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APPENDIX
H
Glossary
of Terms
Abort-T"
terminate or break off an "pemtion.
Accuracy-The
maximum error in terms of measurement
made by an instrument.
For
digital
instruments,
ac-
curacy is usually specified as a percent of reading plus
so many counts of error.
A/D
(Analog-to-Digital)
Converter-A
device
that
converts an analog signal into binary or digital values.
Aliasing-The
introduction
of errors into data resulting
from the discrete sampling of continuous
signals when
the sampling
rate is to" low for the frequency
being
sampled. Generally, the sampling rate must be at least
twice as high as the highest sampled sinusoidal frequen-
cy to avoid aliasing.
Analog-Pertaining
to electronic devices in which the out-
put varies as a continuous
function
of the input.
Analog
Output-An
output that provides an analog signal
derived
from
the digital
information
within
the
instrument.
Aperture
Delay-The
time period that occurs between the
instant the sample and hold in the AID converter is trig-
gered to hold the signal and the actual time that it does.
Aperture
Uncertainty-A
measure of the instability
of the
time base which controls the sample and hold circuitry.
ASCII-Abbreviation
for American Standard Code for In-
formation Interchange (pronounced
ask-w). A standard
code used extensively
in computers and data transmis-
sion in which 128 letters, numbers, symbols, and special
control
characters
are represented
by '/-bit binary
numbers.
Average
Reading-The
sum of all the samples in a
measurement divided by the number of samples in that
measureme"t.
Bandwidth-The
range of frequencies to which an instru-
ment will respond within
certain limits. Usually, band-
width
is defined by the -3dB (0.707V) points.
BASIC-Abbreviation
for Beginners All-purpose
Symbolic
Instruction
Code. A high-level
programming
language
used in many small computers.
Binary-A
number system based on the number 2; used
extensively
in computer-based
equipment.
Bit-An
abbreviation
for binary digit. A unit of binary ins
formation is equal to one binary decision, or the designa-
tion of one of two possible states, generally represented
by 1 and 0.
SNC-A
type of coaxial connector used in situ.ltions
rt'-
quiring
shielded cable for signal connections.
Buffer-A
dedicated area of memory ill \\.hich swnc form
of binary data is stored for later xcess. ~Ihe mcx+~!r~'-
ment buffer stores individual
samples, .md the rwding
buffer stores mathematically
processed readings.
Bus-In
computerized
equipment,
one or more conduc-
tors used as a path over which information
is tr.lnsmit-
ted from any of several source's to ,I"!
of se\'rr~~l
destinations.
Byte-A
group of bits processed together in parallel; b!
definition
d byte is made up of eight bits,
Card-A
slot location on the rear pan4 of the instrumwt
into which AID modules crln be installed.
C.,~rd is ~lsc:
used as another nxnc
for module.
Channel-One
of two AiD modules installed in the tw)
card locations.
Chassis
Ground-A
connection to d common met,4 strut-
tore within
the instrument.
&nerally,
chxsis
gr<~und
is connected through power line gntund to earth ground
via a 3.wire power cord for safety purposes.
Clock-A
pulse generator or signal waveform
used to
achieve synchronization
of digital circuits.
Coaxial
Cable-A
cable in which one conductor cwnplrtc~
ly surrounds
the other, the two being coLaI
.rnd
separated by continuous
solid dielectric.
Command-A
signal, originating
within ', computer, that
triggers or initiates
s*me form of action within
the
instrument.
Common-mode
Rejection
Ratio-A
measure
of the at-
tenuation
of a noise voltage appearing
between input
low and input
high resistively
coupled,
,~nd chassis
ground,
usually specified in dl3.
Common
Mode
Voltage-A
volt:lge ,Ipplied between ill-
put low and chassis ground of the instrument.
H-l
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