MOVING IRON INST..ppt

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CH-2 Analog & Digital voltmeter & ammeter

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MOVING IRON INSTRUMENTS:

BY :LDRP-ITR GANDHINAGAR MOVING IRON INSTRUMENTS

MOVING IRON VOLTMETER:

 Moving iron instuments are classified as: 1)Attraction type 2)Repulsion type MOVING IRON VOLTMETER

Moving Iron Attraction Type Instrument:

Moving Iron Attraction Type Instrument Basic working principle : “ A soft iron piece if brought near the magnet gets attracted bye magnet. ”

ATTRECTION TYPE INSTRUMENT:

ATTRECTION TYPE INSTRUMENT

Construction Of The Attraction Type Instrument:

Construction O f The Attraction Type Instrument  It consist of fixed coil C and moving iron piece D. The coil moving coil is a flat disc which is eccentrically mounted on the spindle.  The spindle is supported between the jewel bearings .  The spindle carries pointer which moves over a graduated scale.  The no. of turns of the fixed coil are dependent on the range of the instrument.  For passing large current through the coil only few turns are required.

Slide 6:

 The controlling torque is provided by the springs but the gravity control may be used for vertically mounted panel type instrument.  The damping torque is provided by the air friction . A light aluminum piston is attached to the moving system .  It moves in a fixed chamber. The chamber is closed at one end. It can also be provided with the help of vane attached to the moving system.  The operating magnetic field is very weak . Hence eddy current damping is not used since it requires a permanent magnet which would affect or distort the operating field.

Moving Iron Repulsion Type Instrument:

Moving Iron Repulsion Type Instrument Basic working principle : “ There is repulsion between two iron pieces as they are magnetized with the same polarity. ”

Construction And Working Of Repulsion Type Moving Iron::

Construction And Working Of Repulsion Type Moving Iron:  A hollow circular coil is used and one of the iron pieces is attached inside the hollow coil.  The other iron piece is attached to the spindle.  The current to be measured is passed through the coil, coil produced the magnetic field.  As both the iron pieces are placed in the same magnetic field , they are magnetized with same polarity.

Slide 11:

 Hence the deflecting torque is produced due to the force of repulsion between two iron pieces.  Independent of the direction of current, the deflection is produced in the same direction.  the force of repulsion between iron pieces is directly proportional to square of current hence scale is non-uniform.  Controlling torque is produced by either spring or gravity control.  Damping is produced by the air friction damping.

REPULSION TYPE INSTRUMENT:

REPULSION TYPE INSTRUMENT

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