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But, for electronics systems, the outdoors poses many threats. Almost everywhere you look in an urban setting there are delicate electronics that are enclosed in cabinets. For example, there are kiosks, advertising displays, ticketing machines and boxes housing the systems for our telecoms and railway infrastructure.
Even in countries that do not normally suffer the worst events that the weather can bring, it can still provide the biggest challenge for designers of outdoor equipment. Temperate climate areas without weather extremes, like hurricanes and tornadoes, can still see unprotected electronics destroyed in a short period of time. Rain, snow and fog all offer a danger of moisture ingress through the casing joints and other openings. Even the relatively mild summer heat can cause problematic overheating in enclosures that don’t have an effective cooling system in place. Ice formation over cooling vents can also cause issues.
Electronics to be situated in outdoor areas must be housed in cabinets that are specially designed for the environment. If they are not, then corrosion can quickly become a problem. Initially corroded areas can allow excess moisture into the cabinet, and, if left unchecked, the corrosion can develop into larger holes that allow access to people and animals.
Humans are a large threat to any electronics systems in the outdoors. It is not unusual for vandals to destroy the enclosures, or even any parts of the system outside the box, such as touchscreens or switches. It makes no difference if the enclosure is in a public area or a restricted area; the enclosures are at risk if weakened by corrosion. It is not only vandals that pose a risk, there is also a threat of people gaining access to enclosures to try to get access to services that they haven’t purchased. In some areas, such as railway trackside cabinets, damage can be very expensive to repair. Fortunately for those looking to implement outdoor designs, there are solutions and products on the market that can make the process of protecting outdoor electronics systems much easier.
Enclosures is one area where improvements over the years have led to designs that are able to protect electronics from the elements, while keeping internal components at maximum operating efficiency. Choosing the correct casing for each application will depend on the exact environment in which the enclosure is situated and the need to secure the electronics from outside interference. There is a variety of choices available in the market, including size, dust and moisture ingress protection, cooling, locking, and access options.
To look at a real world example, Schroff has three ranges of cabinets intended for outdoor use. All three are built from corrosion-proof aluminium and offer dust and moisture protection to IP55. The three ranges also offer an electrical door locking system, which has been designed to provide a tougher challenge to intruders by having three locking points instead of one single point. The enclosures can be configured to unlock from either the front left or right. For flexibility, the enclosures also allow a range of options that allow the cases to be mounted on poles, walls and on the ground.
The entry-level range is named Comline, the middle range Unibody and the premium range Modular. The Comline range has a single wall and is cooled by circulating air through its vents, while the Unibody and Modular ranges have double walls and have a choice of two cooling options: The VENT system, which is a side mounted fan that provides up to 35 W/K cooling, or the HEX system, which uses a door mounted heat exchanger that offers cooling up to 70 W/K. There is also a heater option for enclosures used in colder environments to stop the formation of condensation. The main difference between the Unibody and Modular ranges is that the Modular range has inner and outer removable walls to allow easier access to the electronics, while only the Unibody range’s outer walls are removable. The Modular range also comes in a 1330mm double door option.
Figure 1 demonstrates Schroff Unibody enclosures in actual use. Figure 1a is a Unibody cabinet being used in a meteorology application to record data. The cabinet has to withstand both strong winds and thunderstorms. The enclosure is mounted on a mast, and the electronics are cooled by a fan mounted between the inner and outer walls. The enclosure also has a heater to deal with colder weather conditions. The second image, Figure 1b, shows Unibody cabinets being used for an application overseeing the voltage in cables for the railway. On this occasion, the cabinets are mounted on a wall. There is no need for active cooling in this application, so convection cooling is used to decreases noise and save energy.
Figure 2 demonstrates two practical examples of how the Schroff Modular cabinets have been used in the field. Figure 2a shows two double door Modular cabinets that are being used for VDSL distribution. The enclosures are cooled by fans in the top panel. The air is circulated between the walls to keep the ambient temperature low, while the inside walls are sealed to offer protection to the internal electronics. Batteries and ducting for cables are installed in the cabinet’s stainless steel base. Figure 2b shows a cabinet housing a power supply for mobile communications. In this case, the cabinet is a custom design, based on the Modular range, which has a heat exchanger in the cabinet’s door.
Cabinets that are designed for public use require strong and rugged enclosures, but they must also feature additional protection to interface components to protect them from the weather and vandalism. For applications, such as kiosks and ticket machines, anti-vandal switches are often used to allow access to the application’s features, while protecting the internal electronics.
Schurter’s stainless steel Metal Line series is a good example of the type of features that switches and buttons can offer designers of outdoor applications. Buttons range in size from 16-22mm, can perform up to 20 million activations and are certified to IK07 (DIN EN 50102) for withstanding mechanical shock. They can use either stroke activation or piezo impulse technology. The PSE series, which use piezo activation, can offer environmental protection to IP67, and the classic action MSM series ranges from IP40 to IP67. The devices offer visual activation feedback, in the form of spot or ring lighting. These options are demonstrated in Figure 3.
These buttons and switches have the potential to be used in a large number of applications outdoors, including in installations that have to suffer large temperature swings. The PSE range especially, has no moving parts and is therefore not susceptible to icing. The IP67 environmental protection also means that they are protected from the dust that is often found around outdoor installations.
Although the outdoors can prove a tough environment for electronics systems, choosing the right cabinet and interface components can ensure that the installation is safe from both extreme weather and vandalism for years.
Figure 1 - Schroff Unibody cabinets in the field. (a) Meteorology cabinet. (b) Railway voltage monitoring cabinet.
Figure 2 - Schroff Modular cabinet designs. (a) VDSL cabinets with fan cooling. (b) Mobile telephony infrastructure cabinets with heat exchanger cooling.
Figure 3 - Schurter MSM Metal Line pushbutton switches come in 7 luminescent multicolour options.
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