Ethernet has long dominated IT networking and has been well-established for decades in OT applications. And it continues to advance down to the device level in manufacturing and production automation applications.
In a ControlGlobal.com article, Ethernet-APL becomes a reality, Emerson’s Jonas Berge describes how Ethernet-APL provides a single high-speed infrastructure to manage the wide variety of protocols and devices required in an automation architecture.
Jonas opens by highlighting the challenges both end users and suppliers face today.
There are several bus technologies such as Profibus, DeviceNet, HART and Modbus/RTU using different cables, interface hardware and data formats. It is frustrating for both users and automation vendors.
There is no “one-size-fits-all” approach.
Many bus technologies tried to be the single fieldbus for all vendors to implement and deploy, but since the technologies are good at different things, it did not happen. It must be stressed that within their niches, each bus successfully enabled interoperability. For instance, for field instruments, HART has provided multivendor interoperability between instruments and systems for more than 30 years.
An advancement from IEEE, IEEE P802.3cg (10BASE-T1L) 10Mb/s Single Pair Ethernet, which provides:
…power and communication over just two wires reaching up to 1 km.
Industrial protocol standards organizations FieldComm Group, ODVA, OPC Foundation and PI:
…came together to create a common industrial-grade, two-wire intrinsically safe advanced physical layer (APL) based on the new IEEE standard. Referred to as Ethernet-APL, it is suitable not only for field instruments such as transmitters and valves, but also other kinds of field devices.
Like how regular Ethernet supports multiple communications IP-based protocols such as HTTP, SMTP, FTP, and more, the high-speed 10 Mbits/sec Ethernet-APL supports the IP-based protocols from the four standards bodies, such as:
…HART-IP, EtherNet/IP, OPC-UA, PROFINET, and many more like Modbus/TCP at the same time. Information and communications technology (ICT) protocols such as FTP, HTTP and SMTP are also supported by APL.
Jonas shares an example of how a single Ethernet-APL infrastructure supports complex automation requirements. It:
…can support a distributed control system (DCS) communicating with a Coriolis flowmeter using HART-IP protocol. At the same time, it can communicate with an analyzer management and data acquisition systems (AMADAS) communicating with a gas chromatograph (GC) using Modbus/TCP, or a programmable logic controller (PLC) communicating with a variable speed drive (VSD) for an electric motor using Profinet. In addition, it can enable pump condition monitoring software on a server to communicate with a vibration monitor using OPC-UA.
While the infrastructure supports this protocol diversity, Jonas cautions not to:
…take multiple protocols too far, as some flowmeters use HART-IP while some flowmeters use Profinet and other flowmeters use Modbus/TCP. That would be difficult to support. Try to stick to one protocol for instrumentation, one protocol for motor controls, and one protocol for cameras and so on.
The transition to Ethernet-APL will take time, given the development required for new devices, and the existing infrastructure of 4-20mA and existing digital busses. Even in a mixed environment, communications protocols such as HART support many different topologies.
The good news is that 4-20 mA/HART, WirelessHART, and future Ethernet-APL devices with the HART-IP protocol all have one thing in common: the HART application protocol. They are all part of the same protocol ecosystem. This means instrument technicians can manage all instruments from the same software. Instrument technicians are already familiar with HART terminology, and they get consistent look and feel for all instruments regardless of instrument signal.
Read the article and visit the Ethernet-APL archive of posts here on the blog for more on this rapidly advancing standard.
