What is OPC Protocol ?

The transition from a manpower-based production to an automated, more controlled production has increased production speed and quality in the industry. With the development of devices used in the developing industry, data exchange from systems has become complicated.

In the communication between automation systems, there is a communication problem due to the large variety of devices, therefore a separate driver is required for each device, however, a new software is required for each renewed version of these devices.

Some companies that came together to solve these problems, which complicated the system and lost time when there were any problems or when a new solution was needed, developed the OPC (linking and correlating objects in process control) standard.

OPC is a communication standard known as the OLE / COM (object Linking & Embedding / component object model) standard, based on Microsoft’s object-oriented technology aimed at integration between different applications, to make the connection between different units in automation systems fast and reliable.

A device or protocol driver is required to enable communication in each application. This situation complicates the communication network as seen in the figure below.

 OPC Communication Network

In the world of automation, which consists of different brands and products, programs should be prepared in compliance with certain brands, or driver interfaces should be prepared specifically for other brands.

For example, in order for a program tasked to report data to read data from different hardware, driver interfaces need to be created, which is a reason for time and resource loss.

When using the OPC interface, which is a single interface that makes the complex structure on the side a simpler structure, a standardized, well-known path will be followed.

OPC Standard & Protocol

OPC is not a protocol, but OPC features are a standardized approach based on data connectivity.

These features are supported by the OPC Association. With the OPC Association establishing this new standard, OPC, a communication standard that can be supported with a single interface without having to know the internal structure of closed communication systems in the monopoly of all hardware and software manufacturers and companies producing industrial control devices, has found widespread use.

It is an intermediate layer between the OPC data source (PLC / DCS) and data storage (HMI) units, and allows data exchange between both units without knowledge of each other’s internal structures. However, the dependency on drivers manufactured by different manufacturers for a hardware has now disappeared.

OPC Standard and Protocol

Role of OPC Server & OPC Client

With the spread of OPC, the OPC connector has become available in almost every modern device.

Leaving all these drivers aside, there is only one product that will need to be updated for their new version, which is an OPC compatible agent software. On the other hand, by solving the closed communication structure, time and resources are allocated for a single interface development / update without wasting time.

Since a single standard is used, the solution of the problems encountered becomes simpler. Another benefit that OPC comes to mind is the limitations in the selection of industrial devices and therefore the costs are eliminated since there is no need for the driver.

OPC Server and Client

For example, in a system using firm A devices, in order to use firm B devices, there should be a software that will allow communication between the EU, while OPC is used, if both devices are OPC compatible, no additional software /costs will be required.

So users will be free to choose the best devices and apps. Also, theoretically, an OPC compatible application can communicate with as many OPC compatible devices as needed.

It can be concluded that these features will be sufficient to comprehend the many benefits of OPC.

The most common communication topics in automation are real time data, historical data and alarm & event data.

Taking into account these issues in communication, the needs and demands of the industry world, OPC Association has developed standards for other communication sources. Some of the OPC standards used are shown in the table below

OPC Standard Function
OPC Data Access Real-time data reading and writing
OPC Alarm & Events Viewing the events defined in the system
OPC Historical Data Access Reading historical data
OPC Security For connection security at interfaces
OPC Data Exchange Direct connection between OPC servers
OPC Unified Architecture The new standard that brings together all OPC standards and uses Web services

When examining the standards of OPC, OPC server / client terms should also be emphasized.

OPC server (server); is a software application designed to work with one or more OPC features.

OPC servers can be thought of as interpreters connecting the OPC environment with the devices’ local communication protocols or interfaces.

The task of the OPC server is to receive or send information to the device according to the commands of the OPC client.

If it is an OPC client; are software used by an application to communicate with any compatible OPC server.

OPC clients can be considered as a data-sink, as they carry out the initiation and control of communication with OPC servers. The OPC client sends communication requests to the OPC server.

OPC Communication

When data is returned from the OPC server, the OPC client converts this data to the local format in the application to be used; Thus, correct operation of the application is checked and ensured.

OPC servers can provide communication from one OPC client to another, and if we consider this in reverse, OPC clients can communicate with more than one OPC server at the same time.

OPC-Protocol-Communication

The purpose of the initial creation of OPC was to read data from automation devices such as PLC / DCS. However, OPC interface is also available in software to be found in other data communications today.

The number of software with OPC interface is increasing day by day. Although knowing the internal structure of the OPC is not a requirement to use it, it is useful to be superficially familiar with its main concepts.

OPC’s practicality in data connectivity approach has made it a popular communication standard worldwide.

OPC is used at all company levels and in all industrial environments. From the widespread use of OPC, it can be concluded that; OPC will be a frequently mentioned standard in the field of communication.

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