By Dan Hebert, PE, Senior Technical Editor
Every process plant has a control room with numerous display devices. Some old plants still have large custom-built mimic panels, while newer plants have two main choices for display systems. The first is CRT and LCD monitors connected directly to PCs running off-the-shelf, Windows-based, human-machine interface (HMI) software. Operator input is via touchscreens, keyboards and pointing devices such as a mouse.
A custom-built command-and-control center with multiple flat-screen displays is the second choice. This is obviously a much more expensive option, but these centers provide concrete benefits.
A command-and-control center incorporates mimic panel benefits, including provision of overview information, readability from a distance and simultaneous display of real-time and historical data. It also can overcome mimic board limitations, such as the difficulty of making changes to reflect plant additions or improvements in operating procedures.
A PC monitor can display nearly limitless information and accommodate constant changes, but overview information is hard to present. The relatively small screen size of PC monitors forces users to create hundreds of display pages, each capable of being crammed with excessive detail.
Some PC monitor display problems are due to poor design, but others, such as text size and lack of overview information, are inherent limitations of PC monitors.
“End users often provide too much detail and too many alarms. They may have little human-factor knowledge and incorporate too many colors. Another mistake is single coding with color only, rather than using shape, text and color combinations like the lowly but effective stop sign,” says Ian Nimmo, PE, president of User Centered Design Services. “Text is often too small to read from operating positions because most end users are unaware that text needs to be 1 inch high for every 10 feet away from the display. Other end users try to just use trends, making it hard for operators to orientate with just a glance.”
But PC monitors have their advantages. Great detail, which can be used to diagnose problems, predict failures and optimize processes, is available to those willing and able to dive down into the innards of the HMI program.
A system that uses multiple large displays for overview, combined with smaller displays for detail, can combine the advantages of mimic boards and PC monitors. However, putting these systems together is not for the faint of heart.
Karl Johnson, general manager of networked imaging products at Electrosonic Systems, explains some of the complexity of a modern command-and-control system. “We use video/graphic image controllers to present multiple video and graphic inputs on electronic displays, such as LCD panels, LCD or DLP front- or rear-projection systems or a combination of both. Visualization of complex systems requires the capability to view multiple visual images from many sources to present an overview of system conditions.”
System integration of these components is complex and detailed upfront design is necessary. “The biggest challenge in designing control rooms is definition of client requirements,” according to Matko Papic, manager of engineering and product development at Evans Consoles.
“Two critical questions need to be answered before laying pen to paper: Who are the users and what are their requirements? These questions should be answered collectively by key stakeholders, including operators, managers, IT personnel and plant engineers,” adds Papic.
What are the benefits of a command-and-control system? “Large projection displays improve total system awareness and offer more social decision-making by removing individuals from stovepipe focus,” says Johnson.
Jim Gavolski, director of product management for control room and video wall solutions at Christie, adds, “Video walls can provide large amounts of data and imaging information with extremely high resolution on virtual displays comprised of multiple flat screens seamlessly tiled together. Display systems can be configured in the form factor that best supports the visual content. Overall process information can be shared among many, but each user can have his or her own local displays with content specific to a sub-component of the system.”
