Look into conformal coatings such as Miller Stephenson MS-460H <http://www.miller-stephenson.com/products/detail.aspx?ItemId=56> or MG Chemicals. Sealing all the connectors and sockets will be a problem, but you can get a silicone paste used in sealing connectors such as in irrigation systems. Check out the 3M Scotchlok connectors <https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0CE0QFjADahUKEwjLx8WkjNvGAhVNoogKHfGRCK4&url=http%3A%2F%2Fsolutions.3m.com%2F3MContentRetrievalAPI%2FBlobServlet%3Flmd%3D1413989307000%26locale%3Dpt_PT%26assetType%3DMMM_Image%26assetId%3D1361822756031%26blobAttribute%3DImageFile&ei=DEClVcuRKc3EogTxo6LwCg&usg=AFQjCNGRv6hQtATKwOJJQKu4-Gx-sFpcTw&sig2=6bALbBmsLoRqH9wSS-57jw> which we are testing now in fresh- and salt- water aquatic environments. I like the suggestion of immersing the whole board in some nonconductive, preferably hydrophobic fluid, maybe something on this list <http://www.electronics-cooling.com/2006/05/an-overview-of-liquid-coolants-for-electronics-cooling/> ?
Lightning may be an issue. There are various ESD protective devices. We have used them on Ethernet connections and had good survivability of our (now obsolete) systems used in weather stations where a competitor's (without such precautions) got taken out repeatedly. So consider where any wires enter the enclosure, protect them from ESD and surges, and make your enclosure a Faraday cage. We've have systems we designed in field for more than ten years and still working. Some are used on thruway systems (I'm not sure exactly how), some are in dairy plants, etc. We got back one system a while ago - it had been (accidentally filled with milk which over time curdled and rotted and became conductive and eventually 120V in the system (we voted against having any mains power in the enclosure but were overruled) arced through the milk pudding and killed everything. This system had red 7-seg LED displays which must have been observed to get cloudy as this situation developed but no one did anything until it died. It was a stinky charred mess when we opened it up. They asked if it could be repaired... but I digress. Heat is the enemy, any liquid paste electrolyte caps or batteries will die. You want all solid caps. Redundancy is good. Look at the aging data for components and don't push their operation to the edge of voltage or temp and design to the worst limits of aging, temperature, power supply, etc. Over the years I'd say 90% of system failures we see are the power supplies (usually customer-supplied for one reason or another), so if they are solid you should be good. We typically design local on-board regulators and fuses (sometimes sacrificial PC board traces feeding a heavy zener diode) and have lost very few systems even when power supplies have failed. Then we feed a group of boards with a higher voltage (12V or 24V more recently) DC supply which is locally down-converted where used. The raw supply can fade or misbehave a lot and still not take out the local boards. On a good day you get what you pay for, so use good quality components designed for the task and you'll be happy later when your phone doesn't ring with in-field problems. best regards Bruce Boyes -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
