Flow meters

Flow meters are instruments that quantify the linear and nonlinear, mass or volumetric flow rate of liquids or gases.

Some flow meters measure the rate of flow of substance e.g. 1000 liters per minute while other flow meters measure the total volume of liquid that has passed e.g.  10000 liters. There are however flow meters that display both flow rate and amount.

A flow meter will comprise of two components namely a transducer and a transmitter. The transducer is used to sense the fluid that passes through it where as the transmitter generates a flow signal for the raw signal it receives from the transducer.

Flow meters operate on two simple principles:

Volume = Area * Velocity.    Meaning Volume of fluid (V) equals the cross-sectional area of the pipe (A) times the average velocity of the liquid

Mass flow = Fluid density.    Meaning the mass flow of fluid equals fluid density times volume.   

Volumetric flow meters usually measure the volume of fluid. The positive displacement flow meter is the sole example.

Velocity flow meters measure the velocity of the fluid to calculate the volumetric flow. Ultrasonic flow meters, magnetic flow meters, turbine flow meters, and vortex shedding flow meters fall under velocity flow meters.

Mass flow meters measure the mass flow of fluids. Coriolis mass and thermal flow meters are example of mass flow meters.

Inferential flow meters determine and measure flow by inference from other measured parameters such as heat.

Optical flow meters utilize light to determine the rate of flow. Laser-based optical flow meters calculate the definite speed of particles flowing along with fluids.

Thermal mass flow meters normally use mixture of heated elements and temperature sensors to calculate the difference between static and flowing heat transfer to a fluid.