Example 2
If the time relationship between channels is not critical, you can sample from the same channel multiple times and scan less frequently. For example, suppose an application requires averaging 100 points from channel 0 and averaging 100 points from channel 1. You could alternate reading between channels—that is, read one point from channel 0, then one point from channel 1, and so on. You also could read all 100 points from channel 0 then read 100 points from channel 1. The second method switches between channels much less often and is affected much less by settling time.
Analog Input Data Acquisition Methods
When performing analog input measurements, you either can perform software-timed or hardware-timed acquisitions. Hardware-timed acquisitions can be buffered or non-buffered.
Software-Timed Acquisitions
With a software-timed acquisition, software controls the rate of the acquisition. Software sends a separate command to the hardware to initiate each ADC conversion. In NI-DAQmx, software-timed acquisitions are referred to as having on-demand timing. Software-timed acquisitions are also referred to as immediate or static acquisitions and are typically used for reading a single sample of data.
Hardware-Timed Acquisitions
With hardware-timed acquisitions, a digital hardware signal (ai/SampleClock) controls the rate of the acquisition. This signal can be generated internally on your device or provided externally.
Hardware-timed acquisitions have several advantages over software-timed acquisitions.
•The time between samples can be much shorter.
•The timing between samples is deterministic.
•Hardware-timed acquisitions can use hardware triggering.
Hardware-timed operations can be buffered or non-buffered.