Current sensors appear nothing more than a square piece with a hole in the center. Yet this design allows them to take accurate current and voltage measurements for direct current (DC) systems. This is one of the most notable applications of the Hall Effect, a phenomenon that affects charged carriers like wires.
Discovered by American physicist Edwin Herbert Hall in 1879, the Hall Effect explains the tendency of magnetic fields to behave differently when an electric current passes through the carrier. The field passes through a Hall Effect Device, i.e. the current sensor, where it generates an output signal.
For this reason, current sensors are equipped with powerful magnets. Various magnetic materials are used in current sensors, but the most common are iron-based. In split-core sensors, three of the most well-known magnetic materials are ferrosilicon (FeSi), ferronickel (FeNi), and ferrite. Iron is particularly useful because of its well-known magnetic properties and atomic structure that give it unparalleled magnetism.
Although quite expensive, FeNi transducers are touted as the best type of magnets for the job. Tests show that ferrite transducers are the most accurate, but manufacturers seldom make them due to fabrication limitations. FeSi are the least expensive of the three but also the least accurate; that being said, they still find use in applications that do not require highly accurate readings.