AC/AC converter
a power electronics
device in which an AC input voltage of some
magnitude, frequency, and number of phases
is changed to an AC output with changes to
any of the previously mentioned parameters.
AC/AC converters usually rectify the input
source to a DC voltage and then invert the
DC voltage to the desired AC voltage.
AC/DC converter
See
rectifier
.
AC-DC integrated system
a power sys-
tem containing both AC and DC transmission
lines.
ACARS
aircraft communications ad-
dressing and reporting. A digital commu-
nications link using the VHF spectrum for
two-way transmission of data between an air-
craft and ground. It is used primarily in civil
aviation applications.
ACC
See
automatic chroma control
.
accelerated testing
tests conducted at
higher stress levels than normal operation but
in a shorter period of time for the specific
purpose to induce failure faster.
accelerating power
the excess electric
power at a synchronous machine unit which
cannot be transmitted to the load because of
a short circuit near its terminals. This energy
gives rise to increasing rotor angle.
acceleration error
the final steady dif-
ference between a parabolic setpoint and the
process output in a unity feedback control
system. Thus it is the asymptotic error in po-
sition that arises in a closed loop system that
is commanded to move with constant acceler-
ation. See also
position error
,
velocity error
.
acceleration error constant
a gain
K
a
from which acceleration error
e
a
is read-
ily determined. The acceleration error con-
stant is a concept that is useful in the design
of unity feedback control systems, since it
transforms a constraint on the final acceler-
ation error to a constraint on the gain of the
open loop system. The relevant equations
are
e
a
=
1
K
a
and
K
a
= lim
s→inf ty
s
2
q(s),
where
q(s) is the transfer function model
of the open loop system, including the con-
troller and the process in cascade, and
s is
the Laplace variable. See also
position error
constant
,
velocity error constant
.
accelerator
(1) a positive electrode in a
vacuum tube to accelerate emitted electrons
from its cathode by coulomb force in a de-
sired direction.
(2) a machine used to impart large kinetic
energies to charged particles such as elec-
trons, protons, and atomic nuclei. The ac-
celerated particles are used to probe nuclear
or subnuclear phenomena in industrial and
medical applications.
acceptable delay
the voice signal de-
lay that results in inconvenience in the voice
communication. A typically quoted value is
300 ms.
acceptance
in an accelerator, it defines
how "large" a beam will fit without scrap-
ing into the limiting aperture of a transport
line. The acceptance is the phase-space vol-
ume within which the beam must lie to be
transmitted through an optical system with-
out losses.
From an experimenters point
of view acceptance is the phase-space vol-
ume intercepted by an experimenter’s detec-
tor system.
acceptor
(1) an impurity in a semicon-
ductor that donates a free hole to the valence
band.
(2) a dopant species that traps electrons,
especially with regard to semiconductors.
access channel
a channel in a communi-
cations network that is typically allocated for
the purpose of setting up calls or communi-
cation sessions. Typically the users share the
access channel using some multiple access
algorithm such as ALOHA or CSMA.
c
2000 by CRC Press LLC