National Instruments NI 5102 用户手册
Chapter 3
Digitizer Basics
© National Instruments Corporation
3-5
rate of 20 MHz, the duration of acquisition is 5 ms (100,000
× 50 ns).
The NI 5102 has a buffer size of 663,000 samples. When performing a
single-channel acquisition, you can use the entire available memory to
capture data for a duration of 33.1 ms at 20 MS/s.
single-channel acquisition, you can use the entire available memory to
capture data for a duration of 33.1 ms at 20 MS/s.
The NI 5102 (PCI, PXI) can transfer data to host memory while acquiring
data, thus expanding their single-shot record length to 16 million samples
on each channel.
data, thus expanding their single-shot record length to 16 million samples
on each channel.
Triggering Options
One of the biggest challenges of making a measurement is to successfully
trigger the signal acquisition at the point of interest. Since most high-speed
digitizers actually record the signal for a fraction of the total time, they can
easily miss a signal anomaly if the trigger point is set incorrectly. The
NI 5102 is equipped with sophisticated triggering options, including
256 trigger thresholds, programmable hysteresis, window triggering,
trigger hold-off, and bilevel triggering on input channels as well as on a
dedicated trigger channel. The NI 5102 also has two digital triggers that
give you more flexibility in triggering by allowing you to connect a
TTL/CMOS digital signal to trigger the acquisition. See Chapter 4,
trigger the signal acquisition at the point of interest. Since most high-speed
digitizers actually record the signal for a fraction of the total time, they can
easily miss a signal anomaly if the trigger point is set incorrectly. The
NI 5102 is equipped with sophisticated triggering options, including
256 trigger thresholds, programmable hysteresis, window triggering,
trigger hold-off, and bilevel triggering on input channels as well as on a
dedicated trigger channel. The NI 5102 also has two digital triggers that
give you more flexibility in triggering by allowing you to connect a
TTL/CMOS digital signal to trigger the acquisition. See Chapter 4,
, for more information on triggering.
Making Accurate Measurements
Choosing the correct settings for your NI 5102 requires knowing certain
characteristics of the signal in consideration. These characteristics may
include:
characteristics of the signal in consideration. These characteristics may
include:
•
Peak-to-peak value—This parameter, in units of volts, reflects the
maximum change in signal voltage. If V is the signal voltage at any
given time, then V
maximum change in signal voltage. If V is the signal voltage at any
given time, then V
pk-to-pk
= V
max
–V
min
. The peak-to-peak value affects
the vertical sensitivity or gain of the input amplifier. If you do not know
the peak-to-peak value, start with the smallest gain (maximum input
range) and increase it until the waveform is digitized using the
maximum dynamic range without clipping the signal. Refer to
Appendix A,
the peak-to-peak value, start with the smallest gain (maximum input
range) and increase it until the waveform is digitized using the
maximum dynamic range without clipping the signal. Refer to
Appendix A,
, for the maximum input voltage for your
NI 5102. Figure 3-5 shows that a gain of 5 is the best setting to digitize
a 300 mV, 1 MHz sine wave without clipping the signal.
a 300 mV, 1 MHz sine wave without clipping the signal.