Abstract: An active measuring converter for connection between a two-wire line and an impedance to be measured, wherein an oscillator supplies alternating voltage to the impedance, and the variation in current drawn by the oscillator is in accordance with the value of the impedance. The measurement signal is transmitted together with the power for the active measuring converter via a two-wire line. The oscillator supplies the impedance with stabilized AC voltage independent of its operating current. Electronic switching devices coupled to the impedance either add the alternating current to the measuring signal as an impressed current, or couple it to a resistor-capacitor network for establishing a reference input for the controlled variable voltage. The alternate coupling of the alternating current corresponds to the alternating polarity of the AC current flowing through the impedance. The impedance may be the capacitance of a sonde which varies according to filling level.