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Electronics => Beginners => Topic started by: metrologist on April 24, 2017, 11:06:26 pm

Title: Humidity Spec
Post by: metrologist on April 24, 2017, 11:06:26 pm

I'm trying to recall how humidity specs are applied. I'm looking at a dewpoint chart, and cannot remember how to interpret it.

I think the spec is to indicate a condition where condensation on the circuit results, or something similar. So, if the max non-condensing humidity spec is 95% at 30C, does that mean that 95% at 40C is still OK or would the temp need to be 30C or less?

Title: Re: Humidity Spec
Post by: metrologist on April 25, 2017, 04:29:59 pm

Is this just too painfully obvious or really too tuff for the beginners forum?   :-//

Title: Re: Humidity Spec
Post by: Ratch on April 25, 2017, 06:47:55 pm

Quote from: metrologist on April 25, 2017, 04:29:59 pm

Is this just too painfully obvious or really too tuff for the beginners forum?   :-//

You would do well to read this link.  http://www.shorstmeyer.com/wxfaqs/humidity/humidity.html (http://www.shorstmeyer.com/wxfaqs/humidity/humidity.html)

Ratch

Title: Re: Humidity Spec
Post by: metrologist on April 25, 2017, 07:57:52 pm

The article was getting difficult to read, and I still question if I am understanding the words correctly, or at least understanding them well enough to apply to my situation.

Here is from Myth #1, that warmer air holds more water:
CORRECT TERMINOLOGY:
ON A WARM DAY MORE WATER CAN EVAPORATE BECAUSE
THERE IS MORE THERMAL ENERGY AVAILABLE TO DO THE WORK OF EVAPORATION.

In order to claim a mil spec, the non-condensing RH has to meet 95% at 30C. The spec I am reading says non-condensing RH is 95% at 40C. To me, that says it does not meet the spec because a higher temperature is needed to prevent the associated problems with condensation that would result from the lower (30C) temperature.

The mil spec continues with two footnotes that say:

RH 75% above 40C
RH 45% above 50C

So now I am not sure if the spec I am reading means it exceeds the mil spec, because at 40C it can handle 95% humidity and the mil spec only limits to 75% at that temp.

Title: Re: Humidity Spec
Post by: metrologist on April 27, 2017, 03:56:59 pm

Someone finally explained it to me in a way I could understand. I kept thinking of water on my circuit and if it would be better to dry that out 30C vs 40C. It seems intuitive that 40C would evaporate more water and dry off the circuit.

But the atmosphere at 40C has a greater water density than when at 30C, if RH is 95% in both cases.