18WuD2x

exciter • expandable 269
exciter 1. An amplifier or oscillator (or a system of
such units) that supplies the input (driving) signal
to the output amplifier in a radio transmitter
or similar device. 2. A small direct-current (dc)
generator that supplies direct current to the field
winding of an alternating-current (ac) generator.
3. See INDUCTION COIL.
exciter lamp 1. A concentrated-filament, highintensity
incandescent lamp used in soundon-film
recording and reproduction and in some
types of electromechanical television. 2. In a
facsimile transmitter, the lamp illuminating what
is being scanned.
exciter relay In an electromechanical generator,
the relay that activates the direct-current (dc)
field excitation during machine startup.
exciter response 1. A change in the exciter voltage
of a motor when the field-circuit resistance
changes. 2. A change in the operating conditions
of a radio frequency exciter, as a result of a
change in the impedance at the input of the final
amplifier.
exciter unit See EXCITER.
exciting current 1. The output current produced
by the exciter of a generator (see EXCITER, 2). 2.
The field current of a dynamo-type generator. 3.
Primary current in an unloaded transformer.
exciting power 1. The output power produced by
an exciter. 2. The input-signal power required for
full output from a power amplifier. Also called
DRIVING POWER.
exciting voltage 1. Input-signal voltage. 2. The
input-signal-voltage amplitude required for full
rated output from a power amplifier. Also called
DRIVING VOLTAGE. 3. The output voltage produced
by an exciter.
exciton In a semiconductor or dielectric, a bound
electron-hole pair.
excitron A mercury-pool rectifier whose arc is
initiated mechanically (e.g., by means of a
magnetic plunger in the tube).
exclusion principle The rule that only one particle
of a particular kind can occupy a given quantum
state at one time.
exclusive-NOR A logic function where the output
is 1 if both inputs are 1 or both are 0 (same). The
output is 0 if one input is 0 and the other is 1 (different).
Compare EXCLUSIVE OR.
exclusive-OR A logic function in which the output
is 1 when the two inputs are different, and is 0
when the two inputs are the same.
excursion 1. A change in the value of a quantity in
a given direction. 2. In an oscillatory system, a
body’s moving away from the point of equilibrium
or mean position.
execution A computer’s performance of the operations
required by an instruction.
execution time The length of time required for a
computer to complete a designated operation.
executive routine In computer operations, a program
that controls and processes other routines.
A
B
A B C
0
0
1
1
0 0
1 1
0 1
1 0
exclusive-OR
Also called monitor program. Compare MONITOR
SYSTEM.
exhaust analyzer An instrument for examining
the exhaust fumes of an internal combustion engine,
to measure the presence of noxious materials
and to evaluate air-to-fuel ratio and
combustion efficiency.
exhaustion See EVACUATION.
exit 1. In computer operations, the last instruction
in a program or program segment, often taking a
subroutine back to the main program. 2. To leave
a computer application, routine or subroutine.
exoskeleton A robot that resembles a suit of armor,
and that greatly magnifies the force of physical
movements. A human operator occupies the
interior. Thus, for example, the operator might
use the machine to throw a football 2500 yards,
or to run 50 miles an hour, or to smash through
walls. Primarily a tool of science fiction writers,
this machine is within the scope of current
robotic technology.
exosphere The extreme outer layer of the earth’s
atmosphere.
exothermic Pertaining to a chemical or electrochemical
reaction in which heat is given off. Compare
ENDOTHERMIC.
exothermic reaction In a chemical reaction, the
production of positive reaction energy (i.e., kinetic
energy is gained). Compare ENDOTHERMIC
REACTION.
exp 1. Symbol for EXPONENTIAL. 2. Abbreviation
of EXPERIMENT(AL).
expand 1. In communications, to increase the
bandwidth of a signal, restoring it to normal
bandwidth after it has been compressed. 2. In
communications, to increase the dynamic range
of a signal. 3. In computer operations, to restore
a file to full or normal size after it has been compressed.
4. To widen the scale of a meter. 5. To
widen (or magnify a portion of) the trace of an oscilloscope
beam. Compare COMPRESS.
expandable Capable of being built up into larger
circuits or systems.
C