X20 system modules • Analog input modules • X20AI1744, X20AI1744-3
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X20 system User's Manual 3.10
4.3.2.8 Filter characteristics of the Sigma-Delta ADC
4 x
0
8 x
12 x
16 x
20 x
24 x
1 x f
DATA
Frequency
G
ai
n
4.3.2.9 Effective resolution of the AD converter
The AD converter on the AI1744 provides a 24 bit measurement value. However, the actual attainable noise-free
resolution is always less than 24 bit. This "effective resolution" depends on the data rate and measurement range.
Example:
Because of the conversion methods, a data rate of 2.5 Hz and a specified measurement area of 2 mV/V result in
an effective resolution of 18.7 bits:
0
4
8
12
16
21
3
7
11
15
20
23
24-bit
18.7-bit
Figure 53: Example for the effective resolution of the AD converter
The low-order bits (grayed out) contain only noise instead of valid values and must therefore not be evaluated.
With the multiple sampling function model, only the highest 16 bits are made available.
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