The exact working principle depends on the current sensor Type of. However, the most common type is inductive current transformers, which are mainly used to convert alternating current. In general, its working principle is very similar to that of classical transformers. The working principle of inductive current transformer is introduced as follows:

A conductive material with good magnetism connects two circuits, namely the primary circuit and the secondary circuit. This material is usually ferromagnetic ceramics, which is called ferrite. The primary and secondary circuits are then helically wound around the ferrite. However, there are also designs in which the primary circuit consists of only one cable passing through the center of the ferrite.

The AC to be measured flows through the primary circuit, but it is too high for the ammeter. According to Amper è's law, the magnetic field generated by alternating current changes its polarity continuously just like alternating current.

The mentioned magnetic field is bound in ferrite because ferrite is a magnetic conductor. Therefore, it also exists in the secondary circuit. According to another physical law, the law of induction, this changing magnetic field will generate current in the secondary circuit. In the case of current sensor, the secondary current is less than the primary current.

If people look more closely at the basic physical equations, it is possible to determine the conversion rate.

The conversion ratio indicates how much current the current sensor reduces, which corresponds to the number of windings (N) of the primary and secondary circuits (N_primary/N_secondary).

Note: There are more possibilities to realize the current sensor. For example, well-known structures are based on Hall probes or Rogowski coils.