Whitehouse spheres give pore verification

For filter calibration, Whitehouse Scientific uses glass microspheres in single shot bottles to provide a measure of the mean pore size 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 from 3 to 500µm. To perform the calibration, a standard is selected in the expected pore size range and the content of the bottle is weighed. The microspheres are then sonically sifted through a 90mm diameter disc of the filter under test.

From the percentage of the standard passing through the filter, mean pore size is determined usng a calibration graph on the standard test certificate.

The particle size distribution in each bottle is so narrow that 10% weight variations in the percentage passing through equates to just a 2µm difference in the filter pore size, according to the company.