A basic magnetic flowmeter, also known as a magmeter, measures fluid flow in pipes using the principle of electromagnetic induction. It is specifically designed to measure the flow rate of electrically conductive fluids, such as water, slurries, and certain chemicals. Here's a step-by-step explanation of how it works:
Flow Sensor: The magnetic flowmeter consists of a flow sensor that is installed in-line with the pipe carrying the fluid. The sensor typically has a cylindrical or flanged design, allowing it to be easily integrated into the pipeline.
Magnetic Coils: Inside the flow sensor, there are two sets of coils. One set acts as the excitation coil, which is responsible for generating a magnetic field, and the other set serves as the detection coil. These coils are usually wound around a non-magnetic liner to isolate them from the fluid.
Electromagnetic Field Generation: When the fluid flows through the pipe, it acts as a conductor, and as it moves through the magnetic field generated by the excitation coil, it induces a voltage across the fluid perpendicular to the direction of the flow and the magnetic field lines.
Faraday's Law of Electromagnetic Induction: According to Faraday's law of electromagnetic induction, the voltage induced in a conductor moving through a magnetic field is directly proportional to the velocity of the conductor and the strength of the magnetic field.
Voltage Measurement: The induced voltage is detected by the detection coil, which converts it into a measurable electrical signal. The magnitude of this signal is proportional to the flow velocity of the fluid.
Flow Rate Calculation: The magnetic flowmeter's transmitter processes the signal from the detection coil and uses it to calculate the volumetric flow rate of the fluid based on the cross-sectional area of the pipe and the velocity of the fluid. The transmitter may also account for other factors such as fluid density or temperature, depending on the model and application.
Display and Output: The flow rate information is displayed on the flowmeter's local display or transmitted to a control system or data logger for further processing, monitoring, or recording.
One of the significant advantages of magnetic flowmeters is that they do not have any moving parts in contact with the fluid, which makes them suitable for measuring corrosive and abrasive fluids. However, it's essential to note that magnetic flowmeters are effective only for conductive fluids, and they are not suitable for non-conductive fluids like oil or hydrocarbons.