Glossary of Terms - A through E

Absolute: refers to a feedback device such as a resolver or an absolute encoder that provides unique position information for each discrete shaft location; unlike an incremental feedback device which requires a known reference point, an absolute feedback device retains position information when power to the system is momentarily lost.

AC induction motor: class of motors that derives its name from the fact that current is induced into the rotor windings without any physical connection with the stator windings (which are directly connected to an AC power supply); adaptable to many different environments and capable of providing considerable power as well as variable speed control.

AC synchronous motor: class of motors that has its phases in correct relationship with each other at every rotor position so that the phases of the stator are synchronous with the rotor poles; adaptable to many different environments and capable of providing considerable power as well as variable speed control.

Acceleration: rate of increase in velocity with respect to time; equal to net torque divided by inertia.

Accuracy: difference between the actual value and the measured or expected value.

Ambient temperature: temperature of the surroundings.

Amplifier: electronics that convert low level inputs to high level outputs.

Armature: rotating member of a brushed DC motor.

Back emf: voltage generated when a permanent magnet motor is rotated; a limiting factor for the high speed torque output of a permanent magnet motor as it is opposite in polarity to the supplied voltage and directly proportional to motor speed.

Bifilar winding: indicates two distinct windings in the same physical arrangement; these windings are usually wired together, either in series or in parallel, to form one phase.

Bipolar chopper drive: drive that uses the switch mode method to control motor current and polarity.

Brush: conductor between the commutator and the external circuit of a brushed DC motor.

Brushed DC motor: class of motors that has a permanent magnet stator and a wound iron-core armature, as well as mechanical brushes for commutation; capable of variable speed control, but not readily adaptable to different environments.

Brushless servomotor: class of servomotors that uses electrical feedback rather than mechanical brushes for commutation; durable and adaptable to many different environments.

Case temperature rating: maximum temperature the motor case can reach without the inside of the motor exceeding its internal temperature rating.

Class B insulation: insulation with a temperature rating of 130° C; essentially the industry standard.

Class H insulation: insulation with a temperature rating of 180° C; comes standard with Empire Magnetics extended temperature (HT) and laboratory grade (VX) motors.

Class 220 insulation: insulation with a temperature rating of 220° C; can be provided on a custom basis.

Cleanroom classification: specifies a certain number of particles of a certain size in a given volume; Empire Magnetics standard grade (VS) and laboratory grade (VX) motors and related products exceed Class 10 Cleanroom requirements.

Closed-loop: describes a system where a measured output value is compared to a desired input value and corrected accordingly (e.g., a servomotor system).

Cogging torque: a measure of non-uniform velocity (e.g., jerkiness, momentary stalling, slipping).

Commutation: controlling the currents or voltages in the motor phases in an effort to optimize motor performance; can be achieved mechanically or electrically.

Commutator: mechanical device in a brushed DC motor that passes current from the brushes to the windings.

Connector: device used for connecting cables; usually come in pairs of female and male.

Continuous stall current: amount of current applied to the motor to achieve the continuous stall torque.

Continuous stall torque: maximum amount of torque a motor can provide at zero speed without exceeding its thermal capacity.

Controller: used to describe collective group of electronics that control the motor (e.g. drive, indexer, etc.).

C.O.P.: condensed outgas product; measurement of motor cleanliness in a vacuum environment.

Coupler: device that fastens the output shaft of the motor assembly to the shaft of the load.

Critically damped: describes a system where the response to an input change is achieved in the minimum possible time.

Cryogenic: Empire Magnetics cryogenic motors and related products are rated for an ambient temperature of 20° K though motors rated for an ambient temperature of 4° K have been provided on a custom basis.

Current at peak torque: amount of current required to produce peak torque.

Current sink: transistor output configured so that the load is wired from the (+) side of the power source to the output and the transistor makes the circuit sink to common.

Current source: transistor output configured in such a way that the load is wired from the output of the sensor to the common side of the power source so that when the transistor turns on voltage is sourced to the load.

Damping ratio: ratio of actual damping to critical damping; if the damping ratio is less than one a system is said to be underdamped and if it is greater than one a system is said to be overdamped.

Damping: refers to the rate of decay or settling time of a signal.

Deceleration: rate of decrease in velocity with respect to time.

Decibel: logarithmic measure of gain equal to twenty times the log of the gain.

Demag current: current at which the motor magnets will begin to permanently demagnetize; usually equal to the peak current.

Detent torque: torque that is present in a non-energized motor.

Drive: amplifier that converts step and direction input to motor currents and voltages.

Duty cycle: percentage of time the motor is on.

Dynamic: refers to something that is in motion.

Dynamic braking: braking that can be enacted while the motor is in motion.

EMI: electromagnetic interference, or Empire Magnetics, Inc.

Encoder: feedback device that utilizes an optical source and sensor to provide velocity and position information in the form of a digital signal; not readily adaptable to different environments.

End play: amount of axial displacement resulting from the application of a load equal to the stated maximum axial load.

Excitation: external electrical energy applied to a transducer for its proper operation.

Explosion proof: specification that indicates an enclosure is capable of withstanding and confining internal explosions.

Extended temperature: Empire Magnetics extended temperature (HT) motors and related products have a case temperature rating of -40° C to 155° C.