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Glossary
PCI-4451/4452 User Manual G-16
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National Instruments Corporation
sample counter the clock that counts the output of the channel clock, in other words, the
number of samples taken. On boards with simultaneous sampling, this
counter counts the output of the scan clock and hence the number of scans.
SE single-ended—a term used to describe an analog input that is measured
with respect to a common ground
self-calibrating a property of a DSA board that has an extremely stable onboard reference
and calibrates its own A/D and D/A circuits without manual adjustments by
the user
sensor a device that responds to a physical stimulus (heat, light, sound, pressure,
motion, flow, and so on), and produces a corresponding electrical signal
settling time the amount of time required for a voltage to reach its final value within
specified limits
Shannon Sampling
Theorem
a law of sampling theory stating that if a continuous bandwidth-limited
signal contains no frequency components higher than half the frequency
at which it is sampled, then the original signal can be recovered without
distortion
S/H sample-and-hold—a circuit that acquires and stores an analog voltage on a
capacitor for a short period of time
signal conditioning the manipulation of signals to prepare them for digitizing
SNR signal-to-noise ratio—the ratio of the overall rms signal level to the rms
noise level, expressed in decibels
software trigger a programmed event that triggers an event such as data acquisition
software triggering a method of triggering in which you simulate an analog trigger using
software. Also called conditional retrieval.
source impedance a parameter of signal sources that reflects current-driving ability of voltage
sources (lower is better) and the voltage-driving ability of current sources
(higher is better)
SS simultaneous sampling—a property of a system in which each input or
output channel is digitized or updated at the same instant
S/s samples per second—used to express the rate at which a DAQ board
samples an analog signal
User.book Page 16 Tuesday, April 14, 1998 10:20 AM