Rockwell Automation 1746-NI8 SLC 500 Analog Input Modules User Manual - Manual (Page 45)

5–4 Channel Configuration, Data, and Status
Publication 1746Ć6.8 - April 1997
Important: The processor may continue receiving data values for a
period of time after the open circuit condition occurs
until when the condition is flagged. The module
indicates an open circuit within one module scan times.
The module response time is shown below.
Module Response to Open Circuit
Number of Channels Enabled Response Time (maximum)
1 0.75 msec
2 1.50 msec
3 2.25 msec
4 3.00 msec
5 3.75 msec
6 4.50 msec
7 5.25 msec
8 6.00 msec
Select Channel Filter Frequency (Bits 8-10)
Determine the desired input filter frequency for the channel and enter
the 3-digit binary code in bit field 8–10 of the channel configuration
word.
The channel filter frequency bit field lets you select one of 8 filters
available for a channel. The filter frequency affects the noise
rejection characteristics. A lower filter frequency increases the noise
rejection, and a higher filter frequency decreases the noise rejection.
Select a filter frequency considering acceptable noise and step
response time. See Channel Filter Frequency Selection on page
4–7
for more information on filter frequency.
Select Channel Enable (Bit 11)
Determine which channels are used in your program and enable
them. Place a one in bit 11 if the channel is to be enabled. Place a
zero in bit 11 if the channel is to be disabled.
The 1746-NI8 module only scans those channels that are enabled.
To optimize module operation and minimize throughput times,
unused channels should be disabled by setting the channel enable bit
to zero.
When set (1) the channel enable bit is used by the module to read the
configuration word information you have selected. While the enable
bit is set, modification of the configuration word may lengthen the
module update time for one cycle. If any change is made to the
configuration word, the change must be reflected in the status word
before new data is valid.