Page 282 - Electrical Engineering Dictionary

when the shunt field has lost current flow, field oxide an insulating silicon oxide
then secures the motor before an overspeed layer used in integrated circuits to electrically
condition occurs. isolate components.

field memory video memory required to field propagator the analytical descrip-
store the number of picture elements for one tion of how electromagnetic fields are related
vertical scan (field) of video information of to the sources that cause them. Common
an interlaced scanned system. field propagators in electromagnetics are the
The memory storage in bits is computed defining Maxwell equations that lead to dif-
by multiplying the number of video samples ferential equation models, Green’s functions
made per horizontal line times the number that produce integral equation models, opti-
of horizontal lines per field (vertical scan) cal propagators that lead to optics models,
times the number bits per sample. A sam- and multipole expansions that lead to modal
ple consists of the information necessary to models.
reproduce the color information.
Storage requirements can be minimized field rate the rate at which a field of video
by sampling the color video information con- is generated. The field rate for NTSC televi-
sisting of the luminance (Y) and the two color sion is 59.94 fields per second consisting of
difference signals, (R - Y) and (B - Y). The alternating even and odd fields. Each field
color signal bandwidth is less than the lumi- consists of 262.5 lines of video, generating
nance bandwidth that can be used to reduce the even or odd numbered lines of video.
the field memory storage requirements. Four
samples of the luminance (Y) signal is com- field reversing a method of achieving a
bined with two samples of the (R - Y) signal reversal of rotation of a DC motor by reserv-
and two samples of the (B - Y) signal. The ing the field flux.
preceding video sampling technique is desig-
nated as 4:2:2 sampling and reduces the field field singularity See edge condition.
memory size by one-third. Field memory for
NTSCvideosampledat4times the color sub- field strength in general terms the mag-
carrierfrequencyat8bits/pixelwouldrequire nitude of the electric field vector (in volts
3.822megabitsofRAMwhen4:2:2sampling per meter) or the magnitude of the magnetic
is used. field vector (in ampere-turns per meter). As
used in the field of EMC/EMI, the term is
field mill a measuring instrument for applied only to measurements made in the
electric fields consisting of a rotary array far field and is abbreviated as FS. For mea-
of blades which revolves near a capacitive surements made in the near field, the term
pickup. The AC variation of the pickup’s electric field strength (EFS) or magnetic field
output is proportional to the electric field in strength (MFS) is used, according to whether
the region near the instrument in the direction the resultant electric or magnetic field, re-
of the rotor axis. spectively, is measured.

field orientation a term related to field weakening a method of achieving
the vector control of currents and volt- speed increase in DC motors by reducing the
ages that enables direct control of ma- field flux (increasing field circuit resistance).
chine torque in AC machines. Vector
control refers to the control of both the field-by-field alignment a method of
amplitude and phase angle, and the control alignment whereby the mask is aligned to the
results in a desired spatial orientation of the wafer for each exposure field (as opposed to
electromagnetic fields in the machine. global alignment).

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2000 by CRC Press LLC