Allen-Bradley 1746-NR8/C RTD/Resistance Input Module

Configured for RTD signal acquisition and resistance measurement in SLC 500 I/O backplane systems, the Allen-Bradley 1746-NR8/C (1746-NR8 RTD/Resistance input module) provides direct electrical conversion of low-level temperature resistance signals into backplane digital data. The module operates across an 8-channel input architecture with sigma-delta conversion and internal filtering for sensor-level signal conditioning.

The unit is designed for RTD sensor interfacing including Pt and Ni element types, performing multi-channel temperature acquisition through the SLC 500 chassis communication bus.

Suffix Breakdown & Model Matrix

• 1746: SLC 500 I/O platform

• NR8: 8-channel RTD/Resistance input function block

• C: Revision / series suffix level

Hardware Specifications

I/O Density Scaling within SLC 500 Backplane Architecture

The module participates in SLC 500 backplane bus timing where input data is mapped cyclically during scan execution. Channel multiplexing is managed internally to maintain deterministic update sequencing across 8 RTD inputs, with backplane bandwidth allocation dependent on chassis slot configuration. Signal conditioning is executed prior to bus transfer to minimize scan-cycle distortion under multi-module loading conditions.

Frequently Asked Questions

Q: Can the module be hot-swapped under energized SLC 500 backplane conditions?
A: Hot-swapping is not supported. Removal or insertion requires chassis power removal due to backplane electrical coupling and signal line referencing.

Q: How does backplane current draw affect multi-slot SLC 500 configurations?
A: Backplane consumption at 5 V DC and 24 V DC must be included in chassis power budget calculations to avoid voltage droop during full-slot population.

Q: Does firmware level impact RTD conversion behavior or scaling?
A: Scaling and conversion behavior is fixed in hardware conversion logic; revision suffix affects compatibility but not measurement algorithm.

Field Installation Guidelines

• Install module only in SLC 500 compatible chassis slot with verified backplane alignment.

• Maintain shield continuity for RTD cable pairs and terminate shield at single-point ground reference.

• Separate RTD wiring from high-voltage or switching conductors to reduce inductive coupling.

• Verify channel wiring configuration (2-wire, 3-wire, 4-wire) before energizing system.

• Ensure chassis power is removed prior to insertion or removal of module.

• Confirm terminal block seating and mechanical locking before system startup.