The electromagnetic flow meters works based on the principle of Faraday's Law.

When a conductive medium flows in the flow meter crossing the magnetic field, that will create an induced electromotive force (EMF). Due to the presence of EMF, an induced current is created across the closed loop.

In case of no flow in the flow meter, no induced current will be generated and therefore the meter gives zero flow. As the velocity of conductive medium increases, the value of emf and thus current increases. from the formula: emf = K*B*V*d (K constant, B magnetic flux value, V velocity of medium, d diameter of flow meter), the velocity of the conductive medium is calculated and therefore the volumetric flow (flow = V*pi*d*d/4) is then shown on the flow meter screen.