A method for measuring the degree of fiber concentration in a pulp in a
machine, in particular a refiner for the manufacture of paper pulp, which
machine includes a stator and an opposing rotor, which form a grinding
gap for the pulp. The stator is provided with at least one sensor device,
designed to interact with a rotor surface and including an impedance
meter body with a sensor surface which impedance meter body is mounted in
the stator in such a way that it can move axially. Measurements of the
impedance between the rotor surface and the sensor surface are carried
out during an axial movement of the impedance meter body and the measured
impedance differences are utilized together with the size of the movement
to determine the dielectric constant of the pulp, from which the degree
of fiber concentration in the pulp is dervived.