Page 281 - Electrical Engineering Dictionary

fiber optic bundle an optical system to the device under question. Waveform fidelity
deliver the image to a video monitor. In a degradation is most often characterized by a
conventional endoscope, the image is trans- change in signal shape (time domain), or a
mitted through a series of lenses to a cam- change in the relative scaling of its frequency
era outside of the patient. In an electronic components as the signal propagates through
endoscope the image is collected by a CCD thecircuitorsystem(frequencydomain). See
camera positioned inside the patient. also amplitude linearity.

fiber optic sensor a sensor employing an field (1) the member of an electrical ma-
optical fiber to measure chemical composi- chine that provides the main magnetic flux,
tion or a physical parameter, such as tem- which then interacts with the armature caus-
perature, pressure, strain, vibration, rotation ing the desired machine operation (i.e., motor
or electromagnetic fields. Light is launched or generator).
down a fiber to a transducer or sensing ele- (2) a description of how a physical quan-
ment that alters the properties of the light in tity varies as a function of position and pos-
response to the parameter being measured. sibly time.
The altered light is returned back down a fiber See also electric field, finite field.
to a detector.
field circuit a set of windings that pro-
fiber Raman amplifier provides amplifi- duces a magnetic field so that the electro-
cation of signals through stimulated Raman magnetics induction can take place in electric
scattering in silica fibers. Raman amplifica- machines.
tion differs from stimulated emission in that
in stimulated emission, a photon of the same field controlled thyristor (FCT) a thyris-
frequency as the incident photon is emitted tor controlled by change in the magnitude of
where as in the case of Raman amplification, the field current.
the incident pump photon looses energy to
create another photon at a lower frequency. field current control a method of con-
trolling the speed of a DC motor by varying
fiber-optic cable a glass fiber cable that the field resistance, thus producing a change
conducts light signals and can be used in to- in the field current.
ken ring local area networks and metropoli-
tan area networks. Fiber optics can provide field discharge resistor a resistor used to
higher data rates than coaxial cable. They are dissipate the energy stored in the inductance
also immune to electrical interference. of a field winding. It may be a standard power
resistor that is connected across the winding
fiber-optic interconnect interconnect just prior to opening the supply switch, or
that uses an optical fiber to connect a source a permanent non-linear resistive device that
to a detector. An optical fiber is used for has high resistance at normal voltage but low
implementing a bus. The merits are large resistance when voltage rises at switching.
bandwidth and high speed of propagation.
field loss protection a fault-tolerant
fidelity a qualitative term used to de- scheme used in electric motors. Some DC
scribe how closely the output amplitude of motor control circuits provide field loss pro-
a device faithfully reproduces that of its in- tection in the event the motor loses its shunt
put. Faithful reproduction here refers to the field. Under a loss of field, DC motors may
preservation of those characteristics of the in- overspeed causing equipment damage and/or
put signal (e.g., amplitude, frequency, and/or personal injury. In a motor controller that
phase shift) essential to proper operation of has field loss protection, a sensor determines

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