If I follow you here I guess I would make the measurements just
before the product bursts into flame, unless of course it actually does
stabilize because of thermal mass constraints.
In following my own experience and what I have read on this
discussion 1 degree rise in 15 minutes seems to satisfy the needs for
temperature stability, particularly when you eliminate any perturbation from
a change in ambient over that period.
In practice with ITE equipment I don't think I have every seen anything
longer than 4 hours, and the norm is probably more like 1 to 2 hours max. If
you think its going to take a grunch of time start the test before you go
home for the evening and check in the temp a couple of times in the morning.
Your point that the standards should draw the line and identify end
conditions is well taken but they are not. I would rely on your own
engineering judgement and relized that if the agencies haven't defined
something they don't have any firm ground to stand on to tell you no, so you
can usually reach a logical consensus. If the first guy doesn't agree get to
his reviewer.
Gary
-----Original Message-----
From: Dan Mitchell [mailto:[email protected]]
Sent: Wednesday, June 28, 2000 3:52 PM
To: Peter Tarver
Cc: [email protected]
Subject: RE: UL1950/UL2601 Thermals
Fine and dandy, but when do you draw the line. If you have a product that
slowly increases at less than the 1 deg C in 15 minutes after say 2 1/2
hours, do you keep on testing it say 5 hrs, or 10 hrs, 15 hrs? This could
cause excessively long test times if you are a very zealous person who
follows the letter of the standard (because there is no time limit, or temp
vs. time limit).
Daniel Mitchell
Product Safety Engineer
Condor DC Power Supplies, Inc.
<<snip>>
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