Specifications

Analog Input Modules
31007715 6/2008 65
There are 12 significant bits in each data word—bits 15 through 4. They allow you
to represent voltage data with integer values ranging from -32 768 to +32 752 in
increments of 16. When the sign bit (bit 15) is 0, the value is positive; when bit 15 is
1, the value is negative.
In an ideal linear voltage representation (one without offset or max count settings
(see p. 59)), the value 32 000 represents an input of 10 V and -32 000 represents
an input of -10 V. If the input value exceeds 10 V, the input channel reports an over-
voltage warning (OVW). If the input value drops below -10 V, the input channel
reports an under-voltage warning (UVW). If the input value reaches 10.24 V, an
over-voltage error (OVE) is reported. If it drops to -10.24 V, an under-voltage error
(UVE) is reported.
An ideal linear voltage representation (one without offset or max count settings
(see p. 59)) is interpreted using the formula:
where Cn is the numerical count and Vai is the analog input voltage.
However due to use of manufacturing offset (and also user-configurable offset and
max count, if used), an OVW may be generated before the reported count reaches
32000. Similarly, the reported count may be at 32 752, but you may not receive the
expected OVE.
V
ai
C
n
3200⁄=
V
32 752
32 000
9V
10.24 V
10 V
28 800
-9 V
-10 V
-10.24 V
-32 768
-32 000
-28 800
ai
C
n
OVE
OVW
UVE
UVW
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