Chapter3 DigitizerBasics
©NationalInstruments Corporation 3-5 NI5102 User Manual
rate of 20 MHz, the duration of acquisition is 5 ms (100,000 ×50 ns).
TheNI 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.
TheNI 51 02 (PCI, PXI) can transfer data to host memory while acquiring
data, thus expandingthei r single-shot record length to 16 million samples
on each channel.

TriggeringOptions

Oneo f the biggest challenges of making a measurement is to successfully
triggerthe signal acquisition at the point ofinterest. Since most high-speed
digitizersactually record the signal for a fraction o f the total time, they can
easily miss a signal anomaly if the trigger point is set incorrectly. The
NI5 102 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
giveyoumoreflexibilityintriggeringbyallowingyoutoconnecta
TTL/CMOS digital signal to trigger the acquisition. See Chapter 4,
HardwareO verview,fo r more information on triggering.
Making Accurate Measurements
Choosing the correct settings for your NI 5102 requires knowing certain
characteristicsof the signal in consideration. These characteristics may
include:
•Peak-to-peakvalue—This parameter, in units of volts, reflects the
maximum change in signal voltage. If V is the signal voltage at any
giventime, then Vpk-to-pk =V
max–Vmin.The peak-to-peak value affects
thevertical sensitivity or gain of the input amplifier. If you do not know
the peak-to-peak value,start with th esm allest gain(m aximum input
range)and increase it until the waveform is digitized using the
maximum dynamic range without clipping the signal. Refer to
Appendix A, Specifications, for the maximum input voltage for your
NI5102. Figure 3-5shows that a gain of 5 is the best setting to digitize
a3 00 mV,1 MHz sine wave without clipping the signal.