What is OPC UA?

Definition

What is OPC UA?

OPC UA stands for OPC Unified Architecture and is an open communication standard for industrial data exchange.

With the help of OPC UA, complex data from industrial controllers and other sources can be provided in a standardized format and retrieved and processed by a wide variety of applications. OPC UA also provides an interface for managing and automating processes.

OPC UA is based on a client-server model:

• An OPC UA server provides data from one or more sources (e.g. industrial controllers).
• IT applications such as MES (Manufacturing Execution System), ERP systems (Enterprise Resource Planning) or cloud platforms use OPC UA client software to retrieve the required data from the OPC UA server, transmit data themselves or interact with the source in other ways.

Many modern industrial devices and machines implement their own OPC UA servers and therefore offer native support for OPC UA. However, data from older systems can also be provided and processed in OPC UA format using an external OPC UA server.

OPC UA was published in 2008 and is a successor to the classic OPC standard. You can find out more about the significance of OPC and OPC UA in the last section of this article.

Characteristics

Characteristics of OPC UA

OPC UA was developed by the OPC Foundation to meet industry-specific requirements for data exchange between a wide variety of systems. As a result, the OPC UA communication standard is characterized by some core characteristics:

Platform independence:
In contrast to the classic OPC standard, OPC UA is no longer dependent on the Windows operating system. Previously, OPC servers and OPC clients had to be installed on Windows computers and communication between server and client was only possible via Microsoft’s COM/DCOM model. With OPC UA, data exchange takes place via the common Internet protocols TCP and HTTPS. This means that OPC UA software can be installed on any system that supports Internet communication.

Flexibility and scalability:
OPC UA enables standardized communication with a wide range of industrial systems – from the smallest devices to large distributed systems. New systems can therefore be integrated into an OPC UA-based infrastructure quickly and with comparatively few adjustments. This not only reduces the IT effort for individual solutions, but also offers greater scope for innovation by eliminating compatibility problems.

Complex information modeling:
In contrast to the classic OPC standard, where individual variables are provided as tags, OPC UA supports comprehensive information modeling. This is based on so-called “nodes” and relies on concepts from object-oriented programming. Real objects and their status can be represented digitally. Methods can also be defined that can be called up by OPC UA clients in order to interact with devices and machines in a targeted manner.

Future-proofing:
The OPC UA standard is being continuously developed by the OPC Foundation in order to meet the changing requirements of industry. An important requirement here is compatibility with current and future technologies in order to ensure that investments in industrial automation technologies are future-proof. Many definitions in areas such as data modeling and data transport have therefore been deliberately kept abstract to enable seamless integration of new technologies and innovations.

Security:
The OPC UA standard defines various mechanisms to ensure security in industrial data exchange. In addition to HTTPS encryption during data transport and user authentication, OPC UA supports the exchange of certificates between OPC UA clients and OPC UA servers.

Information Model & Specifications

Information model and specifications

OPC UA enables a wide variety of components, devices and applications to communicate with each other, overcoming the boundaries of the classic automation pyramid. This requires consistent structuring of information, i.e. data must be represented in a sensor in the same way as in a software system for data visualization.

In the following sections, we explain how OPC UA servers enable targeted data access to or control of industrial devices by OPC UA client applications.

OPC UA information model

In contrast to the classic OPC standard, OPC UA features a complex, node-based information model. Due to this, OPC UA is able to describe real objects digitally and provide units, hierarchies, relationships and configuration parameters in addition to values.

Real objects are represented as “nodes” in the OPC UA information model. These are assigned to specific types and have properties that can be read, e.g. the temperature measurement of a sensor.

References are used to display relationships to other nodes. Based on object-oriented programming, methods can be defined to interact with a node (reading and writing data points, operating systems, etc.).

Definitions of object types (and the associated attributes and methods) are summarized under a “domain”. The OPC UA basic information model of the OPC Foundation can be extended by other organizations by providing their own type definitions under a new domain. In this way, extended information models can be created for specific device types (e.g. pumps, scanners, etc.) or industries, which are always based on the basic model. OPC UA servers can optionally implement these information models.

OPC UA clients navigate domains and the associated address spaces in order to interact with specific nodes and retrieve the desired information.

The OPC UA standard is based on a service-oriented architecture: An OPC UA server implements information models and provides services (methods) that can be used by an OPC UA client.

OPC UA specifications

OPC UA is made up of various specifications. These define the functions and services that an OPC UA server implements and/or provides for OPC UA clients.

An OPC UA server does not have to implement all specifications.

The most important OPC UA specifications include the following:

Data Access: Enables an OPC UA client to locate nodes and read and write data.

Historical Access: Enables the retrieval or updating of historical data stored in an OPC server. Time periods can be specified or various statistical parameters applied.

Alarms & Conditions: Enables the receiving and processing of alarm messages and event logs by OPC UA clients.

PubSub: Describes the implementation of a publish-subscribe model in OPC UA communication. Here, the communication participants are divided into publishers and subscribers, which do not communicate directly with each other but publish (publishers) or retrieve (subscribers) information from a central broker.

Industrial Use

Significance of OPC UA for the industry

Open Platform Communications (OPC) (also known as “OPC Classic”), the predecessor of OPC UA, made a significant contribution to the industry when it was introduced in 1996: OPC made it possible to access data from machines by different manufacturers and make it usable for various applications. This offered possibilities for data visualization and process control that were previously only possible with a great deal of effort or a commitment to a single provider.

OPC UA still follows this basic idea. The UA specification solves the existing problems with the classic OPC standard and extends it with numerous functions and features that make OPC UA an essential part of industrial IoT communication.

Thanks to its interoperability, flexibility and scalability, the OPC UA standard is widely used in virtually all industrial sectors. Manufacturers of modern industrial devices are implementing their own OPC UA servers to facilitate integration into existing infrastructures. And many IT software providers are also integrating OPC UA client functionality into their applications.

OPC UA in industrial production

OPC UA is particularly important in manufacturing: Modern production environments contain a wide variety of sensors, devices and machines that can be used as potential data sources for manufacturing execution systems (MES), enterprise resource planning (ERP), predictive maintenance solutions, cloud platforms and many more.

The use of OPC UA standardizes the communication between all these components and thus represents an important step on the way to the intelligent factory (“smart factory”).

manubes, our innovative cloud platform for industrial production management, also relies on the OPC UA standard to communicate with a wide range of industrial systems. Support for OPC UA and other industry standards such as MQTT and REST ensures that production data can be seamlessly collected and transferred to the manubes cloud environment. There, the manubes design tools provide extensive options for structuring, automating and interactively visualizing your production.