Glossary
G-10
©
National Instruments Corporation
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
SNR
signal-to-noise ratio—the ratio of the overall rms signal level to the rms
noise level, expressed in decibels
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
system noise
a measure of the amount of noise seen by an analog circuit or an ADC when
the analog inputs are grounded
T
THD
total harmonic distortion—the ratio of the total rms signal due to harmonic
distortion to the overall rms signal, in decibel or a percentage
THD+N
signal-to-THD plus noise—the ratio in decibels of the overall rms signal to
the rms signal of harmonic distortion plus noise introduced
transducer
See sensor
transducer excitation
a type of signal conditioning that uses external voltages and currents to
excite the circuitry of a signal conditioning system into measuring physical
phenomena
U
unipolar
a signal range that is always positive (for example, 0 to +10 V)
update rate
the number of output updates per second
UM.book Page 10 Tuesday, July 14, 1998 10:37 AM
