How OPC UA and MQTT Enable Interoperability

Welcome to Take Five with Automation World. I’m David Greenfield, Director of Content, and today we’re going to look at how industrial communications—namely OPC UA and MQTT—enable interoperability. While the objectives and goals of production operations within manufacturing and processing companies vary widely, there is one thing that you could probably get every plant manager, engineer, and operator to agree on.

And that's for the various automation technologies that they use to be more interoperable with each other. Whether it's a simple wish to send basic operating data from one device to another and have it be accepted and understood by the receiver, or something more complex like having different devices work together more easily in a plug and play manner, interoperability all starts at the communications layer.

And the two most prominent players in this space are OPC UA and MQTT. Both of these communication methods are supported by all the major industrial protocol organizations as well as most automation technology suppliers. So let’s look at how they both target device and system interoperability.

OPC UA is a platform-independent, service-oriented architecture that’s used in nearly every industry vertical, from oil and gas to pharmaceuticals to automotive. Mike Clark, director of the OPC Foundation North America, says OPC UA is so widely used because of its secure, repeatable data modeling. He explained that OPC UA uses data modeling to scale semantically identical messages across the entire manufacturing enterprise from sensors to the cloud. In particular, Mike noted that, with OPC UA, you don’t need to translate, map, or manipulate data as it moves from sensors to the cloud, as those data models are preserved in OPC UA.

Robert Trask, who works with the EtherCAT Technology Group says the way OPC UA handles information across devices has made it a popular interface for higher level communications between controllers—even controllers from different vendors. He adds that more companies are using OPC UA as an interface to streamline the exchange of real-time data, monitoring of alarms and events, and access to historical data. The use of OPC UA is so widespread across industry that many consider it to be the de facto standard for data transfer in the automation industry since it’s already present in most plants today. In fact, OPC UA use is so ubiquitous that it’s even being transported by MQTT.

MQTT is a low-overhead data transport mechanism originally developed for Phillips 66 in the late 1990s. Since then it’s been adopted for applications ranging from Facebook Messenger and Amazon Web Services to manufacturing facilities and power plants. The data agnostic nature of MQTT, which means that users can publish anything they want on any topic using MQTT, led to its wide use across numerous different types of businesses, but limited its use in the industrial space.

As Arlen Nipper, chief technology officer at Cirrus Link Solutions and co-inventor of MQTT, explained: Many automation hardware and software providers have been using MQTT, but each were using their own definitions of topics and payloads since those structures weren’t designed into MQTT.

This meant that, even though an MQTT infrastructure was being used, there was no plug-and-play or interoperability between the different hardware and software products on the market. And that’s what the open-source software specification known as Sparkplug was designed to address. It defines an operations technology-centric topic namespace and payload definition for industrial process variables in MQTT, as well as session state management, which is needed with real-time SCADA systems. Essentially, Sparkplug provides MQTT with the ability to integrate data from applications, sensors, devices, and gateways in an industrial Internet of Things infrastructure.

In June of 2022, the Sparkplug Working Group, which is run by the Eclipse Foundation, announced the launch of the Sparkplug Compatibility Program. This program is designed to help end users know if the automation systems they’re using are Sparkplug compatible. The program tests automation technologies with the Sparkplug Technology Compatibility Kit, which is an open-source test suite that validates conformance to the specification. Products passing the test will be featured in the official list of compatible products, available on the Sparkplug Working Group’s website. Products that pass the test will also be able to display the “Sparkplug Compatible” logo to make it easy for users to know if the product is, in fact, compatible.

Needless to say, there’s a lot more information about OPC UA and MQTT on the automationworld.com site in addition to the links highlighted in this video. So be sure to check it out.