Description
Key Technical Specifications
| Parameter | Value |
|---|---|
| Manufacturer | ABB |
| Model | TU842 |
| Article Number | 3BSE020850R1 |
| Product Family | S800 I/O |
| Product Type | Module Termination Unit (MTU) |
| I/O Configuration | Redundant |
| Number of Channels | 16 |
| Rated Voltage | 50 V |
| Maximum Current per I/O Channel | 3 A |
| Maximum Process Connection Current | 10 A |
| Mounting | Horizontal DIN rail |
| ModuleBus Connections | 2 |
| I/O Connections | 2 connections per channel |
| Process Power Connections | 4 process-power terminals + 20 process-power 0 V terminals |
| Compatible I/O Modules | AI843, AO845, AO845A, DI840, DI880, DO840, DO880, DP840 |
| Wire Size, Solid | 0.2–4 mm² |
| Wire Size, Stranded | 0.2–2.5 mm² / 24–12 AWG |
| Recommended Terminal Torque | 0.5–0.6 Nm |
| Wire Strip Length | 7 mm |
| Dielectric Test Voltage | 500 VAC |
| Width | 131 mm including connector |
| Depth | 64 mm including terminals |
| Height | 186.5 mm including locking device |
| Weight | Approximately 0.6 kg |
| Operating Temperature | 0 to +55°C |
| Storage Temperature | -40 to +70°C |
| Protection Class | IP20 |
| Hazardous Location | Class I Div. 2, Class I Zone 2, ATEX Zone 2 approvals listed |
| Marine Certifications | ABS, BV, DNV-GL, LR |
ABB’s current hardware selector confirms the 50 V rating, 16 channels, redundant configuration, 3 A maximum per I/O channel, 10 A maximum process connection, and 131 × 64 × 186.5 mm approximate dimensions.
Product Introduction
ABB TU842 3BSE020850R1
The ABB TU842 3BSE020850R1 is a redundant Module Termination Unit for the ABB S800 I/O system. It provides the physical field connections for compatible S800 I/O modules while distributing two ModuleBuses and process power. It supports up to 16 I/O channels and is designed for horizontal DIN-rail mounting.
The important point is that TU842 is not an active I/O module. It is the termination and interface hardware around the I/O module. Its redundant architecture makes it appropriate for S800 installations where I/O availability and dual ModuleBus connectivity are part of the control-system design.
TU842 3BSE020850R1
Application Scenarios & Field Pitfalls
Engineering Pain Point
A failed terminal unit can look like a failed I/O module. This happens often during maintenance because the field signal disappears at the same time the controller reports an I/O problem. With the TU842, engineers need to check the field terminals, ModuleBus connections, mechanical keys, and process-power distribution before condemning the actual S800 I/O electronics.
Typical Applications
- Process Automation — Redundant S800 I/O termination for distributed process signals in chemical and manufacturing plants.
- Power Generation — Redundant digital and analog I/O termination for auxiliary systems, electrical equipment, and process monitoring.
- Oil & Gas — Field termination for critical process signals where redundant I/O architecture is specified.
- Water & Wastewater — Distributed redundant I/O installations for pumps, valves, instrumentation, and process equipment.
Technical Pitfalls to Avoid
- Do not confuse TU842 with an I/O module.
contains the termination and distribution hardware. It does not independently perform analog or digital signal processing. - Verify the I/O module compatibility.
ABB specifically lists AI843, AO845, AO845A, DI840, DI880, DO840, DO880, and DP840 for . Do not assume that every module can be installed on this MTU. - Check the mechanical key positions.
uses mechanical coding to prevent an incorrect I/O module from being inserted. ABB states that four mechanical keys provide 36 possible configurations. The keying is mechanical; it does not alter the electrical function of the I/O module. - Do not ignore ModuleBus wiring.
distributes two ModuleBuses to the I/O module and onward to the next MTU. A poor ModuleBus connection can produce symptoms that resemble an I/O-module failure. - Respect the 50 V rating.
The MTU has a maximum rated voltage of 50 V. Do not use the terminal assembly as though it were a general-purpose high-voltage terminal block. - Observe the 3 A channel limit.
ABB specifies a maximum of 3 A per I/O channel and 10 A for the process connection. These limits matter when process power is distributed through the MTU. - Do not substitute TU843 based only on the same channel count.
TU843 is a related redundant MTU, but it is designed for vertical mounting, whereas is horizontally mounted. Mechanical orientation can be decisive inside a crowded cabinet. - Check terminal torque after maintenance.
ABB specifies 0.5–0.6 Nm recommended torque and a 7 mm stripping length. Loose field terminals can create intermittent process faults that are difficult to reproduce. - Verify redundancy before removing the unit.
is specifically a redundant MTU. Treat both ModuleBus paths and associated redundant I/O architecture as part of the maintenance procedure. - Check the complete assembly, not just the part number.
For replacement work, verify the article number, I/O module type, key positions, terminal arrangement, ModuleBus configuration, and cabinet orientation. A physically similar MTU is not automatically a valid replacement.
Related Products
- ABB TU843 3BSE021443R1 — Redundant I/O MTU with 8-channel configuration and vertical mounting. It is useful where cabinet layout requires vertical installation, but it is not a direct mechanical equivalent of the horizontally mounted .
- ABB TU844 3BSE021445R1 — Redundant 50 V MTU for compatible I/O modules including AI845, AI880, and DP840. It uses horizontal mounting but has a different module-compatibility set from .
- ABB TU845 3BSE021447R1 — Redundant 50 V MTU designed for compatible AI845, AI880A, and DP840 configurations. Its vertical mounting differentiates it from .
- ABB TU839 3BSE046966R1 — 250 V I/O MTU for DI820, DI821, and DI825 applications. This is a significantly different voltage and module-compatibility class; it should not be substituted for without engineering review.
- ABB AI843 — Compatible analog input module listed by ABB for . The supplies the termination and ModuleBus interface; AI843 performs the actual analog input processing.
- ABB AO845 / AO845A — Compatible analog output modules for . These provide analog output functionality while supplies the associated termination and redundant interface.
- ABB DI840 — Compatible redundant digital input module. It uses the termination infrastructure for field connections and ModuleBus communication.
- ABB DI880 — high-density digital input module supported by . It is an active I/O module, unlike the passive/interface role of the MTU.
- ABB DO840 / DO880 — Compatible digital output modules. These provide output functionality through a -based redundant I/O arrangement.
- ABB DP840 — I/O module listed among the -compatible devices. Verify the exact application and redundancy configuration before selecting the MTU/module combination.
