We’re often approached by companies who have designed a prototype system composed of networks sensors, cameras, GPS systems, and other elements with compute platforms over Ethernet. These prototypes often use commercial-grade Ethernet switches. Sometimes they use the enclosure, sometimes they pull the components out of the enclosure and try to jerry-rig the switch components in some sort of fashion. What they soon find out, however, is that these commercial-grade switches (and other commercial-grade componentry) do not stand up the rigorous environmental factors that mobile military and aerospace applications almost always run in to.
So, they ask, how is a MIL-STD Ethernet switch different? Why should they spend the additional money on it or how can they justify the added expense to their superiors or purchasing agents? To help define those differences, here a quick list of how commercial Ethernet switches vary from MIL-STD Ethernet switches.
1) Ground-up rugged componentry: MIL-STD Ethernet switches are designed and produced, from the ground up, with MIL-STD, more compact components such as PCBs and power supplies that are produced to meet more rugged specifications. To ensure that they can handle extreme environmental conditions, components are tested to the MIL-STD 810 specification. They also meet higher electromagnetic/radio frequency interference (EMI/RFI) requirements. MIL-STD 461 is the standard to ensure that these components are shielded from electromagnetic interference enabling operation at required levels. EMI and RFI filters are often added to assure this performance.
2) Power supplies and protection: Mobile military platforms usually have unstable power sources, which is problematic for most commercial and sensitive electronic componentry. We all know that the slightest power surge can destroy our typical commercial-grade computer or electronic device. Therefore, MIL-STD Ethernet switches must have rugged power supplies that can: support a wide range of power inputs (this can vary from 6 VDC-32VDC depending on the vehicle and power source); be shock and vibration-proof; have built-in protection for extreme spikes and ripples; maintain efficiency at high temperatures; have built-in reverse polarity protection; and be immune from external EMI/RFI interference. For military vehicles, power supplies should meet MIL-STD 1275 requirements. For aircraft environments, they should meet MIL-STD 704 requirements.
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3) Passive cooling so there are no moving parts. We all know that moving parts in electronic devices are, by far, the most frequent point of failure in any device. In commercial switches and routers, cooling fans are one of the most necessary, yet antiquated components with the lowest meantime between failures (MTBF) under normal operational conditions. Cooling fans simply won’t hold up in harsh, military environments. MIL-STD devices must be designed with components that put out lower amounts of heat, and the housing must be designed to maximize contact with external air for the release of internal heat and the absorption of cooler, external air. These “cooling system” housings are always designed with the location and position of the installation in mind. For more challenging projects, “cold-plates” can be added to provide liquid cooling and remove the heat from the switch.
4) Conformal coating: Conformal coating material is a thin polymeric film which ‘conforms’ to the contours of a printed circuit board to protect the board’s components. It helps prevent corrosion under extreme condition, it also provides additional adhesive for components to support shocks and vibrations. Even though MIL-STD switch manufacturers attempt to use the smallest components available on the market, sometimes they have no choice but to use larger components that might be more susceptible to vibration and movement. Conformal coating helps to “glue” those components to the PCB and stabilize them. Finally, some components in an Ethernet switch are manufactured using pure tin. Pure tin can spontaneously grow conductive “tin whiskers” of electrical paths that can affect the EMI/RFI of the components. A nice side-benefit to conformal coating is the reduction of the “tin whiskering” effect.
5) Sealed connectors: Commercial RJ-45 connector and power cords connect to commercial devices in ways that make any device or connector subject to environmental elements that MIL-STD devices have been designed to protect against. MIL-STD connectors won’t allow dust, water, or debris in to device. IP-68 rated connectors should allow you to plug and unplug a device under water and the device should remain operational. MIL-STD connectors are also designed with a twist and connect operation that prevents typical disconnects through vibration. Scoop-proof designs prevent bending the pins while inserting them and a blind insert design creates a pin pattern that enables you to insert it without looking on the connector. These connectors also come standard with EMI/RFI shielding, high MTBF [mean time between failure], come with a mix of signals in to one connector (power, data, fiber) and are made with lightweight materials..
6) Ruggedized housing: Finally, one of the most obvious features of a MIL-STD switch is the ruggedized housing. Ruggedized housing is built and totally sealed so that it performs, as specified with no degradation, when exposed to shock and vibration, fluid contamination (water, oils, humidity, etc), corrosion, and direct sun exposure. For water and humidity protection, ruggedized housing should be designed to meet the IP68 water immersion rating which means they are sealed with O-rings and can stand full water immersion as much as 3 meters in depth. For example, when washing trucks or tanks with an installed router there will be no need to remove or cover the device. Also devices installed on autonomous underwater vehicles will continue to operate even when submerged under water.
There are a number of other features built-in to MIL-STD designs, the list is long, but I think I’ve covered the key factors here. If you have more questions, please feel free to reach out to me. RI@milsource.us.
