High-performance graphics (HPG), a major component of the modern human-machine interface (HMI), is a relatively new concept. It evolved through a general industry effort to improve the process operator’s ability to effectively manage the operation, particularly in response to abnormal situations. Its development coincided with the development of modern alarm management and alarm rationalization. Poorly designed HMI, along with poorly configured process alarming, have often been cited as significant contributors to major industrial accidents.
HPG is best defined by describing some of its more important
- Limited use of color, where color is used very specifically and
- Gray backgrounds to minimize glare and to enhance the effective use of
- Embedded, properly-formatted trends of important parameters
- A proper hierarchy of display content to progressively expose detailed
information as needed
- Logical and consistent navigation methods
- Consistent flow depiction and layout to eliminate crossing lines
This article focuses on the last three items in the above list. Specifically, it highlights how the hierarchy of graphics and the navigation within the hierarchy are defined and developed by a facilitation process known as “storyboarding.”
An important attribute of an effective HMI is providing the operator with “situation awareness,” which means, in simplest terms, “knowing when things are running as intended and when they are not.” The graphics hierarchy addresses this need.
The graphics hierarchy
At the top of the hierarchy are level 1 graphics. Their primary purpose is to provide the operator with situation awareness over the entire area of responsibility. This is accomplished through a combination of:
- Trends – important operating and control variables trended over a time scale that best provides awareness of where the process has been operating and where and in what direction it is trending – best thought of as “leading indicators.”
- Key performance indicators (KPIs) – these are typically groupings of real-time depictions of controller faceplates that show where the key analog variable is in relation to its target and alarm limits. Normal range or alarm limit violations are made prominent by using color effectively.
While level 1 graphics provide the operator with situation awareness, they are not meant for operation. That function is provided by level 2 graphics, which may be likened to process flow diagrams (PFDs), and which normally cover major sections of a process. If properly designed, an operator should be able to operate and control the entire area of responsibility 85 to 90% of the time from level 2 graphics alone.
Because level 2 graphics present all the major controllers and critical operating variables for a large section of the plant, the need to navigate between graphics – or to display numerous lower-level displays to cover the same area – is virtually eliminated. It is not unusual to observe only level 2 graphics being displayed on an operating console that has been designed according to HPG best practices, in conjunction with an operation that is adhering to a thorough alarm rationalization program.
When an abnormal situation arises, as noted on level 1 graphics or on one of the level 2 graphics, the operator can normally handle the upset by interacting at level 2. However, there are circumstances when the operator must investigate at a more detailed level to analyze the source of the abnormal situation and to decide how to handle it. Level 3 graphics are designed to assist the operator with piping and instrumentation diagram (P&ID) process information. A single level 2 graphic will often navigate to as many as eight detailed level 3 graphics.
Another type of graphic is the “pop-up.” This is very useful for providing detail about a specific process or piece of equipment when needed. These graphics are usually much smaller in size than a full-size graphic and are called up from a small, familiar target on a level 2 or level 3 graphic. They may present detailed information, such as a burn profile in a catalyst bed, vibration and temperature monitors on a compressor, or the motor run/alarm status of multiple banks of air fan condensers on a distillation column. They pop up on top of the graphic from which they are called up and are closed by the standard Windows closing operation (clicking the “X” in the upper-right-hand corner).
Finally, level 4 graphics are the last ones needed in the hierarchy. These graphics are designed to assist the operator in handling routine tasks (e.g., for preparing a batch of additive, regenerating a catalyst bed or making a stock switch). Typically, they are reached by navigating from the associated level 3 graphic.
The hierarchical approach to graphics design is fundamentally different from traditional DCS graphics design, due, at least in part, to the limitations of the graphics capabilities of first- and second-generation distributed control systems (DCSs). With limited monitor size and resolution, only small sections of the process could be displayed with any detail. Process overviews were meant more for navigation assistance rather than for operation and control. Trending capability was extremely limited. Operators often preferred to operate from traditional operating “groups,” typically displays incorporating faceplates for up to eight related analog and digital controllers.
The greatly enhanced computing power of third-generation DCSs, combined with modern LCD monitor technology, has provided the infrastructure for modern HPG. Even so, migrating from first- and second-generation DCSs and incorporating HPG design guidelines can be disrupting to operating personnel, who are accustomed to their CRT-based, black backgrounded, multi-colored graphics. They must now face the challenge of dealing with gray-scale displays with little color and much greater concentration of process and instrumentation.
The storyboarding process
The design process known as “storyboarding” is a way to develop a visual representation of the layout and hierarchy of the new HPGs that will cover the operator’s entire span of control. The basic objective of storyboarding is to define the graphics hierarchy. This is a multi-step process and usually requires a full day for a typical operating console in a manufacturing facility.
Preparing for a storyboarding session includes a review of the process, ideally via a good set of PFDs along with a complete set of screenshots of all current graphics in use on the console that is being migrated. Several senior operators as well as representatives from process control and process engineering should attend the storyboarding session. One way to overcome the challenge of ensuring operator “buy-in” and getting them involved in developing high-performance graphics is to enlist their participation in the storyboarding design process and session.
A facilitator should lead the session. Ideally, this person is a process/process control engineer who is familiar with the facility being migrated and is also experienced in leading storyboarding sessions. The first and most difficult step in the storyboarding process is to identify the level 2 graphics. These graphics are critical. The success of the overall layout and hierarchy depends on getting these graphics right. The objective is to end up with the minimum number of level 2 graphics required to provide the operator with all the proper handles to operate the entire unit under normal conditions with those graphics alone.
A typical major process unit like a fluid catalytic cracking unit (FCCU) in a refinery will have 6-10 level 2 graphics – most of these are used to cover the process itself and one or two for special use, such as critical alarms, utilities, catalyst regeneration, etc. After the level 2 graphics have been laid out, the storyboard is then filled in with the remaining hierarchy of graphics organized under level 2.
A typical storyboard for an FCCU operating console with an isomerization unit, boilers and wastewater treatment facility is shown in Figure 1. In this case, the entire operation has been condensed to seven level 2 graphics – a very compact and elegant layout.
The names of the existing second-generation graphics, which are being replaced during this migration, are shown in red beneath the graphics taking their place. Note that several of these obsolete graphics can often be combined into one high-performance graphic. HPG migrations typically result in reductions in the number of graphics of between 30 and 50%.
Navigation between graphics must be intuitive and instinctive. This is best accomplished with the use of navigation “ribbons.” A typical ribbon is shown in Figure 2. In this small polystyrene unit, there are two level 2 graphics (top ribbon), eight level 3s, three level 4s, and three pop-ups. Figure 2 indicates that the operator has clicked on the first level 2 graphic. The five level 3 graphics associated with level 2 are shown on the second ribbon and can be navigated to with one click. Likewise, level 4 graphics are shown on a third row when their associated level 3 graphics are displayed.
Another aid to intuitive navigation is shown in Figure 3. Here off-page hyperlinks provide upstream/downstream L2-to-L2 and L3-to-L3 navigation based on process flow from adjacent parts of the process.
What about the level 1 graphics? The storyboard facilitation session does not address layout and design of these graphics. Their design is best addressed after developing the level 2 and level 3 graphics. They are built based on information identified from extensive operator and supervisor discussions that take place near the end of the migration project. They typically incorporate the most important control and operating variables that appear on the level 2 graphics and that provide “leading indication” of process health and stability.
The storyboarding process introduces operators to the concept of HPGs and, at the same time, engages them in the migration process itself, allowing them to take ownership of the design of the new HMI for their area of responsibility. Exposure to examples of the various graphics types during the session introduces them to the many enhanced features of HPGs, with their superior navigation, alarm recognition and one-click features. Change is often uncomfortable, but it is inevitable – beginning the HMI migration process with storyboarding is a great way to put operators in their comfort zone and to guarantee project success.