Module 3 HMI Design Best Practiceegs.pdf

ghappyhafcfgssjfdw

1. HMI Design Best
Practices

2. HMI Design Best Practices
•Most modern manufacturing processes are
controlled and monitored by computer-based
control and data acquisition systems. This
means that one of the primary ways that an
operator interacts with a process is through
computer display screens.
•These screens may passively display
information or be interactive, allowing an
operator to select an object and make a
change which will then be relayed to the
actual process. This interface where a
person interacts with a display, and
consequently the process, is called a Human-
Machine Interface, or HMI.

3. HMI Design Best Practices
•All of the suppliers of computer based control
systems provide software to configure displays
to interact with their controllers. As with any
type of software, each configuration package
has its strengths and weaknesses. There are
also vendors that do not supply control
equipment, but specialize in collecting and
storing data from both the process and the
business activities around the process. These
process data visualization tools provide
configuration packages for displaying data in
unique ways to everyone involved in plant
operation.

4. HMI Classification
•For production related processes, HMI screens can
be classified into four basic groups:
•Tabular and text based screens –lists or tabular
groups of data and status values
•Schematic screens –data are displayed on
schematic diagrams of the actual process
•Trend screens –current and historical values of
data plotted on graphs versus time
•High Performance screens –current data enhanced
by basic graphic elements to convey additional
information

5. The Schematic
Screen
•There is an innate appeal to a
schematic screen. If a level is seen
to be increasing in a tank, as
indicated by a moving bar
indicator within an image of the
tank, it is intuitive to click on a
control valve at the outlet of the
tank and increase the flow out of
the tank to bring the level down.

6. The Schematic
Screen
•The goal of any HMI screen is to
develop “situation awareness”, or
the ability to identify the process
and comprehend the critical
elements of a situation. In the
case of trying to increase
awareness, and also control a
process through a schematic-style
screen, the design of that screen
is going to be a major factor.

7. Color
•A discussion of color has to start
with the selection of a “good”
background color. When DCS
systems were first adopted, the
background color for all screens
was no color at all, or black.
•The problem with a darkened room
is that is makes other normal tasks,
such as paper-based reading and
writing, difficult. It also negatively
affects alertness, especially in
operators with disrupted sleeping
patterns as a result of working
rotating shifts.

8. Color
•The current thinking is to have a
brighter control room. In order to
avoid eye strain, which can occur
as operators shift their gaze from
the room at large to a display, the
display should have
approximately the same
luminescence as the
surroundings. A gray background
fulfills that need and still provides
a background against which other
colors can be seen.

9. Color
•Often process flows are more
obvious if the piping lines are
shown in a color based on the
materials they contain. For
example, a shell and tube liquor
heater would have four lines
attached to it. The two liquor
lines would have the same color,
the steam supply line and the
condensate line out might each
have their own different color.

10. Layout
•Early schematic diagrams were often
based on process and instrumentation
diagrams (P&IDs). These diagrams
were drawn to be used as reference
material by engineering and
instrumentation personnel; they were
not designed to promote the situation
awareness of an operator. A set of
screens based on P&IDs to represent a
process could be called “flat”. Each
screen would display a section of the
process in great detail, and the next
screen in the progression would show
the next part of the process. Control
hardware limitations encouraged
putting as much data on each screen
as possible.

11. Process Values
And Labeling
•The relative importance of dynamic
values and labels needs to be
considered when designing a
schematic screen. Live process
values should be more prominent
(larger or bolded font) than the unit
descriptors which come after them.
Process values which are not
critical, for example the amperage
of a normal pump, should not be on
an upper level, overview-type
screen. This type of reference
information should be placed on a
lower level, detail-type screen.

12. Process Values
And Labeling
•Live values should be displayed
with an appropriate number of
decimal points.
•Live digital values can be
accompanied by a graphical
element such as a bar or circular
analog gauge face. Depending
on the density of the screen,
these analog elements can be
used to show the relationship of
the current value to the normal
range and/or operational limits.

13. Process Values
And Labeling
•Equipment labels are useful,
especially for less experienced
people, but should be small. They
should not dominate or confuse
a screen.
•Live process values should be
located properly and un-
ambiguously on the diagram.
One of the major benefits of a
schematic type screen is to help
an operator visualize the process
and to properly interpret the
information presented.