Magnetic flow meter is based upon Faraday’s law of electromagnetic induction. Electromagnetic flow meters are used when the fluid is electrically conductive. As per Faraday’s law when a conductor moves perpendicular through a magnetic field, an emf is induced in the conductor which is proportional to the strength of the magnetic field, the length of the conductor, and the velocity with which the conductor cuts through the field.For a particular flow measurement the magnetic field and the length of the conductor (i.e the diameter of the pipe) are constant. So the voltage induced is directly proportional to the fluid velocity.
There are two types of magnetic flow meters:-
1. AC magnetic Flow meters.
2. DC magnetic Flow meter
1. AC MAGNETIC FLOW METERS :
Alternating current (AC) magnetic flow meters excite the electromagnetic field with AC current. Noise may be produced within the meter or with the process. The zero must be adjusted when the flow meter is full of process fluid at zero flow. Sensitivity of electrodes may be reduced if the electrodes become coated with a non-conductive material.
2. DC MAGNETIC FLOW METER :
Direct current (DC) magnetic flow meters excite the electro-magnetic field with a DC current. DC magnetic flow meters are not subject to inaccuracies due to the coating