OPC (Classic and OPC UA)
Definition
OPC is a family of interoperability standards for industrial data exchange. OPC Classic (DA/HDA/AE) relies on Windows COM/DCOM, while OPC UA is a platform-agnostic, secure, model-driven architecture with built-in transport, security, and information modeling.
Examples
- A legacy HMI uses OPC DA over DCOM to read/write real-time tags from a PLC gateway on the same OT subnet.
- A historian queries OPC HDA for minute averages and alarms from a DCS server archived in the control center.
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OPC solves the vendor-to-vendor integration problem. OPC Classic brought a common interface for real-time, historical, and alarm/event data but depends on Windows COM/DCOM and LAN trust. OPC UA re-architects the stack: it is cross-platform, secure by design, and adds an expressible information model so systems exchange structured meaning (not just raw points). In modern plants, Classic persists for legacy connectivity, while UA is the strategic path forward.
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