+------------------------------------+ | Custom .NET Client App | | (C# / VB.NET Code) | +---------------------+--------------+ | v +------------------------------------+ | OpcNetApi.dll | <-- Core Abstract API Object Model +---------------------+--------------+ | v +------------------------------------+ | OpcNetApi.Com.dll | <-- Handles NET-to-COM Interop +---------------------+--------------+ | v +------------------------------------+ | COM / DCOM Layer | <-- Windows Operating System +---------------------+--------------+ | v +------------------------------------+ | OPC Classic Server | <-- e.g., Kepware, Matrikon, RSLinx +------------------------------------+
Historically, OPC Classic specifications—such as OPC Data Access (OPC DA), OPC Historical Data Access (OPC HDA), and OPC Alarms & Events (OPC A&E)—were built directly on Microsoft's COM (Component Object Model) and DCOM (Distributed Component Object Model) technologies. Because native COM/DCOM interfaces are written in C++ and can be highly complex to manage in modern managed code environments, the OPC Foundation created .NET wrapper DLLs. opcnetapidll
Because opcnetapidll relies on DCOM, you must grant appropriate permissions: +------------------------------------+ | Custom
Note: The file may be named opcnetapi.dll (without the extra 'd') or opcnetapidll . Some distributions use OpcNetApi.Com.dll . OPC Historical Data Access (OPC HDA)