Designing an operator display that answers a question
Most process graphics accurately depict the plant and answer none of the questions an operator actually has.
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Operator displays
Display hierarchy, colour discipline, trends, navigation and the move away from decorative graphics toward screens that support decisions.
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Operator displays are frequently the oldest thinking in a modernised control system. The hardware is replaced, the software is migrated, and the screens are recreated as faithfully as possible — including every design decision made twenty years earlier by a graphics package that could finally do gradients.
The result is a screen that shows the plant accurately and answers the operator's actual question — is this normal, and if not, how bad — slowly or not at all.
These guides cover the alternative: a display hierarchy with distinct jobs at each level, colour reserved for abnormality, and trends placed where the decision is made rather than on a separate screen nobody opens under pressure.
Attendance records can support staffing and training reviews when they are kept separate from competency evidence. Further details are available in this guide.
Additional industry context is available in the ISA-101 HMI standards.
The display hierarchy, and why level one is usually missing
Most control systems have detail displays and unit displays. The overview that tells an operator whether the whole plant is normal frequently does not exist.
Read the guideColour, contrast and the control room environment
Colour decisions made on a desktop monitor in an office are evaluated on a different screen, in different light, by people who have been awake for eleven hours.
Read the guideTrends: the difference between a value and a direction
A number tells the operator where a variable is. Only a trend tells them whether to act now.
Read the guideNavigation: getting to the right screen in one action
An operator diagnosing an upset should not be searching a menu. Most navigation schemes are designed by people who already know where everything is.
Read the guideDisplays for startup, shutdown and abnormal events
Graphics are designed for the ninety percent of time the plant runs normally, and used most intensively during the other ten.
Read the guideWriting a display style guide people will follow
Without a style guide, every display reflects the preferences of whoever built it, and the operator does the translation.
Read the guideModernising displays without a control system replacement
Display improvement is usually deferred until the next system migration, which may be a decade away.
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