point between the higher (
ω
H
) and lower
(
ω
L
) band edges, expressed in units of ra-
dians/second. The band edges are usually
defined as the highest and lowest frequencies
within a contiguous band of interest at which
the loss equals
L
Amax
, the maximum attenu-
ation loss across the band.
ω
oa
=
ω
H
+ ω
L
2
arithmetic shift
a shift in which it is as-
sumed that the data being shifted is integer
arithmetic in nature; as a result, the sign bit
is not shifted, thereby maintaining the arith-
metic sign of the shifted result.
See also
logical shift
.
arithmetic–logic unit
See
arithmetic and
logic unit
.
arm
a part of a robot. A robot is composed
of an arm (or mainframe) and a wrist plus
a tool. For many industrial robots the arm
subassembly can move with three degrees of
freedom. Hence, the arm subassembly is the
positioning mechanism. See also
industrial
robot
.
arm pin
a pin insulator .
ARMA
See
auto-regressive moving-aver-
age model
.
armature
the magnetic circuit of a ro-
tating electrical machine, including the main
current carrying winding, in which an alter-
nating voltage is induced by the magnetic
field.
armature circuit
components of the ma-
chine that carry armature current. For ex-
ample, in a DC machine the armature cir-
cuit could consist of the armature windings,
brushes, series field winding, compensat-
ing windings, interpoles, starting resistor(s),
main-line contacts, and overload sensor.
armature current limiting
a condition
wherein the stator currents are clamped at the
maximum allowable limit due to excessive
heating of the stator.
armature reaction
(1) in DC machines, a
distortion of the field flux caused by the flux
created by the armature current. Armature
reaction in a DC machine causes lower flux
at one pole-tip and higher flux at the other,
which may lead to magnetic saturation. It
also shifts the neutral axis, causing sparking
on the commutator.
(2) in AC synchronous machines, a volt-
age “drop” caused by the armature current.
In the steady state model of the synchronous
machine, the armature reaction is accounted
for by a component of the synchronous reac-
tance.
armature voltage control
a method of
controlling the speed of a DC motor by vary-
ing the voltage applied to the armature while
keeping the voltage applied to the field circuit
constant.
armature winding
an arrangement of
coils carrying the main current, typically
wound on the stator of a synchronous ma-
chine or the rotor of a DC machine, in which
an alternating voltage is induced by the mag-
netic field.
armless construction
a method of distri-
bution line construction, often used for aes-
thetic purposes, in which pin insulators are
mounted on steel brackets bolted directly to
a utility pole without the use of a crossarm.
Armstrong oscillator
Hartley oscillators
are usually not used at VHF of higher fre-
quencies. Similarly, the circuit is avoided at
very low audio frequencies. It is important
to distinguish the Hartley oscillator from the
Armstrong topology. In the Armstrong oscil-
lator, no ohmic connection exists between the
two inductors. Instead, coupling is entirely
magnetic.
Armstrong, Edwin Howard
(1890–
1954) Born: New York, New York, U.S.A.
c
2000 by CRC Press LLC