ABB TU890 3BSC690075R1 | S800 I/O Compact MTU for Intrinsic Safety

Description

Key Technical Specifications

ABB’s current hardware documentation identifies TU890 / 3BSC690075R1 as a compact MTU for S800 I/O, specifically intended for intrinsic-safety applications. The MTU is passive and provides the physical field-wiring and process-power interface while also carrying part of the ModuleBus.

The 50 V rating and 2 A/channel figure are maximum ratings of the MTU; the actual permitted values remain constrained by the connected I/O module and its certified application.

Product Introduction

ABB TU890 3BSC690075R1

The ABB TU890 3BSC690075R1 is a compact Module Termination Unit (MTU) for the ABB S800 I/O platform. It provides field termination, process-power connections, and ModuleBus distribution for compatible 8-channel I/O modules. ABB specifically lists it for intrinsic-safety applications.

The important distinction is that TU890 is passive termination hardware, not an I/O processor. It works with compatible S800 I/O modules such as AI890, AI893, AI895, AO890, AO895, DI890, and DO890. Its mechanical keying also helps prevent installation of an incompatible module.

TU890 3BSC690075R1

Application Scenarios & Field Pitfalls

Engineering Pain Point

In an Ex-area installation, the terminal unit is often treated as nothing more than a convenient wiring block. That is a mistake. The TU890 is part of the certified S800 I/O interface arrangement. Changing it to a visually similar MTU can change the electrical and hazardous-area characteristics of the installation.

Typical Applications

• Oil & Gas — Intrinsically safe transmitter and sensor connections for pressure, flow, level, and temperature measurement.
• Petrochemical Plants — Ex-area analog and discrete instrumentation connected to S800 I/O.
• Chemical Processing — Intrinsic-safety field interfaces for process transmitters and discrete instruments.
• Power Generation — Hazardous-area instrumentation where I/O is used for process monitoring and control.

Technical Pitfalls to Avoid

1. Do not confuse with the I/O module.
   is the MTU. It provides termination and ModuleBus functions; the actual signal processing is performed by the compatible I/O module.
2. Do not substitute TU891 casually.
   ABB specifies for intrinsic-safety applications and TU891 for non-intrinsic-safety applications. TU891 uses the same general compact architecture but has a different application designation.
3. Check the I/O module before ordering the MTU.
   is compatible with specific modules, including AI890, AI893, AI895, AO890, AO895, DI890, and DO890.
4. Do not interpret 50 V as the permitted field-signal voltage for every application.
   ABB states that the 50 V maximum rating is constrained by the connected I/O module and its certified application.
5. Respect the blue terminal identification.
   uses 27 blue process terminals, distinguishing it from TU891, which uses gray terminals. This matters during field replacement.
6. Check the mounting orientation.
   ABB specifies a maximum ambient temperature of 55 °C for horizontal mounting and 40 °C for vertical mounting. Cabinet orientation can therefore affect the allowable operating temperature.
7. Do not remove the mechanical keying without a documented reason.
   The keyed arrangement is there to prevent an incorrect I/O module from being inserted into the termination unit.
8. Check field wiring torque.
   ABB specifies 0.5–0.6 Nm for the process and power connectors. Loose termination is an easy source of intermittent instrumentation faults.
9. Remember that is not redundant hardware.
   ABB classifies this MTU as single I/O, so a redundant architecture requires the appropriate redundant hardware rather than simply installing two units.
10. Treat Ex-area replacement as a certification issue, not just a wiring issue.
    If the is part of an intrinsic-safety installation, verify that the replacement hardware and associated I/O module remain within the approved hazardous-area configuration.

Related Products

• ABB AI890 3BSC690071R1 — 8-channel intrinsic-safety analog input module for 0–20 mA / 4–20 mA signals. ABB specifically lists and TU891 as compatible MTUs.
• ABB AI893 — Intrinsic-safety analog input module in the family. It can be installed with where the certified application requires this MTU arrangement.
• ABB AI895 — Another intrinsic-safety analog-input module compatible with . The I/O function differs from AI890, so the application configuration must be checked before substitution.
• ABB AO890 — Intrinsic-safety analog output module supported by . It provides an output function rather than the analog-input function of AI890.
• ABB AO895 — intrinsic-safety analog output module compatible with . It should be selected according to the required output application and certification.
• ABB DI890 3BSC690073R1 — 8-channel intrinsic-safety digital input module supporting NAMUR/proximity and voltage-free contact applications. ABB explicitly lists /TU891 as compatible MTUs.
• ABB DO890 3BSC690074R1 — Intrinsic-safety digital output module with four channels, including solenoid-driver functionality. It uses / as its compatible MTUs.
• ABB 3BSC840157R1 — Compact MTU for non-intrinsic-safety applications. It has the same general compact form factor but is not simply the non-Ex version to substitute without checking the application certification.
• ABB TU850 3BSE050930R1 — Extended Module Termination Unit for 50 V applications. It has a different terminal arrangement and is intended for a different class of I/O installation.
• ABB TU852 3BSE069964R1 — Redundant MTU for 50 V applications. It is relevant when the architecture requires redundant I/O rather than the single-I/O arrangement.