The typical Modbus 'hub and spoke' architecture has a central master PLC periodically polling N RTU/TCP slaves and aggregating the data, which it then forwards to the BMS over a different protocol (BACnet, OPC UA, MQTT), enabling scaling without loading the BMS directly.
True
The spokes are the N Modbus slaves (meters, drives, instruments), the hub is the PLC or smart gateway that polls and aggregates, and the backend is the BMS or SCADA reached through a 'modern' protocol such as BACnet or OPC UA. The advantages are decoupling (the BMS is never directly exposed to Modbus), performance (local polling is much faster than reaching slaves across the Internet), security (the hub can act as a firewall and sanitisation point) and scalability (adding slaves is transparent on the BMS side).
Treat the Modbus hub as a single point of failure: redundancy at the hub buys you more reliability than redundancy at any individual slave.
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