Rockwell Automation 1756-OF8H ControlLogix HART Analog I/O Modules - Manual (Page 69)

Rockwell Automation Publication 1756-UM533C-EN-P - February 2011 69
1756-IF16H HART Analog Input Module Chapter 5
Module Filter
The module filter attenuates the input signal beginning at the specified
frequency. This feature is applied on a module-wide basis, affecting all channels.
The module attenuates the selected frequency by approximately -3 dB or 0.707 of
the applied amplitude.
An input signal with frequencies above the selected frequency is attenuated more
while frequencies below the selection receive no attenuation.
In addition to frequency rejection, a by-product of the filter selection is the
minimum sample rate (RTS) that is available. For example, the 1000 Hz selection
does not attenuate any frequencies less than 1000 Hz, and provides for sampling
of all 16 channels within 18 ms. The 15 Hz selection attenuates all frequencies
above 15 Hz and provides only for sampling all 16 channels within 328 ms.
Use the following table to choose a module filter setting.
IMPORTANT Do not use the 1000 Hz module filter with HART instruments.
IMPORTANT 60 Hz is the default setting for the module filter. This setting provides
approximately 3 dB of attenuation of a 60 Hz input.
Table 10 - Module Filter Selections with Associated Performance Data
Module Filter
Selection (-3dB)
(1)
(1) Worst case settling time to 100% of a step change is double the real time sample time.
15 Hz 20 Hz 50 Hz 60 Hz 100 Hz 250 Hz 1000 Hz
Minimum Sample Time
(RTS) 328 ms 275 ms 115 ms 115 ms 61 ms 25 ms 11 ms
Effective Resolution 18 bits 18 bits 17 bits 17 bits 16 bits 16 bits 15 bits
0.08 μA 0.08 μA 0.16 μA 0.16 μA 0.32 μA 0.32 μA 0.64 μA
50 Hz Rejection 74 dB 48 dB 6 dB 6 dB 1 dB 0.1 dB N/A
60 Hz Rejection 74 dB 97 dB 9 dB 9 dB 2 dB 0.2 dB N/A
.707
60 Hz 0