The problem

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.

  1. Hot spots

Our embedded heating solution ensures heat is evenly distributed across the entire panel, reducing the risk of hot spots forming.

  1. 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, we 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.

Embedded LCD heater test results for sub zero operation
Metrospec PID (Passenger Information Display) warming from a cold start.

The key points to take away from the above graph are

  • 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.

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 do not hesitate to contact Metromatics on +61 7 3868 4255 or sales@metrospec.com.au

 

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