Specifications

Analog Input Modules
31007715 6/2008 109
Data
Word Structure
Each STB ACI 1225 data register represents the input voltage of a channel in the
IEC data format. The data has 10-bit resolution. The bit structure in each data
register is as follows:
There are 10 significant bits in each data word—bits 14 through 5. They allow you
to represent current data with integer values ranging from 0 to 32,736 in increments
of 32. A value 32 000 represents an input of 20 mA. A value of 0 represents an input
less than or equal to 4 mA.
Linear current representations can be interpreted using the formula:
where Cn is the numerical count and Iai is the analog input current.
Values greater than 32 000 do not produce over-range indications.
STB ACI 1225 Data Register Format
8
0
2
14
2
13
2
12
2
11
2
10
2
9
2
8
2
7
2
6
always 0
12 3
45
67
910111213
14
15
always 0
2
5
I
ai
C
n
8000+()2000⁄=
I
C
32 736
32 000
15 mA
20.37 mA
20 mA
24 000
ai
n
4mA
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