Key highlights
- The article highlights the persistent disconnect between IT and OT systems, showing how process engineers must ensure data from plant-floor devices is usable by enterprise-level IT systems.
- It reminds engineers that gateways and controllers are not the ultimate data sources—sensors and actuators are.
As IIoT ventures into new areas, it’s not surprising that it’s encountering some obstacles and snags due to differences in networking protocols, data formats, and transmission requirements. What is surprising is that many IT-level network and their users still don’t know how to deal with OT-level counterparts on plant floors or in the field.
“IIoT is all about aggregating data to make more intelligent decisions. However, IT’s perspective is often lacking because its users talk about collecting data from gateways and controllers as if they were the final source—and they’re not,” says Paul Sereiko, marketing, and product strategy director at FieldComm Group. “The real source is the sensors, actuators and other devices doing the actual work, and they’re still using many different protocols, such as HART, Modbus, EtherNet/IP, Profinet and others. Each handle data definition in different ways. Because they grew up, and are still often used only in OT environments, OT host systems and associated users understand how to work with those protocols. But IT systems generally don’t understand automation protocols, so at the presentation layer, information like ‘the temperature from sensor ABC is 30 °F’ is often impossible for an IT system to interpret. What’s needed is common information that bridges the gap between IT and OT.”
This is where FieldComm Group and its co-ownership of the Process Automation - Device Information Model (PA-DIM) standard can help. Developed by eight member organizations, led by FieldComm Group, PA-DIM’s purpose is to provide a protocol-agnostic way to present device information using OPC UA’s information-sharing model to reach IT-level systems, and deliver data reliably in a format that users can access and act on. It’s sometimes described as a unified name space (UNS) for process control applications and networks. Its members include, FieldComm Group, ISA 100 WCI, NAMUR, ODVA, OPC Foundation, Profibus/Profinet International, VDMA and ZVEI.
“PA-DIM was launched in 2020 by the individual organizations agreeing to map their protocols into it,” explains Sereiko. “At the time FieldComm Group and the OPC Foundation were co-owners. In 2022, ownership was extended to accommodate demand from end users and other standards development organizations (SDO) for a protocol-agnostic information model. Several automation suppliers presently include support for PA-DIM in their products. Several large oil and gas companies also have labs evaluating PA-DIM.”
PA-DIM makes sure that valuable measurements can be interpreted by IT systema at either the plant or enterprise level, regardless of the protocol the instrument initially employed to communicate. It accomplishes this by integrating the IEC 61987 standard’s common data dictionaries (CDD), including all the units its devices are likely to need. This is accomplished by using the proper International Registration Data Identifiers (IRDI) for those units.
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“Consequently, no matter how HART, Profinet or EtherNet/IP, etc. represent a measurement and its units, it must map to this IEC code. And, when an IT device sees that string of numbers, it knows it’s reporting a measurement and what it is,” adds Sereiko. “This is done without the IT device knowing the underlying, OT-level network protocol.”
Though it hasn’t quite accomplished plug-and-play interoperability between devices, PA-DIM can help them communicate and coordinate their efforts. For example, an enterprise-level operational-efficiency analyst can combine data from a pressure device with HART and a motor controller with Profinet to determine if the motor controller is responding properly to pressure changes without any knowledge of the protocols used by the devices on the plant floor.
“IT components and systems typically don’t have the architecture to work with process automation,” concludes Sereiko. “PA-DIM also uses OPC UA’s technology to provide a way for IT devices to receive data from the plant floor without requiring them to understand process automation protocols. This could conceivably be done by providing information in a different way without PA-DIM, but it wouldn’t be consistent, and it would be extremely costly.”
