Unlike clothing fashions, enclosure styles don't change a lot from year to year. A 40-year-old enclosure doesn't stand out like your dad's leisure suit. After all, a big metal box is pretty much a big metal box, even with the added glitz of ventilation, temperature control or an explosion-proof or safety rating. However, like a classic, tailor-made suit, enclosure styles are slowly evolving. Driven by the advent of electronic marshalling, as surely as hemlines get shorter, enclosure boxes are getting smaller and becoming more standardized.
Dan McGrath, solutions manager at physical infrastructure products and solutions provider Panduit, explains: "Electronic marshalling provides the ability to more readily distribute enclosures around facilities, rather than needing as many home runs to central consolidation marshalling points. The enclosures can be smaller and more efficient with this technology. Ultimately, we are talking about standardizing with best practice designs rather than 'one-offs,' or every designer needing to sweat the details and develop custom specifications each time."
So how did this happen? The short answer is a shift in the way marshalling is done. Emerson Process Management led the way in 2010 with its "characterization modules" or CHARMs. These signal-conditioning modules are available in a number of types. When the system is installed remotely, each loop's field wiring is landed on one of the special terminal blocks, and the loop signal is characterized by plugging the appropriate CHARM into the terminal, and the marshalling is configured electronically, eliminating the spaghetti nest of cross wiring. To make a change simply remove one CHARM and install a different one. It is the equivalent of traditional wired marshalling, but with far fewer wires.
While Emerson was first out of the gate, other automation vendors have not been far behind. Honeywell Process Solutions is offering its Universal Process I/O for its Series C I/O. The module reduces or eliminates marshalling and allows immediate configuration without the need for additional hardware. Released in May of 2012, the SIL-3-certified solution uses a single, universal, optionally redundant, 32-channel I/O module that can accept DIN, DOU, AIN, AOU or smoke/heat/gas detector signals.
Joe Bastone, Honeywell's solution manager for Experion control I/O, describes it this way: "It's a funny looking module with a termination assembly. What plugs into that is the I/O module. These communicate with the controller. It's totally software-configurable, and it's all done from the engineering console."
Invensys Foxboro's I/A Series Intelligent Marshalling from Invensys, released in late 2011, also takes a crack at eliminating much of the marshalling work. Its FBM247 Universal Fieldbus Module for the Foxboro I/A Series DCS fits into the standard I/A series base plate. Base plate-mounted termination assemblies provide the link between field wiring and the FBM247 modules.
"This module is a hybrid type," says Thad Frost, who oversees Foxboro's intelligent marshalling solution. "It bypasses the marshalling process. It can handle multiple types of I/O signals. [With this system] you are able to bypass the marshalling cabinet and go directly to the control cabinet, and once the cables come into the control cabinet, they can be adapted with software to the required signal types."
Although each of these approaches is technically different in some respects, the result is similar: fewer wires, more flexibility, a much more compact footprint, lower costs, reduced inventory and an installation that is much more forgiving of late changes in engineering plans.
Heading for Size 0?
Anyone who follows women's fashions will tell you that over the past couple of decades, the "ideal size" has shrunk from 6 to 4 to 2 to 0. Is the same thing going to happen to enclosures? Up to a point, yes.
Charlie Norz, product manager for I/O systems at component supplier Wago, says, "We're seeing users continuing to downsize. This need has triggered a push for comprehensive, all-in-one systems for ever-condensing control footprints and enclosures. Ultimately, enclosure issues drill down to I/O size and keeping the control system's footprint compact for future expansion. Thus, the primary focus will continue to be space-efficient I/O."
Scott Pries, marketing manager for Emerson's smart wireless systems, points out, "One of the things that will be going away is one of the two cabinets you need for home-run cable. You don't need one whole cabinet. Intrinsically safe operation is being incorporated into electronics. Now a single card incorporates that and reduces another 20% of the cabinet. If you reuse the old cabinets, you can use the extra space for more I/O."