Method for inductive measurement of a dimension of an object

A method for non-contact measurement of a geometric dimension of,

• and an electrical characteristic of, an electrically conductive object (6) based on electromagnetic induction and a time-varying magnetic field, in which method a substantially constant current is supplied to at least two transmitter coils (3) such that an electromagnetic field penetrates the object (6), subsequently cutting off supply of current to the transmitter coils (3), sensing a voltage induced in at least one receiving coil (8) as a result of a decaying magnetic field and integrating said sensed voltage during a time period in an interval following cutoff of current supply, characterised in that said method comprises the steps of:
• generating opposing magnetic fields by means of said at least two transmitter coils arranged one on either side of said object (6) such that said electromagnetic field penetrating said object (6) is essentially perpendicular to a measurement direction of said geometric dimension,
• measuring the voltage induced in said at least one receiving coil (8) from a first time (T3) after a decay of a magnetic field outside said object (6) as a first signal (S),
• integrating the first signal (S) from the first time (T3) following the decay of the magnetic field outside said object (6) forward till a point at which the field in the material has
• substantially decayed to zero (T4, T5, T6), and
• calculating from the integrated signal a value for said geometric dimension and said electrical characteristic of said object (6) from the first signal (S), and further characterised by calculating the value for said geometric dimension, said value being proportional to the integral of the first signal (S).