NMR method and system for measuring a characteristic of veneer

A system for determining a moisture distribution of veneer in a serial production of veneer, comprising:

• transfer equipment configured to move the whole veneer in a serial production of veneer at a movement speed along a travel direction in a travel plane, wherein the veneer has a width between 10 cm and 200 cm in a transverse direction perpendicular to the travel direction in the travel plane and two sides;
• a time domain NMR spectrometer for determining the moisture distribution of the veneer, the NMR spectrometer including:
• at least one surface coil arranged in connection with the veneer to excite hydrogen protons in water contained in the veneer using frequency pulses;
• two magnets located on opposite sides of the veneer, one side above and another side below the travel plane, and opposite to each other for creating a magnetic field in the veneer in a selected point in the transverse direction of the veneer;
• either i) a pre-magnet for each magnet located prior to the magnet in the travel direction of veneer, length of the pre-magnets being dimensioned in the travel direction of the veneer to a predetermined range relative to the movement speed of the veneer, or ii) second transfer equipment for transferring the magnets in the travel direction of veneer during measurement such that the hydrogen protons of the veneer are exposed to the magnetic field for a time required for a predetermined pre-magnetization with respect to excitation of the hydrogen protons;
• a power source with controllers connected to the surface coil for generating frequency pulses;
• measuring equipment for measuring intensity of current generated by the frequency pulse returning to the surface coil from the hydrogen protons for generating a backward signal;
• a computer with a memory and a software for determining the moisture of the veneer based on the backward signal, wherein a correlation model is stored in the memory, which is a model consisting of three exponential signals Exp=A1*exp(−t/T21)+A2*exp(−t/T22)+A3*exp(−t/T23)+D, where D is a measuring-technical constant, Exp is the backward signal, A1, A2, A3 are amplitudes of the three exponential signals of the backward signal, wherein each of the amplitudes relates to one of three water components of a physical model of water location in fibres of the veneer, namely first component, second component and third component, wherein the first component of water corresponds to water in the cell walls, the second component corresponds to water contained in small pores and the third component corresponds to water contained in structures, respectively, T21, T22, T23 are corresponding relaxation times of the three water components and t is the signal measurement time, thereby obtaining the amplitudes A1, A2, A3 and relaxation times, wherein the software is arranged to:
• fit the backward signal mathematically to the correlation model to determine the amplitudes A1, A2, A3 and the T2 relaxation times T21, T22, T23 of the three different water compartments of the veneer fibres;
• and
• determine the moisture distribution within the veneer based on the amplitudes A1, A2, A3 and the relaxation times T21, T22, T23.