Chapter 2
Analog Input
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National Instruments Corporation
2-31
Figure 2-16.
Interval Sample
The ai/ConvertClock signal controls the convert period, which is
determined by the following equation:
1/convert period = convert rate
NI-DAQmx chooses the default convert rate to allow for the maximum
settling time between conversions. Typically, this rate is the sampling rate
for the task multiplied by the number of channels in the task.
The sampling rate is the fastest you can acquire data on the device and still
achieve accurate results. For example, if an E Series device has a sampling
rate of 200 kS/s, this sampling rate is aggregate one channel at 200 kS/s or
two channels at 100 kS/s per channel illustrates the relationship.
An acquisition with posttrigger data allows you to view data that is acquired
after a trigger event is received. A typical posttrigger DAQ sequence is
shown in Figure 2-17. The sample counter is loaded with the specified
number of posttrigger samples, in this example, five. The value decrements
with each pulse on ai/SampleClock, until the value reaches zero and all
desired samples have been acquired.
Figure 2-17.
Typical Posttrigger Acquisition
Channel 0
Channel 1
Convert Period
Sample Period
1
3
0
4
2
ai/StartTrigger
ai/SampleClock
ai/ConvertClock
Sample Counter
