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Electrical Engineering Dictionary - part 189

Widrow-Hoff learning rule

a gradi-

ent descent learning rule for calculating the
weight vector

Ew for a linear discriminant

which minimizes the squared error objective
function. The vector

Ew is modified as

Ew(n + 1) = Ew(n) + α(n)(d − Ew

(n)Ex)Ex

where

Ex is an input vector, d is the desired

output, and

Ew(n) is the weight vector at iter-

ation

Wien bridge

a bridge circuit where one

arm is a series connection of a resistor and ca-
pacitor, another arm is a parallel connection
of a resistor and capacitor (these two arms are
called reactance arms), and two other arms
(called ratio arms) are resistors. The balance
detector is connected between the common
point of ratio arms and the common point of
reactance arms, a sinusoidal voltage source
is connected to another bridge diagonal. The
Wien bridge was initially designed as a fre-
quency measuring circuit; now the main part
of its application is the Wien bridge oscilla-
tor.

Wien bridge oscillator

(1) an oscillator

where the Wien bridge is used in the am-
plifier feedback. The frequently used cir-
cuit includes equal resistors and equal ca-
pacitors in reactance branches of the bridge;
this arrangement provides easy continuous
tuning of the oscillation frequency.

Tun-

ing of the bridge providing high indirect fre-
quency stability of oscillations is easily com-
bined with application of an operational am-
plifier as oscillator active element. The cir-
cuit of amplitude control is also easily at-
tached. All these advantages provide wide
spread of Wien bridge oscillators in high and
low radio frequency ranges of applications.

(2) a form of feedback oscillator that uses

a noninverting amplifier along with a feed-
back path that produces a phase shift of zero
degrees at the operating frequency. The feed-
back network contains only two reactive ele-
ments of the same type.

Wiener, Norbert (1894-1964)

mathe-

matician whose contributions include Brow-
nian motion, stochastic processes, general-
ized functions, harmonic analysis, control
theory, and optimal filtering. Established the
field of cybernetics, author of “Cybernetics:
or Control and Communication in the Animal
and the Machine.”

Wiener filter

filter that attempts to re-

duce signal noise by separating and sup-
pressing the power spectrum of the noise
from the power spectrum of the signal. The
uncertainty in the estimation of the noise
power spectrum will cause the signal to be
smoothed. Also known as the least-mean
square filter.

Wilkinson coupler

a coupler that splits

a signal into a number of equiphase and
equiamplitude parts. It provides isolation be-
tween output terminals by connecting resis-
tors between each output terminal and a com-
mon junction. A coaxial type coupler was
first proposed by Dr. Wilkinson. In recent
years, not only coaxial type but also MIC
(microwave integrated circuit) type Wilkin-
son couplers are practically used for various
kinds of microwave circuits.

Williams tube memory

a memory device

based on electric charges being stored on the
screen of a cathode ray tube. Now obsolete.

Wilson central terminal

reference point

for forming most of the standard ECG leads.
It is the average of the right arm, the left arm,
and the left potentials. It is a time-varying
reference.

Winchester disk

a type of magnetic disk

for data storage. Its characteristic property
is that the disk and the read-write head are
placed in a hermetically sealed box. This
allows higher recording density as the read-
write head can be moved closer to the disk
surface. See also

disk head

2000 by CRC Press LLC

wind–electric conversion

the process by

which wind (mechanical) energy is converted
to electrical energy, usually by the use of
wind turbine.

wind farm

a plot of land on which several

power-generating windmills are placed.

wind power generator

a system that uti-

lizes the energy in the wind to generate elec-
tricity. The energy in the wind drives a wind
turbine which acts as the prime mover for the
generator. A wind turbine operates at a vari-
able speed, and an appropriate electric ma-
chine and controller converts the mechanical
energy into electrical energy and pumps it
into a utility grid.

winding

a conductive path, usually wire,

inductively coupled to a magnetic core or
cell.

winding factor

a design parameter for

electric machines that is the product of the
pitch factor and the distribution factor.

window

any appropriate function that

multiplies the data with the intent to mini-
mize the distortions of the Fourier spectra.

window operation

an image processing

operation in which the new value assigned to
a given pixel depends on all the pixels within
a window centered at that pixel location.

windowing

the process of opening a win-

dow.

In signal processing, it is common to open

only a certain restricted portion of the avail-
able data for processing at any one time: such
a portion is called a window or sometimes a
mask or neighborhood. For instance, in FIR
filter design, a technique known as window-
ing is used for truncation in order to design
an FIR filter. The design of window becomes
crucial in the design.

In image processing, it is a common prac-

tice that a square window of (for example)
3

× 3 pixels is opened centered at a pixel

under consideration. In this window opera-
tion, the gray level of the pixel is replaced
by a function of its original gray level and
the gray levels of other pixels in the window.
Different functions represent different oper-
ations: in particular, they will be suitable for
different filtering or shape analysis tasks. See
also

median filter

thinning

Windscale incident

a nuclear power plant

accident at the Windscale plant in Great
Britain.

winner-take-all network

a network in

which learning is competitive in some sense;
for each input a particular neuron is de-
clared the “winner” and allowed to adjust its
weights. After learning, for any given input,
only one neuron turns on.

wiped joint

a fused joint used in splicing

lead-sheathed cables.

wipe system

in television, a system that

allows the fading in of one channel of video as
a second channel of video is faded out with-
out loss of sync.

wired OR

a circuit that performs an OR

operation by the interconnection of gate out-
puts without using an explicit gate device.
An open collector bus performs a wired OR
function on active-low signals.

wireframe

(1) 3-D object representation

containing only edge and vertex information.
It may produce ambiguous images (e.g., the
Necker cube).

(2) a model that approximately represents

a solid object by using several hundreds of
triangles. It is used in applications such as
facial coding, facial recognition and indus-
trial component mensuration.

wireless local area network (WLAN)

computer network that allows the transfer of
data without wired connections.

2000 by CRC Press LLC

wireless local loop

a wireless connection

(using a radio link) between a subscriber ter-
minal (for example, a telephone) and the local
exchange of the public switched network.

withstand rating

the maximum voltage

that electrical equipment can safely with-
stand, without failure, under specified test
conditions.

withstand test

a test of an insulator’s abil-

ity to withstand a high voltage of some spec-
ified waveform.

WLAN

See

wireless local area network

WMSE

See

weighted mean squared

error

word parallel

processing of multiple

words in the same clock cycle.

wordspotting

detection or location of

keywords in the context of fluent speech.

work flow management

the process to

monitor work progress through any number
of departments.

work function

amount of energy neces-

sary to take out an electron from a material.

working set

the collection of pages,

w(t, T ), referenced by a process during the
time interval

(t − T , t).

working-set policy

a memory allocation

strategy that regulates the amount of main
memory per process, so that the process is
guaranteed a minimum level of processing
efficiency.

workstation

a computer system designed

for engineering design calculations, charac-
terized by (comparatively) large main mem-
ory, high floating point computational speed,
and a high resolution graphic display system.
It is used primarily in engineering and scien-
tific applications.

world modeling

describes the geomet-

ric and physical properties of the object (in-
cluding the robot) and represents the state
of the assembly of objects in the workspace.
World modeling makes it possible to imple-
ment many of the features of a task-level pro-
gramming system. See also

object-oriented

programming

WORM

See

write once read many

worst-case design

a family of control de-

sign algorithms in which parameter perturba-
tions and/or disturbances are estimated to be-
have in the most unfavorable way from con-
trol objective point of view. This assump-
tion leads usually to various min-max control
algorithms based on static min-max, nonco-
operative game theory or H infinity design.
Since the worst-case estimates are conserva-
tive, the resulting controllers, although ro-
bust, may be in some sense too pessimistic.
See also

robust controller design

worst-case measure of sensitivity

for the

multiparameter sensitivity row vector with
components

having tolerance constants

(these are considered to be positive numbers),
i.e.,

(1 −

) ≤ x

≤ x

(1 +

)

we have

i=1

F (jω,x)

dω

wound rotor induction motor

an induc-

tion motor in which the secondary circuit
consists of a polyphase winding or coils con-
nected through a suitable circuit. When pro-
vided with slip rings, the term slip-ring in-
duction motor is used.

wraparound

(1) a phenomenon in signal

processing that occurs in the discrete case
when signals are not properly manipulated.
For instance, in circular convolution, if the
length of signals is not properly chosen, i.e.,

2000 by CRC Press LLC

there are not sufficient zeros appended at the
end of the signals, the so-called wraparound
error will take place, that is, the contributions
from different periods will overlap.

(2) the returning to a zero state when a

(3) a condition code or indicator that may

be set, or a program segment that is executed
when a register wraps around.

wraps

pre-formed wire grips or ties for

mechanically joining overhead conductors to
insulators.

Wratten filter

a light filter for separating

colors. It is available in transparent sheets of
various colors and is useful in photography
and in several phases of electronics, includ-
ing the operation of color meters and color
matchers.

wrist

for a manipulator, refers to the joints

in the kinematic linkage between the arm and
hand (or end-effector). Usually, wrist allows
an orienting the manipulator. Therefore, the
main role of the wrist is to change the orien-
tation of the hand (or end-effector). See also

spherical wrist

write allocate

part of a write policy that

stipulates that if a copy of data being updated
is not found in one level of the memory hierar-
chy, space for a copy of the updated data will
be allocated in that level. Most frequently
used in conjunction with a write-back policy.

write broadcast

a protocol for maintain-

ing cache coherence in multiprocessor sys-
tems. Each time a shared block in one cache
is updated, the modification is broadcast to
all other caches. Also referred to as write
update.

write buffer

a buffer that stores memory

write requests from a CPU. The write request
in the buffer are then served by the mem-
ory system as soon as possible. Reduces the

number of processor wait cycles due to long
latency write operations.

write instruction

a processor instruction

that stores information into memory from a
processor register or a higher level cache.

write invalidate

a protocol for maintain-

ing cache coherence in multiprocessor sys-
tems. Each time a shared block in one cache
is updated, a message is sent that invalidates
(removes) copies of the same block in other
cache memories. This is a more common
alternative than write broadcast protocols.

write once read many (WORM)

used to

refer for memory devices that allow data to
be written once after device fabrication, and
to be read any number of times. A typical
example is PROM.

write policy

determines when copies of

data are updated in a memory hierarchy. The
two most common write policies are write
through and write back (copy back).

write through

a write policy that stipu-

lates that when a copy of data is updated at
one level of a memory hierarchy, the same
data are also updated in the next outer level.
Write through is usually only used in low-
level caches. Its advantages are that it is fast
and simple to implement, and that it always
guarantees that the next level of the memory
hierarchy has a valid copy of all data. Its
main disadvantage is that it generates much
data traffic to the next level.

write update

See

write broadcast

write-after-read

hazard

See

anti-

dependency

write-after-write hazard

See

output

dependency