Allen-Bradley 1747-SCNR ControlNet Scanner Module

The Allen-Bradley 1747-SCNR, also cataloged as the 1747-SCNR ControlNet Scanner Module, operates as a dedicated communication interface for ControlNet network data exchange within SLC 500 backplane architectures. It provides dual ControlNet port access for cyclic I/O scanning and network scheduling between SLC 5/02 through 5/05 processors and distributed I/O nodes, supporting both non-redundant and redundant media configurations.

Hardware Specifications

Backplane Bus Communication and ControlNet Deterministic Scheduling

The 1747-SCNR integrates into the SLC 500 backplane architecture where it consumes defined 5 VDC and 24 VDC backplane current segments to execute ControlNet scheduling tasks. The module handles cyclic data transfer using deterministic ControlNet media timing, coordinating I/O scan lists across connected nodes.

ControlNet dual-port architecture enables linear or redundant media topologies using 1786-RG6 coaxial trunking. The scanner performs network scan execution through scheduled communication intervals, ensuring synchronized data exchange with remote I/O modules. Slot-based chassis allocation excludes the left-most slot due to processor-reserved addressing constraints within SLC rack mapping logic.

LED indicators (CHA, CHB, OK) reflect network channel state and module health at the backplane execution layer, independent of external HMI diagnostics.

Frequently Asked Questions (FAQ)

Q: Can the 1747-SCNR operate with only one ControlNet port connected?
A: Yes. The module supports single-channel operation, but redundancy and media fault tolerance are disabled when only one port is active.

Q: What is the impact of exceeding backplane current limits?
A: Excess current on the 5 VDC backplane rail may cause module reset or bus fault condition, as the scanner is sensitive to backplane voltage stability during scan cycles.

Q: Is hot-swap supported in SLC 500 chassis for this module?
A: No. Module insertion or removal must be performed under power-off conditions to avoid backplane bus corruption or ControlNet scheduling loss.

Field Installation Guidelines

• Install in any SLC 500 chassis slot except the left-most processor slot.

• Ensure backplane power integrity: 5 VDC and 24 VDC rails must remain within SLC specification before insertion.

• Use only approved 1786-RG6 coaxial media and certified ControlNet taps (1786-TPR, 1786-TPYR, etc.).

• Maintain controlled bend radius for coaxial trunk cable to avoid impedance mismatch.

• Verify CHA and CHB LED synchronization after power-up before enabling I/O scan operations.

• Do not insert or remove module while chassis is energized.