High-performance HMI: the ISA-101 approach operators trust

Most HMI screens fail the same way: a colorful P&ID replica where everything shouts and nothing prioritizes. An operator scanning forty such screens cannot tell normal from abnormal at a glance — which is the only glance that matters when a process drifts at 3 a.m. High-performance HMI, codified in the ISA-101 standard, redesigns displays around a single principle: abnormal situations should be visually obvious because normal is deliberately quiet.

The grayscale foundation

In a high-performance HMI, normal operating state is rendered in muted grays. Color is reserved for abnormality: red and yellow for alarms by priority, plus a small set of status colors (green for running, blue for informational) used sparingly and consistently. The effect is dramatic in practice — a screen with no color demands no attention, and any color on the wall of displays draws the eye immediately to the problem.

This requires unlearning the decorative habits of traditional graphics: no 3D tanks, no photorealistic equipment, no animated flames, no red/green reliance alone (roughly 8% of male operators have red-green color vision deficiency — always pair color with shape or text). Pumps and valves are simple symbols; their state is shown by fill, outline, or label rather than by rainbow Projet colors. The freed visual bandwidth goes to what operators actually need: values near their limits, trends showing direction, and setpoints visible next to process variables.

The four-level hierarchy

ISA-101 organizes displays into levels, each answering one question:

1. Level 1 — overview. One or two screens showing the entire supervised process: is everything normal, and if not, where? Key performance indicators, major flows, and abnormality pointers only.
2. Level 2 — process unit. One screen per unit with its controls, trends, and alarms. An operator runs the plant from this level.
3. Level 3 — detail. Equipment and loop detail: a single controller faceplate, a drive, a valve with its interlocks. Reached by drilling from level 2.
4. Level 4 — diagnostic. Maintenance and engineering detail: I/O states, tuning parameters, device diagnostics. Never mixed into operating displays.

Navigation between levels must take at most two or three clicks, with consistent placement of navigation, alarming, and detail panes on every screen. Operators build muscle memory for emergencies; inconsistent layouts tax exactly the cognition that alarms are already consuming.

Making the migration stick

Converting an existing plant is a bigger change-management project than a graphics project. Start with the level-1 overview and the worst level-2 screens, and involve operators in the redesign — they know which values they actually check and which alarms they ignore. Pair the graphics work with alarm rationalization: quiet graphics plus a noisy alarm system still produces an unmanageable control room. Define a display style guide (symbols, colors, fonts, navigation, faceplate standards) and enforce it in every future project and FAT, or entropy restores the rainbow within two expansions. Measure the result in operator terms: time to detect a drifted loop, alarms per operator per hour, and — the honest metric — whether operators keep the new screens up or revert to the old ones.