Evaluation_Engineering_October_2020 - 25

parts in the chamber, especially the internal temperatures
of massive parts are likely nowhere near the indicated and
required air temperature.
A system should have enough feedback from sensors in
and on the load to be able to minimize test time and have
real knowledge of when parts are at needed temperatures
without blindly waiting for temperature settling. Modern
temperature control algorithms have progressed quite a bit
offering big improvements in speed and setpoint verification
without a lot of specialty hardware and time spent tuning
control parameters.
Good coordination between the driving temperature and
other tests which need to be done at specific temperatures
is important to avoid unnecessary waiting for a setpoint or
performing tests at the wrong temperature. Just having a test
that is going to be repeated many times, and takes more time
than really required to accomplish, can and should be avoided.
Any temperature overshoot must be properly controlled
so that it does not damage parts. While some overshoot is
really a good thing and gradients are needed to make the
temperature of an item change, too much of a good thing
can always cause damage.
More fully thought-out systems are always a good thing
down to the point of when refrigeration systems are used

in a building, they are designed so that the heat they dump
into the room and ultimately building HVAC systems is
considered.
* Everyone wants reliable systems that don't fail, randomly
slow down testing, cost more money or impact production
testing plans.
* Easy to use features and functionality is important for providing real ongoing savings in thermal test without taking
hours and hours to implement.
* Proper automatic monitoring of parameters that could go
wrong and cause test data to be invalid is important too.
Prior thought about choices of saving a long test that may
fail, the ability to resume / restart from the beginning if
required or to have proper corrective action taken in real
time before test parameters go out of range.

Heat Transfer
Conductive heat transfer is almost always faster and more efficient than heat transfer by convection. However, convection
requires direct contact with the device under test. In most cases
in the real world, there is some heat transfer happening from
convection and some by conduction. In many cases the combination of controlled conductive heat transfer with convection can
provide optimal thermal testing speed and better simulation

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OCTOBER 2020 EVALUATIONENGINEERING.COM

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Evaluation_Engineering_October_2020

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