Rockwell-automation 1746-NI8 SLC 500 Analog Input Modules User Manual Instrukcja Użytkownika Pobierz pdf (Strona 14)

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Overview

Publication

17466.8 - 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.

1746NI8

Analog

Input

Module

SLC 500

Processor

Channel

Configuration W

ord

from Ladder Program

Channel Data W

ord

Voltage or Current

Analog Channel Input

Channel Status Word

Data

ransfer 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.

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Rockwell-automation 1746-NI8 SLC 500 Analog Input Modules User Manual Instrukcja Użytkownika Strona 14