Rockwell Automation 1746-NI8 SLC 500 Analog Input Modules User Manual - Manual (Page 14)

1–4 Overview
Publication 1746Ć6.8 - April 1997
The SLC processor reads the converted analog data from the module
at the end of the program scan, or when commanded by the ladder
program. The processor and module determine that the backplane
data transfer was made without error, and the data is used in your
ladder program. A graphic representation of this is shown below.
1746ĆNI8
Analog
Input
Module
SLC 500
Processor
Channel Configuration Word
from Ladder Program
Channel Data Word Voltage or Current
Analog Channel Input
Channel Status Word
Data Transfer Between the Module and Processor
(shown for one channel)
Module Operation
The 1746-NI8 module’s input circuitry consists of eight differential
analog inputs multiplexed into a single analog-to-digital (A/D)
converter.
The A/D converter reads the selected input signal and converts it to a
digital value. The multiplexer sequentially switches each input
channel to the module’s A/D converter. Multiplexing provides an
economical means for a single A/D converter to convert multiple
analog signals. However, multiplexing also affects the speed at
which an input signal can change and still be detected by the
converter.
Module Calibration
The module performs continuous autocalibration for all the channels
that are enabled. There is no need to invoke a calibration cycle to
compensate for changes in temperature.