The closed loop principle makes use of a zero-field detector signal which is processed to drive a current through a compensation coil in such a way, that it balances out the magnetic field of the applied current at any time. Thus the compensation current is proportional to the current to be measured. In contrast to common Hall-detectors the patented soft magnetic VAC-probe made from a small strip of amorphous metal VITROVAC™ is strictly symmetric with respect to the magnetic field. Therefore it generates no offset contribution to the sensor. Moreover, the symmetry is neither affected by temperature changes or any aging effects. This enables for very high accuracy, nearly zero offset, and excellent stability over temperature and time.

In current sensors based on the closed loop principle the primary current conductor is lead through a magnetic core. The magnetic field of the primary current is concentrated in the magnetic core is detected by a soft-magnetic field probe in an air gap of the core. By means of a current through an additional winding on the core, the magnetic flux of the primary current is compensated. The magnetic flux in the core is held at zero value. The compensation current is proportional, and is an image of the primary current.

The current sensors are based on the closed-loop principle. A soft-magnetic probe is used as field detector of the primary current magnetic field. Compared to standard sensors with Hall-probes, the magnetic probe offers the following application advantages: