Siemens Simatic S7-300 CPU 31xC and CPU 31x S7-300 - Manual (Page 146)

Technical data of CPU 31xC
6.6 Technical data of the integrated I/O
CPU 31xC and CPU 31x, Technical data
6-36
Manual, Edition 08/2004, A5E00105475-05
Input filters (software filter)
The current / voltage inputs have a software filter for the input signals which can be
programmed with STEP 7. It filters the configured interference frequency (50/60 Hz) and
multiples thereof.
The selected interference suppression also determines the integration time.
At an interference suppression of 50 Hz the software filter forms the average based on the
last 20 measurements and saves the result as a measurement value.
You can suppress interference frequencies (50 Hz or 60 Hz) according to the parameters set
in STEP 7. A setting of 400 Hz will not suppress interference.
An integrated low-pass filter attenuates analog input signals of channel 0 to 3.
AI
x
Selection in STEP 7
(Software filter)
50-Hz configuration
(mean value filter)
60-Hz configuration
(mean value filter)
A/D converter
400-Hz configuration
Hardware low-pass filter
(RC circuit)
Figure 6-4 Principle of interference suppression with STEP 7