Iron Vane Movement

The iron-vane movement designs is the most frequently used by the current instrument manufacturers. The principle of repulsive force between like magnetic poles operates the vane movement. The current applied to the coil wrapped around the two vanes establish a magnetic field within the coil, magnetizing the fixed and moveable vanes. Since both vanes will be magnetized in the same manner, they will have the same polarity, and a force of repulsion will develop between the two vanes. The stronger the applied current, the stronger are the magnetic field and the force of repulsion between the vanes. The fixed vane will remain in position, but the moveable vane will rotate and provide a measure of the strength of the applied current.
Iron-vane movement.
Fig. 1: Iron-vane movement.
Movements of this type are usually rated in terms of current and resistance. The current sensitivity (CS) is the current that will result in a full-scale deflection. The resistance (Rm) is the internal resistance of the movement. The graphic symbol for a movement appears in Fig. 2(b) with the current sensitivity and internal resistance for the unit of Fig. 2(a).
Iron-vane movement.
Iron-vane movement.
Fig. 2: Iron-vane movement; (a) photo, (b) symbol and ratings.
Movements are usually rated by current and resistance. The specifications of a typical movement may be $1 mA$, $50 Ω$. The 1 mA is the current sensitivity (CS) of the movement, which is the current required for a full-scale deflection. It is denoted by the symbol $I_{CS}$. The $50 Ω$ represents the internal resistance (Rm) of the movement.

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