Moving Iron Instruments - Skills Hub

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Moving Iron Instruments

In this picture, a diagram of Moving Iron instruments will be shown which has been labeled and the information related to it has been written along with it.

These are instruments in which the current-carrying coil (electromagnetic) is stationary while the soft iron moves. The iron is attached to the spindle and the pointer is fixed on top of the spindle. Both the spindle and the pointer move when the iron moves under the influence of the magnetic coil. which shows the reading on the scale. Hence such instruments are called Moving iron instruments. Such instruments are suitable for both AC and DC measurements but are mostly used for AC measurements. In the case of DC measurements, slight errors may occur due to residual magnetism in the iron. These instruments are used as ampere meter and voltmeter. Their range can be extended with the help of an instrument transformer. They have the following two types.

  1. Moving Iron Attraction Type 
  2. Moving Iron Repultion Type

Application of Moving Iron Instruments

Instruments are used almost everywhere like factories, laboratories etc. due to their robust construction, simplicity and cheapness. They can be used in both AC and DC circuits. Their specific uses are as follows.
  1. Ampare Meter
  2. Volt Meter
  3. Power Factor Meter 
  4. Synchroscope

Advantages & Disadvantages

Advantages

  1. They are simple and strong in texture. 
  2. Moving coils are cheaper than instruments. 
  3. Both AC and DC supplies can be used. 
  4. Consume less power. 
  5. Effective air damping can be provided. 
  6. Defects are less likely to occur and repair is easy.

Disadvantages 

  1. Their scale is not uniform. 
  2. Usually, the duplication angle is only 45 degrees. 
  3. Affected by external or atmospheric influences. Therefore magnetic shielding is required for sensitive devices. 
  4. Errors are possible due to hysteresis and eddy currents. Variations in frequency and waveform are prone to errors in their readings. 
  5. In the case of a voltmeter, readings can be affected by temperature. 
  6. They have lower accuracy and sensitivity than moving coil instruments (especially PMMC).

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