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Why are moving iron test instruments not used with DC although they can work in DC?
Wiki User
∙ 9y ago
For moving-iron instrument magnetic field is caused when the current (voltage) passes the fixed circle. When the current (voltage) passes the fixed circle，the two iron plates are magnetized ,rotational torque is resulted, the deflection angle indicate measured current. Because the magnetized polarity is same for AC or DC, moving-iron instrument can be used in AC and DC circuit. For permanent-magnet moving-coil instrument magnetic field is caused by the permanent-magnet, When the DC current passes the moving coil, rotational torque is resulted,so the deflection angle indicate measured DC current. As AC current passes the moving coil ,because inertia of moving parts of meter the deflection angle indicate rotational torque average, but rotational torque average is zero in cycle, moving parts of meter is´t deflec,so permanent-magnet moving-coil instrument only is used in DC circuit.
Wiki User
∙ 9y ago
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