Rockwell-automation 1746-NI8 SLC 500 Analog Input Modules User Manual Uživatelský manuál stáhnout pdf (Strana 41)

4–10

Preliminary Operating Considerations

Publication

17466.8 - 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.

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Rockwell-automation 1746-NI8 SLC 500 Analog Input Modules User Manual Uživatelský manuál Strana 41