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AssigneeSmiths Industries Limited
InventorsPercy Edwin Towndrow, James Bernard Vousden
Estimating the term…
A moving-coil electrical instrument in which an electric coil mounted for angular displacement about an axis embraces an annular core which is disposed between radially-spaced walls of a housing to define two radially-spaced, annular air-gaps through which extend the inner and outer limbs respectively of the coil. The inner air-gap is made shorter (in the direction of the lines of magnetic flux) than the outer air-gap, so that any change in the force induced into the outer limb of the coil, arising from, for example, radial misplacement of the core, is accompanied by a greater change in the force induced into the inner limb. Thus the difference in the radial distances from the axis of the inner and outer limbs is offset, and the changes in the torques induced into the inner and outer limbs balance one another. Alternatively, or additionally, the inner air-gap may be made wider (measured parallel to the respective limb of the coil) than the outer air-gap.
A moving-coil electrical instrument comprising an electric coil having first and second portions, means mounting the electric coil for angular displacement about an axis, a magnetic circuit assembly comprising a housing of magnetic material having inner and outer radially-spaced, substantially annular surfaces, an annular core member of magnetic material, and means mounting the core member between the said inner and outer housing surfaces to define, between the said inner housing surface and the core member, and between the said outer housing surface and the core member, respective inner and outer radially-spaced annular air-gaps, the coil mounting means being so arranged that the coil embraces the core member with its said first and second portions extending through respective ones of the air-gaps to cause electromagnetically-induced torque to be applied to the coil about the said axis, and the nominal dimensions of said radially-spaced annular air-gaps being unequal and so related to one another that, at any angular position of the coil, a change in the component of the said torque induced into the said first portion of the coil, arising from radial displacement of the core member, is compensated by change of opposite sense and substantially equal magnitude of the said torque induced into the said second portion of the coil.
A moving-coil electrical instrument comprising an electric coil, means mounting the electric coil for annular displacement about an axis, and a magnetic circuit assembly comprising a housing of magnetic material having inner and outer radially-spaced, substantially annular surfaces, an annular core member of magnetic material, and means mounting the core member between the said inner and outer housing surfaces to define, between the said inner housing surface and the core member, and between the said outer housing surface and the core member, respective inner and outer radially-spaced annular air-gaps, said means mounting the coil being so arranged that the coil embraces the core member and extends through both of said radially-spaced annular air-gaps, the dimension of said inner annular air-gap measured generally parallel to the lines of magnetic flux to be established in said inner air-gap being less than the corresponding dimension of said outer annular air-gap, such that at any angular position of the coil, a change in the component of the torque induced into the part of the coil in one of said air gaps, arising from radial displacement of the core member, is compensated by change of opposite sense and substantially equal magnitude of the torque induced into the part of the coil in the other of said air gaps.
A moving-coil electrical instrument comprising an electric coil, means mounting the electric coil for angular displacement about an axis, and a magnetic circuit assembly comprising a housing of magnetic material having inner and outer radially-spaced, substantially annular surfaces, an annular core member of magnetic material, and means mounting the core member between the said inner and outer housing surfaces to define, between the said inner housing surface and the core member, and between the said outer housing surface and the core member, respective radially-spaced inner and outer annular air-gaps, the means mounting the coil being arranged such that the coil embraces the core member and extends through both of said annular air-gaps, and the dimension of said inner annular air-gap measured generally parallel to, and in the path of, the portion of the coil extending through said inner air-gap being greater than the corresponding dimension of said outer annular air-gap, such that at any angular position of the coil, a change in the component of the torque induced into the part of the coil in one of said air gaps, arising from radial displacement of the core member, is compensated by change of opposite sense and substantially equal magnitude of the torque induced into the part of the coil in the other of said air gaps.
Dependencies are inferred from the claim text.