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Glossary
©
National Instruments Corporation
G-5
D
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
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.