Notch filter – Rockwell Automation 1756-OF8I ControlLogix Eight-channel Isolated Analog I/O Modules User Manual
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Rockwell Automation Publication 1756-UM540A-EN-P - May 2014
Chapter 3
1756-IF8I Isolated Analog Input Module
Notch Filter
The notch filter is a built-in feature of the Analog-to-Digital convertor (ADC)
that removes line noise in your application for each channel. The removal of line
noise is also known as noise immunity.
The notch filter attenuates the input signal at the specified frequency. That is, the
filter reduces the amplitude of the signal with minimal signal distortion.
Choose a notch filter based on what noise frequencies are present in the module's
operating environment and any sampling requirements needed for control. The
default Notch Filter setting is 60 Hz.
For example, a notch filter is typically set to 60 Hz to filter out 60 Hz AC line
noise and its overtones. A 60 Hz notch filter setting attenuates frequencies of
60 Hz, 120 Hz, 180 Hz and so forth.
The following graphic shows 10 Hz notch filter selection and how the noise is
dissipated over the entire spectrum but especially at the notch filter setting and
its overtones.