NIST Traceable Filter Testing Standards
04 August 2005
Whitehouse Scientific's novel approach to filter calibration uses glass microspheres in single shot bottles to provide a measure of pore size or filter cut point that is traceable to NIST and NPL standards. The method also allows verification of maximum pore size and can be used on most filter media, including all forms of complex woven and non-woven materials that are impossible to calibrate by other means.
More than 20 narrow distribution filter calibration standards cover the size range 3 to 500 microns. To perform the calibration, a standard is selected in the expected pore size range and the content of the bottle weighed. The microspheres are then sonically sifted through a 90mm diameter disc of the filter under test.
From the percentage of the standard passing, the cut point of the filter is determined using a calibration graph on a test certificate provided.
Standards are produced and analysed using electroformed sieves traceable to NIST and NPL, with all data supported by microscopy. The particle size distribution of each standard is so narrow that 10% weight variations in the percentage passing through equates to just a 2 micron difference in the filter pore size.
