Calibration of a fisher air-permeability apparatus for determining specific surface
Calibrating the Fisher sub-sieve sizer at a single particle-size level does not ensure accuracy at other levels unless several variables are controlled. Instrument modification that give better control of the several variables, and a calibration method that ensures accurate air-flow measurement without depending on a particle-size standard, are described. The modified instrument has good precision over the range 2 to 40 µ. A method for extending this range is given.