2-12
|
ni.com
Chapter 2
Using the NI PXIe-4357
You can choose to select an ADC timing mode independent of the requested sample rate using
the
ADC Timing Mode
property. This allows sampling of all channels at a faster rate within a
shorter window after the sample clock. Refer to Table 2-4 for a quick reference about the ADC
timing mode that NI-DAQmx selects based on the number of channels per ADC and the selected
sample rate. Refer to the
Computing Aggregate Sample Rates
section for more detailed
information on determining sample rates.
Channel Ordering
To achieve the fastest possible sample rate while maintaining the highest possible accuracy, it is
important to distribute the channels in use evenly across the five ADCs.
The module samples the channels in the order NI-DAQmx requests and are dependent on the
ADC to which the channel belongs. Inside the module, the requested channels in the task are
divided into five ADC-dependent scanlists in order to optimize the sample rate. These scanlists
are sampled in parallel. As a result, a channel listed later in the original task may be sampled
before another channel that is earlier in the task. Figure 2-5 shows an example of a
non-sequential channel sample conversion sequence. Figure 2-6 shows a typical channel sample
conversion sequence.
Table 2-4.
ADC Timing Mode Quick Reference Chart
Maxim
u
m C
h
an
nels p
e
r AD
C
Sample Rate (S/s)
1
10
20
30
40
50
60
70
80
90
100
1
1
4
6
6
7
7
7
8
8
8
8
2
3
6
7
7
8
8
8
8
8
8
9
3
4
6
7
8
8
8
8
9
9
9
9
4
4
7
8
8
8
9
9
9
9
9
9
1 = High-Resolution Mode, 9 = High-Speed Mode
