ABB TU846 3BSE022460R1 Retrofit-Compatible Termination Unit

ABB TU846 3BSE022460R1 Retrofit-Compatible Termination Unit: Legacy System Compatibility and Smooth Upgrade

The ABB TU846 (part number 3BSE022460R1) is a termination unit designed for use within the ABB AC800M controller platform and the broader System 800xA distributed control architecture. As aging automation infrastructure reaches end-of-life, the TU846 3BSE022460R1 has become a critical component in retrofit projects, discontinued spare part replacement programs, and control cabinet modernization initiatives across process industries including oil and gas, pulp and paper, power generation, and chemical manufacturing.

When planning a retrofit or spare part replacement involving the TU846 3BSE022460R1, engineers must carefully evaluate several key parameters before committing to installation. Power supply capacity at the rack level must be confirmed — the TU846 draws power from the S800 I/O backplane, and any additional modules added during an upgrade cycle, such as the AI810 analog input module or the DI810 digital input module, will affect the total current budget of the power supply unit. Verify that the existing PS800 power supply or its replacement can support the expanded load before proceeding.

Terminal wiring compatibility is another critical checkpoint. The TU846 uses a standard screw-terminal field wiring interface, and technicians migrating from older S100 or Masterpiece 200 systems must confirm that existing cable cross-sections and terminal block pitches are compatible. In many brownfield projects, the field cable harness can be reused directly, significantly reducing downtime during the changeover.

Backplane interface and module addressing must also be verified. The TU846 connects to the S800 I/O station via the ModuleBus interface, and module node addresses must be configured to match the original control program’s I/O mapping. If the replacement is part of a broader migration from a legacy INFI 90 or Advant OCS platform, the control program logic in the AC800M controller — typically managed through Control Builder M — will need to be reviewed to ensure that all I/O channel assignments remain consistent with the new hardware layout.

HMI screen updates are frequently overlooked during retrofit planning. If the plant uses an 800xA Operations workplace or a legacy Conductor NT station, any faceplates or graphic displays referencing the replaced module’s tag names or I/O addresses should be audited and updated before commissioning. Failure to do so can result in alarm suppression or incorrect process value display during the first live run.

Communication link integrity must be maintained throughout the migration. The TU846 operates within an S800 I/O station that communicates with the AC800M controller via the optical ModuleBus or the CI854 PROFIBUS DP communication interface module, depending on the system topology. Confirm that the communication module — whether a CI854A, CI855, or CI856 — is functioning correctly and that the station address has not been inadvertently changed during the hardware swap.

Upgrade Compatibility Table

Retrofit Planning for Existing Automation Systems

A successful retrofit using the TU846 3BSE022460R1 requires a structured approach to hardware selection and sequencing. In a typical S800 I/O station upgrade, the TU846 serves as the physical interface between the field wiring and the I/O module — in this case, commonly paired with modules such as the AO810V2 analog output module or the DO810 digital output module. Before removing the legacy termination unit, document all field terminal assignments using the existing loop drawings or as-built wiring diagrams.

For projects involving communication protocol migration — for example, moving from a proprietary Masterbus 300 network to PROFIBUS DP or FOUNDATION Fieldbus — the TU846 installation must be coordinated with the replacement of the communication interface module. The CI854A PROFIBUS DP interface is the most common choice for AC800M-based systems, and its configuration parameters must be aligned with the new I/O station address scheme before the TU846 is brought online.

I/O expansion projects often accompany termination unit replacements. If the retrofit scope includes adding new measurement points — such as additional temperature inputs via the RTD560 resistance temperature detector module or new discrete outputs via the DO820 digital output module — the rack and power budget must be recalculated. The TB820V2 ModuleBus modem and the TP830 power supply termination unit are frequently involved in these expansion scenarios and should be sourced alongside the TU846 to avoid secondary delays.

Signal isolation requirements should also be assessed during retrofit planning. In environments with high electrical noise or long cable runs, signal isolators or barriers may need to be inserted between the field device and the TU846 terminal block. This is particularly relevant in hazardous area installations where ATEX-rated barriers are mandatory.

Installation space confirmation is a practical but often underestimated step. The TU846 occupies a defined slot width within the S800 I/O station, and the available space in the existing control cabinet must be measured before ordering. In compact cabinets originally designed for older Masterpiece or INFI 90 hardware, physical clearance for the new module and its associated field wiring may require cabinet modifications or the addition of a new marshalling panel.

Downtime Control During System Migration

Minimizing production downtime is the primary operational concern in any retrofit involving the TU846 3BSE022460R1. The recommended approach is to pre-configure and bench-test the replacement hardware — including the TU846, its paired I/O module, and the communication interface — before the scheduled maintenance window. This allows the on-site swap to be completed within a single shift, with the control program already validated offline using Control Builder M simulation tools.

Protecting the original program logic is essential. Before any hardware changes are made, a full backup of the AC800M controller application, including all function block diagrams, sequential function charts, and I/O configuration files, should be archived to a secure location. The backup should be verified by performing a compare operation against the live controller before the retrofit begins.

To maintain field control continuity during the transition, consider using the AC800M’s hot-standby redundancy capability if the system is configured for redundant operation. In non-redundant systems, coordinate with the process team to identify a safe hold state for all affected control loops before initiating the hardware swap. Analog output modules such as the AO810V2 should be set to their last value or a defined safe output before the I/O station is powered down.

After the TU846 is installed and the I/O station is powered up, perform a systematic channel-by-channel verification using the 800xA Asset Optimization or the Control Builder M online diagnostic tools. Confirm that all field signals are reading correctly before releasing the loops back to automatic control. Document the commissioning results and update the as-built drawings to reflect the new hardware configuration.

Retrofit Support FAQ

Q: Is the ABB TU846 3BSE022460R1 a direct drop-in replacement for the original TU846 in my existing S800 I/O station?
A: Yes. The TU846 3BSE022460R1 is the standard part number for the TU846 termination unit and is designed to fit directly into the S800 I/O station without mechanical modification. Field wiring connections and ModuleBus interface are fully compatible with existing S800 configurations.

Q: What pre-shipment testing is performed on the TU846 3BSE022460R1?
A: Each unit undergoes functional verification prior to dispatch, including interface continuity checks and visual inspection for physical integrity. Units are shipped with original or equivalent packaging to prevent transit damage. A 12-month warranty is provided from the date of shipment.

Q: How do I confirm the correct I/O module pairing for the TU846 in my application?
A: The TU846 is designed to work with specific S800 I/O modules. Refer to the ABB S800 I/O hardware documentation or your system’s I/O list to confirm the correct module type. Our technical team can assist with compatibility verification based on your existing hardware configuration and control program I/O mapping.

Q: What is the lead time and stock availability for the TU846 3BSE022460R1?
A: We maintain inventory of the TU846 3BSE022460R1 to support urgent retrofit and breakdown replacement requirements. Standard lead time for in-stock units is 3–7 business days for international shipments. Contact our sales team for current stock status and expedited shipping options.