OPC UA is an open technology and is already in use in many applications today. Almost all control system manufacturers offer OPC UA in their products. This widespread use was made possible because the communication technology above the control level no longer offers any differentiation options for individual manufacturers. OPC UA is jointly distributed and further developed by many manufacturers under the umbrella of the OPC Foundation user organization. The advantage for machine and system operators is that they are no longer dependent on specific providers by choosing a specific communication technology.

Growing number of nodes

On the other hand, new options for differentiation are opening up for manufacturers: Whereas in the past there was an average of 30 to 40 nodes in a network, in future there will be 1000 or more nodes.

The increased number of nodes must be managed and controlled properly. This challenge offers automation providers the opportunity to offer customers added value. Software tools that make it possible to commission large networks, including all participants, in the shortest possible time will become massively more important; in other words, software tools that should also be operable by technicians without in-depth IT know-how.

However, it is not only the number of nodes that will increase, but also the volume of data. In order to maintain an overview of this flood of data, the protocols previously used in the industry are no longer sufficient. This is where OPC UA offers clear added value. The big advantage of OPC UA over conventional fieldbus protocols lies in the information models. Traditional bus systems transmit dimensionless data, i.e. simple numbers without units or other information. The controller runs an application that knows how to interpret this data. In this context, we speak of a semantic description of the data.

As long as machines work independently of each other, this procedure is perfectly practicable. However, as soon as the data is to be transferred to other units - to other machines, SCADA systems or even ERP systems in the cloud - this semantic knowledge is lost. The data are now just dimensionless numbers.

Fewer errors

The semantic descriptions were therefore usually passed on in long tables or even handwritten and entered into the other systems. The effort involved is immense and the probability of errors is very high. OPC UA makes this procedure superfluous. The susceptibility to errors is reduced and flexible machine and system concepts can be implemented much more easily.

The OPC UA information models make it possible to transfer not just individual data, but information. This is understood by every participant without further explanation. Let's take a sensor that measures a temperature of 5 °C as an example. Conventional protocols transmit the value '5' to the controller as a data type integer. The information that the transmitted number is a temperature value in °C, which also has certain limit values, is stored in the application running on the controller.

The OPC UA approach goes in a different direction: the value '5' is made available including the descriptive data. In this case, therefore, with the information that it is a temperature value that was measured in °C and in which limit values the value should move.

Information on request

This information can now be queried by other participants in the OPC UA network. This drastically increases the flexibility of the application. For example, if a new report is to be generated in the ERP system, the ERP system can search the network for information - in OPC UA this process is known as browsing. The information found can then be collected in a database and displayed in the report. Previously, this was only possible if a data transfer was programmed manually and the semantic information for each individual value was stored in the ERP system. This is therefore a static system structure. If a variable was changed in the machine, it also had to be reprogrammed in the ERP system.

OPC UA therefore greatly simplifies communication from the control level to higher-level systems. However, there is still a challenge to be solved: When higher-level systems from the IT area send requests to the machine network - also referred to as OT in this context - the network load increases. If delays in the millisecond range occur in an IT network, this is normally not a problem. However, for high-precision machine processes, accuracy in the sub-millisecond range is essential. Delays in the millisecond range immediately lead to downtimes, reduced quality or, in the worst case, even to danger for man and machine.

For this reason, there is a clear separation between IT and OT networks in almost every production facility. IT networks lack temporal accuracy and cyclical data traffic - two characteristics that are absolutely essential at machine level.