Rockwell Automation 1746-NI8 SLC 500 Analog Input Modules User Manual User Manual
Page 41
4–10
Preliminary Operating Considerations
Publication 1746Ć6.8 - April 1997
Noise Rejection
Rejection of common mode noise is inherent in the hardware design
of the module. Common Mode Rejection is better than –75 dB for
common mode DC signals and better than –100 dB for common
mode 50 Hz and 60 Hz AC signals. The module performs well in
the presence of common mode noise as long as the signals applied to
the user terminals do not exceed the common mode voltage rating
(
±
10.5 Volts) of the module. Improper earth/chassis ground
connections may be a source of common mode noise.
Rejection of normal mode noise is implemented in the firmware and
is a function of the filter frequency selected by the user. A lower
frequency filter will reject more normal mode noise than a higher
frequency filter. Transducer power supply noise, transducer circuit
noise, or process variable irregularities may be sources of normal
mode noise.