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About Environmental Chambers
Environmental test chambers replicate environmental
conditions such as high temperature and humidity, allowing engineers
to evaluate the effects that environmental changes have on products placed
within the chamber. An environmental test chamber evaluates product quality
and identifies flaws and weaknesses. Environmental testing falls under
two categories: climatic and mechanical. Climatic testing evaluates the
effects of natural environmental conditions such as temperature, humidity
and precipitation upon an object but at an accelerated rate. Mechanical
testing evaluates the effects of causal environmental conditions such
as vibration and shock upon an object. The information obtained from
an environmental test chamber is used to improve products before they
are marketed to the public.
Environmental test chambers are utilized in all industries, from automotive
to engineering and construction to medical, pharmaceutical, food processing
and packaging. Manufacturers test such items as cars, cigarettes, makeup,
medicine and medical instruments. There is a growing demand by customers
to have extended warranties and maintenance on products. Manufacturers
would be at high risk in offering these long-term warranties and service
contracts without test data to back up product performance guarantees.
Some manufacturers in industries where there is no pressure to prove
long-term reliability may be tempted to forgo the thousands of hours
required to obtain good test results, but reputations are won or lost
based on product performance, no matter what the product may be.
Environmental test chambers test products in a variety of ways, depending
on the product application. THB (Temperature/Humidity/Bias) testing is
one of the most common tests used for integrated circuit chips, because
the test chambers can hold 1851/4F/851/4C and 85% relative humidity condition
while bias loads are applied to the samples. The HAST (Highly Accelerated
Stress Test) uses high temperature (over 2121/4F/1001/4C), high relative
humidity (about 85%) and high atmospheric pressure conditions (up to
4 atms) to test products, such as integrated circuits. The HAST greatly
decreases the time needed to achieve useful test results, especially
in evaluating non-hermetic packaging of solid state equipment in humid
conditions. High temperature chambers are used to assess potential product
failure such as damage, junction thermal resistance increase and depolymerization.
Products are subjected to temperatures of about 3021/4F/1501/4C for more
than 1,000 hours, after which electrical measurements are taken. Mixed
flowing gas chambers subject products to a mixture of pollutant gases
in a controlled temperature and humidity environment in order to assess
the damage to a product after long-term use in office and light to heavy
industrial settings.
Terms regarding thermal shock testing are often used incorrectly. Liquid-to-liquid
thermal shock is a process in which a product is alternately dipped in
non-toxic, noncombustible, chemically inert and low viscosity fluids
maintained at a specific temperature. Air-to-air, or two-zone, thermal
shock is the transferring of a product from a hot chamber to a cold chamber
or some other sudden change in air temperature, and vice versa. Sometimes,
in a transfer, there is an intermediate step in which the product is
exposed to room temperature conditions, which is called three-zone thermal
shock. Simply changing the air as quickly as possible in a single chamber
is more accurately referred to as thermal cycling or stress screening.
Before investing in an environmental test chamber for thermal shock testing,
be sure to have a clear definition of the requirements; otherwise, it
is very easy to purchase the wrong equipment.
Featured
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http://www.besttest.com/BestTest_Newsletters/Dec_1_2005.htm#FeatureArticle2
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Types of Environmental Chambers
- can produce fast temperature
changes of 41-104¼F (5-40°C)
per minute, even with large loads. Vibration test systems can be
integrated within agree chambers,
as they have removable floors.
- test the effects of low
pressure on an object and are capable of replicating low-pressure environments
found at altitudes of
up to 200,000 feet above sea level.
- reduce test time
when testing small items.
- accommodate large items,
such as vehicles, and are useful when performing batch testing.
- change
the temperature of a product at a highly accelerated rate through high
air velocity conditioning.
- replicate environmental conditions for engineering tests.
- replicate
environmental extremes that an airplane typically endures when in operation.
- are
able to simulate a variety of humidity conditions in order to test
the effects of humidity on an object. Used for specific testing in industrial
and biotechnology applications.
- are
used to expose electronic equipment to a mixture of pollutant gases in
an
environment in which the temperature
and humidity are controlled.
- often contain shelves
and other amenities for easy storage and user convenience.
- test
the corrosion resistance of an object. The object usually hangs from
a rod while the
chamber introduces a salty
residue, which creates a foggy atmosphere, although the object remains
visible throughout the process.
- test
the effects of temperature on an object. Temperature cycling is performed
alone or in conjunction with other tests, such as altitude and vibration
tests.
- involve
the subjection of an object to extreme changes in temperature within
a single chamber
in which the temperature alternates between cold and hot for a given
number of cycles.
- initiate automatic
changes between two compartments, in which one compartment contains an
extremely cold environment and one
compartment contains an extremely hot environment. The rapid transference
of the object between these two compartments of extreme temperatures
causes a shock to the object.
- are used for thermal
and dynamic testing and have shock and vibration capacity.
- are chambers from which
almost all matter, especially air, has been removed.
- apply
shock vibrations of varying frequencies to an object, including the
bumping, shaking and
bouncing of an object, and
can be administered in conjunction
with temperature and humidity testing. Vibration chambers have sensors
that perceive and monitor the object’s
reaction to the vibration.
- vary in size and can usually accommodate one or more persons.
Walk-in chambers are useful when testing large objects and performing batch testing.
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