Page 293 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Moving iron instrument
The deflecting torque in any moving-iron instrument is due to forces on a small piece of magnetically ‘soft’ iron
that magnetized by a coil carrying the operating current.
Moving iron type(both for DC/AC)
a Attraction type
b Repulsion type
Parts and essential t orques of moving iron

• Moving element: a small piece of soft iron in the form of a vane or rod.
• Coil: to produce the magnetic field due to current flowing through it and also to magnetize the iron pieces.
• In attraction type, a vane of soft iron piece is attached to the spindle
• In repulsion type, a fixed and movable vane is also used and magnetized with the same polarity.

Attraction type

Working
• It consists of an electromagnetic coil with air core
• When coil is connected to the supply,magnetic field is produced and it attracts the iron piece.
• It’s turn moves the pointer to deflect

• Attraction of soft iron piece independent on the current direction and can be used in Ac and DC
Repulsion type

Construction
• It consists of coil wound on brass bobbin, inside which two strips of soft iron vanes set axially

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CITS : Power - Electrician & Wireman - Lesson 50-53