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. "Peter Tarver" <ptar...@nortelnetworks.com> on 06/28/2000 01:15:16 PM To: emc-p...@ieee.org cc: (bcc: Dan Mitchell/CondorDC) Subject: RE: UL1950/UL2601 Thermals That's really just a rule of thumb. A working premise that provides reasonable results in a relatively short time. As Kaz mentioned, it's not uncommon for some circuits/parts to exhibit a cycling of temperature, either by cyclical loads presented to them or some form of (generic) limiting circuitry. Even using that rule of thumb, it doesn't account for minor increases in ambient temperature over the relevant time frame. One might find that some circuits/parts continue to increase in temperature, while others in the same product have reached thermal equilibrium (within the somewhat loose definition that applies here). Best answer: use engineering judgment. If you clearly have increasing temperatures that aren't resulting from unintentional outside influences, the test is not completed. Regards, Peter L. Tarver, PE Homologation Engineering Nortel Networks ptar...@nortelnetworks.com -----Original Message----- From: Dan Mitchell [mailto:dan_mitch...@condordc.com] In UL2601 Clause 42.3.3) Duty Cycle - for Equipment for Continuous operation it lists 2 ways to conclude the test a) temperature of the windings stabilize and do not increase by more than 2 deg. C in 1 hr, or b) 2.5 hr, which ever is shorter. UL1950 only states that; "for continuous operation, until steady conditions are established". I haven't been able to establish what is meant by "Steady Conditions". I was told once by a rep. of a large safety company that it meant "no more than a 1 deg. C rise in 15 minute period". However, since I can't find this written in the standard, I am a bit skeptical. If anybody has a good definition of "Steady Conditions" and can point it out to me in UL1950 or in the PAGs, I would appreciate it. Daniel W. Mitchell Product Safety Engineer Condor DC Power Supplies, Inc. P: (805) 486-4565 x323 F: (805) 483-4307 ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: jim_bac...@mail.monarch.com Michael Garretson: pstc_ad...@garretson.org For policy questions, send mail to: Richard Nute: ri...@ieee.orgTitle: RE: UL1950/UL2601 Thermals
That's really just a rule of thumb. A working premise that provides reasonable results in a relatively short time. As Kaz mentioned, it's not uncommon for some circuits/parts to exhibit a cycling of temperature, either by cyclical loads presented to them or some form of (generic) limiting circuitry.
Even using that rule of thumb, it doesn't account for minor increases in ambient temperature over the relevant time frame. One might find that some circuits/parts continue to increase in temperature, while others in the same product have reached thermal equilibrium (within the somewhat loose definition that applies here).
Best answer: use engineering judgment. If you clearly have increasing temperatures that aren't resulting from unintentional outside influences, the test is not completed.
Regards,
Peter L. Tarver, PE
Homologation Engineering
Nortel Networks
ptar...@nortelnetworks.com
-----Original Message-----
From: Dan Mitchell [mailto:dan_mitch...@condordc.com]
In UL2601 Clause 42.3.3) Duty Cycle - for Equipment for Continuous
operation it lists 2 ways to conclude the test a) temperature of the
windings stabilize and do not increase by more than 2 deg. C in 1 hr, or b)
2.5 hr, which ever is shorter.
UL1950 only states that; "for continuous operation, until steady conditions
are established". I haven't been able to establish what is meant by
"Steady Conditions". I was told once by a rep. of a large safety company
that it meant "no more than a 1 deg. C rise in 15 minute period". However,
since I can't find this written in the standard, I am a bit skeptical.
If anybody has a good definition of "Steady Conditions" and can point it
out to me in UL1950 or in the PAGs, I would appreciate it.
Daniel W. Mitchell
Product Safety Engineer
Condor DC Power Supplies, Inc.
P: (805) 486-4565 x323
F: (805) 483-4307
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