Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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:

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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  

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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

Re: [PSES] Thermal equilibrium - 10% rule

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