National Instruments DAQ M Series - Manual (Page 37)

Chapter 4 Analog Input
© National Instruments Corporation 4-13 NI 6236 User Manual
M Series devices use ai/SampleClock and ai/ConvertClock to perform
interval sampling. As Figure 4-8 shows, ai/SampleClock controls the
sample period, which is determined by the following equation:
1/Sample Period = Sample Rate
Figure 4-8. Interval Sampling
ai/ConvertClock controls the Convert Period, which is determined by the
following equation:
1/Convert Period = Convert Rate
Note The sampling rate is the fastest you can acquire data on the device and still achieve
accurate results. For example, if an M Series device has a sampling rate of 250 kS/s, this
sampling rate is aggregate—one channel at 250 kS/s or two channels at 125 kS/s per
channel illustrates the relationship.
Posttriggered data acquisition allows you to view only data that is acquired
after a trigger event is received. A typical posttriggered DAQ sequence is
shown in Figure 4-9. In this example, the DAQ device reads two channels
five times. 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.
Channel 0
Channel 1
Convert Period
Sample Period