Moving Iron Type of Instruments:
The MI type of instruments are suitable for measuring current and voltage both for AC and DC and that's why these are called universal type of instruments. They are classified into two types.
1) Attraction Type of Moving Iron Instruments:
Attraction type of MI instruments is shown in the figure. The coil is flat and has a narrow slot-like opening. The moving iron is a flat disc or a sector eccentrically mounted. When the current flows through the coil, a magnetic field is produced and the moving iron moves from the weaker field outside the coil to the stronger field inside it or the moving iron is attracted in. The moving iron tries to occupy the least reluctance path because the flux is inversely proportional to reluctance and reluctance is inversely proportional to the area of cross-section so flux is directly proportional to the area of cross section and hence the disc gets attracted towards the inside of the magnetic field. The controlling torque is provided by spring but gravity control can be used for panel type of instruments which are vertically mounted. damping is provided by air friction usually by a vane moving in a sector-shaped chamber.
2) Repulsion type of Moving Iron Instruments:
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