The task may sound intimidating, but
designing a human-machine interface
(HMI) screen actually isn’t too different
from creating a word document or presentation.
Just follow some basic rules:
- Remember your audience;
- Stick to the point (task-oriented displays);
- Avoid unknown jargon (If advanced control
is not understood, use simple terms); and
- Use a template (keep your information/
functions in consistent locations).
Designing HMI screens doesn’t mean copying
a piping and instrumentation design (P&ID) onto
a graphic. It means
process so an operator
can easily see
what’s going on in a
Before developing a
screen, talk to your
users! Console operators
are the best
source of information
for designing an
Here are four
basic steps to follow
to achieve effective
HMI screen design:
1. Create, define standards
Take into account operators’ physical environments,
such as control room lighting, how many
screens they monitor, and how close they sit to
the screens. These factors help determine standards,
such as font sizes, symbols, and colors. A
shape or picture library will help ensure consistency
in the desired images. Consider these tips:
Make wise use of colors. Make primary data
(process values) stand out with high contrast.
Secondary or support data (text descriptors)
should be smaller and/or blended with the background.
Alarm data must be easily recognizable
with bright colors. Dedicated colors should be
chosen for each alarm priority.
Make sure process lines flow left to right.
Avoid line bends and crossings when possible.
Be consistent. Maintain absolute consistency
in detail, layout, symbols, and abbreviations.
Indicate major process flows with wider
lines (from feed to principal products). This
approach helps differentiate between major
product/process flows and utility lines.
2. Gather, review data
Data sources may be any combination of P&IDs,
existing displays, procedures, incident or nearmiss
analyses, and operator interviews.
A P&ID might seem the most complicated element.
But remember that while all components
outlined in a P&ID are vital to that process,
they’re not all vital for an HMI display.
Sometimes the most basic of tools—a box of
colored pencils—is the most helpful. When
studying a P&ID, use pencils to determine
instrumentation and flows. Don’t worry about
lines that don’t have instrumentation connected
to the DCS; color in the ones that do.
3. Create a first draft
The first draft can be a markup of existing displays,
a Microsoft Visio or a CAD drawing, or
even a paper sketch.
When beginning with a paper sketch, draw
the diagram lines you’ve marked on the P&ID,
straightening and uncrossing lines as you go. The
result should yield a complete picture of everything
that needs to be included on the HMI
screen. And you’ll minimize room for error by
eliminating unnecessary lines and data.
Base equipment representation on importance
or value, not on physical size. Give objects
the prominence they deserve. The largest object
isn’t always the most important.
4. Refine, approve
Cluster, but don’t clutter, information/functions.
Make sure related information is visually positioned
in easily understandable groups. Evenly
distributing information and drawings across the
screen will reduce clutter. Finally, graphics and
flow charts are usually easier to read if the core
task/function is in the center. Apply this logic to
your display screen.
In the end, all these suggestions are based on
the principles that an operator should be able to
easily understand an HMI display, prioritize
tasks, and focus on required information. Clear,
organized, and uncluttered information help an
operator respond to an alarm more quickly and
better understand a process.
For more on HMI screen
design, visit the following
Web sites: Abnormal
and International Engineering