Patent ID: 7066008

Claim:
A method of measuring the concentration of particulate matter suspended in a gaseous carrier medium whilst transported via a duct made of electrically conductive material, said method comprising the steps: (a) generating a radio frequency electromagnetic wave within the duct, (b) measuring wave parameters across a range of frequencies, including a wave cut-off frequency, at two arbitrary points on a wave transmission path the two arbitrary points lying in a plane that intersects both a duct axis and a wave generation point, (c) determining the wave cut-off frequency, based on changes in wave parameters, and (d) calculating a value of dielectric permittivity of a two-phase flow of a carrier gas and a particulate matter with which the duct is loaded and ascribing to this value of dielectric permittivity a corresponding value of a particulate matter concentration in actual flow conditions, wherein measured wave parameters include a rate of change of phase shift in two points along a wave propagation (d(Δφ 1 )/df), and wherein a value of a waveguide cut-off frequency (f g1 ) is determined as a value at which the rate of change of phase shift against frequency (d(Δφ 1 )df) reaches a maximum, and the value of dielectric permittivity ( ∈ 1 ) is derived from a dielectric permittivity formula ɛ 1 = ( 1 ⁢ , ⁢ 81118 ⁢ c 2 ⁢ π ⁢ ⁢ rf g1 ) 2 ⁢ 1 μ 1 .