As the name suggests, a Liquid-crystal display (LCD) is filled with a liquid crystal between two polarizing filters. In low temperature environments this liquid crystal will suffer from a loss of brightness and much slower response times. In sub-zero environments the liquid-crystal may freeze, causing the screen to cease functioning without the use of supplemental heating.
Traditional methods warming LCD displays in sub zero environments have three main drawbacks.
1.
They are
terribly inefficient, increasing cost of ownership.
2.
They create
hot spots in the LCD matrix which risks damaging the display. This is because heat
does not travel well laterally or vertically across the panel.
3.
There is a
high risk of condensation forming on the LCD. Condensation can shorten the life
of electronics and accelerate corrosion in mechanical components.
The solution
Metromatics has developed a series of rugged high bright LCD displays capable of operating from -40 to +50 degrees Celsius which address the 3 drawbacks listed above.
1.
Efficiency
and cost of ownership
Air is a
fantastic insulator. When you put on a coat in winter, it’s not the wool or
synthetic fibres that keep you warm, it’s the tiny pockets of air the coat
traps around your body that help insulate you from the cold. By leveraging this
principle and creating a pocket of still air around the screen, we have been
able to reduce thermal losses and keep the heat where it needs to be, inside
the panel.
2.
Hot spots
Our embedded
heating solution ensures heat is evenly distributed across the entire panel,
reducing the risk of hot spots forming.
3.
Condensation
Condensation
risk is reduced since our embedded heater raises the temperature of the display
quicker than the temperature of the surrounding insulating air.
How we tested
To verify the design, Metromatics hired an industrial freezer and tested a display for months on end, cycling the temperature to test different heating configurations and evaluate reliability.
The results can be distilled down into the following graph.
·
The display
was warmed to above 0oC in under 18 minutes in a -20 oC
ambient environment.
·
The LCD is
evenly heated across the whole surface (left, middle and right).
·
The internal
insulating air pocket temperature remains below the LCD screen temperature,
reducing the risk of condensation forming.
Immediate operation
If 18 minutes is too long for the display to reach the optimum operating temperature, our ruggedized displays support immediate operation in below zero environments. There is a trade-off is a reduced response time of each pixel while the screen warms above 0oC, but for largely static images like those used on passenger information displays (PID’s) this is not an issue. As you can see from the videos below, there is some motion blur for fast movements, but slow movements or transitions are still highly legible.
<Insert video of screen operating below
zero degrees>
Remote
management
Using our networked monitoring and control solution
(the MPMS) screen heating can be remotely managed to optimise power consumption
and monitor temperatures.
The Metromatics PID Monitoring System (MPMS) is Australian designed
technology providing remote monitoring and control of Passenger Information
Displays (PID) and digital signage. Its compatibility with SNMP allows ease of
interface with existing IT infrastructure and management tools. The integrated
Ethernet switch allows for network traffic to be forwarded to other devices
without additional hardware, creating a simple, cost effective design.
The configurable inputs and outputs means the MPMS can interface
with 3rd party hardware including temperature, power, door and shock
sensors, as well as fans, modems, video cards, heating pads, humidity
controllers and power relays. This combination makes MPMS a powerful SNMP tool
for a broad range of remote hardware monitoring applications, not just digital
signage. The MPMS can be purchased either as a feature of a Metromatics digital
sign, or as a standalone circuit board ready to be integrated into your own
solution.
For further information, please contact Metromatics on +61 7 3868 4255 or sales@metrospec.com.au
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