Product Overview
When designing intrinsic safety (IS) systems for hazardous industrial environments, the ABB TU891 provides a robust and reliable interface between field signals and I/O modules. This MTU (Module Termination Unit) features gray terminals for field signals and process voltage connections, with a maximum rated voltage of 50 V and a maximum rated current of 2 A per channel. These values are primarily constrained by the design of the I/O modules for their certified application. The TU891 distributes the ModuleBus to the I/O module and to the next MTU, and it generates the correct address to the I/O module by shifting the outgoing position signals to the next MTU.
Technical Specifications
- Channels: 8
- Voltage: 24 V
- Maximum current per I/O channel: 2 A
- Dielectric test voltage: 500 V a.c.
- Acceptable wire sizes (Process Connector): Solid 0.2–4 mm²; Stranded 0.2–2.5 mm², 24–12 AWG
- Recommended torque: 0.5–0.6 Nm
- Dimensions: Width 64 mm (1.77 in.) including connector, Depth 58 mm (2.28 in.), Height 194 mm (7.6 in.) including latch
- Weight: 0.17 kg (0.37 lbs)
- Protection class: IP20 according to IEC 60529
- Operating temperature: 0 to +55 °C (+32 to +131 °F); Storage -40 to +70 °C (-40 to +158 °F), RH=5 to 95 % non-condensing
- CE mark: Yes
- Marine certification: ABS, BV, DNV-GL, LR
Industry Applications
The TU891 is designed for use with IS I/O modules such as AI890, AI893, AI895, AO890, AO895, DI890, and DO890. This makes it ideal for applications in oil and gas, chemical processing, and marine environments where intrinsic safety is critical. The compact design and DIN rail mounting allow for space-efficient installations in control cabinets. With single I/O configuration, it suits non-redundant systems where reliability and safety are paramount.
Installation & Setup Guidance
Mount the TU891 horizontally on a DIN rail using the integrated latching device. Use the 27 gray terminals for process connections and ensure proper torque of 0.5–0.6 Nm for both process and power supply connectors. Acceptable wire sizes range from 0.2 to 4 mm² solid or 0.2 to 2.5 mm² stranded (24–12 AWG) for process connectors, and 0.25–2.5 mm² (24–14 AWG) for the power supply connector. The two mechanical keys configure the MTU for different types of I.S. I/O modules—this is purely mechanical and does not affect functionality. The keys on the TU891 are of the opposite gender to those on any other type of MTU and will mate only with IS I/O modules.
Maintenance & Reliability
Regularly inspect the TU891 for signs of corrosion or contamination, as it is rated for pollution degree 2 (IEC 60664-1) and corrosion protection class ISA-S71.04: G3. The operating temperature range of 0 to +55 °C ensures reliable performance in most industrial environments. For vertical mounting, the maximum ambient temperature is 40 °C (104 °F). The IP20 protection class allows for use in clean, dry indoor locations. Periodically verify that all terminal connections remain tight and that the DIN rail latch is secure.
Compatibility & Integration
The TU891 is part of the ABB I/O system and works exclusively with IS I/O modules (AI890, AI893, AI895, AO890, AO895, DI890, DO890). It distributes the ModuleBus to the I/O module and to the next MTU, enabling daisy-chain configurations. The single I/O design supports non-redundant architectures. The MTU complies with EMC standards EN 61000-6-4 and EN 61000-6-2, and electrical safety per IEC 61131-EN 61010-1 and EN 61010-2-201.
Selection Guide & Purchasing Advice
Before ordering the ABB TU891 (article number 3BSC840157R1), verify that your I/O modules are from the compatible IS series (AI890, AI893, AI895, AO890, AO895, DI890, DO890). The TU891 is a compact MTU with 8 channels and 24 V voltage rating. For reliable supply, contact SpareTechPLC to confirm availability and current lifecycle status. Please verify current lifecycle status and availability with SpareTechPLC before ordering.
