Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

hysteresis
(1) the phenomenon that the magnetic state of a substance is dependent upon its magnetic history, so that its magnetization for an increasing magnetizing force differs from that for a decreasing magnetizing force.

(2) the characteristic of magnetic materials that causes the trajectory of the flux density vs. field intensity curve as the intensity is increased to be different from that when the intensity is decreased, giving rise to a loss, which is proportional to the area enclosed by the two trajectories.
hysteresis brake
a braking device utilizing hysteresis to provide a constant braking torque irrespective of slip speed.
hysteresis control
a time-optimal feedback control method in which the control variable reaches a reference value in the shortest possible time and then stays within a prescribed hysteresis band around the set point through manipulation of the system state between two configurations. The actual variable is compared with the reference value, and if the error exceeds the hysteresis band, then the control input is changed such that the control variable is forced to decrease. On the other hand, if the actual variable falls below the hysteresis band then the control input is changed such that the control variable increases in magnitude.
hysteresis curve
a graph describing the relationship between the magnetic flux density and the magnetic field intensity in a (usually ferromagnetic) material.
hysteresis drive

See hysteresis torque coupling
hysteresis loss
the energy loss due to hysteresis in a magnetic material subjected to a varying magnetic field.
hysteresis motor
any of a variety of single-phase AC motors that use the hysteresis properties of hard magnetic materials to develop torque. Stator windings of a hysteresis motor can be of any design that produces a rotating flux within the machine. Motion of the rotating flux over the rotor magnetizes the hard magnetic material on the rotor; however, the hysteresis characteristics of the material cause the alignment of magnet flux to lag the rotating stator flux. This misalignment produces rotor torque. Because of the nature of the torque production, hysteresis motors operate at synchronous speed and have a constant torque characteristic, which permits them to synchronize any load that they
can accelerate.
hysteresis torque coupling
a magnetic drive in which the magnetizing stator magnet drives a rotor of hysteresis material through the complete hysteresis cycle once per rotation, resulting in a constant torque characteristic irrespective of relative speed.
major hysteresis loop
for a magnetic material, the loop generated as intrinsic or magnetic induction (Bi or B) is plotted with respect to applied field (H) when the material is driven from positive saturation to negative saturation and back, showing the lag of induction with respect to applied field.
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