29-06-2013, 03:01 PM
MOVING IRON INSTRUMENTS
[attachment=56234]
Construction Of The Attraction Type Instrument
It consists of fixed coil C and moving iron piece D. The 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.
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.
[attachment=56234]
Construction Of The Attraction Type Instrument
It consists of fixed coil C and moving iron piece D. The 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.
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.