LINEARIZATION OF TWO-COIL MAGNETOELASTIC SENSOR TRANSFER CHARACTERISTIC
Jan Bydžovský – Mojmír Kollár – Luděk Kraus – Peter Švec
Magnetoelastic sensors of elongation, or acting force, are currently based on the change of core permeability, caused by mechanical stress, while altering its magnetization. The sensor, like an “open transformer” works either in the constant current or constant secondary voltage mode. The linear relationship between mechanic stress or strain (bound as σ = εE, through the Young modulus) is preserved only if the amplitude of voltage induced in the secondary winding is constant and determined by the changes of magnetic polarization J of the core. If the susceptibility of the sensors changes from 1850 to 90 (when the applied stress changes up to 600 MPa) the unfavorable influence of the secondary coil window filling leads to a noticeable loss of the transducer linearity. Inclusion of an additional coil of mutual induction into the driving circuitry of the two-coil sensor and its influence on the linearity of the transducer characteristic are described in the paper. The improved performance not only allows easier calibration, it also widens the possible applications of magneto-elastic sensors with build-in affordable measuring electronics.
Keywords: susceptibility, magneto-elastic sensors