A basic magnetic flowmeter, also known as a magnetic flow sensor or magmeter, measures fluid flow in pipes using the principle of electromagnetic induction. The working principle of a magnetic flowmeter involves the following steps:
Installation: The magnetic flowmeter is typically installed in-line with the pipe carrying the fluid whose flow rate needs to be measured. It is essential to ensure the flowmeter is properly sized and installed to get accurate measurements.
Magnetic field generation: The flowmeter consists of a non-magnetic pipe lining and a pair of electromagnetic coils (usually made of copper) mounted on the outside of the pipe. These coils are known as the excitation or drive coils.
Fluid flow through the pipe: As the fluid flows through the pipe, it acts as a conductor moving through a magnetic field.
Induction of voltage: When the fluid (conductor) flows through the magnetic field created by the excitation coils, it generates an electromotive force (EMF) due to electromagnetic induction. The magnitude of this induced voltage is directly proportional to the fluid velocity.
Measuring the induced voltage: The voltage generated due to electromagnetic induction is picked up by two electrodes mounted on the interior surface of the flowmeter, perpendicular to the magnetic field. These electrodes act as the sensing or pickup coils.
Output signal: The induced voltage signal is then amplified and processed by the flowmeter's electronics to produce a flow rate reading, which is often displayed as volumetric flow rate (e.g., liters per minute, gallons per hour) or mass flow rate (e.g., kilograms per second).
Advantages of magnetic flowmeters include their non-intrusive nature (no moving parts within the pipe), suitability for measuring conductive fluids (e.g., water, acids, slurries), and their ability to handle a wide range of flow rates. However, they may not be suitable for non-conductive fluids (e.g., oils, hydrocarbons) and applications with low conductivity fluids or gases. Proper grounding and calibration are critical for accurate measurements.