Electrical Engineering Dictionary - part 177

torque

the product of a force acting at a

distance. The output of an electric motor.

torque angle

the displacement angle be-

tween the rotor and rotating magnetic flux
of the stator due to increases in shaft load
in a synchronous machine. See also

power

angle

torque pulsation

oscillating torque pro-

duced by the interaction between the air gap
flux, consisting mainly of the fundamen-
tal component, and the fluxes produced by
harmonics in the rotor. Torque pulsations
can stimulate complex mechanical vibrations
that can flex and damage rotor and turbine el-
ements.

torque ripple

in variable speed motor

drives, refers to the torque not being smooth
as the rotor moves from one position to an-
other. Torque ripple may be produced from
space harmonics within the machine or time
harmonics generated by the supply.

torque servo

a servo where the output

torque is the controlled variable and the op-
erating speed depends on the load torque. See
also

servo

torus

a donut-shaped magnetic core used

in electric transformers.

total demand distortion (TDD)

an in-

dex that quantifies the amount of distortion in
the voltage or current waveform with respect
to the maximum 60-Hz demand load current
I

over a 15–30 minute demand period.

T DDi = 100 ×

h6=1

total efficiency

dimensionless ratio of the

total RF power delivered to a load versus the
total DC and RF incident power into the am-
plifier.

total harmonic distortion (THD)

an in-

dex that quantifies the amount of distortion in
the voltage or current waveform with respect
to the fundamental component.

T DDi = 100 ×

h6=1

total harmonic distortion disturbance level

an electromagnetic disturbance level due to

all emissions from equipment in a system.
This is expressed as a ratio of the RMS value
of the harmonic content to the RMS of the
fundamental and is calculated as a percent-
age of the fundamental component.

total internal reflection

when light is

incident on a boundary between two media
from the one having the higher refractive in-
dex,

, then the angle of refraction is larger

than the angle of incidence.

At an angle

of incidence times arc sin

) the light

is totally reflected and remains in the denser
medium.

total reflection

the phenomenon where a

wave impinging on a certain medium inter-
face is totally reflected without being damped
by and without penetrating the boundary
medium.

totem-pole output

the standard output of

transistor–transistor logic (TTL) gates con-
sisting of two bipolar junction transistor in se-
ries between the source voltage and common.
In normal operation, either one is driven into
saturation while the other is at cutoff; alter-
nating these conditions changes the output
logic level.

touch input

a means for selecting a loca-

tion on the surface of the display unit using
a variety of technologies that can respond to
the placing of a finger or other pointing de-
vice on the surface. These are essentially data
panels placed either on the display surface or
between the user and the display surface.

2000 by CRC Press LLC

touch screen

a specialized type of video

display where a control circuit is actuated
when areas of the display are touched by ones
finger or similar object. The types of touch
screen technology include capacitive overlay,
force vector, guided acoustic wave, resistive
overlay, scanning infrared, strain gage and
surface acoustic wave.

touch voltage

used in power system safety

studies, the voltage between any two conduc-
tive surfaces which can be touched simulta-
neously by a person.

tower

a structure for elevating electric

transmission lines, distinguished from a pole
cf by its greater height and structural com-
plexity.

TPBVP in optimal control

two-point

boundary value problem resulting from nec-
essary conditions for control optimality given
by the Pontryagin maximum principle. For
continuous-time control systems described
by the state equation in the form

˙x = f (x, u, t); x (t

) = x

with performance index defined as

J =

L(x, u, t)dt + q x t

, t

where

x, u are respectively state and con-

trol vectors,

, t

] is an optimization hori-

zon and

f, L, q are sufficiently smooth func-

tions of appropriate dimensions, the TPBVP
is given by the state equation and costate
equation defined as follows:

˙p = −

∂H (x, u, p, t)

∂x

;

p t

∂q x t

, t

∂x

where

H(x, u, p, t) = L(x, u, t)+p

(t)f (x,

u, t) is a Hamiltonian, p is a costate vector,

u should be found by minimizing the Hamil-
tonian with

x found from the state equation

driven by the optimal

trace length

the physical distance be-

tween electronic components connected by
a circuit path.

trace loading

the electronic load on a cir-

cuit path.

tracing

in software engineering, the pro-

cess of capturing the stream of instructions,
referred to as the trace, for later analysis.

track

a narrow annulus or ring-like region

on a disk surface, scanned by the read/write
head during one revolution of the spindle; the
data bits of magnetic and optical disks are
stored sequentially along these tracks. The
disk is covered either with concentric rings
of densely packed circular tracks or with one
continuous, fine-pitched spiral track.

See

also magnetic disk track,

optical disk track

magnetic tape .

track buffer

a memory buffer embedded

in the disk drive. It can hold the contents of
the current disk track.

trackball

the earliest version of an input

device using a roller ball, differing from the
mouse in that the ball is contained in a unit
that can remain in a fixed position while the
ball is rotated. It is sometimes referred to
as an upside-down mouse, but the reverse is
more appropriate, as the trackball came first.

tracking

conduction along the surface of

an insulator and especially the establishment
of a carbonized conduction path along the
surface of a polymer insulator.

tracking bandwidth

See

lock range

traffic channel

a channel in a commu-

nication network that is used to carry the
main information or service, which is typi-
cally voice, data, video, etc. Compare with

control channel

traffic decomposition

the decomposition

approximates the steady-state behavior of the

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traffic by “decomposing” it into long- and
short-term behavior.

trailing edge

when a pulse waveform

switches from high to low, it is called a trail-
ing edge.

trailing-edge triggered

a device that is

activated by the trailing edge of a signal.

trainability

the property of an algorithm

or process by which it can be trained on sam-
ple data and thus rendered adaptable to differ-
ent situations. See also

training procedure

supervised learning

unsupervised learning

training algorithm of self-generating neu-
ral network

given as follows:

1. Initially, the network contains nothing.

When the first training example comes in, the
system creates a neuron for it.

2. When a new training example comes

in, the neurons in the hierarchy are examined
for similarity to the training example, hierar-
chically from the root(s). Each time, the last
winner and all the neurons in its child net-
works are examined to find a new winner. If
the new winner is the old winner, the exam-
ination stops and the old winner is the final
winner; otherwise, the new winner and its
child network are examined until a leaf node
is found to be the winner. During this pro-
cess, the weights of all the winners and their
neighbors should be updated according to the
same rule as that of self-organizing network.
After the final winner is found, the network
structure should be updated according to the
following rules:

3. If the winner is a terminal node (i.e., it

has no child network(s)), generate two new
neurons, and copy the training vector and
the original winner into them, respectively.
Make them as two neurons in a new child
network of the updated winner.

If the winner is a nonterminal node (i.e., it

has a child network), generate only one neu-
ron, copy the training vector into it, and put
it in the child network of the updated winner.

4. Repeat the above process until all the

training examples are exhausted. One train-
ing epoch has been completed at this point,
and more than one epoch may be required for
the network of neural networks to reach an
equilibrium. See also

self-generating neural

network

training procedure

the method of calcu-

lating the set of free parameters of a function
given a set of training data.

training sequence

a sequence of trans-

mitted symbols known at the receiver, which
is used to train an adaptive equalizer or echo
canceller.

training set

data used as the basis for

determining the best set of free parame-
ters. Typically used in iterative training al-
gorithms.

trajectory

a path on which a time law is

specified for instance in terms of velocities
and/or accelerations at each point.

trajectory planning

a trajectory planning

algorithm is the path description, the path
constraints imposed by manipulator dynam-
ics as inputs and position, velocity, and ac-
celerations of the joint (end-effector) trajec-
tories as the outputs. See also

path

transceiver

a device that can serve as both

transmitter and receiver.

transco

contraction of "transmission

company," a firm which owns electric power
transmission lines but does not engage in
power generation or distribution.

transconductance

a quantity used to

specify a field-effect transistor, defined as the
differential change in drain current upon a
differential change in gate voltage.

transducer

a device that converts a phys-

ical quantity into an electrical signal. Typi-
cally, transducers are electromechanical en-

2000 by CRC Press LLC

ergy conversion devices used for measure-
ment or control. Transducers generally oper-
ate under linear input-output conditions and
with relatively small signals. Examples in-
clude microphones, pickups, and loudspeak-
ers.

transducer gain

ratio of the power deliv-

ered to the load to the power available from
the source.

transducer power gain

See

transducer

gain

transfer characteristic curve

one of a set

of device curves derived from the expression
for the output current as a function of the
input voltage.

transfer function

(1) a mathematical

model that defines the relationship between
the output and the input of a linear system.
It is usually expressed as the ratio of the
Laplace transform of the output function di-
vided by the Laplace transform of the input
function. A typical transfer function model
has the form

g(s) =

+ b

s + b

+ b

+ · · · + b

+ a

s + a

+ a

+ · · · + a

without deadtime, or

g(s) =

+ b

s + b

+ b

+ · · · + b

+ a

s + a

+ a

+ · · · + a

−sτ

with deadtime. The numerator and denom-
inator polynomials are co-prime and the co-
efficients are real constants. For causality,
the order of the numerator polynomial must
not exceed that of the denominator (

m ≤ n

). For larger systems with multiple inputs
and outputs, the concept is generalized to a
transfer function matrix in which each

(i, j)

element is a simple transfer function that de-
fines how output

(i) is affected by input (j).

Although not uniquely defined, it is possible
to transform any transfer function or transfer

function matrix to a state space model hav-
ing the same input–output behavior. See also

state space model

Equivalent pulse trans-

fer function models exist for digital (discrete-
time) systems:

g(z) =

+ b

z + b

+ b

+ · · · + b

+ a

z + a

+ a

+ · · · + a

where the polynomials are based on the z-
transform. Though not as common, these
can also be collected into matrices for MIMO
systems to form pulse transfer function ma-
trices. See also

z-transform

and

modified

z-transform

(2) the Fourier transform of the output sig-

nal divided by the Fourier transform of the
input signal. Alternatively, the Fourier trans-
form of the impulse response function.

transfer matrix

of linear stationary con-

tinuous time dynamical system,

K(s) repre-

sents controllable and observable part of dy-
namical system and is defined by the equality

K(s) = C(sI − A)

−1

B + D

for systems with

m inputs and q outputs K(s)

q × m dimensional matrix.

transfer rate

a measure of the number of

bits that can be transferred between devices
in a unit of time.

transfer time

in a hierarchical memory

system, the time required to move a block
between two levels.

transform

the process of converting data

from one form into another. Often used to
signify a system that rotates the coordinate
axes. Examples of transforms include the
Fourier transform and the discrete Fourier
transform. A discrete linear transform can
be described as a product of the input vector
with a transform matrix. See also

transform

kernel

2000 by CRC Press LLC

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