The industry today is in a state of confusion regarding basic process control systems' (BPCSs) human-machine interfaces (HMIs). The industry has about 40 years experience with man- or human-machine Interfaces in one form or another. With the evolution of the BPCS, the HMI has evolved over a period of 50 years and has transitioned from physical lights, switches and annunciator panels with analog gauges and trend displays to electronic simulations and finally to computer interfaces.
But, the computer interfaces were designed with little knowledge or science added into the design, and many issues still remain because of this. To help understand the issues and the proposed solutions, we need to understand the current state of the industry. What specific problems we are trying to eliminate?
A quick survey of the current state of the HMI design using a strengths, weaknesses, opportunities and threats (SWOT) analysis reveals that the industry has fully adapted to the current state, and, in spite of known problems and limitations, is reluctant to change. This is mainly because change requires commitment to learn a new system, which involves design, implementation, testing, documentation and training.
Process control operators learn to live with design flaws, and often take the easy way out and continue to live with the less than perfect systems they grew up with. The strength of the existing system is that it evolved from panels to electronics to a first-generation faceplate equivalent and finally to a crude, graphical interface based on plant design.
The HMI many people have been using evolved from a hard panel to group faceplate displays and then to P&ID graphics-integrating faceplates. This has been an easy solution, first taking the controllers from the panel and placing them into groups on a computer display, and then using the faceplate live values within a P&ID graphic.
The black backgrounds and bright, fully saturated colors were not designed. They were more a symptom of the technology, one that the vendors did not mind because bright, fully saturated colors are aestheticly pleasing to the eye, even though they may be 180° from the best practices learned from the science of using color. The vendors still sell their systems based on this premise, rather than on the science of using color correctly.
This statement can be proved by looking at automation vendors' websites and viewing the examples they use to promote their systems. Even though they may have policies supporting the new ASM Consortium-promoted graphics, grey-scale does not sell systems.
As we examine the weakness or problems that are created by this solution, we can read of multiple accident/incident reports that identify the HMI as a contributor to these incidents. We also discover that operators struggle with tracking information or getting overloaded with information because their graphics are not task-based, and information is scattered by the P&ID design. The old groups were faster, as they were assembled based on tasks.
Problems with the Old Way
We see navigation issues caused by lack of hierarchy, in which everything is designed at the same level with no overview. We also see inconsistencies in design because no structure was anticipated by the design. We also see operators trying to get around this issue by requesting more screens. I have actually seen a single operator with more than 24 screens, even though the new standards and guidelines recommend only four process control screens per operator based on short term memory (STM) issues and the limitations on the operator's ability to track more screens.
In additon, ergonomic design principles also help us understand that main screens should be within a 30° and 60° design.