
132
Scale
(uneven)
Damper
Diagram 98 Moving-iron instrument
The moving-iron instrument (repulsion type)
Diagram 98 illustrates a moving-iron instrument of the repulsion type.
It comprises a coil, with a fixed iron, a pointer with an iron vane attached
(moving iron) and a damping device inside it.
When a supply, either a.c. or d.c, is applied to the coil, both fixed
and moving irons are magnetized to the same polarity and will therefore
repel each other.
The design of the irons ensures that the repulsion is always in the
same direction.
The damper ensures a slow and even movement of the pointer. It
consists of a cylinder closed at one end an ...