Five Tricks For Using LCDs In Cold Environments

Liquid crystal displays, or LCDs, are widely used in user interface assemblies in almost all sectors, places, and working conditions. Because LCD screens are now far less expensive than they were 20 years ago, many of the everyday gadgets we depend on now have LCD technology.

It is very likely that you are reading this blog article on a laptop or tablet, and that the screen itself renders the image onto a low-profile pane of glass using LCD technology. Check your pocket. Yes, the screen on that smartphone most likely employs LCD technology. Does your dashboard spring to life as soon as you go inside your automobile with an intricate user interface? How about the menu at your go-to drive-thru restaurant in the area? These are a few examples of commonplace applications for LCD technology.

However, did you know that LCD displays are being used by the US military to enhance our warfighters' equipment interaction capabilities? Life-saving medical equipment is monitored and managed by an LCD touchscreen interface at hospitals all over the world. While at sea, captains can get real-time position, direction, and speed data using maritime GPS and navigation systems. It's obvious that these devices' ability to function in a variety of settings is essential to people's lives.

One fundamental shortcoming of LCDs persists: they perform badly at low temperatures. This problem will only get worse as the use of LCDs grows and larger panel sizes become even more affordable. LCD screens won't work at all at low temperatures for various applications. This is significant because the LCD crystal's performance will start to decline in automotive, outdoor consumer goods, military aircraft, and other applications where the temperature drops below freezing. The LCD display's usability in cold situations will be restricted if it shows signs of permanently damaged pixels, slow resolution, or poor colour viewing. There are a number of design strategies that can be investigated in order to lessen the effect that low temperatures have on LCDs.

1. Pick An LCD Display Off-The-Shelf That Has The Correct Low-Temperature Rating.

TFT (Thin-Film-Transistor) Colour Liquid Crystal pixels, the foundation of the billions of LCD panels in use today, are used in the majority of LCD displays. As the ambient temperature drops, the fluid that the individual pixels use to make their crystal material becomes more viscous, which will compromise performance. Temperatures below 0°C are often used to indicate the degradation of performance for LCD displays.

Have you ever attempted to use your smartphone for ice fishing or skiing? For those of you who reside in northern latitudes, have you ever unintentionally left your phone in your car during an evening when the temperature falls well below freezing? It's possible that you've seen slow screen response, low colour contrast, or, worse yet, irreversible screen damage. Even though this is typical, it's still inconvenient. The objective of a design engineer is to choose an LCD technology that provides optimal performance within the specified temperature range. Examine the manufacturer's data sheets for the operating and storage temperature ranges if your LCD display must function at or below freezing. Two distinct off-the-shelf LCD displays with varying temperature ratings are listed below. It should be mentioned that off-the-shelf screens that can withstand extremely low temperatures are not widely available.

2. Take Into Account Mounting A Low-Profile Heater On The LCD Display's Back.

Many military applications require a product to be rated for -30°C operating temperature and -51°C storage temperature in order to comply with various mil standards. The question still stands: given that the device is rated for a maximum operating temperature of -20°C, how can one use an LCD display at -30°C? Using a heat source to get the display temperature up to a reasonable range is the solution. The display may warm up on its own if there is a nearby engine or other heat-producing source. If not, a specialised low-profile heater is a great choice to think about.

A flat flexible polyimide heater, which is composed of an etched layer of steel and covered in an electrically insulating substance, is a great choice in situations when power and space are restricted. These gadgets function as resistive heaters and can be powered by a variety of voltages up to 120V. Furthermore, these heaters are compatible with both AC and DC power supplies. Their heat output needs to be sized in accordance with the product specifications and is commonly expressed in watts per unit area. Additionally, the back of these heaters has a pressure-sensitive adhesive that enables them to be "glued" to any surface. Any kind of bespoke connector can be supported by further customising the flying leads that come off the heater. Any LCD application that calls for a customised low-profile heater can benefit from the assistance of a full-service manufacturing partner such as Kelai in creating a unique solution.

3. Include A Real-Time Feedback Loop And Temperature Sensors

In less than a few minutes of operation, polyimide heaters can attain temperatures beyond 100°C because they lack thermal bulk to dissipate the heat. To control the impacts of low temperature on an LCD display, a heater alone is insufficient. What happens if the LCD display is harmed by an incorrectly sized heater? What happens if you leave the heater on for an extended period of time and it destroys other parts of your system? It's crucial to include a real-temp temperature detecting feedback loop to regulate the heater's on/off operation, just like your home's thermostat.

The first step is to choose temperature sensors that are tiny enough to fit inside a small envelope and can be attached to the display. The surface temperature of the display can be measured with comparatively low cost and great reliability using resistor-thermistor displays (RTDs), thermocouples, or thermocouples. Additionally, these kinds of sensors offer an electrical output that is adjustable to the required temperature range.

Finding the quantity of temperature sensors and their general location on the display is the next stage. It is advised that the heater be controlled by using a minimum of two temperature sensors. This minimises non-uniform heating by employing a weighted average of the temperature data and several sensors to provide circuit redundancy. The position of the temperature sensors and the thermal mass of the materials involved will determine how best to optimise the control loop in order to regulate the heater's on/off function.

How the various sensors will be mounted on the display is a crucial factor to take into account when choosing a temperature sensor. The majority of LCD screens have a sheet metal backer built in, which provides the perfect surface for mounting the temperature sensors. Thermally conductive epoxies come in a variety of forms and offer a reliable and affordable solution for attaching the fragile objects to the display. Selecting an epoxie with the right working life and cure time is crucial, as there are various varieties to pick from.

For instance, you might find it difficult to finish the project before the epoxy starts to solidify if you are kitting 20 LCD displays and the thermal epoxy has an 8-minute working life.

4. Examine The System's Heat Transfer.

It's crucial to thoroughly understand the system's heat transmission before constructing any kind of prototype LCD heater assembly. The flexible polyimide heater will produce heat, which will then be transferred to the LCD display and other components of the system. Heat will transfer mostly through conduction, though it will also radiate, convect, and be carried away from the heater. This is crucial because heat will be attracted towards the heat sink if your heater is in contact with a large heat sink, such as an aluminium chassis, which will affect its capacity to warm your LCD display.

Air gaps, insulating materials, and other techniques can be used in the design to control the flow of heat in your system as it approaches the "steady state" condition. Prototypes with many temperature sensors can be constructed to map the heat transfer during development. This enables the best location of temperature sensors, a heater that is the right size, and an appropriately managed feedback loop.

5. Include Testing At Low Temperatures In Your Development Strategy.

It's crucial to undertake low temperature testing first on any project that calls for an LCD panel to function at low temperatures before freezing the design, pun intended. A thermal chamber, a method for running the system, and a device to gauge temperature against time are often needed for this kind of testing. The majority of thermal chambers have an access port or another way to pass cables within the chamber without sacrificing functionality. In this manner, data can be obtained from the temperature sensors and electricity may be given to the heater and display.

Finding out the true impacts of exposure to cold on the LCD panel is the primary goal of the low-temperature testing. Does the LCD screen work when it's cold? Does the cold affect some colours more than others? How slow does the screen appear? Does the system function better when it is back in ambient conditions on the LCD display? Without conducting actual testing, it is practically hard to provide meaningful and pertinent answers to any of these concerns.

Synopsis

LCD screens will be used even more widely as long as they are a vital component of our culture. With bigger and bigger displays going into production every year, costs will only go down. This implies that further applications—including those requiring them to function in extremely cold or hot climates—will arise. LCD screens are practically always usable due to the use of design elements that reduce the negative effects of cold on them. However, it's not always easy. Engineers need to be aware of the constraints placed on design as well as strategies for overcoming the main obstacles.

A high-value way to be able to design, develop, and produce systems that push the boundaries of off-the-shelf hardware, such LCD screens, is to work with a full-service manufacturing partner like Kelai. This fact shortens the time to market for any high-risk development project and lowers the effective programme cost.