Method and apparatus for on-line monitoring of specific surface of mechanical pulps

An apparatus for on-line determining specific surface of a pulp as defined in clam 1 wherein said turbidity meter comprises, a light source for directing light through pulp passing through a transparent pipe section, a detector on the opposite side of said pipe section;

• said pipe section, said detector and said light source being in a first straight line relationship, a pair of detectors on opposite sides of said pipe section, said pair of detectors and said pipe section being a straight line relationship arranged substantially perpendicular to said first straight line relationship.

A method of on-line determining the specific surface of fibrillated wood fibres forming a pulp suspension, said method consisting essentially of:

• continuously measuring the turbidity of said suspension by sensing light reflected from said suspension as said suspension continuously passes a light source, measuring the density of said suspension to determine the consistency of said suspension substantially independent of other properties of pulp suspension and determining the specific surface of said suspension fibres based on a pre-determined relationship of said turbidity measurement and said consistency measurement to specific surface.