Glossary of Terms S through Z

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.