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

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Chapter 5 Analog Output
NI USB-621x User Manual 5-2 ni.com
• AO Sample Clock —The AO Sample Clock signal reads a sample
from the DAC FIFO and generates the AO voltage. Refer to the
AO Sample Clock Signal section for more information.
• Isolation Barrier and Digital Isolators —Refer to Chapter 9,
Isolation and Digital Isolators on USB-6215/6216/6218 Devices ,
for more information.
AO Range
The AO range is ±10 V for USB-621 x devices.
Minimizing Glitches on the Output Signal
When yo u u se a DAC to generate a waveform, yo u may observe glitches
on the o u tp u t signal. These glitches are normal; when a DAC switches from
one voltage to another, it prod u ces glitches d u e to released charges. The
largest glitches occ u r when the most significant bit of the DAC code
changes. Yo u can b u ild a lowpass deglitching filter to remove some of
these glitches, depending on the freq u ency and nat u re of the o u tp u t signal.
Visit
ni.com/ s upport
for more information abo u t minimizing glitches.
Analog Output Data Generation Methods
When performing an analog o u tp u t operation, yo u can perform
software-timed or hardware-timed generations:
• Software-timed generations —Software controls the rate at which
data is generated. Software sends a separate command to the hardware
to initiate each DAC conversion. In NI-DAQmx, software-timed
generations are referred to as on-demand timing. Software-timed
generations are also referred to as immediate or static operations.
They are typically
u sed for writing a single val u e o u t, s u ch as a
constant DC voltage.
• Hardware-timed generations —A digital hardware signal controls
the rate of the generation. This signal can be generated internally
on yo
u r device or provided externally.
Hardware-timed generations have several advantages over
software-timed acq
u isitions:
– The time between samples can be m u ch shorter.
– The timing between samples can be deterministic.