November 2015
24
I
ndustrial
C
ontrol
& C
ommunications
for driving the LCD panel. Graphic control
boards offer a variety of interfaces including
USB and Ethernet. It should be remembered
that all of these components can be affected
by obsolescence, causing a redesign of the sys-
tem and should be considered carefully by the
designer so that it is as flexible as possible.
The backlight is fundamental to the longevity
of the panel, all having a finite lifetime depen-
dent on their total operating time, which can
vary dramatically depending on the applica-
tion. Table 1 shows the standard operating
lifetimes of current backlight technologies
and the equivalent time in years of 100% usage.
(Times are measured to 50% brightness).
In practice there will be periods when the
equipment may not be operating such as
maintenance, holidays and weekends, which
is of course dependent on the application and
industry. Some industries operate almost 100%
of the time, for example a factory when the sys-
tem may only be turned off during the main-
tenance downtime. Maintenance downtime
however does not have a big impact, adding
only around 336 hours life, assuming a shut-
down of once per year for two weeks. However
you can see fromtable 1 that by careful selection
the operating life of the panel can be achieved
without necessarily having to do anything spe-
cial, but what if the backlight is dimmed or
switched off during periods of inactivity, what
is the impact on the life of the panel? Let’s com-
pare a scenario of operating the backlight for
100%, 50% and 25% of the time.
It is clear from figure 4, that dimming or
switching off the backlight or even the whole
panel can save power but deliver a lifetime
that could suit many industrial applications
and utilizing the latest LED technology, a
20 year life is possible. Applications that say
only operate during the working week would
require a total 124,000 hour life if operated
100% of the time. When factoring in the
effects of dimming, switching off the backlight
or powering off the whole panel, achieving the
required life is definitely possible especially as
both CCFL and LED backlights are usually
replaceable providing an additional level of
security against failure.
It is not the intention here to discuss the
respective merits of touch technologies, but
to consider touchscreen endurance and its
effects on the lifetimes of the panels. The most
common types used today in industrial panels
are 5-wire resistive and Projected Capacitive
Technology (PCT), offering good touch sen-
sitivity, interface options and they can be sup-
plied as an add-on unit or factory-installed by
the manufacturer. The use of a touchscreen of
any type will decrease the luminance of the
panel by up to 20% for resistive and 10 to 15%
for PCT, which may result in using a higher
level on the backlight decreasing its operating
life. Resistive panels tend to be made using
a softer surface material resulting in lower
impact and scratch resistance and an endur-
ance of around 3 million touches. Linearity
and drift can be a problem that could require
recalibration and interfaces can be direct ana-
log or serial (RS232, USB) via an integrated
touch controller device. Projected Capaci-
tance Technology panels are generally made
of a harder material offering better impact
and scratch resistance and a virtually unlim-
ited touch endurance. Linearity and drift are
non-existent requiring no recalibration. Inter-
faces are generally RS232 or USB supplied by
the capacitive touch controller.
Touchscreen endurance is difficult to answer
as the question: how many touches are made
per day? will vary from application to applica-
tion. Both resistive and PCT are designed to
Figure 2. MCU LCD direct interface
Figure 4. Backlight operating life
Figure 5. Panel mounting example
