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Humidity in Check Selecting the Right Humidity Testers for Clean Rooms and Calibrating Them Correctly

| Editor: Sonja Beyer

It is essential to select the right equipment in order to achieve reliable results when measuring humidity. The same is true of calibration processes which are carried out at regular intervals and should be based on traceable standards. This will serve to guarantee reliable results in the long term.

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The clean room is used not only for the production of pharmaceuticals but also for the manufacture of humidity measuring devices. (Picture: Vaisala)
The clean room is used not only for the production of pharmaceuticals but also for the manufacture of humidity measuring devices. (Picture: Vaisala)

Parameters such as humidity, temperature, particle concentration and pressure can have a considerable influence on the quality of medicines. That is why pharmaceuticals are made in clean rooms where these parameters can be precisely monitored. Temperature and humidity can then be controlled and recorded in strict compliance with GMP rules (Good Manufacturing Practice). A high level of precision is required of humidity sensors first and foremost. Accurate calibration also ensures that the sensors are not affected by drift over the long term.

Relative humidity (RH) is the term used to express the proportion of water vapor in a gaseous mixture of air and water vapor. It specifies the current ratio of the water vapor content in a room to the maximum possible water vapor content at the same temperature. Processes such as expansion and contraction, hardening and softening of materials, changes in the viscosity of a liquid, the growth of microbes, increases in static electricity, corrosion and rust formation are largely influenced by humidity.

The dewpoint is the temperature to which a gaseous mixture must be cooled in order to generate condensation. It is therefore a variable that can be used to specify the volume of very small amounts of water in a gaseous mixture such as air. Two types of humidity sensor are used in practice to measure the water content in the air. One type measures the relative humidity and the other type measures the dewpoint. The direct humidity measurement method is used in atmospheres with a moisture content of at least ten percent relative humidity, while the dewpoint measurement method is preferred in atmospheres with low moisture content. In special cases, however, it is also used where moisture levels are high.

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