Rockwell Automation 1769-IF16V Compact High Density Analog Input Modules - Manual (Page 40)

40 Publication 1769-UM018A-EN-P - October 2008
Chapter 3 Module Data, Status, and Channel Configuration
Common Mode Rejection is better than 60 dB at 50 and 60 Hz, with
the 50 and 60 Hz filters selected, respectively. The modules perform
well in the presence of common mode noise as long as the signals
applied to the IN+ and COM input terminals do not exceed the
working voltage rating of the module. Improper earth ground may be
a source of common mode noise.
Channel Step Response
The selected channel filter frequency determines the channel’s step
response. The step response is the time required for the analog input
signal to reach 100% of its expected final value. This means that if an
input signal changes faster than the channel step response, a portion
of that signal will be attenuated by the channel filter.
Module Update Time and Scanning Process
The module update time is defined as the time required for the
module to sample and convert the input signals of all enabled input
channels and provide the resulting data values to the Data Input file.
Module update time can be calculated by adding the sum of all
enabled channel update times. Channel update times include channel
scan time, channel switching time, and converter configuration time.
The module sequentially samples the channels in a continuous loop.
The 1769-IF16C and 1769-IF16V modules use parallel sampling to
update the entire module (all 16 channels, if enabled) in an amount of
time equal to only 8 channel update times. The module performs
parallel channel sampling on pairs of inputs.
The input channels are paired as follows: [0,1], [2,3], [4,5], [6,7], [8,9],
[10,11] [12,13], [14, 15]. The channels in the same pair are sampled at
the same time. Channel update time is thus input pair update time. If
channels in the same input pair have different filter settings, the input
pair update time is determined by the channel with the lowest filter
setting. A channel that is not enabled has a channel update time of 0
ms. If neither channel of an input pair is enabled, the input pair
update time is 0 ms.
Filter Selection Channel Step Response
16 Hz 1550 ms
50 Hz 500 ms
60 Hz 420 ms
315 Hz 90 ms
1365 Hz 35 ms