A basic magnetic flowmeter, also known as a magnetic flow sensor or magmeter, is a device used to measure the flow rate of electrically conductive fluids (liquids) in pipes. It operates on the principle of Faraday's law of electromagnetic induction. Here's how it works:
Principle of Faraday's Law: Faraday's law states that when a conductor (in this case, the fluid) moves through a magnetic field and cuts across the lines of magnetic flux, an electromotive force (EMF) is induced in the conductor. This EMF is directly proportional to the velocity of the fluid and the strength of the magnetic field.
Construction: A basic magnetic flowmeter consists of a pipe or tube section through which the fluid flows. Coils of wire are wound around the pipe, typically perpendicular to the direction of flow. These coils are the primary and secondary coils.
Magnetic Field Generation: An external magnetic field is generated by passing an electric current through the primary coil. This creates a magnetic field that is orthogonal (perpendicular) to the direction of flow. The magnetic field lines intersect the fluid flowing through the pipe.
Fluid Flow: As the conductive fluid flows through the pipe, it cuts across the magnetic field lines. According to Faraday's law, an EMF is induced in the fluid proportional to its velocity.
Induced Voltage Measurement: The induced EMF generates a voltage in the fluid, which is picked up by the secondary coil. This voltage is proportional to the fluid's velocity, which in turn is related to the flow rate. The secondary coil is connected to a signal processing circuit.
Signal Processing: The signal processing circuit amplifies and processes the induced voltage signal. The circuit measures the voltage's frequency or amplitude changes, which correspond to the fluid's velocity. This processed signal is then converted into a digital value that represents the flow rate.
Output Display and Communication: The digital flow rate information can be displayed on a local indicator or sent to a remote control system for further analysis, recording, or control purposes.
It's important to note that magnetic flowmeters work effectively with electrically conductive fluids, such as water, slurries, acids, and bases. Non-conductive fluids or gases are not suitable for measurement using this type of flowmeter.
Overall, a basic magnetic flowmeter offers advantages like accuracy, low pressure drop, and minimal obstruction to flow. However, it's crucial to ensure proper installation, calibration, and maintenance to achieve accurate and reliable flow measurements.