Open Platform Communications Unified Architecture (OPC UA) is an open standard that specifies machine to machine data exchange for industrial communication It is an interoperable framework that enables the exchange of data across disparate systems like programmable logic controllers (PLC), human machine interfaces (HMI), and other machinery ensuring consistent interconnectivity and uninterrupted flow of information.
The major difference between OPC UA and its predecessors lies in that the machine data can now not only be transported but also interpreted in a way understood by machines.
OPC UA enables a common communication architecture for a variety of objectives like data access, historical data access and security. To enable such variety in objectives, OPC UA follows a two-layer approach. The base layer consists of code for common services across applications over which code for specific applications can be built.
Ideally, two mechanisms are used for exchanging data – client-server model and subscriber-publisher model. It is noteworthy that both these mechanisms are detached from the actual protocol. Let us briefly look at the functioning and implications of each of these mechanisms and the respective protocols involved.
The TCP and hyper-text transfer protocol secure (HTTPS) represent the client-server mechanism, which can facilitate peer-to-peer transmission for secure, and validated transport with limited number of connections.
The user datagram protocol (UDP) along with advanced message queuing protocol (AMQP) and MQ telemetry transport (MQTT) represent the subscriber model. This is mostly preferred for a large number of connections with minimalistic security features – under the category of “fire and forget”.
Since OPC UA combines the features of both, it eliminates the dilemma of choosing between OPC UA or AMQP or MQTT.
The advantages of OPC UA in manufacturing processes also forms an important argument in the assessment that OPC UA will continue to be widely adopted and utilized in manufacturing industries in the forthcoming years.
Manufacturing activities are constantly transitioning towards processes that derive muscle from technologies like machine learning, big data, and artificial intelligence. These technologies are not completely immune to security breaches.
OPC UA ensures the authentication and authorization of applications using standard security techniques. All applications involved in the communication process must authenticate the other party in the hand-shake, which in practice is an open secure channel service message.
OPC UA information modelling is the glue that binds industry 4.0 together. OPC UA information modelling is loosely based on the concepts of object oriented programming (OOP) with its main pillars being features like data abstraction, inheritance, and polymorphism. These functions can very easily be utilized to derive information from a sub-system or machinery.
For instance, by defining subsequent objects and variables information about a running motor can be inherited with attributes like temperature, vibration level, and current. It can also include member methods such as start and stop.
From an engineering standpoint, this means significantly reduced effort and better reusability.
