Glossary of Terms M through R

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.

Rotor: rotating member of a motor.