Hello from San Diego:
Kevin Harris asks some questions about temperature
measurements.
1. Is this a valid temperature measurement for the PCB? I'm of two minds
on this. It could said that I'm really measuring the diodes temperature
and not the PCB. On the other hand the diode pad
...@compaq.com
To: 'dmck...@paragon-networks.com'; 'IEEE Product Safety Technical
Committee -' emc-p...@majordomo.ieee.org
Subject: RE: EN 60950 and component heating
Date: Wednesday, September 17, 1997 4:27 PM
Doug,
To answer your question of which is better:
The primary concern should
Mark:
I don't really think that you'd want to have a shiny, conductive piece of
aluminium foil bouncing around inside your power supply, shorting things
out and compromising your spacings. These self-adhesives don't last too
long under ageing ...
Cheers,
Egon :-)
Hi Kevin,
I had a rather bad experience between UL and CSA in
the older days when there wasn't so much discussion
and agreement between them. I had set up an MOU
between them with UL as the test location.
Went like this ...
Switching power supply. Has a transformer.
Must do abnormals
Product Safety Technical Committee -
Subject:Re: EN 60950 and component heating
Hi Kevin,
I had a rather bad experience between UL and CSA in
the older days when there wasn't so much discussion
and agreement between them. I had set up an MOU
between them with UL as the test location
Kevin,
Good question. By measuring the pad there are several items to consider.
1st, is the thermocouple in electrical contact with the pad? If so, you may
have an incorrect reading caused by currents from the pad through the probe.
2nd, In measuring the pad, you are measuring the junction
To add to Art Michael's ways used to work around the problem of PCBs
getting too hot, if the heat is being radiated (rather than conducted
through the leads) from the component to the PCB, put a shiny reflective
surface on the PCB (self adhesive aluminium foil, or just an area of
copper on the
We run into this quite often, and yes, I do consider the PCB measurement
to be a valid measurement of the PCB temperature whether you are on a
pad, a trace, or laminate. My experience with agencies is that they
agree, and will allow (for example) a power resistor to be as hot as it's
Good point. Local heating can damage a board locally.
Although people often do not test the way you indicate,
I've seen several failures due to long-term heat aging
of the board under a hot component.
Some things I've done:
1. Space the component body off the board and/or use longer leads to
Hello Kevin,
This is not an uncommon problem as you have probably guessed. Rather than
get embroiled in discussing the details of what one should measure, I'd
rather offer a couple of ways I've seen used to work around the problem.
A) Assuming you are using leaded diodes; Raise the diode off of
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