Rockwell Automation 1746-NR8 SLC 500 RTD/Resistance Input Module User Manual - Manual (Page 43)

Publication 1746-UM003A-EN-P
Preliminary Operating Considerations 3-7
Channel Cut-Off Frequency
The channel filter frequency selection determines a channel’s cut-off frequency,
also called the -3 dB frequency. The cut-off frequency is defined as the point
on the input channel frequency response curve where frequency components
of the input signal are passed with 3 dB of attenuation. All frequency
components at or below the cut-off frequency are passed by the digital filter
with less than 3 dB of attenuation. All frequency components above the cut-off
frequency are increasingly attenuated, as shown in the following illustrations.
The cut-off frequency for each input channel is defined by its filter frequency
selection. The table on page 3-5 shows the input channel cut-off frequency for
each filter frequency. Choose a filter frequency so that your fastest changing
signal is below that of the filter’s cut-off frequency. The cut-off frequency
should not be confused with update time. The cut-off frequency relates how
the digital filter attenuates frequency components of the input signal. The
update time defines the rate at which an input channel is scanned and its
channel data word updated. See page 3-10 for determining the channel update
time.
Figure 3.3 28 Hz Filter Frequency Response