After differential pressure and positive displacement flow meters, the magnetic flow meter is the most popular type of flow meter. Technically, it is called an electromagnetic flow meter; however, most people know it as simply a mag meter. At work in a mag meter is the principle of electromagnetic induction.
The mag meter requires a conducting fluid and electrical insulating pipe surface. Water containing ions and a rubber-lined steel tube may be used. The magnetic field of a mag meter is constantly reversed. This is done to cancel out static potential different. A draw back is the impeded use of permanent magnets for magnetic flow meters.