| 摘要 |
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.
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