Popeye's electronics 2

[zappedagain]

Well, my customer wants to operate his laboratory equipment in a 'salt-air' environment... for a few hours occasionally'. Eek! Now sales wants to know what it would take to 'harden' the existing design.

It has been a long time since I was involved in harsh environment design. Here are concerns I can think of:

- condensation (leakage currents)
- corrosion (PCB traces)

Above fixed by conformal coating; I expect the power supplies would be the first to go. The fans that are busily cooling the system with all that 'fresh' air might be second.

- connector corrosion
- wire insulation - any degradation

What else are concerns? Can you recommend a good reference for harsh environment design?

Thanks,

John D

 

[mcgyvr]

any reason they can't simply keep the electronics outside of the enclosure and run the wires in through a bulkhead or something?

 

[IRstuff]

Connectors and connector pins simply require a decent environmental seal. I would think that 38999 connectors would be up to that task. There are systems that operate 24/7 in a marine environment, so it should be manageable.

We've had thermal control units with fans, and as far as I know, they were never a failure item. With some judicious application of strip heaters, you could minimize exposure to condensation in critical areas.

TTFN

FAQ731-376

 

[ScottyUK]

We used fans with ceramic bearings because of corrosion and very high wear rates due to a coastal environment with a steel works to one side and a heavy chemicals plant to the other. Steel bearings used to have a short and troubled life - ceramics did very well.


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If we learn from our mistakes I'm getting a great education!

 

[zeusfaber]

If your equipment is air-cooled, then internal connectors and associated wiring are likely to be a vulnerable areas.

Unless your insulation is prone to wet-tracking, wiring problems are more likely to come in the shape of degradation of the conductor and of any soldered terminations. All the insulation does most of the time is conceal the damage.

Anything you can do to coalesce the salt mist out of your cooling air before it goes anywhere near the inside of your enclosure is going to pay dividends. Once the salt gets in, it sticks to everything and will continue to rot the electronics every time the air is humid enough to let the salt deposits get damp - even long after the equipment has been removed from the salty environment.

For shipboard equipment that only runs intermittently and is subject to swings in ambient temperature, it's common to fit anti-condensation heaters in the bottom of electronic enclosures. As well as keeping the air inside above its dewpoint, these help keep any salt deposits dry.

A.

 

[VEBill]

The applicable military standard is MIL-STD 810F. Test 509.4 is the Salt Fog test method.

The basic way to meet this requirement is to seal the box. If you need cooling, then use a heat exchanger or a sealed heatsink. Using fans would probably add complexity and headaches; better to ban them at the start and avoid the redesign cycles. As already mentioned, use sealed connectors such as 38999-series.

 

[IRstuff]

temp-humidity too, I would think. Also from MIL-STD-810

TTFN

FAQ731-376

 

[zappedagain]

Thanks all! My control electronics can get mounted in an environmental enclosure. My sensor head and the associated cabling needs to be out in the salt-air environment.

810-F is interesting reading.

John D

 

[rovineye]

Maybe you can use VCIs. Vapor-phase Corrosion Inhibitors are foam emitters through which the corrosion inhibitor is slowly released and moisture and air pollutants can enter to be absorbed. It provides long-term protection against corrosion even in the presence of adverse conditions including salt, moisture, and airborne contaminants.

I use them in non-ventillated enclosures but they might work in other applications. There are several manufacturers.

 

[zappedagain]

Ooh, that's a star for you! I learned something new today!

John D