6 DESIGN CONSIDERATIONS FOR EX CERTIFIED WIRELESS ENCLOSURE SYSTEMS

There are a few important steps to go through when determining the suitability of an Ex certified wireless enclosure system for the chosen wireless device. It is important to ensure it is still compliant to the Ex certification, does not invalidate other product certification such as product safety and make sure that the wireless device performs as the original manufacturer intended, especially from the RF signal perspective.

The key points you must go through when installing an Ex wireless solution into a hazardous area are summarized in this article.

1 – Does the wireless device meet the parameters set out by the Ex certification requirements?

  • Operating voltage
  • Regulatory compliance, such as product safety e.g., EN62368
  • Maximum power dissipation allowed in the enclosure
  • Cross sectional area and volume stipulations for Ex d explosion proof certified enclosures.

2 – Will the wireless device fit in the enclosure?

It is important that size is taken into consideration to ensure any future maintenance is trouble free. It is critical to avoid compromising the routing of the RF cables to the external antenna ports and tight bend radiuses of the internal RF cables to ensure RF performance is not affected.

It is also worth noting that in the US you cannot buy an empty enclosure and install your choice of wireless device yourself. This would invalidate the manufacturing facility and process audits required for all Ex-manufacturers. In the US, all installations must be checked and signed off by an Authority Having Jurisdiction (AHJ) appointed by the state to ensure OSHA rules are applied correctly.

3 – Does the device require North American certification?

If the Ex Certification is for North America the notified bodies stipulate that any equipment inside the enclosure must be certified to an appropriate UL safety standard by an NRTL. This can often be a challenge because many wireless devices will have been tested for product safety to a standard such as IEC62368, but they were not done by an NRTL.

They can still be sold in the North American market without concern because they are classed as low power equipment so don’t need to have an NRTL safety approval, however, for Ex certification under the NEC500 or NEC505 it is a requirement. This can present a serious challenge and restrict the possibility of installing the chosen device in a hazardous area. Extronics wireless enclosures have been designed to overcome this issue and our internal processes and protective components allow such devices to be installed.

4 – Can you achieve the required RF performance?

The RF path is very important to achieve the same level of performance from the standard wireless device when installed in an enclosure.

High quality low loss RF cables and connectors with a minimum bend radius are essential to obtain maximum performance. If using intrinsically safe RF barriers standard antennas can be used – ensure that these have a low insertion loss.

Finally, when direct mounting antennas to the enclosure it is important to ensure that the antenna ports are optimally spaced for the radio frequency concerned when using devices that have multiple antennas such as MIMO radios. If the antennas are installed too close or even too far apart this can affect the RF performance. These key considerations should be carefully addressed to ensure the standard wireless device will provide the required level of performance when installed in a hazardous area certified wireless enclosure system.

5 – Do you require more than one device in the same area?

In more recent times, it has become common place to install multiple wireless devices into the same enclosure system. This is often done to cater for specific use cases or to utilise the best wireless technology available from different manufacturers. For example, combining WiFi with WiHART or WiFi with LTE are quite common use cases across the process industry.

Ensuring that the antenna port spacing provides suitable RF isolation between the two radios is essential as they can interfere with each other. This only applies in applications where the antenna is directly mounted to the wireless enclosure. A typical value of isolation required to prevent a transmitting radio saturating the receiver of the other radio is 30dB to 40dB.

The wireless devices can even interfere with each other when working on different frequencies. Ideally, the devices would be spaced more than a meter apart but that is not possible when installed inside the same enclosure. There are two practical options available in this scenario. Firstly, one antenna can be remotely mounted to create the required distance. If remote mounting is not an option, then mounting one radios antenna on the top of the enclosure and the other on the bottom will usually provide the appropriate level of isolation.

6 – Antenna port spacing

Antenna port spacing on the enclosure is important when using MIMO radios. MIMO radios typically have 3 or 4 antennas per radio. The spacing of these ports from one to the other is important to ensure optimal performance when omni directional antennas are mounted directly on to the enclosure.

For more information or to see how Exloc Instruments can help you with your hazardous area wireless connectivity, please contact a member of our team at 281-978-2040 or sales@exloc.com.

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