TU844 ABB 800xA System Processor Termination Unit

Product Overview

The ABB TU844 (Part Number: 3BSE021445R1) functions as a robust Module Termination Unit (MTU) specifically engineered for the AC 800M controller family. This brand-new, original module base provides the mechanical and electrical foundation for mounting processor units and CEX-bus communication expansion modules. By centralizing field wiring and backplane power distribution, the TU844 ensures seamless connectivity between the main CPU (such as PM861 or PM866) and external network interfaces. It serves as a critical infrastructure component for the 800xA DCS platform, maintaining high-speed data integrity across the controller backplane.

Technical Specifications

The TU844 utilizes a high-density terminal layout and standardized mounting for industrial control cabinets:

Engineering Advantages

The ABB TU844 eliminates the complexity of multi-module wiring in high-density automation racks. Traditional termination methods often require extensive point-to-point jumpers; however, the TU844 incorporates an integrated CEX-bus backplane. This design allows you to snap communication modules directly onto the base, establishing instant data and power links without external cabling. This "plug-and-play" architecture drastically reduces the footprint required for network expansions like Profibus DP or Modbus.

To address the challenge of vibration and mechanical stress, the TU844 features a reinforced DIN-rail locking mechanism. This ensures that the heavy processor modules remain securely seated even in environments with constant machinery oscillation. The module base also provides dedicated grounding points and isolated screw terminals, which effectively shield the controller’s sensitive logic from field-side electromagnetic interference (EMI). Furthermore, the wide –25°C to +70°C operating range permits installation in non-climate-controlled remote instrument enclosures, making it a versatile choice for oil & gas wellheads and outdoor power distribution substations.

FAQs

Which specific AC 800M CPUs can I mount on the TU844?

The TU844 supports the entire high-performance range of the AC 800M series, including the PM861, PM864, PM865, and PM866. It also accepts various CEX-bus communication modules (such as CI853 or CI854) for expanded connectivity.

Does the TU844 require manual configuration for the CEX-bus?

No. The TU844 provides the physical path for the CEX-bus signals. The AC 800M processor automatically identifies and addresses the modules plugged into the base during the system boot sequence, simplifying the hardware setup.

Can I replace a damaged base without re-wiring the entire system?

While the field wiring connects to the terminals on the TU844, the modular design allows you to remove the CPU and communication modules first. Since the wiring terminates directly into the base, ensure all power is disconnected before migrating field cables to a brand-new TU844 replacement unit.

How does the TU844 manage internal power distribution?

The unit accepts a 24 VDC redundant feed and distributes it via the internal backplane to the processor and all attached communication modules. This centralized power management prevents individual module power failures from affecting the entire controller stack.