Allen‑Bradley 1756‑CN2R_B – ControlLogix ControlNet Module with Redundant Media (Series B)

The 1756‑CN2R_B is a ControlNet communication module for ControlLogix that supports redundant media (Channel A/B) on coax. From my experience, teams choose this Series B version when they need deterministic, scheduled ControlNet for remote I/O or peer control—and want the extra resilience of dual-media paths. You might notice the front BNC connectors and the rotary node switches; that combination typically makes addressing and commissioning pretty predictable during a short outage.

Company’s Order Placement Process and Guarantees

• The warranty period is 365 days
• Delivery time: 1 week for in-stock; no more than one month at the latest
• Payment method: 50% advance payment, full payment for delivery
• Express delivery methods: FedEx, UPS, DHL
• Pre‑shipment checks: visual/label verification and port integrity; ESD‑safe, shock‑resistant packing

Key Features

• Redundant ControlNet media – Dual BNC (Channel A/B) for higher availability on 75 Ω RG‑6 coax runs.
• Deterministic scheduled updates – Supports ControlNet’s scheduled/unscheduled traffic for time‑critical I/O and coordination.
• Simple addressing – Rotary node switches on the front simplify swaps and keep addressing consistent.
• Backplane bridge – Routes data between ControlNet and the 1756 backplane for controllers, remote I/O, or peer modules.
• Proven in 24/7 duty – Series B mechanics and status LEDs make diagnostics straightforward in the field.
• 5 Mbit/s speed – Standard ControlNet throughput for predictable, time‑sliced transfers.

Technical Specifications

Application Fields

I tend to see the 1756‑CN2R_B in plants that want deterministic, high‑uptime ControlNet segments:

• Remote I/O for process skids and MCCs where scheduled updates matter.
• Peer‑to‑peer ControlLogix coordination on redundant A/B media.
• Drive and motion islands that still rely on ControlNet determinism.
• Brownfield expansions where ControlNet is standard and uptime is critical.

A maintenance lead told me, “We set the node on the rotaries, landed both A and B, and the scheduled connections went green on the first scan.” That’s been typical when taps and terminations are tidy.

Advantages & Value

• Reliability – Redundant media and clear status LEDs reduce nuisance downtime.
• Compatibility – Native to ControlLogix; works with established ControlNet infrastructure and devices.
• Cost control – Drop‑in replacement that preserves existing topology and cabinet wiring.
• Maintainability – Rotary addressing and predictable diagnostics shorten outage windows.
• Support – We can help confirm node plans, tap types, and basic scheduling checks before your window.

Installation & Maintenance

• Cabling & topology: Use approved 75 Ω RG‑6 quad‑shield coax, ControlNet taps, and terminators; keep stubs short; maintain both A and B paths if using redundancy.
• Addressing: Set node with front rotary switches; document node IDs on the panel door for quick reference.
• Grounding/EMC: Bond shields per Rockwell guidance; route coax away from VFD motor leads to reduce noise.
• Scheduling: Validate the network schedule in RSNetWorx for ControlNet (or equivalent); check connection status bits after download.
• Routine care: Periodic visual inspection, re‑torque of BNC/tap connections, and a quick review of link health and error counters.

Quality & Certifications

• Manufactured under Rockwell Automation quality systems (ISO 9001 aligned).
• CE/UL/cUL markings apply at the system/module level per Rockwell documentation.
• RoHS status depends on series/lot; we can confirm by part/serial if needed.
• Warranty: 365 days repair/replace coverage from delivery.