Flow monitoring in cleanrooms and clean zones
A direction-defined air-flow in cleanrooms protects the products against contaminations and unwanted particles will safely be evacuated. To do so, a uniform air flow from the ceiling to the floor (“oriented, low-turbulence displacement flow“) is maintained in clean rooms of strong 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. Since the recirculation of air is reduced during standstill periods, an extremely precise measurement of the air velocity is mandatory from 0.1 m/s on.
The solution: Air flow measurement by SCHMIDT® Flow Sensors SS 20.515 LED or SS 20.415 LED
According to the standard EN ISO 14644 - 3, the air velocity is measured at a distance of approx. 150 to 300 mm below the front surfcae of the filter. To facilitate an installation into ceiling or wall systems, the thermal SCHMIDT® Flow Sensors SS 20.415 LED and SS 20.515 LED are supplied with a cleanroom-compliant quick assembly kit. Both sensors are extremely compact since all electronic components are installed in the sensor tube and therefore no turbulence is generated in the low-turbulence displacement flow. For a use of supply air systems, the SS 20.415 LED offers an option for simultaneous detection of the flow direction – which is interesting in case of back flows.
Measuring accuracy in black and white
One special feature of these sensors is the compensation and calibration in a novel “vertical flow channel“. This offers the advantage that effects from the measurement steps on site are eliminated and highest precision will be achieved. The renowned laser doppler measurement process (LDA) is used as reference measurement process.
Upon request they will be supplied with an additional high-precision calibration system. This system enhances the precision even more by the use of more calibration points, and the documentation of the target and actual values as ISO calibration log. This calibration can be renewed in accordance with the specifications set by the user, which in – general is after one year. Also DAkkS accredited calibrations can be offered to achieve the highest calibration level.
