What it is
The ABB 3BDZ000398R1 is an RLM01 PROFIBUS Redundancy Link Module that sits on a Profibus-DP segment as a single-channel redundancy device, joining two physical Profibus lines into a fault-tolerant logical network for the controller downstream. It belongs to the ABB PLC Expansion Modules family and lives on the fieldbus side of the controller — not on the I/O backplane — so its job is topology, not point I/O.
Where this class of part sits in the panel
PLC expansion modules in the Profibus-DP class are deployed where the line cannot tolerate a single-cable fault — process cells with redundant fieldbus, vessel automation where the bridge is a safety-relevant signal path, and packaging lines where a Profibus break means a starvated line. Because the RLM01 sits between two physical DP segments rather than on the I/O backplane, it does not consume a standard PLC slot; it is mounted as a standalone Profibus device and addressed as a DP slave on the redundancy side of the topology.
Sourcing posture
Lead time on a typical order runs in the 1 to 10 working day window, which is the planning anchor a maintenance buyer uses to decide whether to hold one in the cabinet against a Profibus redundancy fault rather than wait it out.