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Glossary
© National Instruments Corporation G-3 NI 5620 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