A basic magnetic flowmeter, also known as a magnetic flow sensor or electromagnetic flowmeter, is a type of flow measurement device used to determine the flow rate of conductive fluids (such as water, slurry, or chemicals) in pipes. It operates on the principle of electromagnetic induction to measure the fluid flow. Here's how it works:
Construction: A magnetic flowmeter typically consists of a non-magnetic pipe made of materials such as plastic, glass, or ceramic, through which the conductive fluid flows. Inside the pipe, two coils are mounted: one coil acts as the primary coil (excitation coil), and the other coil serves as the secondary coil (detection coil).
Magnetic field generation: An AC current is passed through the primary coil, creating a magnetic field that is perpendicular to the direction of fluid flow. This magnetic field is usually constant and does not vary with the flow rate.
Fluid flow through the magnetic field: As the conductive fluid flows through the magnetic field, it cuts across the lines of magnetic flux. The movement of the conductive fluid induces a voltage in the fluid perpendicular to both the magnetic field and the fluid flow direction. This voltage is called the "induced electromotive force" (EMF) or "flow velocity signal."
Measurement of induced voltage: The secondary coil is used to measure the induced electromotive force (EMF) or the voltage generated due to the fluid flow. The magnitude of the induced voltage is directly proportional to the velocity of the fluid and, therefore, to the flow rate.
Flow rate calculation: The induced voltage signal is then amplified and processed by the flowmeter's electronics. The electronics calculate the flow rate based on the relationship between the induced voltage and the fluid velocity. The flow rate is typically displayed on a digital or analog output, providing real-time measurement of the fluid flow.
It's important to note that magnetic flowmeters are effective for measuring the flow of conductive fluids but are not suitable for non-conductive fluids like oils, hydrocarbons, or gases. Additionally, the flowmeter's accuracy may be affected by factors such as the presence of air bubbles or solid particles in the fluid, pipe material, and the quality of the flowmeter calibration. Calibration and proper installation are critical for accurate and reliable flow measurement.