Siemens SIMATIC S7-300 Reference Manual page 242
Programmable logic controllers module data
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Analog Modules
Conversion and scan times for analog input channels in channel groups
When the analog input channels are grouped in channel groups, you must take into
account the conversion time channel group by channel group.
Example
Two analog input channels of the analog input module SM 331; AI 2 12 bits are
combined to form a channel group. You must therefore grade the scan time in
steps of 2.
Setting smoothing of analog values
You can set the smoothing of the analog values in STEP 7 for some analog input
modules.
Using smoothing
Smoothing of analog values ensures a stable analog signal for further processing.
It makes sense to smooth the analog values with slow variations of measured
values – for example, with temperature measurements.
Smoothing principle
The measured values are smoothed by digital filtering. Smoothing is accomplished
by the module calculating average values from a defined number of converted
(digitized) analog values.
The user assigns parameters to smoothing at not more than four levels (none, low,
average, high). The level determines the number of analog signals used for
averaging.
The higher the smoothing level chosen, the more stable is the smoothed analog
value and the longer it takes until the smoothed analog signal is applied after a
step response (refer to the following example).
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Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
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