High Humidity Design

[cwerther]

I'm designing some add on's for my telescope (mirror fan control, temperature sensors, etc) and depending on the time of year it can easily be operating in the 90%+ relative humidity range.  Do y'all have any suggestions for circuit design for high humidity environments?

[Benta]

Nothing special on circuit design, but conformal coating the assembly comes to mind.

[Neomys Sapiens]

Also it would be advisable to use a 'breather valve' with a semipermeable membrane so that vapour can get out. Further, use proper cable glands. Select connectors for external connections which are sealed back and front. Maybe use a heater (resistor) in the electronics too to drive any humidity out.

[cwerther]

Thanks for the suggestions.  I hadn't considered the breather valve.  I'm not sure how I feel about just using the heater, but hey, when it works, why not?

[coppice]

Consider connector materials carefully, as you can seldom fully seal them from the environment. For example, in modest humidity areas you might have used silver plated connectors for your RF stuff without any problems. Try putting them in a warm moist environment, like Singapore or Hong Kong, and they go black in days. Other materials may not perform as well from an RF connection point of view, but you will need to tolerate them for their greater longevity.

[coppice]

I'm not sure how I feel about just using the heater, but hey, when it works, why not?

What happens when the heater is off? There is nothing to stop condensation then, and it might cause corrosion. What interlocks will you have, so things don't start up until the heater has had time to dry things out?

If the equipment will be subject to regular inspections, you might look at trying to seal up some areas as well as you can, and put a desiccator inside. Desiccator replacement can be part of the inspection.