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SCADA Supervisory control and data acquisition.
scanner A photoelectric control that contains the light source and the detector in the same housing.
SCR Silicon controlled rectifier. A solid-state unidirectional latching switch.
sensor A device that detects or measures something and generates a corresponding electrical signal to an input circuit or controller.
serial pertaining to time-sequential transmission of data over a single conductor.
service factor (SF) When used on a motor nameplate, a number that indicates how much above the nameplate rating a motor can be loaded without causing serious degradation (i.e., a motor with 1.15 SF can produce 15 percent greater torque than one with a service factor of 1.0).
setpoint The value selected to be maintained by an automatic controller.
slip The difference between rotating magnetic-field speed (synchronous speed) and the rotor speed of an ac induction motor. Usually expressed as a percentage of synchronous speed.
soft start (motor starting) An electronic motor starting circuit where less than full voltage is applied to the motor during starting.
star configuration In an arrangement of parallel (bus) connections a physical configuration such that each device is connected on the bus at the same junction of conductor segments.
star connection The arrangement of phase windings in a poly-phase circuit in which one end of each phase winding is connected to a common junction. In a three-phase circuit, it is sometimes called a WYE connection.
star topology A network where all devices are connected to a central or master communication device that routes messages.
status indicator LED or other type of indicator that is illuminated when an input circuit or output circuit is energized.
summing point (summing junction) A mixing point where the setpoint and process variable feedback signals are compared.
surge A transient wave of voltage, current, or power.
surge suppression 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 A type of serial transmission that maintains a constant time interval between successive events.
synchronous speed The speed of an ac induction motor's rotating magnetic
field. It is determined by the frequency applied to the stator and
the number of magnetic poles present in each phase of the
This page was last updated: Tuesday, August 19, 2008 23:33