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Electrical Engineering Dictionary - part 120

neural tree

a tree-structured neural net-

work. Such networks arise in the application
of certain kinds of constructive algorithm.

neuro-fuzzy control system

control sys-

tem involving neural networks and fuzzy sys-
tems, or fuzzy neural networks. See also

adaptive fuzzy system

neuron

a nerve cell. Sensory neurons

carry information from sensory receptors in
the peripheral nervous system to the brain;
motor neurons carry information from the
brain to the muscles.

neutral axis

the axis near which the di-

rection of the velocity of armature conduc-
tors is exactly parallel to the magnetic flux
lines so that the EMF induced in the conduc-
tors is zero. This axis, also referenced as the
magnetic neutral axis, shifts in the direction
of rotation of the machine as a generator or
motor. The amount of shift depends on the
armature current and hence on the load of the
machine.

neutral

a conductor which completes the

electric circuit from the load to the source
in three-phase Y-connected and single phase
AC electric power systems, typically at or
near the potential of the earth.

neutral plane

See

neutral axis

neutral zone

in permanent magnets, a

plane through which all lines of flux are par-
allel to the direction of magnetization, i.e.,
the plane between north and south poles.

neutrino laser

laser in which the ampli-

fied field consists of neutrinos rather than
electromagnetic waves; suggested impor-
tance in the early universe.

New York City blackout

a particularly

disastrous failure of the power system in New
York City in 1977.

Newton’s method

a class of numeri-

cal root-finding methods; that is, to solve
f (x) = 0. The methods are based on iter-
atively approximating

f using a low order

polynomial and finding the roots of the poly-
nomial. The most commonly used first-order
method iterates the following equation:

n+1

= x

−

f (x

)

where

represents the derivative of

f .

Newton–Euler recursive algorithm

used

in robotics, to calculate joint generalized
forces as a result of two recursions along
the kinematical structure of the robot. First
one, a forward recursion, calculates spatial
velocities and accelerations from the base of
the manipulator towards its tip. Second one,
a backward recursion calculates the spatial
forces and torques along the structure in the
opposite direction. Projection of the spatial
force and torques at the joint axis results in
the generalized force at the joint. The result-
ing Newton–Euler equations of motion are
not in closed form as opposite to the result of
using Lagrange formalism to the dynamical
system of the robot itself. See also

Lagrange

formulation

Newton–Raphson method

a numerical

method for finding the solution to a set of si-
multaneous nonlinear equations. Variations
of this method are commonly used in circuit
simulation programs.

Neyman–Pearson detector

a detector

that minimizes the miss probability within
an upperbound constraint on the false-alarm
probability.

NFPA

See

National Fire Protection

Association

nibble

four bits of information.

nibble-mode DRAM

an arrangement

where a dynamic RAM can return an extra

2000 by CRC Press LLC

three bits, for a total of four bits (i.e., a nib-
ble), with every row access.

The typical organization of a DRAM in-

cludes a buffer to store a row of bits inside
the DRAM for column access. Additional
timing signals allow repeated accesses to the
buffer without a row-access time. See also

two-dimensional memory organization

NIC

See

network interface card

Nichols chart

in control systems, a plot

showing magnitude contours and phase con-
tours of the return transfer function referred
to ordinates of logarithmic loop gain and ab-
scissae of loop phase angle.

night vision

See

scotopic vision

NMD connector

See

network measurement

division connector

NMI

See

nonmaskable interrupt

NMR

nuclear magnetic resonance. See

magnetic resonance imaging

NMOS

See

n-channel MOSFET

no fetch on write

strategy in the write-

through cache policy where a line is not
fetched from the main memory into the cache
on a cache miss if the reference is a write ref-
erence. Also called non-allocate on write, as
space is not allocated in the cache on write
misses.

no load tap changer

device that pro-

vides for changing the tap position on a
tapped transformer when the transformer is
de-energized. Different taps provide a differ-
ent turns ratio for the transformer.

no voltage holding coil

a holding coil that

keeps the main-line contactor closed on zero
voltage conditions.

DC motor controllers

that contain this feature are used in places
where the motor is vital to the operation of
a process. These controllers can maintain

control to the motor under momentary line
power loses, by using the CEMF of the coast-
ing armature to keep power to the main-line
coil/contactor. If power to the motor con-
troller is not restored within a short period
of time, the motor coasts to a speed where it
can no longer keep the main-line contactor
closed. At this point, the m-coil drops out
to insure starting resistors are placed back in
the circuit.

no-load test

measurement of input param-

eters of an induction motor while running at
nearly synchronous speed, with zero output
on the shaft. This test is used to determine the
magnetizing reactance of the motor equiva-
lent circuit. See also

open-circuit test

no-op

a computer instruction that per-

forms no operation. It can be used to reserve
a location in memory or to put a delay be-
tween other instruction execution.

no-write allocate

part of a write policy

that stipulates that if a copy of data being up-
dated are not found in one level of the mem-
ory hierarchy, space for a copy of the updated
data will not be allocated in that level. Most
frequently used in conjunction with a write-
through policy.

nodal cell

cell with a radius of up to 300

m. Typically an isolated cell acting as a high
capacity network node. See also

cell

nodal system

a secondary system of equa-

tions using nodal voltages as variables.

node

a symbol representing a physical

connection between two electrical compo-
nents in a circuit. See also

graph

node analysis

a circuit analysis technique

in which KCL is used to determine the node
voltages in a network.

noise

(1) any undesired disturbance,

whether originating from the transmission
medium or the electronics of the receiver it-

2000 by CRC Press LLC

self, that gets superimposed onto the original
transmitted signal by the time it reaches the
receiver. These disturbances tend to interfere
with the information content of the original
signal and will usually define the minimum
detectable signal level of the receiver.

(2) any undesired disturbance superim-

posed onto the original input signal of an
electronic device; noise is generally cat-
egorized as being either external (distur-
bances superimposed onto the signal before it
reaches the device) or internal (disturbances
added to the signal by the receiving device
itself). See also

noise figure

noise power

ratio

. Some common examples of external

noise are crosstalk and impulse noise as a re-
sult of atmospheric disturbances or manmade
electrical devices. Some examples of inter-
nal noise include thermal noise, shot noise,
1/f noise, and intermodulation distortion.

noise bandwidth

an equivalent band-

width,

, of a system expressed as

inf

|H(ω)|

|H(ω

where

H (ω) is the transfer function of the

system and

is the central frequency.

noise circles

circles of constant noise fig-

ure plotted on the Smith chart. These circles
can be used to graphically impedance match
a device to achieve a desired noise figure.

noise clipping

a process by which high

noise peaks are clipped or limited to elimi-
nate most of their energy, thereby removing
the worst effects of impulse noise.

noise factor

See

noise figure

noise figure

an indication of the contribu-

tion of that component or system to the level
of noise observed at the output. The noise
figure therefore gives an idea of the amount
of noise generated within the component or
system itself. It is usually expressed in deci-
bels (dB) and is given by the ratio of the input
signal-to-noise ratio to the output signal-to-

noise ratio of the component or system. This
is defined as

Noise Figure (NF)

(S/N)

input

(S/N)

output

In decibels this is given by:

[NF]

= 10 log

(S/N)

input

(S/N)

output

noise figure meter

a system that makes

accurate noise figure readings possible. It
measures the amount of the noise added by a
device. Noise figure is the ratio of the signal-
to-noise ratio at the input of a device to the
signal-to-noise ratio at the output of that de-
vice.

noise floor

the lowest input signal power

level which will produce a detectable output
signal in an electrical system. Noise floor is
determined by the thermal noise generated in
the electrical system.

noise immunity

a logic device’s ability

to tolerate input voltage fluctuation caused
by noise without changing its output state.

noise power

the amount of power con-

tained within a noise signal. The noise power
can be found by integrating the power spec-
tral density (PSD) of the noise signal over
all possible frequencies. If the power spec-
tral density is given by

S(ω), the power, p,

contained in the noise signal, is then given by

∞

−∞

S(ω)dω .

In most cases, noise signals are bandwidth
limited to between say

and

and in these

cases the noise power will be given by

S(ω)dω .

Generally, the power spectral density is ex-
pressed in watts per hertz (W/Hz) and the
noise power is expressed in watts. See also

noise

noise spectrum

2000 by CRC Press LLC

noise power ratio (NPR)

intermodula-

tion distortion product generated in nonlin-
ear transfer components such as high power
amplifiers (HPAs) amplifying multiple carri-
ers. It is defined as a ratio of an averaged
power of white noise having a narrow notch,
which represents multiple carriers, to an av-
eraged power falling into a narrow bandwidth
of notch.

noise rejection

the ability of a feedback

control system to attenuate (reduce) the am-
plitude of any unwanted signal generated by
the measurement of its output variable.

noise smoothing

any process by which

noise is suppressed, following a comparison
of potential noise points with neighboring in-
tensity values, as for mean filtering or median
filtering.

noise spectrum

indicates the frequency

components in a noise signal.

For ideal

thermal noise (AWGN), the spectrum is flat
across all frequencies and is referred to as
the noise power spectral density expressed in
watts per hertz (W/Hz). See also

noise

power

noise subspace

in an orthogonal decom-

position of a space, the orthogonal comple-
ment to the signal subspace.

noise suppression

any process by which

noise is eliminated or suppressed: a more
general term than noise smoothing, since it
includes such processes as noise clipping and
band-pass filtering.

noise temperature

an alternate represen-

tation of noise power. It is generally accepted
that noise is the result of the random mo-
tion of electrons within components in elec-
tronic systems. The greater the temperature
of a component, the greater the random mo-
tion of electrons within the component, and
this causes an increased instantaneous noise
current to be present within the component.
With an increase in noise current, the noise

power also increases. The noise power gen-
erated within a component at

T Kelvin, over

a bandwidth of

B hertz is given by

p = kT B

with

k = 1.38 × 10

−23

J/K, which is Boltz-

mann’s constant.

From this equation, it is clear that a com-

ponent at absolute zero temperature (0 K),
generates no noise power. Therefore, given
a particular bandwidth,

B noise power can

also be expressed as a temperature in Kelvin
(K).

noise whitening

a process by which noise

whose power spectrum is not white (i.e., not
identical at all frequencies) is brought to this
condition, e.g., by means of a frequency de-
pendent filter.

noiseless source coding

See

lossless

source coding

noiseless source coding theorem

states

that any source can be losslessly encoded
with a code whose average number of bits
per source symbol is arbitrarily close to, but
not less than, the source entropy in bits.

noisy channel vector quantization

a gen-

eral term for methods in vector quantizer
transmission for noisy channels. See also

channel robust vector quantization

channel

redundancy-free channel coding

noisy channel VQ