Principle:

Magnetic resonance makes use of a fundamental property of atoms and in effect makes it possible to “count” hydrogen atoms. Since oil, gas and water all contain hydrogen atoms, multiphase flow can be measured using magnetic resonance.

For this purpose the fluids are magnetised and subsequently excited by radio frequency pulses. The hydrogen atoms respond to the pulses and send back echoes which are recorded. The amplitude of the echoes and the rate at which they decay is used to calculate the flow rates. The difference in magnetic resonance properties allows making a distinction between the flowrates of oil, gas and water.

Conceptually, a magnetic resonance multiphase flowmeter consists of three sequential steps:

1. Creating a net magnetization by aligning the magnetic moments of hydrogen atoms in an applied, constant magnetic field.

2. Perturbing the alignment of hydrogen atoms by employing electro-magnetic radio frequency (RF) pulses.

3. Detecting the radio-frequency signal emitted by the hydrogen atoms during their return to equilibrium alignment in the external magnetic field

This measurement principle also forms the basis of magnetic resonance based flow metering.

Article Source: krohne