Very well placed point Brian!

A thing that makes a difference between the heavy industry and civil engineering, on one hand, and the electronics industry on the other is that in the heavy world you can compute almost everything. Based on stress, strain and safety coefficients, man has developped formulae that can be used to optimize constructions and you can get minimum material consumption at minimum labor costs. This is why we can build bridges, sky scrapers and roller coasters and know they will not collapse.

This is not exactly true for the electronics world. With the exception of reliability, there doesn't seem to be much calculus involved. We cannot even compute if a panel will warp in the oven or not. Why? Maybe because the industry is still young and there is not enough empirical data for developping efficient models.

So my bet is that you are right, we definately exaggerate, to buffer up for the unknown.

Ioan

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis
Sent: Thursday, June 01, 2006 10:02 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
-- 
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