Overview

This chapter describes the four-channel 1746-NR4 RTD/Resistance

Input Module and explains how the SLC controller gathers RTD

(Resistance Temperature Detector) temperature or resistance-initiated

analog input from the module.Included is:

• a general description of the module’s hardware and software features.

• an overview of system operation.

For the rest of the manual, the 1746-NR4 RTD/Resistance Input

Module is referred to as simply the RTD module.

Each time a channel is read by the module, that data value is tested by

the module for a fault condition, for example, open circuit, short

circuit, over range, and under range. If such a condition is detected, a

unique bit is set in the channel status word and the channel status

LED indicator blinks, indicating a channel error condition.

The SLC processor reads the converted RTD or resistance data from

the module at the end of the program scan or when commanded by

the ladder program. The processor and RTD module determine that

the backplane data transfer was made without error and the data is

used in your ladder program.