5
How HMI Has Been Evolving
FIGURE 1.6 Process and instrument drawing ( P&ID) colourful display screen.
example, today, it is well known that people with a colour deficiency (c olour blind)
cannot discriminate between the colours red and green. These two colours were
dominant in the HMI design and differentiated open (g reen) versus closed (r ed) and
running ( green) versus stopped (r ed). Colour is a coding system, and this HMI design
produced coding systems that were compromised due to human limitations.
For example, the colour “R ed” was used to represent the most critical high priority alarm colour and should remain reserved for this purpose on a graphic. However,
as just discussed, it sometimes indicated the status of the valve positions and motor
de-energized, and many other equipment states.
Colour is just one type of coding method. I have witnessed some graphics using
“R ed” for over 13 different codes, rendering it no longer a sensible coding system.
As an example of more acceptable coding, from a recent HMI project, we used
line thickness instead of colour to portray different electrical line voltages for an
electrical transmission centre overview display.
Lack of human factors and ergonomics knowledge also led to poor readability
and lack of display graphics clarity. Incorrect viewing angles and distance from the
user to the screen were challenges that were often ignored making readability and
noticing a change impossible. In addition, the use of too small fonts, wrong font style,
and too much information squeezed onto a display also hindered readability. Thus,
sometimes viewing text and numbers contributed to poor display quality as seen in
Figure 1.7.
How HMI Has Been Evolving
FIGURE 1.6 Process and instrument drawing ( P&ID) colourful display screen.
example, today, it is well known that people with a colour deficiency (c olour blind)
cannot discriminate between the colours red and green. These two colours were
dominant in the HMI design and differentiated open (g reen) versus closed (r ed) and
running ( green) versus stopped (r ed). Colour is a coding system, and this HMI design
produced coding systems that were compromised due to human limitations.
For example, the colour “R ed” was used to represent the most critical high priority alarm colour and should remain reserved for this purpose on a graphic. However,
as just discussed, it sometimes indicated the status of the valve positions and motor
de-energized, and many other equipment states.
Colour is just one type of coding method. I have witnessed some graphics using
“R ed” for over 13 different codes, rendering it no longer a sensible coding system.
As an example of more acceptable coding, from a recent HMI project, we used
line thickness instead of colour to portray different electrical line voltages for an
electrical transmission centre overview display.
Lack of human factors and ergonomics knowledge also led to poor readability
and lack of display graphics clarity. Incorrect viewing angles and distance from the
user to the screen were challenges that were often ignored making readability and
noticing a change impossible. In addition, the use of too small fonts, wrong font style,
and too much information squeezed onto a display also hindered readability. Thus,
sometimes viewing text and numbers contributed to poor display quality as seen in
Figure 1.7.