Siemens SIMATIC ET 200AL, System Manual

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What you should know about analog technology
2.2 Precision/resolution
Analog value processing
14
Function Manual, 06/2014, A5E03461439-AC
Measuring ranges
For the display of the measuring range, SIMATIC S7 distinguishes between the rated range,
the overrange and underrange, and the overflow or underflow. This distinction allows you to
recognize whether the measured value is actually in the measuring range determined in the
technical specifications. The overflow and underflow ranges are reserved for error detection.
At a resolution of 16 bits the theoretically possible 32768 increments are distributed across a
voltage range of 11.852 V, which means that only 27648 increments are actually available
for the resolution of a measuring range of 10 V. The minimum value which can be
represented is therefore 0.3617 mV (see table).
Table 2- 1 Example of resolution for the 0 to 10 V measuring range of a SIMATIC S7 module
Value (increments) Voltage measuring range
Decimal 0 to 10 V Range
32767 11.852 V Overflow
32512
32511 11.759 V Overrange
27649
27648 10.0 V Rated range
20736 7.5 V
1 361.7 μV
0 0 V
not relevant for this example
as negative values are not possible Underrange
Underflow
The digitized visualization of the input ranges, separated into bipolar and unipolar input
ranges, is shown in the section Visualization of the input ranges (Page 62). The digitized
visualization of the output ranges, separated into bipolar and unipolar output ranges, is
shown in the section Visualization of the output ranges (Page 63). You will find a summary of
all measuring ranges which you can use with your analog module in the corresponding
device manual.