What is OPC?
OPC is a set of specifications that define the communication between client and server applications. It enables the exchange of data from a wide variety of devices (such as PLCs and RTUs) from different vendors to a wide variety of software applications that consume that data. The specifications are written in such a way that allows true interoperability between the OPC software applications from different vendors.
OPC-DA stands for OPC Data Access. OPC-DA is the most common and widely-used protocol in the Industrial Automation field. It was the original specification developed in the 1990’s and still is still in use in many manufacturing plant floors, oil and gas fields, and utilities plants today.
OPC-DA clients use a ProgID (Program Identifier) to specify the OPC Server they want to talk to, and then ask the server for a specific tag (piece of data from the field device). They can either do a one-shot read, or ask the server to send it updates any time the data changes in the field device. With the OPC Data Client, reading a tag is as easy as a few lines of code:
OPC-DA Clients can also send values back to a field device by writing to it: