In a relay, the armature is the moving part.

In an electric motor the armature is the rotating part.

Armature from a brush motor.

Active Iron

The amount of iron in the stator and rotor of a motor. Usually the amount of active iron is increased or decreased by lengthening or shortening the rotor and stator.

Air Gap

The space between the rotor and stator in an electric motor, through which magnetic lines of force pass.

Armature Current

Rated full load armature circuit current.

Armature Inductance

Armature inductance in milli-henries (saturated).

Armature Reaction

The current that flows in the armature winding of a DC motor tends to produce magnetic flux in addition to that produced by the field current. This effect, which reduces the torque capacity, is called armature reaction and can effect the commutation and the magnitude of the motor′s generated voltage.

Armature Resistance

Armature resistance is measured in ohms at 25°C.


A cylindrical device mounted on the armature shaft and consisting of a number of wedge-shaped copper segments arranged around the shaft.


An auxiliary set of field poles carrying armature current to reduce the field flux caused by armature reaction in a DC motor.


Arrangement of laminations on an armature to produce a slight angular pattern of their slots with respect to the shaft axis. This skew or twisted pattern helps to eliminate low speed cogging effects in an armature and minimize induced vibration in a rotor as well as reduce associated noise. This can help to increase starting torque.

See also: Armature Losses, Armature Reaction, Commutator, Electric Motor Windings, Electric Motors, Interpoles, Relay, Stator, Turn, Wave Winding.

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Subjects: Electronics Physics