Difference Between Moving Iron and Moving Coil

The basic difference between the Moving iron and Moving coil instruments is that. A moving iron instruments uses a soft iron whereas moving coil instrument uses a coil as moving mechanism.

Comparison Table

PropertiesMoving IronMoving Coil
ConstructionIron is used as moving mechanismConductor Coil is used as Moving mechanism
Working PrincipleMagnetismsame as Dc motor
Damping torqueAir frictionEddy current damping
Power consumptionMoreLess
ScaleNon-UniformUniform
SensitivityLessMore
AccuracyLessMore
ApplicationDC and ACDC only

What is Moving Iron Instrument

A soft iron piece when attracted or repelled by the magnetic field a coil is moves. A pointer is attached with the moving piece. Then shows deflection on a calibrated scale. These instruments are simple cheap and reasonably accurate and can be used for ac/dc measurement. Hence if finds use in practical fields.

What is Moving Coil Instrument

The coil rotates between the magnetic field of a permanent magnet in Moving coil. instruments. Such instruments are used for dc measurements only. It works on the principle of that when a current carrying conductor (coil) placed in a magnetic field then it experiences a force. Because of this magnetic field the coil rotates.

Difference Between the Instruments

  1. Construction: Moving coil instruments are simple and robust in construction and are therefore, cheaper in cost. Moving iron instruments are costlier in comparison to moving iron instruments because of delicate construction and necessary accurate machining and assembly of various parts.
  2. Damping torque: Air friction damping is provided in moving iron which is not effective while in moving coil instruments very effective and reliable eddy current damping is provided.
  3. Power consumption: Moving coil instruments consume less power as compared to moving iron.
  4. Scale: Moving Coil instruments have uniform scale while moving iron instruments have non
  5. Sensitivity: Moving iron instruments are less sensitive as compared to the Moving coil
  6. Accuracy and reliability: Moving coil instruments are more accurate and reliable as compared to moving iron because they have no hysteresis loss and they are not affected by stray magnetic fields.
  7. Applications: Moving iron instruments can be used both in dc as well as in ac circuits. But moving coil instruments cannot be used in ac circuits