ABB CI840A (3BSE041882R1) – Communication Interface for S800 I/O on AC 800M/800xA Systems

The ABB CI840A is the communication interface module that links S800 I/O clusters to AC 800M controllers. In many cases it’s the simplest way to expand I/O while keeping the control application stable and serviceable. One thing I appreciate is how it drops into standard S800 I/O MTUs (e.g., TU846/TU847), so you can scale or replace with almost no cabinet rework. It seems to be the go-to choice when customers want dependable ModuleBus communication with room for redundancy.

Our Order Placement Process and Guarantees

Key Features

• ModuleBus interface for S800 I/O – Provides the communication backbone between AC 800M and distributed S800 I/O clusters.
• Supports redundant architectures – When paired with the proper MTU (e.g., TU847) and bus extender, it typically enables high-availability I/O communication.
• Hot-swap serviceability – Designed for fast replacement with minimal downtime; status LEDs simplify diagnostics during commissioning.
• Compact S800 mechanical footprint – Narrow width helps conserve DIN-rail space; fits neatly into existing S800 I/O cabinets.
• Stable firmware and broad compatibility – Commonly used across 800xA/AC 800M projects; typically backward-compatible within the S800 I/O family.

Technical Specifications

Application Fields

The CI840A is commonly used wherever AC 800M needs robust, distributed I/O: oil & gas processing, chemicals, power generation, metals, pulp & paper, and water/wastewater. From my experience, it’s especially useful in brownfield upgrades—keep the cabinet, swap the interface, and extend I/O without rewriting the whole application. A plant maintenance lead told us their crew could replace a CI module in minutes during a night shift, with the diagnostic LEDs giving enough confidence to bring the loop back online fast.

Advantages & Value

• Reliability – Stable operation in industrial temperatures; supports redundant chains to cut unplanned downtime.
• Compatibility – Fits into existing S800 I/O footprints and typically aligns with standard 800xA configurations.
• Lifecycle savings – Minimal cabinet changes, quick swap time, and simple diagnostics reduce service costs over the long run.
• Technical support – Well-documented platform; spare availability is generally strong, making procurement simpler.

Installation & Maintenance

• Cabinet & mounting – Mount on DIN rail using the appropriate S800 MTU (TU846/TU847). Keep at least moderate ventilation; avoid heat sources and vibration.
• Power & wiring – 24 VDC supply via backplane. Use proper grounding and segregate low-voltage signals from noisy power wiring. For redundancy, wire per ABB redundant MTU guidance.
• Safety & ESD – De-energize before insertion/removal unless the system is designed for hot-swap; use ESD protection when handling modules.
• Routine maintenance – Check connectors and MTU terminations quarterly. Clean dust with dry air. Verify firmware/project compatibility during upgrades and keep a tested rollback package.
• Commissioning tips – Confirm ModuleBus configuration in the control project and verify LED states. In most cases, addressing is straightforward once the MTU slots are mapped correctly.

Quality & Certifications

• CE and UL compliance (typical for ABB S800 I/O modules)
• RoHS conformity for hazardous substances
• Manufactured under ISO 9001 quality systems
• Manufacturer warranty as per ABB policy; sales warranty coverage: 365 days

Supporting Components You Might Need

• ABB TU846 – S800 MTU for single ModuleBus configurations; easy DIN-rail mounting.
• ABB TU847 – S800 MTU supporting redundant ModuleBus; often chosen for high-availability systems.
• ABB TB820V2 – ModuleBus extender for longer distances or ring topologies; useful in larger cabinets or distributed enclosures.