National Instruments Data Acquisition Device NI USB-621x User Manual
Page 163
Glossary
© National Instruments Corporation
G-5
D
D GND
Digital ground signal.
DAC
Digital-to-Analog Converter—An electronic device, often an integrated
circuit, that converts a digital number into a corresponding analog voltage
or current.
In the instrumentation world, DACs can be used to generate arbitrary
waveform shapes, defined by the software algorithm that computes the
digital data pattern, which is fed to the DAC.
DAQ
Data acquisition—The process of collecting and measuring electrical
signals from sensors, transducers, and test probes or fixtures and inputting
them to a computer for processing.
DAQ-STC2
Data acquisition system timing controller chip.
data acquisition
The general concept of acquiring data, as in begin data acquisition or data
acquisition and control. See also DAQ.
data transfer
A technique for moving digital data from one system to another.
Options for data transfer are DMA, interrupt, 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 acquire a single data
point. Interrupt-based data transfers occur when the DAQ device sends an
interrupt to the CPU, telling the CPU to read the acquired data from the
DAQ device. DMA transfers use a DMA controller, instead of the CPU, to
move acquired data from the device into computer memory. Even though
high-speed data transfers can occur with interrupt and programmed I/O
transfers, they require the use of the CPU to transfer data. DMA transfers
are able to acquire data at high speeds and keep the CPU free for
performing other tasks at the same time.
dB
Decibel—The unit for expressing a logarithmic measure of the ratio of two
signal levels: dB = 20log10 V1/V2, for signals in volts.
DC
Direct current—although the term speaks of current, many different types
of DC measurements are made, including DC Voltage, DC current, and
DC power.
device
An electronic board that performs general analog or digital I/O functions
on one or multiple channels, connected to a PC through a bus or I/O port,
such as PCI, PXI, Ethernet, USB, or serial.