Glossary
©NationalInstruments Corporation G-3 NI5620 User Manual
CMRR common-moderejection ratio—ameasure of an instrument’sability to
rejectinterference from a common-mode signal, usually expressed in
decibels(dB)
coupling the manner in which a signal is connected from one location to another
Ddata path logic asi gnal 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
RFand microwave work. Using this standard, 0 dBm equals 1 mW, 10 dBm
equals 10 mW,and so on. In a 50 Ωsystem, 0 dBm equals ±0.224 Vrms.
DC directcurrent
DDC See digital downconverter.
dead time ap eriod oftime in which no activity can occur
defaultsetting adefault parameter value recorded in the driver. In many cases, the default
inputof a control isa certain value(often 0) that means use the current
default setting.
differentialinput ananalog input consisting of two terminals, both of which are isolated from
computerground, whose difference is measured
digital downconverter aDSP that selects only a narrow portion of the frequency spectrum, thereby
eliminating unwanted data before it is transferred into memory
dither randomnoise ad ded to a signal before it is digitized to minimize distortion
createdby differential nonlinearity
DMA directmemory access—a method by which data is transferred to/from
computer memory from/to a deviceo r memory on the buswhile the
processor does something else. DMA is the fastest method of transferring
data to/from computer memory.
double insulated adevice that contains the necessary insulating structures to provide electric
shock protection without the requirement of a safety ground connection