Standard_Drives_Guide

Industry White Papers Glossary– Drives Terminology

Torque Control: A method of using current limit circuitry to regulate torque instead of speed. Transducer: A device that converts one energy form to another (ex. mechanical to electrical). Also, a device that when actuated by signals from one or more systems or media can supply related signals to one or more other systems or media. Transient: A momentary deviation in an electrical or mechanical system. Transistor: A solid-state, three-terminal device that allows ampli- fication of signals and can be used for switching and control. The terminals are called the emitter, base, and collector. Vector: A quantity that has magnitude, direction, and sense. This quantity is commonly represented by a directed line segment of which the length represents the magnitude and worse orientation in space represents the direction. VVI: A type of ac adjustable frequency drive that controls the volt- age and frequency of the motor to produce variable speed opera- tion. A VVI-type drive controls the voltage in a section other than the output section where frequency generation takes place. The frequency control is accomplished by an output bridge circuit which switches the variable voltage to the motor at the desired frequency. X-Axis: The axis of motion that is always horizontal and parallel to the work-holding surface. Y-Axis: The axis of motion that is perpendicular to both the X and Z axes. Z-Axis : The axis of motion that is always parallel to the principal spindle of the machine.

Speed Regulation: The numerical measure, in percent, of how accurately the motor speed can be maintained. It is the percent- age of change in speed between full load and no load. Stability: The ability of a drive to operate a motor at constant speed (under varying load) without “hunting” (alternately speeding up and slowing down). It is related to both the characteristics of the load being driven and electrical time constants in the drive regulator circuits. Surge Protection: The process of absorbing and clipping voltage transients on an incoming ac line or control circuit. MOVs (Metal Oxide Varistors) and specially designed R-C networks are usually used to accomplish this. Synchronous Speed: The speed of an ac induction motor’s rotat- ing magnetic field. It is determined by the frequency applied to the stator and the number of magnetic poles present in each phase of the stator windings. Mathematically, it is expressed as: Sync speed (rpm) = 120 x applied frequency (Hz)/number of poles per phase. Tachometer - Generator (Tach): A small generator normally used as a rotational speed sensing device. Tachometers are typically coupled to the shaft of dc or ac motors requiring close speed reg- ulation. The tach feeds a signal to a controller which then adjusts the output voltage or frequency to the motor. This feedback sig- nal can be either an analog dc signal (V/rpm) or digital (pulses/revolution). Thread Speed: A fixed low speed, usually adjustable, supplied to provide a convenient method for loading and threading machines. May also be called a preset speed. Torque: A turning force applied to a shaft, tending to cause rota- tion. Torque is normally measured in ounces/inches or pounds/feet and is equal to the force applied times the radius through which it acts. Torque Constant (in/lbs): This motor parameter provides a rela- tionship between input current and output torque. For each ampere of current applied to the rotor, a fixed amount of torque will result.

Standard Drives Buyers Guide

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