Ammeter, Eccentric Iron Disc.
This ammeter comprises a cylindrical electro-magnet excited by the
current to be measured. A disc of iron free to rotate is suspended on
pivots below it. A piece is cut off the disc at one part of its
periphery so as to give more metal to one side than to the other. In its
zero position this portion of the disc swings towards the magnet. As the
latter is more and more excited the other or more projecting portion of
the disc turns towards it, being attracted like an armature, and moves
against the force of gravity, the disc rotating. An index attached to
the disc swings over the face of a graduated scale. The disc is so
counterpoised that in its natural position the index points to zero.
Ammeter, Electro-magnetic.
An ammeter depending for its working upon the action of an
electro-magnet, which is excited by the current to be measured.
Ammeter, Gravity.
An ammeter whose hand or index is drawn into the zero position by
gravity, and whose displacement therefrom is produced by the action of
the current to be measured.
Fig. 11. GRAVITY SOLENOID AMMETER.
Ammeter, Magnetic Vane.
A fixed plate of soft iron is placed within a coil. Facing it is a
second disc free to move or swing on an axis. When the field is excited
the two repel each other because like polarity is induced in each, and
the motion of the movable disc indicates the strength of the current.
The same instrument is wound for high resistance and constitutes a
Magnetic Vane Voltmeter.