National Instruments Data Acquisition Device NI USB-621x, Руководство пользователя

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Glossary
© National Instruments Corporation G-5 NI USB-621x User Manual
D
D GND Digital gro u nd signal.
DAC Digital-to-Analog Converter—An electronic device, often an integrated
circ
u it, that converts a digital n u mber into a corresponding analog voltage
or c u rrent.
In the instr u mentation world, DACs can be u sed to generate arbitrary
waveform shapes, defined by the software algorithm that comp u tes the
digital data pattern, which is fed to the DAC.
DAQ Data acq u isition—The process of collecting and meas u ring electrical
signals from sensors, transd u cers, and test probes or fixt u res and inp u tting
them to a comp u ter for processing.
DAQ-STC2 Data acq u isition system timing controller chip.
data acq u isition The general concept of acq u iring data, as in begin data acq u isition or data
acq u isition and control. See also DAQ.
data transfer A techniq u e for moving digital data from one system to another.
Options for data transfer are DMA, interr u pt, and programmed I/O. For
programmed I/O transfers, the CPU in the PC reads data from the DAQ
device whenever the CPU receives a software signal to acq
u ire a single data
point. Interr u pt-based data transfers occ u r when the DAQ device sends an
interr u pt to the CPU, telling the CPU to read the acq u ired data from the
DAQ device. DMA transfers u se a DMA controller, instead of the CPU, to
move acq u ired data from the device into comp u ter memory. Even tho u gh
high-speed data transfers can occ u r with interr u pt and programmed I/O
transfers, they req u ire the u se of the CPU to transfer data. DMA transfers
are able to acq u ire data at high speeds and keep the CPU free for
performing other tasks at the same time.
dB Decibel—The u nit for expressing a logarithmic meas u re of the ratio of two
signal levels: dB = 20log10 V1/V2, for signals in volts.
DC Direct c u rrent—altho u gh the term speaks of c u rrent, many different types
of DC meas u rements are made, incl u ding DC Voltage, DC c u rrent, and
DC power.
device An electronic board that performs general analog or digital I/O f u nctions
on one or m u ltiple channels, connected to a PC thro u gh a b u s or I/O port,
s u ch as PCI, PXI, Ethernet, USB, or serial.