These Ferrous Metal Sensors have a magnet and a magnetic field sensing element at the sensor tip. There is an internal PC board that zeros out the magnetic field at the sensing element when there is no ferrous metal within the magnet’s range. If a piece of ferrous metal (AKA Target) is brought into the magnet’s range, the field lines are attracted to it. The larger the target, and the closer the target is to the sensor face, the more the field lines are attracted to it. The internal PC board converts the increased magnetic attraction to an electrical output. This PC board requires a user-supplied DC power supply to work, any voltage from 8 to 30V DC.