What is the working principle of a magnetic flow meter?

Magnetic flow meters (magmeters) work on Faraday's law of electromagnetic induction - a conductor (conductive fluid) moving through a magnetic field generates a voltage proportional to its velocity. Electrodes in the pipe wall measure this voltage, which is proportional to flow rate. Magmeters require minimum fluid conductivity (typically >5 microS/cm), have no moving parts, cause zero pressure drop, and work well with slurries and corrosive fluids.