OPC UA stands for OPC Unified Architecture. It is an extensible and platform-independent standard for the secure exchange of information in industrial systems. OPC UA came to light in 2008 from the Open Platform Communications (OPC) foundation, which regulates and maintains the interoperability standard, protocols and specifications for data communication, mainly in industrial automation operations.
OPC UA is supported on Windows, macOS, Android, and Linux. It can also be used in embedded systems and bare-metal servers, which do not use an operating system. OPC UA works on PCs, cloud infrastructures, PLCs, microcontrollers, and cyber-physical systems (CPS).
The goal of OPC UA is to increase intercompatibility between physical equipment and automation and business planning software, providing a framework for industrial companies to converge different technologies.
The differences between OPC UA and OPC
It is worth starting by noting that OPC, the predecessor of OPC UA, is based on Microsoft technologies, while OPC UA is platform independent.
OPC does not integrate security for access control, authentication and encryption, while OPC UA enables encryption of data at its source, making secure transfers possible, without the need for firewalls at the heart of the system. This means that security is provided from the start of the data transfer, rather than only confirmed when it reaches the network firewall. OPC UA implements cross-platform public key infrastructure (PKI)-based security using industry standard x.509 digital certificates.
Unlike OPC UA, OPC does not support information system modeling, allowing manufacturers to define custom data models that meet the requirements of their industry.
In OPC UA, the OPC specifications provide functional modules that can be meaningfully queried. These specifications are: OPC DA (Data Access), OPC AE (Alarms and Events), OPC Security, OPC Batch, OPC Command, OPC XML, OPC DX (Data Exchange) and OPC HAD (Access Data History). They are generally called OPC Classic or simply OPC. The aforementioned are profiles in OPC UA. For example, the OPC DA standard is an OPC UA DA profile.
These profiles form a layer above the OPC UA base layer, which runs common services. All OPC UA profiles use the same common code base, while each standard has its own code base in an OPC configuration. This creates duplicates on systems, where multiple OPC specifications are implemented.
The benefits of OPC UA
Historically, the industrial systems automation pyramid has a hierarchical structure, describing the flow of information from low-level equipment such as controllers, sensors, or meters to high-level ERP applications (and vice versa). Low-level devices are connected by MES networks through PLCs and HMIs.
OPC UA eliminates this pyramid structure, decentralizing system components and facilitating the use of more flexible data modeling structures in a mesh network. OPC UA accomplishes this by defining consistent data structures that are used by all components. For example, an ERP application and a field sensor can use the same information model.
OPC UA enables business intelligence applications to obtain raw data from a wide range of data sources in real time, event data, and historical data.
- Independent platform
Historically, industrial systems run on Windows-based software. OPC UA is platform independent and industrial systems can integrate software from many vendors, using all operating systems. OPC UA can be installed on embedded systems and in the cloud.
OPC UA is sustainable. It allows companies to develop scalable SCADA systems, so that existing equipment can be integrated with new software modules, without the need for additional configuration. Very significant cases can be found in the oil and gas industry, where calibration, metering and flowmeter data can be collected remotely, eliminating the need for inspectors to perform physical checks on site.
- Automatic discovery
OPC UA is plug-and-play compatible. When new sites are integrated into a company or new providers are referenced, OPC UA can automatically perform an automatic discovery of their networks and integrate them into the company network.
OPC UA interoperability allows users to create industrial systems using equipment and software from different vendors.
The disadvantages of OPC UA
- Equipment Specific Limitations
Some proprietary software vendors have found specific limitations between some servers and HMI/SCADA components used in enterprise software automation products. These limitations include lack of support for specific features such as electronic signatures, enhanced database failover, and historical data sources.
- Complex configurations
In reality, OPC UA manages the data exchange between MES and SCADA information systems and between lower level equipment. It is ideal for monitoring and reporting. Although OPC UA was designed to handle interoperability between heterogeneous computers, it has been criticized for its lack of flexibility in handling diverse data structures from different vendors and for its complicated implementation.