Language is the protocol used to express human thoughts among each-other, but it may be like French which is a regional language and can be understood by the people of that region, or it may be like Hindi which is central communication medium that can be interpreted by different regional people over the country. Today we discuss Basics of OPC & OPC UA vs OPC DA

What is OPC?

Thus OPC can be considered as language for the communication between machines in industries, in which one of the latest version of OPC that is OPC UA (Unified Architecture) is a cross-platform protocol for machine to machine communication like English and on the other hand the older version of OPC is OPC DA (Data Access) not compatible with multi-platform.

OPC stands for OLE (object linking and embedding) for process control and it is a client-server based communication.

A Series of standards and specifications are developed for industrial telecommunication, which is commonly known as Open Platform Communications (OPC).

It provides assurance regarding security and reliability while exchanging data in the industrial automation space and even in other industries.

Must Read : Modbus ASCII Vs Modbus RTU Vs Modbus TCP/IP

Must Read : IEC61850 Protocol and Standard

What are OPC UA and OPC DA

The communication between the control devices by a different manufacturer in real time is specified by OPC?

Initially, the requirement to form a common bridge for different window based software application and process hardware gave rise for designing OPC.

The protocols that are included in classical OPC model are DA (Data Access), AE (Alarm and Events), HAD (Historical Data Access), XML DA (XML Data Access), AND DX (Data Exchange), and on the other hand, there is OPC UA (Unified Architecture).

OPC DA (Data Access Protocol) is the most basic protocol of OPC. The representation of the data for DA is as follows: first the Value i.e. the data itself along with Name comes, and to that other information comes along with it such as Timestamp that provides the exact time when the value was read, and at last the information regarding the validity of data which is called Quality comes

For Automation in industries, a protocol called OPC Unified Architecture (OPC UA) is developed by the OPC Foundation that was mainly focused on the communication between machines, i.e. machine to machine communication.

Must Read Our Best Article on OPC :

What is OPC UA Communication
What is OPC UA Protocol
What does OPC UA stand for ? how does opc UA work
What is OPC Protocol ?
What does OPC Stand for ?| OPC Meaning

The features that UA supports are:

  • It is a cross-platform protocol and that’s why it does not depend on any particular operating system or programming language.The architecture of OPC UA is service-oriented
  • And the security provided by OPC UA is robust.

Must Read : What is Profibus ? How Profibus Work ?

Must Read : Modbus TCP/IP


The basic difference between OPC DA vs OPC UA is the version, in which the older version of OPC is DA, where it supports the older version of data modeling which is not as great as the data modeling provided by OPC UA. Also, the transfer of the information that takes place between the server and client in OPC DA is only VQT that stands for Value Quantity and Time.

But on the other hand, OPC UA which is the new version of OPC provides data and information modeling as well as many properties that can be shared between the client and server about a variable.

As OPC DA comes under OPC classic model, it supports DCOM communication for connecting the client and server, where DCOM is dependent on the operating system and supports only Window OS.

And on the other hand, OPC UA do not rely on DCOM communication for connecting client and server, thus it is a platform or OS independent and it supports platform such as Linux (Java), Apple, or Windows.

OPC DA allows to access only the current data and is incapable to generate alarms, historical events whereas OPC UA supports features like historical events, multiple hierarchies and provides methods and programs (that are called commands).

One of the limitations of OPC DA is its inadequate security, as in today’s world security is the major issue because systems are more frequently attacked by some sophisticated viruses and malware and this security issue is solved in a higher version that is OPC UA.

It is an OPC DA specification that defines how real-time data can be exchanged between a data source and a data sink (for example a PLC and an HMI) without either of them having to know each other’s native protocol. It is an OPC UA specification that states how real-time data is communicated between machine to machine for industrial automation.

Must Read : Profibus vs Profinet

Must Read : Protocol Overview

Application of OPC DA

One of the applications of OPC DA is in factory automation for the communication from DCS and PLC to Management Information System.

OPC DA specification resolves the problem of data conformity between different platforms and decreases the costs of software development and maintenance.

Must Read : Devicenet Protocol and Network

Must Read : Communication Overview

Application of OPC UA

As there is a change in the Industrial revolution the requirements of industry increases as per their increase in their needs and to adopt the new changes they choose to adopt the new ways or technologies.

As per the revolution, Industrial 4.0 is the current trend for automation and manufacturing industries. It is nothing but a one step up, focussing in the field of cybersecurity, cloud computing and the industrial internet of things.

This revolution brings a great challenge for the manufacturers which were using OPC DA or older versions in terms of security and slow communication speed with less innovation in their process.

So it has been stated that there is no Industry 4.0 without OPC UA. The main challenge as per Industrial 4.0 and IIOT (Industrial Internet Of Things) is the secure, exchange of data its information between different devices, machines etc. across different industries which may or may not be located at the same place.

As it is recommended by the IEC standard, OPC UA is the best-suited standard for communication in this revolution. It has also been said that OPC UA is not just a protocol, it is a whole IoT into one.

Must Read : Protocol in Computer Network

What does OPC Stand for ?| OPC Meaning

What is OPC Protocol ?

11 thoughts on “OPC-UA vs DA”

  1. Thanks for the information. Can you share more details regarding the connectivity of different SCADA systems to a single platform through OPC UA, what are all the system requirements to connect b/w two systems or SCADA to PLC.

    • It’s Depend On which make scada you have used.If You Use Citect Scada then OPC UA driver is by default come.You only Select that driver whenever you create tag.if you use Rockwell Factory Talk View than you need to buy license of third party OPC provider.

  2. very useful article, I have a question.
    Does OPC UA solve the problem of communicating with for example with all type of PLCs ?
    The problem is for us , PLCs are different, and we want to grab data from all !
    Can OPC UA do anything in here to simplify the process ?

    • This article refers to the communication standard, DA vs UA. What you are asking about is more related to driver issues. Kepware Server EX with Manufacturing Suite will allow you to communicate with most PLC flavors found in the wild, as it includes the drivers for them. KepServerEX allows both DA and UA.

  3. Thanks for your feedback
    It depends upon PLC Features. It depends on does PLC Supported OPC UA and OPC DA based on that you are able to communicate third party any device. I hope you understand. Let me know your comments if you have any douts

  4. Thanks for your feedback
    It depends upon PLC Features. It depends on does PLC Supported OPC UA and OPC DA based on that you are able to communicate third party any device. I hope you understand. Let me know your comments if you have any doubts

  5. Thank you and good insight of knowledge in OPC ( UA and DA ) data access, as be mentioned that the UA more better compared than DA as older system. May I have question relating security in case the OPC -UA be used for on-premises compared with cloud system, which one more secure? and also which one more reliable.Thank

  6. If cyber security is not built into individual industrial application protocols. Is it still possible to manage cyber security if FF-HSE, PROFINET-IO, EtherNet / IP, HART-IP. and Modbus / TCP each do a different cybersecurity.
    Or is it done in the opposite way, cybersecurity is done at a lower level using Transport Layer Security (TLS) / Secure Socket Layer (SSL) encryption and IEEE 802.1x authentication in such a way that cybersecurity mechanisms will become common to all devices regardless of the application protocol where they are use for data transfer.
    And whether this will also avoid duplication of effort and also provide authentication, autorizaiton, integrity and confidentiality, etc. Please give enlightenment

  7. Hi, great article.
    Could you give me some more information about that part?
    “One of the limitations of OPC DA is its inadequate security”


Leave a Comment