Page 201 - Intro Predictive Maintenance

192 An Introduction to Predictive Maintenance

Relay An electromagnetic switching device using
low current to open or close a high-current
circuit.

Resistance (R) A term describing the opposition of ele-
ments of a circuit to alternating or direct
current.
Resistor A device installed in an electrical circuit to
permit a predetermined current to flow with
a given voltage applied.
Rheostat A device for regulating a current by means
of a variable resistance.
Rotor The part of the alternator that rotates inside
the stator and produces an electrical current
from induction by the electromagnetic
fields of the stator windings.
SCR (semiconductor, or silicon, An electronic DC switch that can be trig-
controlled rectifier) gered into conduction by a pulse to a gate
electrode, but can only be cut off by reduc-
ing the main current below a predetermined
level (usually zero).
Shielding Protective coating that helps eliminate
electromagnetic and radio frequency
interference.

Shunt A conductor joining two points in a circuit
to form a parallel circuit, through which a
portion of the current may pass, in order to
regulate the amount of current flowing in
the main circuit.
Sine wave A fundamental waveform produced by
periodic oscillation that expresses the sine
or cosine of a linear function of time or
space, or both.

Single-phase That portion of a power source that repre-
sents only a single phase of the three phases
that are available.
Solenoid A tubular coil containing a movable mag-
netic core, which moves when the coil is
energized.
Stator The stationary winding of an alternator (the
armature in a DC generator).