Effects Of Filter Frequency On Noise Rejection - Spectrum Controls 1769 User Manual

3-8 Chapter 3: Module, Data, Status, and Channel Configuration
Input
Filter
4.17
Hz
10.0
Hz
16.7
Hz
19.6
Hz
62
Hz
470
Hz
6 If lead compensation is enabled, use this column for channel update times.
User's Manual Pub. 0300241-02 Rev. A
• Module update time
The table below summarizes the effects of each filter selection.
Table 3-5. Filter Effects
Channel
Channel
Update
Update
Time
Time
Lead
Lead
Compensation
Compensation
Disabled Enabled
242 ms 964 ms
102 ms 404 ms
62 ms 244 ms
53 ms 208 ms
18 ms 68 ms
4 ms 10 ms

Effects of Filter Frequency on Noise Rejection

The filter frequency that you choose for a module channel determines the amount
of noise rejection for the inputs. A lower frequency (4.17 Hz versus 470 Hz)
provides better noise rejection and improves repeatability, but also increases
channel update time. A higher filter frequency provides lower noise rejection but
decreases the channel update time and negatively affects repeatability.
When selecting a filter frequency, be sure to consider the cut-off frequency to
obtain acceptable noise rejection. Choose a filter frequency so that your fastest-
changing signal is below that of the filter's cut-off frequency.
Table 3-5 above lists the expected normal mode rejection for each of the filter
settings.
Common Mode Rejection is better than 115 dB at 50 and 60 Hz, with the 50 and
60 Hz filters selected, respectively, or with the 10 Hz filter selected. The module
performs well in the presence of common mode noise as long as the signals
applied to the user positive and negative input terminals do not exceed the
Cut-Off
6 Frequency Repeatability
1 Hz See Appendix
A
2 Hz See Appendix
A
4 Hz 2× (4.17 Hz
values)
From
Appendix A
5 Hz 2× (4.17 Hz
values)
From
Appendix A
14 Hz 4× (4.17 Hz
values
From
Appendix A)
109 Hz 10× (4.17 Hz
values)
From
Appendix A
NMRR NMRR
50 Hz 60 Hz
Rejection Rejection
74 dB 74 dB
70 dB 70 dB
65 dB NA
NA 74 dB
NA NA
NA NA