20 AnALytICAL & LABoRAtoRy EquIpMEnt
Achieving accurate humidity
measurement in cleanrooms
P
roducts manufactured in cleanrooms result, the control of humidity and dewpoint in
Choosing the right
cover a wide range, including the manufacturing process has become stricter.
type of measurement pharmaceuticals and semiconductors. In the manufacturing mini-environments, very
instrumentation is
Humidity, temperature, particles and high level control with an accuracy of ±per cent
important in order to
pressure are often controlled, as these parameters RH is often required.
reach the best humidity
can have serious effects on product quality and Humidity control is also important at liquid
measurement results.
production efficiency. crystal display plants and paint plants. In this
Calibration should also be
carried out regularly, and
Relative humidity (per cent RH) describes case, the durability and accuracy of the humidity
to traceable standards.
the amount of water vapour that exists in a sensor is very important. These plants use
Daisuke Fujisawa
gaseous mixture of air and water. It is a ratio of various gases, which can affect sensor elements.
explains.
the amount of water vapour present compared
to how much could be present at a given Humidity and dewpoint sensors
temperature. Issues at production sites, such
Il est important de choisir
Humidity sensors, which measure water content
as expansion and contraction, and hardening
le bon type d’appareillage
in the air, are broadly divided into two types.
and softening of material, change in viscosity
de mesure afin d’obtenir
One measures humidity and the other dewpoint.
les meilleures résultats
of liquid, growth of microbes, increase in static
In an atmosphere where the humidity level is
de relevé d’humidité.
electricity, and corrosion and rust, are largely
at least 10 per cent RH, humidity measurement
L’étalonnage doit
affected by humidity.
is often used, while in low humidity, dewpoint
également être effectué
Dewpoint (Td) is a temperature at which
measurement is preferred. In some cases it is
régulièrement et selon dew, or condensation, forms on cooling a gas.
convenient to use dewpoint measurement even in
des normes de traçabilité. Dewpoint is a parameter suitable for expressing
high humidity conditions.
Explications de Daisuke
very small water content in a gas like air. In
Fujisawa.
the micromachining of semiconductors
the conditions are very dry as water
Die Auswahl der richtigen
molecules are regarded as contaminants.
Messinstrumente
In this condition relative humidity is
ist für optimale
practically stagnated at 0 per cent RH but
Feuchtigkeitsmessungen
dewpoint scale is still sensitive for water
besonders wichtig. content changes in the measured gas.
Auch Kalibrierung sollte
regelmäßig und im
Applications and needs
Rahmen nachvollziehbarer
A pharmaceutical manufacturing plant
Standards durchgeführt
werden. Ein Bericht von
often has a large number of cleanrooms.
Daisuke Fujisawa.
The control and recording of temperature
and humidity is strictly designated by
Good Manufacturing Practice (GMP). The
most important feature required from
humidity sensors is small deviation. It is
important to be able to perform precise
calibration to check that the sensor does
not drift over the long-term.
In food processing plants, it is
necessary to keep the manufacturing
site at or below certain humidity. For
example, 40 per cent or below seems to
be a commonly used value. This helps
in restricting the growth of germs and
bacteria that can cause food poisoning.
In semiconductor and electronics Fig. 1. Vaisala’s own cleanroom produces sensors for
product plants, the generation of products radiosondes as well as different humidity, barometric
changes more and more rapidly. As a pressure and carbon dioxide measurement products.
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