Magnetic transducer torque measurement

A magnetic transducer system comprising:

• a magnetic transducer element in the form of a member of magnetizable material having an axis about which it is rotatable;
• wherein said member is a portion of a shaft, and
• said member being magnetized to have a first and second annulus of axially-directed stored magnetization about said axis extending inwardly from an external surface of said member, the first and second annuli being axially spaced and, preferably, each annulus of magnetization emanating no significant component of circumferential (tangential) magnetic flux externally of said surface when the member is subject to torque applied to said member about said axis, and each annulus emanating a magnetic field the distribution of a component of which in the axial direction exhibits a magnetic field profile which shifts in the axial direction as a function of torque applied to said member about said axis;
• said first annulus exhibiting a magnetic field profile of said component which shifts in the opposite direction to the shift of the magnetic field profile of said component exhibited by said second annulus in response to a given torque applied about said axis;
• and
• a sensor system comprising respective sensor assemblies responsive to the magnetic field profile exhibited by the first and second annulus respectively and means for combining the responses of said sensor assemblies to provide an output signal representing a torque applied to the shaft or an axial displacement of the shaft or respective signals representing the aforementioned torque and axial displacement.

A transducer arrangement comprising:

• a magnetic transducer element which comprises:
• a member of magnetizable material having an axis about which it is rotatable or capable of flexing;
• wherein said member is a portion of a shaft, and
• wherein said member being magnetized to have an annulus of axially-directed stored magnetization about said axis extending inwardly from an external surface of said member, and said annulus of magnetization emanating no significant component of circumferential (tangential) magnetic flux externally of said surface when the member is subject to torque applied to said member about said axis and/or to a force applied to cause said member to flex about said axis, said annulus emanating a magnetic field having a distribution in the direction of said axis, the magnetic field profile of the axial component of which distribution shifts in the axial direction over at least a portion of the distribution of the emanated magnetic field in the axial direction as a function of the torque or the force applied;
• and at least one magnetic field sensor located adjacent said annulus of magnetisation to sense the field emanated by said element,
• wherein the at least one sensor is located axially at a point (sweet spot) at which the magnetic field profile exhibits least variation as a function of the rotational angle of said member.