Precision/Resolution - Siemens SIMATIC ET 200AL System Manual

2.2

Precision/resolution

The resolution of an analog module depends on the converter and its external circuitry. An
approximation of the analog signal to be acquired/output is returned by a stepped curve. The
resolution determines the number of increments of the analog value along this stepped
curve. A higher module resolution reduces the length of increments and adds precision to
the digitization of the analog signal.
Approximation of an analog value
The figures below show the approximation of an analog value by means of a stepped curve.
A low resolution only returns a rough approximation of the actual curve (left figure), while the
approximation is more precise at higher resolutions (right figure).
①
②
Figure 2-4
Visualization of the measuring range at a resolution of 13 bits and 16 bits
The unipolar measured value from a module having a resolution of 13 bits (= 12 bits + S) is
segmented into a total of 2
range of 0 to10 V is 10 V/4096, equal to 2.4 mV.
A module with16-bit (= 15 bits + S) resolution thus provides an increment of 0.3 mV. If the
resolution increases by one bit, the number of increments doubles and the width of an
increment halves.
If the resolution increases from 13 bits to 16 bits, the number of increments increases
eightfold from 4096 to 32768. With a resolution of 13 bits, the smallest value that can be
displayed is therefore 2.4 mV. By contrast, this value is approximately 0.3 mV at a resolution
of 16 bits.
Analog value processing
Function Manual, 06/2014, A5E03461439-AC
Analog value
Digital value
Approximation of an analog curve with a stepped curve
= 4096 increments. The smallest increment in a measuring
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What you should know about analog technology
2.2 Precision/resolution
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