Project execution: Removing automation from the critical path

This leads to incomplete information and new automation requirements that continue to trickle in long after the design-freeze milestone, explain Alicia Dubay and Roy Tanner.

A big part of this inability to be more flexible—to respond to change and deal with incomplete information—derives from longstanding project practices based on outdated technology and workflows.

A chief offender is the hard-wired analog instrument that, despite the availability of digital alternatives, is still often used.

Analog instrumentation has long relied on traditional, non-configurable multi-channel I/O modules that might include 8, 16 or 32 fixed input/output channels. While one module may accommodate a limited mix of common signal types, they are fixed at the factory early in the project cycle, and cannot be changed after shipment. This requires the project automation team to know, with a high degree of accuracy, the exact mix of I/O channels that will be required for any given application—or face rework and delay.

With an alternative approach, automation engineers could dramatically streamline workflows while increasing the ability of their designs to gracefully absorb even late changes.

A big part of this inability to be more flexible derives from longstanding project practices based on outdated technology and workflows. A chief offender is the hard-wired analog instrument

New digital communications technologies increase system flexibility by effectively eliminating the need for traditional I/O hardware. Any new measurement points or outputs added to a project must still be digitally mapped to the broader control system strategies, but that can be done relatively late in the project via software, rather than reengineering new hardware components.

Using modularized process units and other higher level subsystems such as intelligent electrical devices (IEDs) where possible can also help.

These subsystems arrive at the project site not with a bundle of analog wires to physically marshal into the main automation system, but with a single (or redundant) Ethernet cable connection.

The subtleties of lower level field device connectivity are left to the subsystem supplier and the measurement and control parameters digitally mapped to broader strategies in the main control system. By some estimates, more than 50 percent of today’s measurement and control points are wired not at the project site, but come already embedded within larger pieces of equipment and skids.

This approach streamlines project execution in two ways. Firstly, since the base hardware for every type of signal is the same, automation system designers need only know an approximate I/O count at the design-freeze milestone. Designers can order standard I/O module bases and enclosures, with the freedom to alter the mix of I/O types at any point in the project.

This also eliminates the need for factory acceptance testing (FAT) of control system hardware. Secondly the need for physical marshalling, as well as all cabinets and terminations, disappears as each channel can take on any signal type and be marshalled digitally to any controller.

Now, instrument installation techs can land analog signal pairs on any convenient I/O channel without regard for signal conditioning specifics—much as they might when connecting a digital device to a digital network.

Importantly, that specialized conditioning is added to the channel late in the project, and only then is the instrument digitally marshalled to the plant’s full automation and information architecture and bound to the appropriate controller and applications.

Moving automation off the critical path of project execution requires agility as well as speed. The move to configurable single-channel I/O systems and fully digital instrument communications facilitates both. First, by improving the ability of automation system designs to absorb and mitigate midstream changes in a project’s functional requirements. Second, by eliminating hardware and software interdependencies, and allowing more project execution tasks to advance in parallel rather than sequentially.

Alicia Dubay and Roy Tanner are respectively strategic marketing manager and systems marketing manager, ABB