Despite these innovative ways of eliminating traditional I/O engineering dependencies, old habits die hard. Indeed, a recent survey of Control readers indicates that analog instruments still account for some 55% of capital project I/O points, whereas 38% is connected via fieldbus and 7% by wireless (Figure 1). Clearly, the process industries still appreciate the simplicity and familiarity of analog instrumentation. So, a third innovation was needed to free project engineers from the rigid tyranny of fixed-functionality I/O modules: single-channel, flexible I/O such as
ABB’s Select I/O offering.
Available for process automation and safety applications, this extension to the System 800xA family of Flexible I/O Solutions allows for each I/O channel to be individually characterized using a plug-in hardware module. This approach streamlines project execution in a number of ways.
First, because 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 then order standard—not custom—I/O module bases and enclosures, knowing that they have full flexibility to alter the mix of I/O types at any point in the project. Further, since control system hardware components are now standard issue, the factory acceptance test (FAT) of control system hardware is a thing of the past.
Second, because each channel can take on any signal type and be digitally marshalled to any controller, the need for physical marshalling—and all those cabinets and terminations, too— disappears completely (Figure 3). In addition to lowering costs and speeding execution, this has the added benefit of significantly reducing overall system footprint, which can be critically important in an application such as an off-shore oil rig where floor-space and even allowable weight are at a premium. Instrument installation techs save time, too, because they can simply land their wire pairs on the most convenient pair of I/O terminations and move on to the next.