Publication 1769-UM005A-EN-P
4-16
Module Data, Status, and Channel Configuration
Effects of Filter Frequency on Noise Rejection
The filter frequency that you choose for a channel determines the amount
of noise rejection for the inputs. A smaller filter frequency (e.g. 10Hz)
provides the best noise rejection and increases effective resolution, but
also increases channel update time. A larger filter frequency (e.g. 1 kHz)
provides lower noise rejection, but also decreases the channel update
time and effective resolution.
When selecting a filter frequency, be sure to consider channel cutoff
frequency and channel step response to obtain acceptable noise rejection.
Choose a filter frequency so that your fastest-changing signal is below that
of the filter’s cutoff frequency.
Common mode noise rejection for the module is better than 110 dB at 50
Hz (50 Hz filter) and 60 Hz (60 Hz filter). The module performs well in
the presence of common mode noise as long as the signals applied to the
input terminals do not exceed the common mode voltage rating (±2.5V)
of the module. Improper earth ground can be a source of common mode
noise.
Channel Step Response
Another module characteristic determined by filter frequency is channel
step response, as shown in the following table. The step response is the
time required for the analog input signal to reach 100 percent of its
expected final value, given a full-scale step change in the input signal.
Thus, if an input signal changes faster than the channel step response, a
portion of that signal will be attenuated by the channel filter. The channel
step response is calculated by a settling time of 3 x (1 / filter frequency).
NOTE
Transducer power supply noise, transducer circuit noise,
and process variable irregularities can also be sources of
common mode noise.
Table 4.7 Filter Frequency vs. Channel Step Response
Filter Frequency
Step Response
10 Hz
300 ms
50 Hz
60 ms
60 Hz
50 ms
250 Hz
12 ms
500 Hz
6 ms
1 kHz
3 ms
Содержание Compact 1769-IR6
Страница 1: ...Compact I O RTD resistance Input Module Catalog Number 1769 IR6 User Manual AB PLCs ...
Страница 10: ...Publication 1769 UM005A EN P P 4 ...
Страница 40: ...Publication 1769 UM005A EN P 3 16 Installation and Wiring ...
Страница 74: ...Publication 1769 UM005A EN P 4 34 Module Data Status and Channel Configuration ...
Страница 115: ...AB PLCs ...
Страница 116: ...Publication 1769 UM005A EN P February 2001 2001 Rockwell International Corporation Printed in the U S A ...