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The effect of stray magnetic fields on the actuating torque of a portable instrument is the maximum when the operating field of the instrument and the stray fields are

The effect of stray magnetic fields on the actuating torque of a portable instrument is the maximum when the operating field of the instrument and the stray fields are Correct Answer parallel

Stray Magnetic Field:

  • It is also called demagnetization fields.
  • This is weak at full-scale deflection hence it can easily be distorted.
  • Due to the external magnetic field inside, the operating field inside the meter is disturbed.
  • This will lead to the weakness of the operating magnetic field.
  • The stray magnetic field depends on the magnitude of the external magnetic field and its direction.
  • When the magnitude of the external magnetic field is in phase with the main field, stray magnetic field error will be more.

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This error is minimized by the following methods:

  • By shielding the instrument with the help of a steel case.
  • By sheet steel lining to the case.

 

In PMMC instrument permanent magnets are used. Therefore it will have a strong magnetic field.

In an MI instrument, the Air core is used. Therefore it will have a weak magnetic field.

The stray magnetic field error is more in the MI instrument compared to the PMMC instrument.

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