18WuD2x

auxiliary equipment • avalanche breakdown 53
auxiliary equipment 1. Also known as peripherals.
An apparatus not directly governed by the
central processing unit of a digital computer,
such as a printer or personal robot. 2. Peripheral
equipment in any system. 3. Backup equipment.
auxiliary memory In a digital computer, a unit
that is supplementary to the main memory,
which it augments.
auxiliary receiver Also called standby receiver. In
a radio communications system, a receiver that is
available for use if the main receiver fails.
auxiliary relay 1. A standby relay. 2. A relay
whose operation supports that of another relay.
3. A relay that is actuated by the operation of another
relay.
auxiliary switch 1. A standby switch. 2. A switch
wired in series or parallel with another switch. 3.
A switch that is operated by another switch.
available gain The ratio P o /P i , where P i is the available
power at the input of a circuit and P o is the
available power at the output.
available line The percentage of the length of a facsimile
scanning line that is usable for picture signals.
available power The mean square of the opencircuit
terminal voltage of a linear source divided
by four, times the resistive component of the
source impedance. The available power is the
maximum power delivered to a load impedance,
equal to the conjugate of the internal impedance
of the power source.
available power gain In a power transistor, the ratio
of available transistor output power to the
power available from the generator. It depends on
the generator resistance, but not on the transistor
load resistance.
available signal-to-noise ratio The ratio P s /P n ,
where P s is the available signal power at a given
point in a system and P n is the available randomnoise
power at that point.
available time 1. The time during which a computer
is available and ready for immediate use. 2.
The amount of time a computer is available to an
individual.
avalanche The phenomenon in semiconductors
operated at high reverse bias voltage, whereby
carriers acquire sufficient energy to produce new
electron-hole pairs as they collide with atoms.
The action causes the reverse current to increase
sharply.
avalanche breakdown In a semiconductor P-N
junction, a condition that occurs when the reverse
bias voltage exceeds a certain value. If the
electric field in the vicinity of the junction becomes
strong enough, charge carriers are dislodged
from the atoms and the carriers (electrons
and holes) flow freely across the P-N junction in
the opposite direction from normal. The mini-
auxiliary transmitter Also called standby transmitter.
In a radio communications system, a
transmitter that is available for use if the main
transmitter fails.
a/v Abbreviation of AUDIO-VISUAL.
aV Abbreviation of attovolt.
availability The proportion of time during which
an apparatus is operating correctly. It is usually
given as a percentage.
available conversion gain The ratio of the input
power to the output power of a transducer or converter.
It is generally given in decibels.