“SE SEUS PROJETOS FOREM PARA UM ANO,SEMEIE O GRÂO.SE FOREM PARA DEZ ANOS,PLANTE UMA ÁRVORE.SE FOREM PARA CEM ANOS,EDUQUE O POVO.”

“Sixty years ago I knew everything; now I know nothing; education is a progressive discovery of our own ignorance. Will Durant”

OBRIGADO DEUS PELA VIDA,PROTEGENOS E GUARDANOS DE TODO MAL


AUTOR DO BLOG ENG. ARMANDO CAVERO MIRANDA SAO PAULO BRASIL

terça-feira, 23 de fevereiro de 2010

IR Thermography







The design of reliable power electronic converter systems depends
partly on an accurate knowledge of the power stage component
operating temperatures under extremes of load and input voltage.
This article demonstrates how the use of modern infra-red (IR)
imaging techniques can significantly enhance the design qualification
process and show up potential problems at a very early stage in
the product development cycle. The techniques highlighted are
applicable to any power converter system or electronic product
where knowledge of component operating temperatures is
important for reliability modelling and lifetime prediction.
By Dr. Iain Mosely, Technical Director, Converter Technology Ltd

One of the main limiting factors affecting the power capability and
reliability of any electronic power converter system is the operating
temperature of key power stage components. Excessive component
temperature will reduce product operating lifetimes and could result
in early field returns. Traditionally, thermocouples are used to
measure the operating temperature of components.
Whilst thermocouples can give very accurate temperature
measurements, they do have a few potential drawbacks:
• Thermocouples can pick up noise if they are placed near to power
components with high dv/dt switching waveforms present and this
can give misleading measurement results.
• Thermocouples will sink a small amount of heat away from the device
they are attached to. For physically small components, this can lead
to measurement inaccuracy.
• Thermocouples are often only placed on components which are
expected to show a reasonable temperature rise. Other components
may not be monitored at all and this could lead to problems if a
design error leads to a high operating temperature on a component
which hasn’t been monitored.

IR thermography is a non-contact measurement technique which
uses a calibrated infrared camera to form athermal image of the
system under test.
As the measurement technique is noncontact, the noise susceptibility
and heatsinking effects sometimes encounteredwith thermocouples
are no longer an issue. More importantly, an entire PCB can be imaged
which immediately shows up any hotspots or problem components that
may have otherwise been overlooked.

An example thermographic image ofa power converter is shown
in Figure 1.The power converter used has an issue with a snubber
TVS diode which can be seen to be running at >150°. Using the
thermal imaging camera is this example would immediately alert
the designer to a potential problem with the PSU before it reaches
the pre-production or production stage. The real value of thermography
in power electronic design is this ability to rapidly flag potential
design issues at a very early stage.

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