[time-nuts] wwvb weak on east coast especially when the pre-amps under wa...

[Michael Blazer]

Here's comparison for various type of conformal coating: 
http://mgchemicals.com/downloads/appguide/appguide0404.pdf.<https://assist.daps.dla.mil/quicksearch/>

I think there is a type that is 'serviceable' and removable with alcohol.

Mike

On 5/14/2012 6:01 PM, GandalfG8 at aol.com wrote:
> 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,
> arnold.tibus at gmx.de 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.
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