Rockwell Automation 1746-NR4 SLC RTD/Resistance Input Module User Manual - Manual (Page 56)

Publication 1746-UM008B-EN-P - December 2006
56 Preliminary Operating Considerations
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 figures.
The cut-off frequency for each input channel is defined by its filter
frequency selection. The Notch Frequencies table 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 58 for determining the channel update time.
10 Hz Filter Notch Frequency
-200
-180
-160
-140
-120
-100
-80
-60
-40
-20
0
0 10 20 30 40 50 60 Hz
Frequency
2.62 Hz
-3 dB
Amplitude (in dB)
Frequency Response