Page 237 - Electrical Engineering Dictionary

ing. Theyacceptawiderangeofpopulartele- circuit in order to dissipate the stored energy
com and networking input frequencies and in the magnets/capacitors.
can be programmed to generate a range of
output frequencies. Used for wide area net- duoplasmatron a type of ion-producing
work (WAN) and ISDN applications. source that develops protons by extracting
positive ions from an arc struck in hydrogen
dual port memory memory system that gas.
has two access paths; one path is usually used
by the CPU and the other by I/O devices. duplex a method of winding the arma-
ture of a commutated electric machine such
dual-cage rotor a three-phase induction that the number of parallel electrical paths
motor rotor with two separate squirrel cage between brushes is double that provided by a
windings, that give the effect of varying ro- simplex winding. Duplex windings are con-
tor resistance. The outer cage has high re- structed by placing consecutive coils in al-
sistance to obtain high starting torque, while ternate coil slots and continuing the winding
the inner cage has low resistance to reduce twice around the rotor, filling the empty slots
losses at full load. on the second pass. The result is two com-
plete, identical windings between brush posi-
dual-element fuse a fuse constructed with tions rather than the one winding that is pro-
two different types of fusible elements in se- duced when coils are placed in adjacent slots.
ries. One element is designed to melt very See also simplex, multiplex, reentrancy.
quickly in the presence of fault current. The
other is designed to melt after a time delay duplex channel two-way simultaneous
when exposed to overload conditions. The (and independent) data communication, e.g.,
fusible elements are somewhat similar in op- between a computer and remote terminals.
eration to the thermal and magnetic elements
of an inverse-time circuit breaker. Dual- duplex ultrasound simultaneous display
element and time-delay are often used inter- of speed versus time for a chosen region and
changeably. the two-dimensional B-mode image.

duality property of Fourier transform duplication with complementary logic
the property that results from the symmetry fault detection based on circuit duplication
between the Fourier transform synthesis and and comparison. One module is designed us-
analysis equations. To illustrate, let f(w) ing positive logic and the other module uses
be the Fourier transform of the time func- negative logic. This assures detecting com-
tion g(t) (f(w) = F{g(t)}). Substituting mon mode faults.
t for w in f gives the time function f(t).
Applying a Fourier transform to f(t) gives dust cover a cover to protect the terminals
the function 2πg(−w), a frequency domain of a pad-mount transformer.
function similar to the original time function
1
g(t) (g(−w) = F{f(t)}). dust-ignition-proof machine a machine
2π
designed with a casing or specialized en-
DUF See diffusion under field. closure to safely contain any internal ig-
nition or flammable substances or compo-
dump an area of steel and dense concrete nents, and prevent them from igniting exter-
into which unwanted particle beam can be nal flammables such as explosive gases, va-
steered so that its energy can be dissipated pors, and dust particles.
in a safe and controlled manner. The dump
resistor is switched into the magnet/capacitor DUT device under test.

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2000 by CRC Press LLC