The present invention provides an apparatus for use in measuring
permeability of a material. The apparatus 1 comprises a non-contact probe
6 comprising an inner pipe 8 and an outer pipe 10 which are arranged
coaxially; a gas inlet for admitting a flow of gas into a first space 9
defined between the inner and outer pipes; and pressure difference
measuring systems DP for measuring a pressure difference .DELTA.P between
said first space (P1) and a second space (P2) comprising the interior of
the inner pipe 8. The probe 6 is mounted on a moveable head assembly 11
and the apparatus 1 further includes a position control system 12, 22 for
controlling the movement of the head assembly 11 so as to cause the probe
6 to scan across a surface 2 of the material to be analysed, while
maintaining the probe 6 at a constant distance Z from said surface 2, and
for collecting pressure difference .DELTA.P measurements, using said
pressure difference measuring device DP during scanning movement of the
probe 6.
