coil inductance l 2 regulates the already mentioned difference voltage udiff across the plunger type coil and keeps it constant this closed loop control results in the measurement current that is forced to flow through the plunger type coil being converted across r 1 to a defined voltage utemp not shown which is then used as a measurement variable if a disturbance ac voltage were now to be present in the sensor coil during this dc voltage measurement for example as a result of an external magnetic alternating field this alternating signal voltage or ac voltage would corrupt the entire measurement and would make the measurement result unusable the second compensation winding rcu 2 l 2 is used in this situation the transformer principle results in a further ac voltage or an alternating current being produced in this second winding which as a result of the two windings being connected to one another and together with the operational amplifier op 1 counteracts the original disturbance voltage and is fed with a phase shift of precisely 180 u00b0 into the plunger type coil in consequence the alternating signal components in the two coils cancel one another out so as to overcome the disturbance it should be noted that the two measurement methods described above as well as the first and the second circuit parts can be provided both separately from one another and in combination with one another because of the capability to use the switches s 1 to s 3 for switching as a function of accuracy requirements or required disturbance insensitivity to magnetic alternating fields one preferred example of a combination such as this is illustrated in fig2 the major advantages of the preferred exemplary embodiments of the proposed circuit.