Rockwell Automation 1746-NI16V SLC 500 Analog Input Modules User Manual - Manual (Page 14)

Publication 1746-UM001A-US-P
1-4 Overview
Each time a channel is read by the module, that data value is tested by
the module for a fault condition (i.e., open-circuit, over-range, and
under-range). If a fault condition is detected, a unique bit is set in the
channel status word and the channel status LED blinks.
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. If the processor and module determine that the backplane
data transfer was made without error, the data is used in your ladder
program. A graphic representation of this is shown below.
Data Transfer Between the Module and Processor (shown for one channel)
Module Operation
The 1746-NI16 module’s input circuitry consists of four
analog-to-digital (A/D) converters. Each of the 4 A/D converters
multiplex 4 inputs for a total of 16 single-ended inputs.
The A/D converters read the selected input signal and convert 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 1746-NI16 module is already factory calibrated and ready for use.
Although factory calibration is suitable for most applications, the
module can be calibrated by the user. See Appendix D for more
information on calibration.
1746-NI16
Analog
Input
Module
SLC 500
Processor
Channel Configuration Word
from Ladder Program
Channel Data Word
Channel Status Word
Voltage or Current
Analog Channel Input