OPC UA Is Going to Make Your Life Easier, but...
The OPC UA communications standard has made OPC communications much easier to use. We're seeing an increasing number of devices with an integrated OPC UA server, which enable such systems as HMI SCADA, MES and ERP to collect data directly from them. Yet there are also disadvantages. Let's look at what OPC UA is all about and why you still can't do without a classic OPC server on your computer.
OPC Communications Briefly Explained
In general, OPC communications allow for data exchange among various industrial systems. In the automation industry, an example of this would be a communications platform that can connect to hundreds of disparate devices from multiple manufacturers and convert data from all of these devices to a single OPC format, which is then easily understood by various higher systems, such as ERP, MES and SCADA.
As time went by, a number of OPC communication protocols emerged, serving different purposes: Data Access (DA) for access to live data, Alarm & Events (AE) for alarms and events, Historical Data Access (HDA) for access to historical data, and other protocols.
All these protocols are fully independent of each other – for example, each of them has its own commands for data read and write operations. In short, the protocols are incompatible.
Why Was OPC UA Created?
The OPC UA communications standard came into existence for a number of reasons. First, it appeared as a result of the disparity among OPC DA, OPC AE, OPC HDA and other protocols. Second, when it came to interconnecting various systems, it was sometimes impossible to configure them in a such a way that they would communicate with each other. Third, OPC DA data transfer was not very secure. Above all, OPC DA was dependent on the Microsoft operating system. Making OPC DA work on Linux or iOS was a big challenge.
How It Works Now
"Connecting an OPC UA client to a device's OPC UA server is much easier now. For example, the Simatic S7-1500 features an integrated OPC UA server. The OPC UA client connected to this server can display data directly from the PLC. This is much more user-friendly than ever before," said Petr Šplíchal, a FOXON Technician.
Device manufacturers are offering more and more devices with an integrated OPC UA server. These include PLC systems, CNC systems, drives, routers and other systems. In their OPC UA server, you can often find predefined tags that can be immediately read by an OPC UA client.
What Advantages OPC UA Has
One of the key advantages of OPC UA is the fact that for its operation it doesn't rely on Microsoft's DCOM libraries. Put differently, it's compatible with such operating systems as iOS, Android, Linux and others. So it's much more versatile. For OPC UA communications to work, you don't have to spend hours configuring your computers.
OPC UA is also more robust and more secure – it supports authentication of users and UA applications and data encryption.
Yet There Are Also Disadvantages
A common problem is that customers try to connect their OPC DA applications to devices with an integrated OPC UA server (e.g. the Simatic S7-1500). This can never work. Nevertheless, the question still remains of how to transfer data from the OPC UA server to an OPC DA client.
"We've also seen situations where a device's OPC UA server was unable to deal with requests from multiple OPC UA clients. The higher the number of OPC clients that are trying to communicate with a given device, the more likely it is that a problem will come up. Hopefully, these are just the birth pangs of this new technology," pointed out Jaromír Peterka, the owner of FOXON.
Although revolutionary, the OPC UA interface still has a long way to go before it becomes a standard functionality in most devices and software applications. At the moment you can find it in such systems as the router Ewon Flexy 205, the Simatic S7-1500 PLCs, the Simotion and others. As OPC UA isn't supported by older devices, their data has to be accessed in a different way.
Why You Still Need a Classic OPC Server
"We'd been a bit concerned about the arrival of OPC UA servers. But experience shows that in the coming years OPC DA servers will still be very much relied on. Connecting OPC UA servers to existing applications isn't always so easy," explained Jaromír Peterka.
"In FOXON, we use the KEPServerEX communications platform from the company Kepware. It allows you to connect to hundreds of different systems and convert data from these systems to such standardised formats as OPC DA, OPC UA, ODBC, MQTT and many others. Kepware indeed offers a wide range of drivers for various devices and excellent technical support. And its software updates and upgrades come out very often – even a few times a year," added Petr Šplíchal.
The problem mentioned above with connecting OPC UA servers to OPC DA clients is easily solved with KEPServerEX. You only need the OPC UA Client driver for KEPServerEX. Using OPC UA, the driver allows you to connect, for example, the S7-1500 PLC to KEPServerEX. KEPServerEX then provides you with the PLC's data in the OPC DA or UA format. You can also log this data to an ODBC database.
"The OPC UA Client driver has been very popular recently. It's available as an individual driver or as part of such driver suites as Siemens Plus Suite and Manufacturing Suite. Both these suites are among our best-selling OPC products because they're suitable for the most frequently deployed PLC systems and other data sources of our customers – production plants," pointed out Petr Šplíchal.
Trial KEPServerEX and See for Yourself
OPC UA communications in KEPServerEX are very easy to configure. If there's a problem, you can take advantage of the KEPServerEX's diagnostic tools, which allow for monitoring communications bellow as well as above the OPC UA server. If you're planning on collecting data from control systems, try out KEPServerEX's drivers and OPC UA communications.
The company FOXON is proud to be a Preferred Distributor for Kepware in the Czech Republic, Slovakia, Hungary and the Ukraine.