Yes,My first experience with that was a 300 lb piece of equipment. I figured the thermal time constant should be many hours. It took me several hours of waiting to finally realize my ambient temps were also cycling. It was the air conditioning in my case as well. The German inspector from LGA sug
Doug et al,
Well, you don’t have to have 100K lbs of equipment to get
porpoiseing.
I remember a 500W product project where the test house engineer came in to
witness the testing and was disturbed by the porpoiseing swings when the
product temp seemed stable. He finally
My experience is that agencies frown on any form of averaging. So my approach
is to monitor it or all maxima and apply the +/- 2 degree rule. If it so
happens that these cycles was wide spread (greater than 15 minutes, I simply
take the last three maxima and check for +/- 2 degrees. If I have
Correct, so for multiple duty cycles or varying loading intervals, possible
solution would be to use windowed average (queue size based on 1/f and dT/dt
and previous sample interval) with a 'delayed' least-squares fit thru the
maxima to see if flat. [hear the ghosts of my math instructors yellin
Standards can't necessarily cover every possibility. For cyclical effects, I
would say that conditions are stable if two successive temperature maxima are
equal (within a reasonable tolerance). This doesn't necessarily work if more
than one cycle frequency is involved, in which case you have to
Thanks!
I'll take a look. I generally log with LabView or direct into an Excel
spreadsheet, maybe I can get an Excel VB Script to post expected times.
One of the concerns I am dealing with now is how to determine stability
when there are cyclical operations going on. I am using the prescribed
s
Rough pseudo code for my transformer algorithm for logging and monitoring
temperatures for normal operating conditions:
time constant = (material ksp * mass) / (24*60)
sample interval = time constant / (mass * material kx)
breakpoint flags = false
if sample interval < min interval
sample inte
Thermal time constants deal with thermistors and how it changes from one
temperature to another or from one ‘ambient state’ to another. One thermal
time constant is approximately 63.2% of the total difference in temperature
form the initial temperature to a new temperature. They do not however
I’m not sure I would consider IEC 62368-1 as having entirely practical
criteria. In particular, I dislike the “10%” clause. Is it 10% of the
temperature measured in Kelvin or Centigrade? All of the specific references in
that part of B.1.6 are to Kelvin.
“With reference to those tests that are
Hi Doug:
My comments are imbedded in your message.
Best wishes for the New Year!
Rich
From: Doug Powell [mailto:doug...@gmail.com]
Sent: Friday, January 06, 2017 6:32 AM
To: EMC-PSTC@LISTSERV.IEEE.ORG
Subject: Re: [PSES] Thermal equilibrium - 10% rule
I agree that thermal equil
1 minute measurement interval was what I suggested. That has worked well for
power converters from 10W to 1MW. Excel is a good way of determining “steady
state”, and I’ve used that technique for some time.
Ralph McDiarmid
Product Compliance
Engineering
Solar Business
Schneider Electric
As others have said a fixed number of minutes to wait, doesn’t make sense. How
long it takes to reach thermal equilibrium to a given number of degrees depends
on the thermal time constant(s) of the system under test and the size of the
thermal step imposed on the system. I had some success est
Please do tell us about the nonsense statement about diodes. I'd like a Friday
morning smile.
Ralph McDiarmid
Product Compliance
Engineering
Solar Business
Schneider Electric
From: John Woodgate [mailto:jmw1...@btinternet.com]
Sent: Friday, January 06, 2017 6:51 AM
To: EMC-PSTC@LISTSERV.IEEE.
I think:
Those who know me personally have often heard me say what I consider to be a
corollary, "Common sense is usually neither.. common or sensible".
is a bit too cynical or pessimistic. It isn't common enough, for sure, but it
is often sensible. For example, does someone born and educa
John,
I agree with the common sense approach and use it frequently. It's always
interesting to me how I can look at a screen plot of 60 thermocouples and
in a second or two decide, "yes this is stable". I can even estimate how
much time it will take to become stable as a test nears the end (usua
Oops, sorry Mr. Khrushchev, wherever you are!
Ralph McDiarmid
Product Compliance
Engineering
Solar Business
Schneider Electric
-Original Message-
From: John Woodgate [mailto:jmw1...@btinternet.com]
Sent: Friday, January 06, 2017 10:40 AM
To: Ralph McDiarmid ;
EMC-PSTC@LISTSERV.IEEE.ORG
Ralph,
I have used 1-minute as well . In fact for Solar PV systems the Sandia
Efficiency test protocol recommends 5 second and 30 second intervals with a
fairly complex averaging algorithm to boot.
http://www.gosolarcalifornia.ca.gov/equipment/documents/Sandia_Guideline_2005.pdf
Doug
On Fr
That's Nikita, not Makita. And if you look at the clip carefully, he's
wearing two shoes, so the one he's using as a gavel must have come from a
sputnik.
With best wishes DESIGN IT IN! OOO Own Opinions Only
www.jmwa.demon.co.uk J M Woodgate and Associates Rayleigh England
Sylvae in aeternum man
Minor comment:
Having been the Secretary to a number of BSI committees many years ago, I
sympathise with Ralph's last para as the Chairmen can be even worse than the
other Members - they "know what they know" and it can take an awful lot of
"effort" to "persuade" them that they need to "think again
I'm sorry, I can't remember the details and it was around 30 years ago. If
anyone has a copy of the original IEC 386 (not 384), the offending words should
be obvious.
With best wishes DESIGN IT IN! OOO – Own Opinions Only
www.jmwa.demon.co.uk J M Woodgate and Associates Rayleigh England
Sylvae
For what it's worth, we measure and log temperatures at 1 minute intervals
(sometimes quicker, depending on what is being tested) and graph each data set
in Excel and look at the curves. When they go flat (even with some ripple), we
call it stable. Good enough for all the agencies we work with
IEC 62368-1 seems to have a fairly practical criteria for thermal “steady
state” (not “equilibrium”) in B.1.6. Steady state is considered to exist if
the temperature rise does not exceed 3 K in 30 min. If the temperature is at
least 10% below the specified limit, then steady state is considere
I understand that if the system is poorly designed there can be catastrophic
results, but the test is written assuming the equipment temperature does
equilibrate, right?
Ken Javor
Phone: (256) 650-5261
> From: John Barnes
> Reply-To:
> Date: Fri, 06 Jan 2017 00:06:24 -0500
> To: Ken Javor
> C
Standards committees will re-use text if no-one tells them not to. It may take
many tellings, too. It took me several years to get a total nonsense statement
about diodes deleted from IEC 60384 and equally long times to get a typo in
the electrochemical table in IEC 60065,60950-1 and 62384-1 f
I agree that thermal equilibrium can never be achieved especially in light
of the zeroth law of thermodynamics, but also for more reasons than the
exponential nature of the thing. Possibly a better phrase to use is
thermal stability.
I actually believe that the standards committees will re-use th
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