The other option of course is to pressurise the box with dry air to ensure a positive pressure differential, such that the net flow is always outwards at all points, but it's probably easier just to provide a drain hole:-) However, whilst a drain hole will prevent the build up of a lake inside the enclosure it still doesn't prevent condensation forming on circuit boards, and powered circuit boards and condensation don't really go well together. As per earlier comments, it's quite difficult to keep any externally mounted enclosure totally moisture free, so it's much easier to accept the inevitable and allow for it. In a past life I designed quite a few circuit boards that were required to be fitted in externally mounted vented enclosures, so not a great deal of pressurisation there then:-), and I usually specified that both sides should be sprayed with a plastic coating following final test. I can't remember now exactly what this stuff was called, but it was readily available in the UK from both RS and Farnell as an aerosol plastic spray that provided a good barrier but was a bit more flexible than the usual MOD spec conformal coatings. It melted easily under a soldering iron, albeit with a foul pong:-), so reworking was no problem, and resisted moisture remarkably well..... problem solved:-) Nigel GM8PZR In a message dated 14/05/2012 23:10:30 GMT Daylight Time, [email protected] writes:
The only solutions I think: Apply air pressure tight boxes having a breathing hole an the bottom, mount the box that no rain and water can penetrate from the top or sides. If the hole is big enough, eg. 2mm, no pressure difference is possible and no pumping effect will occur. (If the hole is too wide, small animals may penetrate). Or, when using a pressure tight box, it must be stiff and sealed to withstand under all temperature conditions more then 1 bar/ 100 kPa. Do not forget that all feed throughs must be of real hermetic type, normal coaxial connectors are not tight! Don't route cables directly in, because no cable braid or mesh is vapor tight. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
