Humidity affects many properties of air and the
materials that are exposed to it. Monitoring and
measuring humidity is important wherever there is
a need to prevent condensation, corrosion, mold,
warping or spoilage of products. For example, it’s
important to measure humidity in industries that
manufacture and distribute foods, pharmaceuticals,
chemicals, fuels, wood, textiles, and paper.
The sensors that measure humidity need to be
calibrated regularly to ensure they continue to
operate within their specifications. Humidity sensor
calibration is typically done using an instrument
called a humidity generator.
Most humidity generators are based on one of two
designs. A mixed-flow generator controls humidity
by using the split-stream method. In this method,
dry gas is drawn into the generator and divided
into two parts. One part is partially or completely
saturated with water vapor; the other part is mixed
in until the targeted humidity output is reached. The
humidity depends on the wet air’s humidity and the
mixing ratio. A high-volume fan in the test chamber
keeps the temperature and humidity uniform.
A two-pressure generator has two chambers. The
first, called the saturator, contains air saturated with
water vapor at a high pressure. The air passes from
the saturator to the second chamber, called the test
chamber. The test chamber is at a lower pressure.
As the air passing into the test chamber reduces in
pressure, its relative humidity also drops.
A mixed-flow generator is faster than a typical
two-pressure generator, and is also more portable,
which makes this type of calibrator a good solution
for work in the lab or on-site in the field.
Humidity calibration
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Humidity calibration
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