Patent ID: 8165825

Claim:
A method for electromagnetically measuring physical parameters of a pipe (CS) by means of a measuring arrangement comprising a transmitter coil and a receiver coil, both coils being coaxial to and longitudinally spaced from each other, the measuring arrangement being adapted to be positioned into the pipe and displaced through the pipe, the pipe physical parameters being the pipe inner diameter (ID) and the pipe ratio of magnetic permeability to electrical conductivity (μ 2 /σ 2 ), the method comprising the steps of: a1) exciting the transmitter coil by means of a transmitter current (I i ), the transmitter current having a first excitation frequency (f 1 ), a2) measuring a receiver voltage (V i ) at the receiver coil, a3) determining a transimpedance (V i /I i ) between the transmitter coil and the receiver coil based on the transmitter current (I i ) and the receiver voltage (V i ), and determining a measurement ratio (M i ) based on said transimpedance, wherein the method further comprises the steps of: b) repeating the excitation step a1), the measuring step a2), the transimpedance and the measurement ratio determination step a3) for at least a second excitation frequency (f 2 ) so as to define a measurement ratio vector ([M 1 , M 2 , . . . M n ]), c) calculating a prediction function vector ([G 1 , G 2 , . . . G n ]) based on the first frequency and at least the second excitation frequency, a plurality of potential pipe ratios of magnetic permeability to electrical conductivity and a plurality of potential pipe inner diameters, and d) applying a minimizing algorithm onto the measurement ratio vector ([M 1 , M 2 , . . . M n ]) and the prediction function vector ([G 1 , G 2 , . . . G n ]) and determining the pipe inner diameter (ID) and the pipe ratio of magnetic permeability to electrical conductivity (μ 2 /σ 2 ) corresponding to a maximum solution of the algorithm.