Working Principle of Attraction Type Moving Iron
Instruments
The working principle of these instruments is according to this:
“If a piece of a non-magnet soft iron is brought near, either of the two ends
of a current-carrying coil, it would be attracted into the coil in the
same way as it would be attracted by the pole of a bar magnet.” Hence, if we
attach a disc of soft iron on a spindle the iron disc will rotate into
the coil and the electric current will pass through it and the pointer
will deflect.
Working Principle of Repulsion Type Moving Iron
Instruments
These instruments consists of a fixed coil which is placed between
the two soft iron rods and are parallel to each other and one rod is fixed and
the other is movable and it carries a pointer. When the current is passed
through the coil, it makes its own magnetic field and magnetizes the two rods
which are parallel to each other and these two rods repel each other and as a
result the pointer deflects opposing the controlling torque of a
spring.
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