For measurements of currents from 10 amperes upward, there is no need
to employ a complete coil as the deflecting agent; one half-coil or one
strip passing close under the needle gives sufficient deflecting force,
and thus the construction of the instrument is rendered extremely
simple. The current, after entering at one of the flat electrodes,
splits in two parts, each part passing round the winding of an electro
magnet of horseshoe form, the similar poles of both magnets pointing
toward each other and toward the needle. After traversing the winding,
the current unites again, and passes through a metal strip close under
the needle, and finally out of the instrument by the other electrode,
which lies close under that at which the current entered, but is
insulated from it by a sheet of fiber. The metal strip is set at an
angle, to balance or overbalance, as may be preferred, the magnetic
influence of the exciting coils. The effect of this overbalancing is
shown in Fig. 5, where the full curve represents the current as a
function of the deflection--obtained by comparison with a standard
instrument--and the dotted curve shows what that relation between
deflection and current would be if the law of tangents held good for
these instruments.
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