There are many factors to consider when installing wireless devices into a hazardous area. One area that should not be overlooked is the impact of the environment in which your chosen device is going to be deployed in.
In this article we consider key factors that can affect the success of a hazardous area wireless installation
1 – Materials of Construction
Often hazardous areas are also subject to extreme weather conditions or corrosive substances. It is therefore extremely important that the materials of construction used in any Ex enclosure be carefully considered to ensure the product can withstand the extreme condition long term.
For instance, when installing an Ex wireless enclosure into a marine environment the material of the enclosure becomes paramount for a successful installation. When we think about marine environments in the process industries, we often think about offshore platforms, but the same material consideration must be given to process plants by the coast in a hot humid environment. In a hot humid environment, the saline atmosphere can be very corrosive and if the correct materials are not used the equipment will soon become corroded and eventually fail.
Typically, a high-grade marine aluminum with special coatings should be selected or stainless-steel constructed enclosures. In some cases, nonmetallic enclosures that use glass reinforced polyester can also provide a high degree of environmental protection. It’s very important to ensure the enclosure is designed for these extreme environments otherwise what looks good when first installed will soon be a liability to the owner.
2 – IP Rating
The minimum level of IP rating for an outdoor Ex enclosure is IP54, but this level of protection is not suitable for extreme outdoor environments. In these environments the minimum level of protection that should be considered is IP65. IP66 provides a higher level of protection in applications that are exposed to high volumes of liquid for clean downs or deluges such as on an offshore platform or ship.
3 – Ambient Temperature
When installing a wireless radio device into your hazardous area it is important to consider the operating temperature. Most standard indoor wireless radio devices will likely only have a 0°C to 40°C operating temperature range and would be unsuitable for extreme hot or cold environments. A truly industrial Ex wireless device must have an operating temperature range of -40°C to over +50°C to provide reliable performance in the most extreme environments.
It is also important to consider the heat rise that your chosen wireless device will be subject to by being installed in an Ex enclosure. It is not uncommon to see a heat rise of 0.5°C per Watt of power dissipated. For example, a 25W WiFi access point could generate a 12.5°C heat rise. This heat rise must be added to the upper temperature limit. If your enclosure is subject to extreme cold, then enclosures can be fitted with heaters to ensure that the lowest temperature the wireless device is exposed to is within its normal operating temperature range.
For example, if an indoor rated WiFi access point (AP) is only rated up to 40°C and there is a 10°C temperature rise within the enclosure, the enclosure should be installed in an area that would not exceed 30°C, otherwise the WiFi AP will be exposed to temperatures outside of its rated range.
For this reason, it may be better to fit outdoor or industrial indoor AP’s inside the enclosure because they typically offer a wider range of operating temperatures.
4 – Solar Loading
Solar loading is often overlooked but can cause significant operating issues if not addressed. The heating effects of the sun can be considerable, especially in hot climates. If not properly protected the surface temperature can rise to considerably dangerous levels, especially if the enclosure is dark in colour. When specifying your enclosure, be sure to understand the potential solar loading effects for the area where the enclosure will be installed.
Enclosures designed for outdoor high ambient temperature environments will have been thermally engineered. The use of light colours helps reflect the suns heating rays and minimizes the amount of heat conducted into the enclosure. It is also possible to provide sunshades if the heating effect is deemed to be too large. When using a sunshade, consideration should be given to the material of construction as it may affect the RF propagation and thus the wireless performance. It is also important to ensure the shade is made from an anti-static material. This is because the large surface area of the shade could become an electrostatic ignition hazard.
Image caption: Sunshade on iWAP 107
5 – Metallic Environments and the Effects of Multipath Interference
One of the most common challenges seen in almost all process industry sites is the effect metallic structures have on the wireless signal. It is essential you chose a device and enclosure system capable of operating in a dense metallic environment. These tend to be on large process plants such as refineries, but they can also exist in smaller chemical plants or on offshore platforms and FPSO’s.
Typical communication wireless signals will not penetrate metal, so the complete signal is attenuated and therefore no communication link is possible. Many of these areas include metal rooms or walkways with bulkheads, scaffolding and pipes, making it very difficult to obtain a strong signal. When designing wireless networks for these dense metallic environments you must consider the position of your wireless enclosures and the density you need to obtain the required performance levels.
Another phenomenon that must be considered is the effect of RF multipath interference.
Radio signals will bounce off metallic structures and this causes the wireless signal to be received multiple times by a receiver. This can mean signals are received out of phase and cancel each other out. This results in a poor or no communication link.
Image caption: Multipath interference diagram
Certain radio technologies have evolved to be tolerant to this and use multipath interference to increase the bandwidth. For instance, MIMO radios have become common place nowadays.
Technology, such as 802.11b/g WiFi was fine in line-of-sight applications but became useless as soon as it was deployed in heavy metallic environments with severe multipath interference. This was one of the main reasons that held up the deployment of WiFi in the process industries. The advent of 802.11n WiFi was a game changer in that it was the first WiFi standard to utilise this radio technology. It made it as practical to use in a refinery processing unit as it did in an office.
For more information or to see how Extronics can help you with your hazardous area wireless connectivity, please contact a member of our team on +44 (0)1606 738 446 or email us at firstname.lastname@example.org.