OPC (OLE for Process Control) is a standard designed for real-time data exchange between a software application and process control devices (e.g., PLCs). OPC defines an interface independent of the device type. As a result, the end user is almost not limited in the choice of hardware and software for their application. The only requirement is OPC compatibility.
There are two kinds of OPC components: OPC client and OPC server.
An OPC client is a program that gets (reads) data from an OPC server for further processing. Typical examples are MMI and SCADA/HMI systems.
An OPC server is a program that provides data to OPC clients. It is usually designed to read the data from a specific hardware device.
An OPC client communicates with an OPC server through a strictly defined interface. As a result, any OPC client can communicate to any OPC server regardless of the type of device for which the server has been created.
The OPC standard is developed by the OPC Foundation, which consists of hundreds of software companies and hardware manufacturers (OPC Foundation members) worldwide. New features are continuously added to keep the standard up to date.
A tutorial demonstrating the basic aspects of the OPC standard is available on the website of Matrikon, a renowned OPC product developer company.
Reliance OPC Server is a Reliance module allowing access to a visualization project's tags via the standard OPC interface.
Reliance OPC UA Server is a Reliance module allowing access to a visualization project's tags via the OPC UA interface.