Fieldbus

Is fieldbus dead?

Settling for less is fine for the simple minded and poorly led.

By John Rezabek

Why did I talk my wife into an Android smart phone? All her sisters and her daughters have iPhones, and the famous IOS and Apple networks facilitate easy sharing of pictures and videos among iPhones and i-everything else. It seemed like a good idea—she liked using a stylus, as the tiny screen of her old iPhone 4 was not very responsive to her touch. So a big-screen Samsung Note with a built-in stylus seemed like a good choice. But even after a couple years of continuous use, her aggravation with the incompatibility between the operating systems and networks continues. You can imagine my dismay at having made the recommendation, and reluctance to ever proffer advice on the matter again.

Some have experienced a similar sentiment when it comes to fieldbus technology. In our zeal to seize the new digital day, we have created unintended pain and frustration for our end users. Not that long ago, the many paths to the “trough of despair” following adoption of this revolutionary technology seemed to overshadow the numerous benefits of digitally integrated field devices on a two-wire bus. Lacking the leadership to learn from the mistakes of the early adopters, the ensuing flight back to yesteryear’s technologies has continued unabated for projects in many world regions.

The mistakes of those early adopters were rudimentary and have been well documented, as have the best practices that help ensure success. Still, fieldbus—an imaginative and robust solution for efficient deployment of a 100% digital measurement and control system—continues to be underutilized. It has become so under-marketed compared to wireless, some end users have been asking me: Is fieldbus dead?

In a recent Automation.com blog post, Emerson’s Dale Perry does a reasonable job of comparing fieldbus technology choices. While recounting many of the better attributes of fieldbus (both PA and Foundation), the concluding recommendation is we’re better off deploying HART and WirelessHART, which is perhaps a foregone conclusion considering the author’s place of employment (the inventors and chief proponents of all things HART). I’d contend Dale’s conclusion is correct if you include the following qualification: A blend of HART and WirelessHART is often the best choice if one lacks any energy, desire or acumen to deploy the superior solution for process control, which is Foundation fieldbus. As it is so often the case that this energy and desire are lacking in projects, the recommendation is hard to dispute. It’s unfair to vilify Dale for taking the position he does, since no vendor, not even the great and powerful, is wise to confront their paying customers with an unflattering truth.

It’s unfair to vilify Dale for taking the position he does, since no vendor, not even the great and powerful, is wise to confront their paying customers with an unflattering truth.

I wouldn’t dispute the contention that wireless infrastructure should have a prominent role in any process plant environment. My experience with WirelessHART measurements supports the assertion that it’s sufficiently robust for many closed-loop control solutions. But control valves have challenges: Wireless is not a slam-dunk since our paradigm for valve fail positions requires a continuously powered pneumatic transducer (I/P) to oppose a powerful spring. There will be wires for decades to come. If you can wrest yourself from 4-20 mA, the same copper pair that powers your control valve can provide power and deterministic digital integration for dozens of other useful measurements, including the PV that you’re aiming to control.

Smart digital devices and digital hosts should interconnect digitally. If you’re an end user or consultant who comprehends the intrinsic value and logic of this concept, delivered by fieldbus and wireless, don’t be dismayed by flaccid vendor marketing. Like converting an iPhone diehard to Android, you will be well served to engage all likely stakeholders—designers, installers, commissioning teams, operators and maintainers—and enlighten them about how their experience will be different, and how to make the best of it. Experienced end users have documented recommendations and best practices for simple and efficient project execution, and the ISA 108 committee is codifying the key practices to exploit device intelligence at all points in the process plant lifecycle. Successful and prosperous fieldbus projects are not outliers.

Fieldbus is often the least expensive installed cost, assuming one’s host supports both wireless and fieldbus. Since this contradicts the automation.com post, next month we’ll do the math.