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Glossary Of Terms
Click the Letters below to find the Glossary section beginning with the corresponding letter..
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.
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.
Feedback: necessary for closed-loop control, it is the signal that provides the motor output information (e.g., speed, position, etc.) to the controller.
Feedthru: device that physically interfaces one side of a separating surface to the other (e.g., an electrical feedthru passes electrical signals from one side of a wall to the other).
Hall sensors: feedback device used for commutation.
Hazardous duty: Empire Magnetics hazardous duty (PT) motors and related products can be designed into a system that meets NFPA class I, II, and/or III requirements.
Holding torque: maximum torque the motor can provide to hold itself in a fixed position; also called static torque.
Horsepower: measurement of power, usually mechanical.
Hybrid step motor: class of step motors that utilizes a permanent magnet to polarize soft iron pole pieces around the rotor.
Hysterisis: describes a type of error whereby the system response to an increasing input signal is not equal and opposite to a decreasing input signal of equal magnitude.
Idle current reduction: drive feature that reduces the motor current at a standstill to reduce motor heating; a typical value is 50% for a step motor drive.
Incremental: refers to an output that is measured in known increments from a known reference point; e.g., a step motor provides incremental motion based on an initial position and an incremental encoder provides incremental feedback information based on a known zero point.
Indexer: electronics that convert high level computer or PLC commands to step and direction pulses.
Inductance: measurement of a conductor’s ability to resist a change in current flow; analogous to an object’s ability to resist a change in velocity.
Inertia match: refers to the ratio of the reflected load inertia to the rotor inertia; a general rule is that this ratio should be no more than 10:1 for an inertia match.
Inertia: measurement of an object’s ability to resist a change in velocity, this property is dependent upon the mass and shape of the object.
IP: European rating system for specifying equipment compatibility with dust, water, and shock; also recognized in the U.S.
Magnetic stack: one set of soft iron pole pieces and permanent magnet; step motors typically have one, two, and three magnetic stack versions for each frame size.
Microstepping: a method of proportioning current so that the full steps of the step motor are broken into smaller, microsteps; a typical microstepping drive can provide up to 25,000 steps per revolution.
Motor efficiency: mechanical power output of the motor divided by electrical power input to the motor.
MTBF: mean time between failure, a measurement of reliability.
NEC: National Electric Code, a safety document produced by the NFPA.
NEMA: National Electrical Manufacturer’s Association; responsible for providing many industry standards (e.g., NEMA frame sizes).
NFPA: National Fire Protection Association; responsible for providing safety information (800-344-3555). The N.F.P.A. also writes the National Electric Code.
NFPA 496: a guideline published by the NFPA that among other things describes the application of positive pressure with dry air or nitrogen to convert the interior of a motor to a non-hazardous area; NFPA 496 is available by calling the NFPA at 800-344-3555.
Oil-filled: describes an enclosure (e.g., a submersible motor) that has been filled with oil to prevent leakage.
Open-loop: describes a system that operates without feedback.
Opto-isolated: method of sending a signal from one piece of equipment to another without the usual requirement of common ground potentials.
Outgassing: evaporation of oil, dirt, or any other substance from a surface after it is placed in a low pressure or vacuum environment.
Parallel: refers to a motor winding configuration; motors that are wired in parallel produce more torque at high speeds but less torque at low speeds than motors wired in series.
Peak torque: maximum torque that can be delivered for even a short period of time.
Permanent magnet motor: general class of motors that uses permanent magnets to produce torque.
Phase: describes one or more signals that neither lag nor lead one another; step motors typically have two phases and brushless motors typically have three phases.
Phase angle: angle at which the steady state input signal leads the output signal.
PMDC motor: permanent magnet DC motor; also called a brushed DC motor.
Power: rate at which work is done; equivalent to torque times rotational speed, voltage times current, etc.
Pressure compensator: device that equalizes the internal pressure of the motor with the external pressure of the environment.
Pulse rate: frequency of pulses applied to the drive.
Pulse Width Modulated (PWM) drive: drive that utilizes a method of switching voltage on and off at fixed but variable frequencies.
Purged and Pressurized: NFPA 496 describes the application of positive air or dry nitrogen to purge and then pressurize an enclosure for hazardous area duty.
Radiation hardened: Empire Magnetics radiation hardened (RH) motors and related products are rated to 2 x 108 T.A.D. gamma radiation.
Rated current: maximum allowable current a motor can receive without exceeding its thermal limit.
Rated torque: torque producing capacity at a specified speed.
Reflected load inertia: refers to the load inertia as seen by the motor; e.g., a gearhead reduces the inertia of the load as seen by the motor by a factor of the gear ratio squared.
Regeneration: refers to the electrical energy returned to the drive when a motor acts like a generator as it is slowed mechanically.
Related products: resolvers, brakes, gearheads, etc.
Repeatability: degree to which a parameter can be duplicated.
Resolution: smallest distinct increment of a parameter.
Resolver-to-digital converter: electronics that convert an analog resolver signal to a digital, encoder-like signal.
Resolver: rugged electromagnetic feedback device that acts like a rotating transformer to provide an analog signal with velocity and position information; adaptable to many different environments because of its construction.
Resonance: unfavorable oscillatory behavior (e.g., slow single step response and settling times) caused by mechanical limitations.
RMS: root mean square; derived from power dissipation by an AC current.
Series: refers to a motor winding configuration; motors that are wired in series produce more torque at low speeds but less torque at high speeds than motors wired in parallel.
Servomotor: class of motors that operates within a closed-loop system with respect to both position and velocity.
Settling time: time required for the motor to come to rest at its commanded position; a measure of system performance.
Single step response time: time required for the motor to rotate one step and settle at that position; a measure of system performance.
Slew: portion of a move made at a constant, non-zero velocity.
Speed: change in position with respect to time.
Stall torque: amount of torque developed with voltage applied and shaft locked.
Static torque: see holding torque.
Stator: stationary member of a motor.
Step angle: angular distance of a single full step; 1.8° is a typical value.
Step motor: class of motors that provides incremental motion, or steps, in response to pulses of current that alternately change the polarity of the stator poles; step motors do not require feedback.
Stress-relieved: refers to a material that has undergone a process to eliminate or reduce the residual stresses that result from things such as thermal cycling; Empire Magnetics cryogenic motors and related products are made from stress-relieved materials.
Stiffness: relationship describing motor displacement from a fixed position due to an applied torque of specified value.
T.A.D.: total accumulated dosage.
TEFC: totally enclosed, fan cooled meaning that the motor is equipped for fan cooling by means integral to the motor but external to the enclosing parts.
TENV: totally enclosed, non-ventilated meaning that the motor is not equipped for cooling by means external to the enclosing parts.
Thermal current: see rated current.
Thermal cycling: refers to the expansion and contraction of a material that is heated and cooled repeatedly over time.
Thermal resistance: temperature rise per unit of power loss.
Torque: force that tends to rotate a body.
Torque constant: relationship of torque output per ampere.
Torque to inertia ratio: measurement of the motor’s maximum (i.e., no load) acceleration.
Torr: unit of measurement equal to 1 mm of Hg; commonly used for specifying vacuum pressure levels.
Transducer: device that produces an electrical output that is proportional to a mechanical input.
TTL: transistor transistor logic.
Tuning: adjusting the parameters of a system in an effort to optimize performance.
Type C Face: face mounting with a male pilot (rabbet) fit with threaded holes in the mounting surface.
Unipolar drive: drive that is capable of driving phase current in only one direction.
Vacuum: refers to a volume of space that has little or no pressure due to the absence of air or any other gasses; there are differing degrees of vacuum, which is why Empire Magnetics offers three different grades of vacuum rated motors and related products.
Variable reluctance motor: class of motors whose rotor has neither permanent magnets nor electrical windings; capable of high speeds, but produces little torque.
Velocity: change in position with respect to time; velocity has both a magnitude and a direction.
Voltage constant: also called the back emf constant, it is the amount of voltage generated by the motor per rpm.
Winding: an aggregate of magnet wire turns all on the poles of a given phase.
Sealed Motors
Sealed motors for wet, dusty or hazardous environments
Specialty Motors
Specialty motors for vacuum, radiation & extreme temperature
High-power Motors
High-power stepper and servo gearmotors that perform
Custom Motors
Custom motors and system integration services upon request
Frequently Asked Questions (FAQ)
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Learn About Vacuum Rated Motor Selection & Installation
Operating a motor in a vacuum is often perceived as a design challenge. Among engineers, the problems -- outgassing, contamination and temperature -- are well known. What is less well known is that there are now well-developed solutions to each of these problems.
Why Choose Empire Magnetics
Government Projects & Defense Applications
Empire Magnetics has been awarded and completed US Navy contracts in excess of $100,000 as a prime contractor. The Cage code number assigned was OYMU1, CEC code 19665900H. As a subcontractor to RSI/Comsat, SAIC, Lockheed Martin, Westinghouse, General Electric and other prime contractors for the US Government, contracts in excess of $200,000 have been awarded and completed.
Nationwide & International Distributors for Specialty Motors & Complete Motor System Solutions
Empire Magnetics products are distributed by a nationwide and international network of motion control sales professionals. Your local distributor carries the drives and controls, and the accessories needed to build a complete motion control system.