Robert Chamberlain of W L Gore & Associates GmbH explains how vents can ensure electronic components in smart city applications have long, effective service lives by protecting them from environmental conditions.
Smart city systems require sensors and other intelligent electronic components that are connected and capable of communicating with each other. These components help improve safety and mobility on our roads, manage utility networks more efficiently, improve the transparency of administrative processes and reduce the overall cost of systems across the service life. They allow smart cities to use resources and energy more sustainably and sparingly as well as to enhance the quality of life of the people living there. The more complex and extensive the electronic components’ functions are, the more important it is to protect the components from environmental conditions so that they can work reliably throughout their entire service life.
Smart city technologies are already available for a range of applications. Taking waste collection as an example, to make it more efficient, every waste container distributed around the city can be fitted with sensors that recognise when it needs to be emptied. This means that the waste collection truck then calls only at those containers that are actually full, leading to fewer empty runs, less traffic congestion for residents, and of course, lower costs.
Another area with the potential for major energy savings is street lighting. Most street lamps today are still switched on and off using timers, whereas modern lighting systems are equipped with brightness and motion sensors. These ensure the lamps are switched on only when needed – when pedestrians are around or when it gets dark earlier because the sky is overcast, for instance. These kinds of intelligent lighting systems can achieve energy savings of more than 40 percent.
There’s just as much potential for optimization in the energy sector, where smart meters – intelligent measuring and control systems – monitor consumption and tell the energy provider what demand is likely to be at any given time. This allows public utility companies to align energy distribution based on demand and to improve grid efficiency.
Protecting the electronics
Just how important it is for electronic components to perform flawlessly and last a long time varies, however, depending on the application or area of use. If the sensitive electronics in a waste container fail, all that happens is that the waste collection truck makes an additional empty run. But should a smart meter malfunction, it could cause an entire building to lose power.
These kinds of defects are often the result of faulty housing seals that can no longer provide adequate protection to the electronics inside. So the more complex and important the smart city application, the more crucial it becomes to ensure these sensitive electronics are protected from harmful environmental influences throughout a service life of over 20 years.
Topping the list of stress factors for electronics housings are daily temperature fluctuations. As the temperature rises in the morning, the air inside the housing expands, pushing the seal outwards. At night, the air inside cools down again, causing it to contract and pull the seal inwards. The strain this puts on the seals only gets worse whenever, say, a cool shower of rain follows a hot summer’s day or when the sun shines directly on the housing. Over time, the constant fluctuations in pressure wear the seal out, making it brittle and unable to provide the required protection. This in turn allows dirt particles, liquids or water vapour to get into the housing, damage the electronics and cause them to short-circuit.
The graph shows pressure differences in electronics housings. In a housing with 5 litres of free air, a drop in temperature from 65 to 15 degrees Celsius creates a negative pressure of -140 mbar. A pressure difference of 70 mbar can be enough to damage the seal and repeated stress will wear the material out. Another possible cause of fluctuations in air pressure is when the electronic components are exposed to various altitudes during transport. Today, products can be produced anywhere in the world and then flown to where they are needed. Going from comparatively low air pressures of around 850 mbar inside the aircraft to those of over 1,000 mbar on the ground puts the housings under enormous strain.
Equalizing pressure spares the seals
There are various ways to prevent such differences in pressure, including hermetically sealing the inside using thicker housings, additional bolts, more rugged seals or potting compounds. The catch is that these methods are very expensive and add extra weight. What’s more, such systems don’t actually combat the causes of the leak – worn-out seals – but are simply attempts to delay when water will penetrate the housing.
Even bidirectional mechanical vents can suffer mechanical wear and tear after a while and fail. Another option would be open labyrinth systems, but these can allow water to get inside the housing. Venting made from felt or sintered material does possess the required pressure equalizing properties, but these can become blocked by dirt and water over time.
This effectively leaves modern vents that feature chemical-resistant membranes made from expanded polytetrafluoroethylene (ePTFE) as the only way to achieve continuous pressure equalization. The microporous structure of ePTFE ensures a bidirectional exchange of air. At the same time, the membrane pores – which are around 20,000 times smaller than a drop of water – prevent liquids, dust or dirt from getting into the housing. These vents can therefore provide reliable protection for electronic components used in smart city applications and extend their service lives.
Gore has carried out extensive tests that show that this type of vent is capable of withstanding a variety of weather conditions in any application scenario. These tests are used to determine the IP protection level against solid objects and liquids for standards up to IP69k. Various temperature resistance tests examine how the vents react to changing temperature cycles, extreme temperatures of -40 to +150 degrees Celsius, as well as high humidity. The vents are also subjected to particularly demanding environmental conditions, for example in the hail test, in the salt-spray test that simulates coastal conditions, and to the corrosive gases found in smog and acid rain.
Intelligent vents for smart cities
Modern vents that feature an ePTFE membrane with very fine pores are the most effective, long-term method for protecting sensitive sensors and radio modules against pressure and temperature fluctuations and other environmental conditions. By ensuring a continuous exchange of air, they are a reliable way of equalizing pressure and of providing the sensitive electronics with long-term protection from liquids and dirt particles. Since different smart city applications require different vents, Gore offers three variations: Screw-In Vents offer considerable mechanical stability and are easy to mount; Adhesive Vents are especially compact and can be flexibly integrated into even the smallest electronics housings and Snap-In Vents are ideal for fast, partly or fully automated assembly, making them suitable for cost-effective, mass-produced housings.
WiFi data transfer example
In smart cities, sensors and concentrators are used to measure how much CO2 or pollen is present in the air and relay that data over WiFi to the appropriate organisation – health authorities, for instance. These electronic devices must be protected from environmental conditions so that they can deliver reliable measurement data throughout their service life. If the sun shines on the housing on a cold winter morning, the temperature inside can very quickly go from -20 degrees Celsius to +40 degrees Celsius.
The graph shows how a vented housing equalizes the pressure within two minutes. In an unvented housing, however, a pressure of 225 mbar builds up that stresses the seal and can eventually damage it.