Page 267 - Electrical Engineering Dictionary

ing of the system. As an example, a bus error exchangeable disk See removable disk.
handleristhesystemsoftwareresponsiblefor
handling bus error exceptions. excimer a molecule formed by the excited
state of one atom and one or more other atoms
excess delay the arrival times of a compo- that remains a molecule only as long as the
nent of the impulse response of a wideband excited state lifetime.
communication channel relative to the first
arriving component. Hence the total excess
excimer laser laser using a gas or gases
delay, the difference in arrival time between
to create an excited dimer (e.g., KrF), usually
the first and last significant components.
resulting in pulsed deep-UV radiation.
excess loss the ratio of the actual propa-
excitation population of excited states of
gation loss between two antennas to the free
a laser medium at the expense of some energy
space loss for two antennas separated by the
source.
same distance in a vacuum. Usually ex-
pressed in decibels.
excitation system the DC voltage source
excess noise (1) thermal noise in excess and its accompanying control and protection
◦
or exceeding thermal noise at 290 K. The ex- systems connected to the synchronous gen-
cess noise ratio (ENR) is the ratio of the ex- erator rotor.
◦
cess noise to the noise at 290 K, expressed
in decibels. exciter a DC source that supplies the field
(2) Noise in excess of the thermal noise current to produce a magnetic flux in an elec-
(n e ), which is a function of the device, fre- tric machine. Often it may be a small DC
quency and bias current, also known as 1/f , generator, placed on the same shaft of the
1/f a , flicker or popcorn noise. This noise electrical machine.
rapidly dies off such that above a few mega-
hertz it becomes insignificant. It is a major exciting current the current drawn by a
concern in generating phase noise in oscilla- transformer primary with its secondary open
tors. circuited. It is the vector sum of the core loss
◦ current I c and the magnetizing branch cur-
T − 290 K
ENR = 10 log 10 rent I m . The exciting current I e is also the
290 K
◦
current measured in the open circuit test on
a
n e = f device, 1/f ,I bias a transformer. The exciting current is cal-
culated as the ratio of the primary induced
EMF and the impedance of the tank circuit.
excess noise ratio (ENR) a noise source
On load, it is equal to the difference between
used in noise figure measurements. ENR is
the primary and reflected secondary currents
theratioofthesource’snoisepowerwhenitis
of the transformer.
on to the noise power when it is off. The ENR
values are entered and stored in the noise fig-
ure meter to calibrate a measurement. exciton laser laser (or laser-like system)
in which the amplified field consists of ex-
excess-N representation method of rep- citons rather than electromagnetic waves or
resenting floating point numbers, in which a photons.
positive or negative exponent is stored as a
positive integer by adding the value N to it. exclusive OR Boolean binary operator
For example, in excess-128 representation, typically used for comparing the status of
an exponent of −40 would be stored as the two variables or signals. Sometimes written
value 88. “XOR.” The truth table for ⊕≡ X XOR Y

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2000 by CRC Press LLC