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Glossary
©
National Instruments Corporation
G-3
NI PXI-562x User Manual
CMRR
common-mode rejection ratio—a measure of an instrument’s ability to
reject interference from a common-mode signal, usually expressed in
decibels (dB)
coupling
the manner in which a signal is connected from one location to another
D
data path logic
a signal router
dB
decibel—the unit for expressing a logarithmic measure of the ratio of two
signal levels: dB = 20log10 V1/V2, for signals in volts
dBm
decibels with reference to 1 mW, the standard unit of power level used in
RF and microwave work. Using this standard, 0 dBm equals 1 mW, 10 dBm
equals 10 mW, and so on. In a 50
Ω
system, 0 dBm equals ±0.224 V
rms
.
DC
direct current
DDC
See
digital downconverter.
dead time
a period of time in which no activity can occur
default setting
a default parameter value recorded in the driver. In many cases, the default
input of a control is a certain value (often 0) that means
use the current
default setting
.
differential input
an analog input consisting of two terminals, both of which are isolated from
computer ground, whose difference is measured
digital downconverter
a DSP that selects only a narrow portion of the frequency spectrum, thereby
eliminating unwanted data before it is transferred into memory
dither
random noise added to a signal before it is digitized to minimize distortion
created by differential nonlinearity
DMA
direct memory access—a method by which data is transferred to/from
computer memory from/to a device or memory on the bus while the
processor does something else. DMA is the fastest method of transferring
data to/from computer memory.
double insulated
a device that contains the necessary insulating structures to provide electric
shock protection without the requirement of a safety ground connection