ABB TU891 S800 I/O Module Termination Unit

ABB TU891 Module Termination Unit

Configured for field signal termination and ModuleBus distribution within ABB System 800xA S800 I/O architectures, the ABB TU891 (TU891 Module Termination Unit) provides direct physical execution of I/O addressing and process voltage routing.

Hardware Specifications

Backplane Bus and I/O Density Scaling

The TU891 acts as the mechanical foundation for S800 I/O modules, regulating backplane bus communication velocity by facilitating the daisy-chaining of the ModuleBus to adjacent termination units. It implements automated I/O density scaling through integrated position-based address generation, which allows the system to identify module slot locations via signal shifting. The unit maintains deterministic network operation by ensuring consistent electrical contact points across the bus interface. Firmware flash compatibility and system module recognition are managed through the mechanical keying profiles, which ensure that only authorized module types can be seated in designated safety-rated or standard I/O slots.

Frequently Asked Questions (FAQ)

Q: Does the TU891 support live insertion/removal (hot-swap) of the attached S800 I/O module?

A: Yes. The TU891 design allows for the hot-swapping of I/O modules without removing field wiring, provided the specific I/O module and controller firmware support hot-swap operations.

Q: How is the physical address of the I/O module determined when using the TU891?

A: The TU891 handles address generation through a physical shifting of the outgoing position signals. Each MTU in the bus chain increments the address signal for the subsequent module, allowing the central processor to map each channel accurately.

Field Installation Guidelines

1. Mounting: Secure the TU891 to a grounded, corrosion-resistant DIN-rail. Ensure the rail is sufficiently rigid to support the cumulative weight of the MTU and the attached I/O module during operation.
2. Grounding: Verify that the rail mounting point provides a low-impedance path to the cabinet protective earth (PE) busbar to ensure proper electromagnetic shielding of the ModuleBus signals.
3. Wiring: Use ferrules for all field signal terminations to ensure high-contact pressure. Strictly separate field power conductors from low-voltage signaling lines to prevent inductive noise coupling.
4. Keying: Check the mechanical keying pins before seating the I/O module. If the keying profile does not match the module, do not attempt to force the insertion, as this indicates a mismatch between the intended safety zone (IS vs. non-IS) and the module type.