1660238359003 Johnrezabek

Advanced physical layer: One bus to rule them all

Sept. 29, 2020
Part 1: Innate security and consistent host interfaces will be key to APL adoption

Since the commercial availability of systems that could access and aggregate data from intelligent devices, many seem to have become slower. A notable DP transmitter from 1999 would “synchronize”— update all its current data—in a fraction of the time required by its 2020 replacement. As network bandwidth, memory and computing power have increased, frustration with application performance seem about the same—sometimes worse?

A glance at archived websites from 20 years ago demonstrate how our expectations have grown, so you might conclude that content expands to fill the available bandwidth. Routine patching and updates of operating systems, database engines and software mean applications may likewise need to accommodate new security enhancements. And so it's been with digitally-integrated field devices, as manufacturers adapt to changes in hosts, diverse protocols and evolving specifications. Once viewed as fairly speedy, the 31.25 KB baud rate of fieldbus has lost some of its luster when accessing complex devices over busy segments.

If you’ve been in the discipline for three or four decades, you’ve seen a few generations of offerings that supported then-contemporary communications, like 1,200 baud HART from the 1980s and 31.25 KB fieldbus from the 1990s.

You most likely also remember that Ethernet was not always fast or ubiquitous. But in 2020, multi-gigabit speeds are common over fiber and twisted-pair copper, and the protocol extends easily to wireless 802.11 infrastructure. Is it safe to assume then, that Ethernet is the de facto network standard of today and tomorrow?

As soon as next year, you'll be able to extend it to instruments and other field devices in hazardous areas over single twisted-pair cable. The Advanced Physical Layer (APL) is being created based on IEEE 802.3cg (10BaseT1L), and will be capable of using your fieldbus infrastructure for device power and 10 MB communications over one twisted-pair.

The demonstrations are all plausible, and standards and approvals are in the works. APL may be a tempting choice for your post-2021 grassroots plant or field-device upgrade. All the key developers and standards organizations in the business of process automation have convened to create this new bus to rule them all.

Users must speak up

What lessons-learned from the bus wars and troubled HART and fieldbus deployments should be front-and-center in this standards creation consortium? Suppliers will forever be compelled to seek market dominance and POs. So, if users fail to make their concerns heard, we could end up with another generation of perplexing, kludged-host implementations. Now is the time to get developer time and minds focused on solutions that will fulfill end users’ needs and expectations.

Security is the most important duty of the controls professional, the most likely malady that will garner visibility at the board and shareholder level, as “company Y was struck by ransomware X” or something akin to that. At the same time, it's the most banal waste of a control professional’s time, which you'd hope is focused more on process safety, reliability and efficiency achieved through measurement and control. If the network can ensure that security is innate, it will be one less creature in the thickening morass of patches, upgrades, group policies, etc. that have become routine duties.

Safety: FF-SIF and ProfiSafe both exist as protocols for safety instrumented functions (SIF), but with no logic solvers and few conforming devices. If APL checks the security box, that might be 90% of what’s needed for SIF. Maybe we can get out of the business of stocking two devices for every service: one (4-20 mA) for SIF and one for process control.

Pervasive utilization of digital PV: End users don’t want to futz with mappings, OPC or middleware to create and display measurement variables, statuses, alarms and diagnostics. Hosts should speak the same language as the bus.

Can APL cure all the ills of modern fieldbus integration? Why not? More to consider next month.

About the author: John Rezabek
About the Author

John Rezabek | Contributing Editor

John Rezabek is a contributing editor to Control

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