ABB TU841 3BSE020848R1 S800 I/O Termination Unit for Non-Redundant I/O

Product Overview

When configuring ABB S800 I/O systems for non-redundant I/O with redundant optical ModuleBus modems, the TU841 provides a cost-effective termination solution. This module termination unit (MTU) connects two TB840/TB840A modems to a single electrical ModuleBus, eliminating the need for redundant I/O modules while maintaining communication path redundancy. The passive design reduces power consumption and component costs, making it ideal for applications where I/O redundancy is not required but communication reliability is critical.

Technical Specifications Breakdown

Power and Current Distribution

The TU841 operates on a 24 V DC supply (19.2 – 30 V) with a maximum ModuleBus current distribution of 5 V at 1.5 A and 24 V at 1.5 A. This dual-voltage capability supports both logic and field-side power needs without separate supplies, reducing wiring and installation costs. The power dissipation of only 2.0 W minimizes heat generation, allowing higher density cabinet layouts and lower cooling expenses.

Mechanical Keying and Addressing

Four mechanical keys, each with six positions, provide 36 different configurations to prevent insertion of wrong module types. This keying system eliminates costly miswiring errors and reduces commissioning time. A rotary switch sets the cluster address from 1 to 7, enabling up to seven TU841 units on a single ModuleBus without address conflicts.

Environmental and Safety Certifications

With an operating temperature range of 0 to +55 °C (approvals issued for +5 to +55 °C) and storage from -40 to +70 °C, the TU841 suits demanding industrial environments. CE marking, electrical safety per EN 61010-1 and UL 61010-1, and hazardous location certifications (cULus Class 1 Zone 2, ATEX Zone 2) ensure compliance for global installations, avoiding costly rework or non-compliance penalties.

Industry Applications

Process Control with Communication Redundancy

In chemical or oil and gas facilities, the TU841 connects redundant TB840/TB840A modems to non-redundant I/O, ensuring continuous data flow even if one modem fails. This approach saves the cost of redundant I/O modules while maintaining critical communication paths, reducing total system expense by up to 30% compared to fully redundant I/O configurations.

Discrete Manufacturing with High Availability

For automotive or packaging lines, the TU841 supports single I/O with redundant ModuleBus modems, allowing fast replacement of failed modems without affecting production. The mechanical keying prevents incorrect module insertion during maintenance, reducing downtime and repair costs.

Installation and Setup Guidance

Mount the TU841 on a DIN rail using the integrated latching device for secure locking and grounding. Acceptable wire sizes range from 0.2 to 2.5 mm² (solid or stranded, 24-12 AWG) with a recommended torque of 0.5 Nm. The unit can be mounted vertically or horizontally; for vertical mounting, the maximum ambient temperature is 40 °C (104 °F) instead of 55 °C. Set the cluster address via the rotary switch before connecting the ModuleBus cable. Insert the TB840/TB840A modems into the designated positions, ensuring the mechanical keys align correctly. No software configuration is required for the passive MTU.

Maintenance and Reliability

The passive design of the TU841 contains no active components, resulting in high reliability and minimal maintenance. The IP20 ingress protection (per IEC 60529) requires installation in a clean, dry cabinet. Periodic inspection of connections and mechanical key integrity is recommended. The 0.45 kg (0.99 lbs) weight and compact dimensions (124 x 186 x 47 mm) simplify handling and reduce storage costs. Operating within the 5 to 95% non-condensing humidity range ensures long-term stability without corrosion-related failures.

Compatibility and Integration

The TU841 is designed for the ABB S800 I/O system and works exclusively with TB840 or TB840A optical ModuleBus modems. It supports a single electrical ModuleBus connection and is intended for non-redundant I/O configurations. The unit is not hot-swappable, so system power must be cycled when replacing modules. For redundant I/O applications, use the TU840 termination unit instead. Always verify compatibility with your existing S800 I/O modules and controller before ordering.

Selection Guide and Purchasing Advice

Before purchasing the ABB TU841, confirm that your application requires non-redundant I/O with redundant ModuleBus modems. Verify the cluster address range (1-7) meets your system layout. Ensure the power supply provides 24 V DC within the 19.2 – 30 V range and can deliver at least 1.5 A at both 5 V and 24 V on the ModuleBus. BluePLC Industrial offers the TU841 with full traceability and fast shipping. Contact our team to confirm lifecycle status and availability before placing your order.