1734-ACNR ControlNet Adapter Replacement

Overview

The Allen-Bradley 1734-ACNR is an active legacy component within the POINT I/O product line. It serves as a ControlNet adapter featuring redundant media (dual-channel coaxial BNC ports) designed to route I/O data back to a Logix controller. For over two decades, ControlNet was a preferred network topology for deterministic, high-speed remote I/O arrays. However, because Rockwell Automation has transitioned ControlNet products into "End of Life" (EOL) and "Discontinued" lifecycles, industrial maintenance teams face challenging hardware sourcing environments.

When a 1734-ACNR fails, or system architects plan facility-wide communication modernizations, a decision must be made: perform a like-for-like swap with a high-quality refurbished or surplus 1734-ACNR unit, or convert the physical drops and network architecture to an EtherNet/IP platform using a dual-port 1734-AENTR adapter. This guide covers the critical technical data, migration procedures, and product compatibility metrics required to execute either route successfully.

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Legacy Product Information

The 1734-ACNR is a specialized head-module adapter that mounts on a standard 35mm DIN rail. It coordinates backplane communications for up to 63 POINT I/O modules, power supplies, and field-potential modules. It supports scheduled and unscheduled I/O transactions over a deterministic 5 Mbps ControlNet connection, utilizing BNC network taps and dual coaxial cabling (Link A and Link B) for physical layer redundancy.

Key Specifications:

• Catalog Number: 1734-ACNR (Series A and Series B)
• Protocol: ControlNet
• Transmission Speed: 5 Mbps (fixed)
• Physical Connectors: Dual BNC (75 Ohm coax) ports for redundant trunks
• Decimal Node Address Selection: Two rotary switches on the top panel (Range: 01 to 99)
• Backplane Output Current: 1.0 A maximum @ 5V DC (POINTBus current)
• Input Voltage Range: 10–28.8V DC (24V DC nominal)
• Power Consumption: 8.0 W maximum at 24V DC
• Regulatory/Protection Rating: IP20, open-type footprint

Hardware Lifecycle Status:

The entire Allen-Bradley ControlNet ecosystem, including the 1734-ACNR, is classified as Discontinued. Standard factory-new models are no longer shipped from Rockwell Automation. Finding reliable, tested surplus or meticulously refurbished units is now the primary path to maintaining factory uptime without rebuilding full automation networks.

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Recommended Replacements

Depending on your facility's budget, architectural layout, and scheduled downtime window, three primary replacement paths are available. Refer to the matrix below:

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Compatibility Considerations

Replacing a 1734-ACNR requires careful consideration of mechanical configurations, wiring parameters, software tools, and firmware dependencies.

Wiring and Cabling Compatibility

• Like-for-Like (ACNR to ACNR): Simply unplug the BNC connectors from Channel A and Channel B and route them to the new module. No tooling changes are necessary.
• Migration to AENT/AENTR: ControlNet uses RG-6 coaxial cables with BNC terminations. Upgrading to the 1734-AENTR requires swapping coax trunks out for shielded Category 5e (or better) RJ45 cables. If the distance of the run exceeds 100 meters, fiber optic media converters will also be required.

Footprint & Mounting

All POINT I/O adapters share a universal form factor designed to latch securely to a standard 35mm DIN rail. The 1734-ACNR, 1734-AENT, and 1734-AENTR are drop-in equivalents regarding physical dimensions. The replacement or upgraded module fits into the slot at the far-left end of the rail. The backplane contact pins interface natively with any existing standard 1734 expansion slide.

Software and Backplane Configuration

• ControlNet (ACNR): Scheduled bandwidth parameters must be maintained using RSNetWorx for ControlNet. Replacing a failed adapter with identical hardware only requires matching the physical decimal node dials; the active Network Keeper (typically a 1756-CN2R or equivalent) will download the stored scheduling parameters to the newly installed node ID automatically.
• EtherNet/IP (AENT/AENTR): RSNetWorx is completely eliminated from the engineering workflow. Network routes are configured directly inside RSLogix 5000 / Studio 5000 Logix Designer through the I/O Configuration tree. IP addresses can be designated via BOOTP/DHCP utility software or physical rotary switches for a fixed network subnet.

Firmware & Keying

When slotting in a replacement 1734-ACNR, match the device Series (Series A vs. Series B) and major/minor firmware version to the Offline controller configuration. In Studio 5000, verify the Electronic Keying settings. If "Exact Match" is active, firmware versions must line up precisely. If mismatched, switch the parameter to "Compatible Module" or "Disable Keying" temporary to accept older or newer series compatibility.

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Upgrade Benefits

If your engineering group elects to migrate from the legacy 1734-ACNR to a 1734-AENTR EtherNet/IP model, your process benefits from significant hardware and operational enhancements:

1. Higher Data Throughput: ControlNet tops out at a 5 Mbps transmission lock. EtherNet/IP functions at 10/100 Mbps (Full Duplex), radically reducing overall system latency.
2. Simplified Diagnostic Engineering: ControlNet configurations require compiling a Network Update Time (NUT) and scheduling network Keepers inside specialized RSNetWorx programs. Modern 1734-AENTR units communicate natively, resolving commissioning hassles.
3. Optimized Network Diagnostics: Integrated web browsers embedded within the 1734-AENT/AENTR platforms offer status details page-loads via default IP addresses, easing local troubleshooting without specialized diagnostic analyzers.
4. Resilient topology via DLR: The 1734-AENTR supports Device Level Ring (DLR) installations to continue operations despite single-point cable failures without the specialized BNC taps needed for ControlNet schemes.

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Common Migration Challenges

• Physical Node Overlapping & Re-Indexing: When relocating a ControlNet line item, physical address rotary dial numbers can easily be set wrong. Always double-check standard octal or decimal node numbering schemes to prevent address collisions on existing active systems.
• Keepers out of Sync: If the overall network schedule isn't updated in RSNetWorx after replacing an adapter with a model with differing firmware signatures, the PLC may register an "I/O Connection Error" (Code 16#011b). Running a fresh "network save" resolves the fault.
• Power Supply Backplaning (PointBus Constraints): Older POINT I/O layouts with high module counts draw closely to the 1.0 A current limit of the adapter. Ensure total draw is within bounds when migrating because EtherNet/IP models occasionally have minor field-power design variations.

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Step-by-Step Replacement Procedure

Follow this procedure for a direct, like-for-like replacement of a 1734-ACNR with a refurbished/surplus 1734-ACNR:

Step 1: Safety and Isolation

1. Obtain the proper hot-work permits or isolate physical hazards down-stream of the target control panel.
2. Ensure the main power supply feeding the 24V DC terminal block on the 1734-ACNR is locked and tagged out (LOTO).

Step 2: Record Physical Settings and Label Wiring

1. Record the positions of the dual rotary switches (tens and ones digits) located at the top-front of the failed 1734-ACNR module.
2. Label both coax lines: note which is plugged into Port A and which to Port B.

Step 3: Remove Cabling and Terminal Blocks

1. Disconnect the BNC coaxial network connections from Ports A and B by twisting and pulling. Lock the cables in a clean area to prevent contamination of the contacts.
2. Unplug the 24V DC auxiliary power connector block from the lower front-face of the module.

Step 4: Disengage the Adapter from the DIN Rail

1. Pull the black locking latch upward on the bottom of the adapter to free the module from the DIN rail.
2. Slide the adapter horizontally to the left, away from the adjacent POINT I/O module to disengage the backplane socket. Remove the module.

Step 5: Mount and Pre-configure the Replacement Unit

1. Using a small screwdriver, set the rotary switch decimal node selectors on the replacement 1734-ACNR to match the exact value recorded from the failed unit.
2. Guide the replacement module onto the 35mm DIN rail, sliding it to the right so its right-side interface connector plugs into the first I/O module’s backplane block.
3. Securely push the bottom black locking latch-pin down to lock the module to the DIN rail.

Step 6: Cable Reconnection & Power-Up Testing

1. Reinstall the 24V DC terminal power block.
2. Push and lock the BNC cabling onto Port A and Port B according to your labels.
3. Remove lockout tags and switch the 24V DC power supply on.
4. Monitor the adapter's LEDs. The SYS and PWR LEDs should show steady green. The NET status LED should flash green and transition to solid green once the active PLC controller schedules the node.

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Frequently Asked Questions

Q1: Is it necessary to reboot or run RSNetWorx after replacing a 1734-ACNR with an identical refurb unit?

No, as long as the rotary node switches on the new unit match the failed module's settings, and the firmware is compatible. The existing Network Keeper node (PLC master bridge) stores the network schedule offline and will push down configuration parameters automatically once the physical link is established.

Q2: What should I do if the "NET" LED flashes red on the replacement unit?

A flashing red Network LED indicate a media configuration error, duplicate node address, configuration mismatch, or that physical noise is present on the segment. Confirm that your rotary switches are dialed into the correct node, evaluate the coaxial run with a BNC terminator tester, and double-check your RSNetWorx configurations.

Q3: Can I run a standard 1734-AENT EtherNet/IP adapter on a ControlNet system?

No. ControlNet and EtherNet/IP run on entirely different physical layers and protocol stacks. You cannot combine physical ControlNet adapters and EtherNet/IP adapters on the same passive media trunk. An upgraded system requires replacing the entire network link from scanner to adapter.

Q4: Will standard Series A and Series B 1734-ACNR physical units fit on the same type of terminal bases?

Yes. The physical chassis dimensions and mechanical slider interfaces across series lines are fully backward and forward compatible, snapping to both 1734-TB and 1734-TBS wiring bases without mechanical interference.

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Related Products & Families

To complete your maintenance projects or execute network migrations, you may require these compatible components:

• Digital Inputs: 1734-IB4, 1734-IB8 (24V DC Input Modules)
• Digital Outputs: 1734-OB4E, 1734-OB8E (24V DC Output Modules)
• Power & Expansion: 1734-EP24DC (24V DC POINT I/O Expansion Power Supplies)
• ControlNet Bridges: 1756-CN2R, 1756-CN2 (ControlNet Scanner Modules for ControlLogix)
• EtherNet/IP Transitions: 1734-AENTR, 1756-EN2TR, 1756-EN4TR (Modern PLC Communications Bridges)

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Need Help?

Replacing or upgrading older ControlNet products can introduce unexpected compatibility challenges. Palm Parts Solution can assist you with your equipment needs. We supply a selection of brand-new, premium refurbished, and certified industrial surplus parts—including the 1734-ACNR and current 1734-AENTR replacements. Every part we ship comes standard with an industry-leading warranty. Contact the technical team at Palm Parts Solution today to verify part availability and secure fast shipment options to keep your facility running smoothly.