Allen‑Bradley 1756-CNBR/D – ControlLogix ControlNet Bridge with Redundant Media (High-Availability Networking)

The Allen‑Bradley 1756-CNBR/D is a ControlNet communication module for the ControlLogix platform, designed for redundant coax media (channels A and B). In many cases it’s the go-to choice when you need deterministic, scheduled I/O across multiple racks with higher network availability. From my experience, the redundant media design is what keeps lines running when a single cable segment has a problem—you simply keep producing while you plan a clean repair window.

It supports both scheduled and unscheduled messaging at the ControlNet standard 5 Mbps and fits any standard 1756 chassis slot. You might notice that commissioning is straightforward: set the node address with the rotary switches, confirm the NET A/NET B LED status, and you’re ready to schedule I/O in Studio 5000 (RSLogix 5000).

Company’s Order Placement Process and Guarantees

• Warranty: 365 days
• Delivery: 1 week if in stock; no more than 1 month at the latest
• Payment: 50% advance payment; full payment before delivery
• Express options: FedEx, UPS, DHL

Key Features

• Redundant ControlNet media (A/B) – Two coax channels for higher uptime; if one path degrades, the other typically keeps traffic flowing.
• Deterministic scheduled I/O – Stable, predictable updates for motion, drives, and time-critical interlocks.
• Unscheduled messaging – Supports diagnostics, HMI, and configuration traffic without impacting scheduled bandwidth.
• Chassis-based integration – Plugs into any 1756 ControlLogix chassis and bridges the backplane to ControlNet nodes.
• Rotary node addressing – Quick setup; address range typically 01–99 on a ControlNet segment.
• Status LEDs for fast troubleshooting – OK, NET A/NET B, and activity indicators help pinpoint issues on the floor.
• Studio 5000 / RSLogix 5000 compatible – Configure and schedule network I/O in the familiar Logix environment.

Technical Specifications

Application Fields

The 1756-CNBR/D fits discrete and process applications where deterministic updates and network resilience matter:

• Automotive body and paint shops – tightly scheduled I/O across multiple stations.
• Food & beverage packaging – redundant media helps avoid downtime during cable damage or maintenance.
• Continuous process (chemicals, water/wastewater) – stable, predictable update cycles for interlocks and PID loops.
• Drives and MCC integration – deterministic scanning of drive adapters and remote I/O racks.
• Legacy ControlNet expansions – drop-in replacement in existing ControlNet architectures while keeping forward compatibility with Logix.

Advantages & Value

• High availability – Redundant A/B media seems to be the simple insurance policy many plants rely on.
• Seamless Logix integration – Works natively with ControlLogix controllers and Studio 5000, reducing engineering time.
• Predictable performance – Deterministic scheduling keeps cycle times tight for coordinated machines.
• Lifecycle-friendly – Typically a straightforward replacement in installed ControlNet systems, keeping existing cable infrastructure.
• Procurement confidence – Clear warranty, fast shipment options, and technical backing for commissioning and firmware alignment.

Quick feedback from a maintenance supervisor who recently swapped one: “We replaced a failed CNBR in under 10 minutes. Network kept running on the other channel, so production never stopped.”

Installation & Maintenance

• Cabinet & chassis – Install in a 1756 ControlLogix chassis with adequate ventilation; follow standard spacing and ambient temperature limits.
• Wiring & media – Use ControlNet‑rated 75 Ω coax and approved taps/terminators; segregate from high‑noise power cables.
• Addressing – Set node address on the front rotary switches (typically 01–99) before power‑up.
• Grounding & shielding – Maintain proper shield continuity on coax; bond to cabinet ground per ControlNet guidelines.
• Firmware – Match module firmware to your Logix controller project version; update with ControlFlash/Studio 5000 as needed.
• Routine care – Periodically inspect connectors, check terminators, clean dust from the module face, and confirm LED health on both channels.
• Safety – De‑energize the chassis before inserting/removing modules. Verify the network is terminated correctly to avoid reflections.

Quality & Certifications

• CE marked, UL/cUL Listed, CSA certified
• RoHS compliance for most manufacturing lots
• Manufacturer quality system typically ISO 9001
• Standard warranty from us: 365 days