Operation Theory
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4
Operation Theory
The operation theory of the functions on the DAQ/PXI-20XX is described in
this chapter. The functions include the A/D conversion, D/A conversion,
Digital I/O and General Purpose Counter/Timer. The operation theory can
help you understand how to configure and program the DAQ/PXI -20XX.
The whole DAQ/PXI-2000 series cards, including DAQ/PXI-20XX,
DAQ/PXI-22XX and DAQ/PXI-25XX, are designed based on the same
logic-timing template of DAQ/PXI-22XX. In the DAQ/PXI-22XX cards, all
the A/D related timings are for multiplexing A/D sampling based on scan-
ning, so that DAQ/PXI-20XX also adopts the same concept, except there is
only one conversion signal in a scan which could generate up to 4 samples
from the different 4 channels at the same time. In the following description,
to conform to the original timing design, we still use “scan” as the unit of
A/D data acquisition. All the DA and GPTC functions are the same in
DAQ/PXI-20XX and DAQ/PXI-22XX, while DAQ/PXI-25XX provides im-
proved DA timing comparing the former 2 series.
4.1
A/D Conversion
When using an A/D converter, users should first know about the properties
of the signal to be m easured. Users can decide which channel to use and
where to connect the signals to the card. Please refer to 3.2 for signal
connections. In addition, users should define and control the A/D signal
configurations, including channels, gains, and A/D signal types.
There are 2 ways to initiate A/D conversion, either by Software Polling or
Programmable Scan Acquisition; these are described in 4.1.3 and 4.1.4.
The A/D acquisition is initiated by a trigger source; users must decide how
to trigger the A/D conversion. The data acquisition will start once a trigger
condition is matched.