Calibration method for an electromagnetic induction method, measuring arrangement for carrying out and applying the method

An indirect calibration method for electromagnetic induction for determining physical parameters of an electrically conductive medium from a ratio (HS/HP) of a magnetic secondary field (HS), received in a receiving coil, to a magnetic primary field (HP) emitted from a transmitting coil electrically connected to a transmission signal generator, in which, as measurement for the ratio (HS/HP), a received voltage (URx) is measured at an output of a receive amplifier electrically connected to the receiving coil, which is calibrated by a series connection of at least one calibration coil and of a changeable calibration resistor and of a calibration factor (HCx/HP) adjustable therethrough, the receiving coil being permanently inductively coupled with the calibration coil, a calibration pulse, generated in the calibration coil, inducing a calibration field (HCx), that induces a magnetic flux in the receiving coil, areas and winding numbers of the receiving coil and the calibration coil being known, the indirect calibration method comprising:

• a first stage, in which the transmitting coil is inactive or shielded, and a calibration signal generator is connected to the series connection of calibration resistor and calibration coil, and in which the calibration pulse is generated electrically by the calibration signal generator, and, with adjusting a resistance of the calibration resistor, a calibration voltage (Ucal) at the series connection of the calibration coil and the calibration resistor and the received voltage (URxin) at the receiving coil at an input of the receive amplifier are measured simultaneously for determining a generated mutual inductance (MRC) between the calibration coil and the receiving coil, from which, with inclusion of the known areas and winding numbers of calibration coil and receiving coil, the calibration factor (HCx/HP) is derived;
• and
• a second stage, in which the transmitting coil is active via the transmitting signal generator, and the calibration coil is short-circuited via fixing the resistance of the calibration resistor, and in which the calibration pulse is generated inductively through a primary field (HP) generated by the transmitting signal generator and the transmitting coil, and in which the received voltage is measured at the output of the receive amplifier so as to calibrate the received voltage to the ratio, using the calibration factor (HCx/HP), the calibration factor (HCx/HP) being determined metrologically in the first stage.