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Today in this article we are going to see What is OPC and OPC UA? OPC technologies were created to allow information to be easily and securely exchanged between diverse platforms from multiple vendors and to allow seamless integration of those platforms without costly, time-consuming software development.

Table of Contents

What is OPC?

As per defined by Wikipedia,

OPC stands for Online Platform Communications, is a series of standards and specifications for industrial telecommunication.

In 1996, the Industrial Automation task force developed the original standard under the name of OLE for Process Control(Object Linking and Embedded for Process Control).

OPC is used to communicate real-time plant data between control devices from different manufacturers. OPC is a software interface that provides a bridge between windows based application and control process hardware devices.

What is OPC and How OPC works?

OPC is a client-server based communication. OPC client is a software program that is installed on a computer in which SCADA is installed or which is directly connected with the process hardware like HMI. OPC clients use the OPC server to collect data from the process control hardware devices.

OPC Protocols

There are different OPC classical protocols based on the information user wants to collect like,

OPC DA(OPC Data Access)
OPC AE(OPC Alarms & Events)
OPC HAD(OPC Historical Data Access)
OPC XML DA(OPC XML Data Access)
OPC DX(OPC Data exchange)

OPC Data Access (OPC DA)

OPC DA is the most basic protocol in OPC. This gets data outs from the control system into another system. The data contains information about Value, Name, Timestamp, and Quality.

Value and Name is basic information. The timestamp is a time on which value was read and Quality gives the user a basic understanding of the data is valid or not.

OPC Alarms & Events (OPC AE)

OPC AE is the protocol different from the OPC DA protocol. With this protocol, the client gets all the events that come in.

The client doesn’t get any tag name and therefore it doesn’t get any current value. Just only a timestamp where the event comes in. After the event goes there is no data on the server in this protocol.

OPC Historical Data Access (OPC HDA)

OPC HDA allows the client to access historical data stored in the SCADA. This protocol supports long records of data sets.

This protocol is not so popular nowadays after the introduction of OPC UA(OPC Unified Architecture).

OPC Unified Architecture (OPC UA)

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OPC Unified Architecture (OPC UA) is a vendor-independent communication protocol for industrial automation applications.

OPC UA is platform-independent and features a built-in mechanism. It is flexible and completely independent, So it is regarded as an ideal communication protocol for the implementation of industry 4.0.

Image Credit ni.com

OPC UA is the successor of previous OPC standards generally known as an OPC Classic. OPC Classic has a disadvantage of that it is based on the Microsoft technologies COM and DCOM and therefore it is limited to Microsoft Windows operating systems and networks.

The standard OPC UA consists of individual specifications. OPC servers and clients do not have to support all the specifications. It is important to consider the particular specifications while implementing the OPC server.

OPC UA consists of these specifications ⇒