  150 A,  150 B,  150 C, and  150 D are disposed. 
         [0064]    Illustrated in  FIG. 7  is an exemplary alternative embodiment of the magnetoelastic sensor  100 , generally designated in  FIG. 7  as  700 , in accordance with an exemplary embodiment of the present invention. In the magnetoelastic sensor  700 , the sensor assemblies  150 A through  150 D are replaced with sensor assemblies  750 A through  750 D. The magnetoelastic sensor  700  is otherwise similar to the magnetoelastic sensor  100 . 
         [0065]    Illustrated in  FIGS. 8A and 8B  are cross-sectional views of the magnetoelastic sensor  700 , in accordance with an exemplary embodiment of the present invention.  FIG. 8A  illustrates a right-side view along a cross-section of the magnetoelastic sensor  700  at the centerline  180 , and  FIG. 8B  illustrates a left-side view along a cross-section of the magnetoelastic sensor  700  taken at the centerline  170 . 
         [0066]    The sensor assemblies  750 A through  750 D comprise respective sensor platforms  752 A,  752 B,  752 C, and  752 D, respectively, having inside surfaces  751 A,  751 B,  751 C, and  751 D and outside surfaces  753 A,  753 B,  753 C, and  753 D. The sensor assemblies  750 A through  750 D further comprise, respectively, first sensors  754 A,  754 B,  754 C, and  754 D disposed, respectively, on the inside surfaces  751 A,  751 B,  751 C, and  751 D and second sensors  755 A,  755 B,  755 C, and  755 D disposed, respectively, on the outside surfaces  753 A,  753 B,  753 C, and  753 D. The first sensors  754 A,  754 B,  754 C, and  754 D and the second sensors  756 A,  756 B,  756 C, and  756 D are symmetrically disposed about the center point  165  of the plate  110 . 
         [0067]    The second sensors  756 A,  756 B,  756 C, and  756 D are disposed near the first sensors  754 A,  754 B,  754 C, and  754 D but at a distance greater from the magnetic band  140  than the first sensors  754 A,  754 B,  754 C, and  754 D. The first sensors  754 A,  754 B,  754 C, and  754 D are chosen to have a direction of sensitivity opposite (180°) from their respective paired second sensors  756 A,  756 B,  756 C, and  756 D. The pairing reduces the sensitivity of the magnetoelastic sensor  700  to ambient magnetic fields compared to the magnetoelastic sensor  100 . 
         [0068]    The first sensors  754 A and  754 C are disposed above the magnetic band  140  along the centerline  170 , and the first sensors  754 B and  754 D are disposed above the magnetic band  140  along the centerline  180 . The centerline  170  longitudinally bisects the first sensors  754 A and  754 C, and the centerline  180  longitudinally bisects the first sensors  754 B and  754 D. The sensors  754 A,  754 B,  754 C, and  754 D are disposed over the magnetic band  140  such that a centerline  145  of the magnetic band  140  laterally bisects the sensors  754 A,  754 B,  754 C, and  754 D. 
         [0069]    The second sensors  756 A and  755 C are respectively disposed above the first sensors  754 A and  754 C along the centerline  170 , and the second sensors  756 B and  756 D are respectively disposed above the first sensors  754 B and  754 D along the centerline  180 . The centerline  170  longitudinally bisects the second sensors  756 A and  756 C, and the centerline  180  longitudinally bisects the second sensors  756 B and  756 D. The sensors  755 A,  755 B,  755 C, and  755 D are disposed over the magnetic band  140  such that a centerline  145  of the magnetic band  140  laterally bisects the sensors  755 A,  755 B,  755 C, and  755 D. 
         [0070]      FIGS. 9 ,  10 A, and  10 B illustrate an exemplary alternative embodiment of the magnetoelastic sensor  700 , generally designated in  FIGS. 9 ,  10 A, and  10 B as  900 , in accordance with an exemplary embodiment of the present invention.  FIGS. 10A and 10B  illustrate cross-sections of the magnetoelastic sensor  900  taken along the centerlines  180  and  170 , respectively. The magnetoelastic sensor  900  comprises the elements of the magnetoelastic sensor  700 . In the magnetoelastic sensor  900 , the sensor assemblies  750 A through  750 D are replaced with sensor assemblies  950 A through  950 D. 
         [0071]    The sensor assemblies  950 A through  950 D comprise respective sensor platforms  952 A,  952 B,  952 C, and  952 D respectively having inside surfaces  951 A,  951 B,  951 C, and  951 D and outside surfaces  953 A,  953 B,  953 C, and  953 D. The sensor assemblies  950 A through  950 D further comprise, respectively, first sensors  954 A,  954 B,  954 C, and  954 D disposed, respectively, on the inside surfaces  951 A,  951 B,  951 C, and  951 D and second sensors  956 A,  956 B,  956 C, and  956 D disposed, respectively, on the outside surfaces  953 A,  953 B,  953 C, and  953 D. 
         [0072]    The sensor assemblies  950 A through  950 D are similar to the sensor assemblies  750 A through  750 D, but they differ in that the second sensors  956 A,  956 B,  956 C, and  956 D are inset radially relative to the center point  165  of the magnetic band  140  compared to the second sensors  755 A,  755 B,  755 C, and  755 D. This inset is best seen in  FIG. 9 . The magnetoelastic sensor  700  includes no such inset. 
         [0073]    Referring now to  FIG. 11 , there is illustrated a schematic drawing of an exemplary embodiment of a sensor assembly, generally designated as  1100 , in accordance with an exemplary embodiment of the present invention. The sensor assembly  1100  comprises a magnetoelastic sensor  100 ,  700 , or  900  connected to circuitry  1110  via a communications link  1115 . The magnetoelastic sensor  100 ,  700 , or  900  outputs the signals from its sensor assemblies via the communications link  1115  to the circuitry  1110 . The circuitry  1110  combines the signals provided by the sensor assemblies and outputs the combined signal via an output  1120 . The output  1120  indicates the amount of tension or compression sensed by the magnetoelastic sensor  100 ,  700 , or  900 . 
       EXAMPLE 1 
       [0074]    Referring now to  FIG. 12 , there is illustrated a graph of data from a test of an exemplary implementation of the magnetoelastic sensor  100 . Weights were hung from the exemplary implementation of the magnetoelastic sensor  100 , and the output voltage was recorded. The slope in the graph shows a sensitivity of 0.56 mV/pound. 
         [0075]    These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it is to be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It is to be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention.

Technology Category: 3