The Hall Sensor measures the Hall Effect, which is a production of a voltage difference across an electrical conductor, transverse to an electric current in the conductor as well as a magnetic field perpendicular to the current. The output of the continuous-time switch Hall sensor on this Twig switches low and turns on when a magnetic field (south polarity) perpendicular to the Hall sensor exceeds the BOP threshold, and it switches high and turn on when the magnetic field disappears.