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June 2006

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Subject:
From:
"Barmuta, Mike" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Barmuta, Mike
Date:
Thu, 1 Jun 2006 10:48:46 -0700
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Brian: In general I agree with you. Let's not over test more than we have to. Although it may be hard to quantify what is excessive.

I think part of the rationale for doing humidity/temperature exposures at higher than practical conditions is based on the product being built.

Example: Your product has sensitive circuitry that can be influenced by moisture/high humidity condition resulting in leakage paths or signal alteration. Then instead of testing at 35C/75% you might want to use a slightly higher condition such as 35C/85% to prove out the design. Then use a similar approach to monitor material and processing conditions to provide an acceptable product. 
Set the bar a little higher than needed i.e. at 11/10ths to assure day in and day out product quality.

Let me give you an example (similar to yours below) of where higher than ambient achievable testing conditions may be needed. If you are manufacturing HVAC test and measurement equipment you could be going from a -20C refrigerated environment to an outside 35C+ high humidity condition such as the Florida Keys. This can cause moisture conditions to form in the meter which can effect the measurement circuitry resulting in an inaccurate reading. 

In this case you should be testing at higher than the 35C/75% real world condition.


                                                                                        Regards
                                                                                                        Michael Barmuta
                                                                                                        Staff Engineer
                                                                                                        Fluke Corp.
                                                                                                        Everett WA
                                                                                                        425-446-6076

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Thursday, June 01, 2006 7:02 AM
To: [log in to unmask]
Subject: [TN] Do we exaggerate?

I have discovered that there is a real limit to the conditions of
natural temperature and humidity that are possible. To put it simply, if
the temperature and humidity are high at ground level, clouds will form
at a given altitude, reflecting solar radiation. This will result in a
lowering of the temperature. I haven't yet determined the exact limit
conditions, but it would seem that (very roughly), you can obtain 100%
RH only if the temperature is under about 15°C. At 25°C, the max
humidity is ~85%. At 35°C, 75%. At 50°C, 55%.

When I have more exact data, it is clear I'll be able to determine a 
limit curve, on the right side of which it will be impossible for 
natural conditions to exist. However, we can create conditions in 
climatic chambers which will be far to the right of the curve, and we 
use such conditions in SIR/ECMR testing. Are we exaggerating when we 
pump up the temperature and humidity to excessive levels, to create 
conditions which can never occur in real life? Is there even a rationale 
to do so? Remember that the inside of an enclosure with active 
electronics is warmer than ambient. The real dangerous conditions are 
with high humidities, which can occur only at artificially low 
temperatures, such as when going into a tropical rain forest conditions 
from an over-air-conditioned room (e.g., 20°C to 30°C/80% RH), when 
condensation may occur for a short time.

Views are welcome, please.

Brian
-- 
http://www.cypenv.org Cyprus environment/energy
http://www.cypenv.org/worldenv World environment/energy
http://www.cypenv.org/weather Cyprus weather
http://www.cypenv.org/smf/index.php Environment/energy forums
http://groups.yahoo.com/group/cypnature/ Cyprus nature forum

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