Working principle of magnetic flowmeter

flowmeasurement

#1

Magnetic flowmeter works on the principle of electromagnetic induction. When an electrical conductor moves perpendicular to a magnetic field, a voltage is induced in that conductor perpendicular to both the magnetic flux lines and the direction of motion.

Here the conductor is the flowing water and external magnetic field is applied using magnets placed outside the pipe perpendicular to the flow channel.

magnetic flowmeter

The liquid passing through the pipe should be a good conductor. The liquid flow cuts perpendicularly through the magnetic field.Metal electrodes opposite each other in the pipe wall intercept this voltage, making it readable to an electronic circuit.

The induced emf in the circuit by the linear motion of the conductor is:

e= Blv

e = induced emf
B = Magnetic flux intensity
l = length of conductor passing through the magnetic field
v = velocity of conductor

Assume the magnetic field flux intensity is fixed and also the length of the conductor is fixed which is the diameter length of the pipe. Now the only varying factor is which influence the voltage is the velocity of the conductor that is the fluid velocity. The emf is induced across the wire

Requirements for magnetic flowmeter:

  • The liquid must be a good conductor.

  • The pipe must be completely filled with liquid to ensure contact with both probes as well as
    to ensure flow across the entire cross-section of the pipe

  • The pipe must be completely filled with liquid to ensure contact with both probes as well as
    to ensure flow across the entire cross-section of the pipe