Question

A flow meter that is independent of liquid density is

• A. Rota meter
• B. Electromagnetic flow meter
• C. Venturi meter
• D. Orifice meter

Hint:

Electromagnetic flow meters are "obstructionless," meaning they have no moving parts in the flow stream. This makes them perfect for measuring "slurries" or corrosive liquids.

Answer 1

The Correct Option is B

Many flow measurement devices rely on pressure differences or buoyancy, which are inherently dependent on the density of the fluid being measured. However, the electromagnetic flow meter operates on a completely different physical principle. 1. Faraday's Law of Induction: The electromagnetic flow meter works based on Faraday's Law, which states that a voltage is induced in a conductor moving through a magnetic field. In this case, the conductive liquid itself is the moving conductor.

2. Independence from Physical Properties: The induced voltage ($E$) is given by the equation: $$E = B \cdot v \cdot D$$ Where:

• $B$ is the magnetic field strength.

• $v$ is the average velocity of the liquid.

• $D$ is the diameter of the pipe.

3. Analysis: Note that

density ($\rho$) does not appear in the voltage equation. As long as the liquid has a minimum level of electrical conductivity, the meter provides an accurate flow rate measurement regardless of changes in density, viscosity, temperature, or pressure. In contrast, rotameters (buoyancy-based) and Venturi/Orifice meters (pressure-based) are all significantly affected by the density of the fluid.