A direction-defined airflow in clean rooms protects the products against contaminations and unwanted particles will safely be evacuated. To do so, a uniform airflow from the ceiling to the floor (“oriented, low-turbulence displacement flow“) is maintained in cleanrooms of high purity levels. The monitoring range is from 0.36 to 0.54 m/s flow velocity (EU GMP guide, Annex 1 in class A). In the cleanroom the measurements are made behind terminal filters.

Defined overpressures ensure process safety in cleanrooms through overflow from one room to the other. This overflow is usually monitored indirectly via pressure sensors. When doors or airlocks are opened, the pressure often falls below the desired operating limit of the pressure sensor, thus indicating no overpressure. In this phase, the cleanroom operator has no information (measured values) on the actual overflow. However, a backflow can be present and, consequently, contamination may have occurred. This will not be noticed despite a correctly performed pressure measurement.

The lecture will look at the various fields of application for flow measurement in cleanrooms, the conditions on site and the normative requirements, and also the relationship between differential pressure and airflow. In addition, commonly used methods will be discussed and common mistakes will be pointed out.

Fields of application in cleanrooms - overflow
• Measuring situation
• Relationship between pressure and flow
• Requirements
Fields of application in cleanrooms - laminar flow
• Methods used
• Vane probe anemometers
• Thermal anemometers
• Positioning
• Common errors
• Adjustment and calibration by the manufacturer
Summary