Water Flow Meter: A Basic Guide For Beginners

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A water flow meter measures the amount of water that flows through a pipe. There are several factors to consider when choosing water flow meter technologies. These include water measurement application, budgetary terms, and maintenance requirements. There are four primary types of water flow meters.

Ultrasonic flow meters

Obvious from its name, these use ultrasound to measure the speed of a fluid flowing in the pipe to measure volumetric flow. Let’s take a transit-time ultrasonic liquid flow meter for an example. An ultrasonic signal gets transmitted in the direction of the flowing fluid downstream. Another signal gets transmitted against the flowing fluid upstream. The time for the sonic pulse to travel downstream gets compared to the time for it to travel upstream. The calculation of the velocity of the flowing fluid uses this differential time. This fluid velocity can help in calculating the volumetric flow rate in the pipe. Clamp-on ultrasonic meters measure water from outside of the pipe. The meters do this by shooting pulses of sound  through the pipe walls. That is why ultrasonic flow meters are ideal for measuring water flow in large pipes.

Mechanical flow meters

The mechanical types of water flow meters are the most common and affordable type. They measure flow through turbine rotation with a propeller, shunt, or paddle wheel design. These meters measure the speed of flowing water needed to rotate a turbine or piston. The rotational speed of the blades is proportional to the volumetric flow rate of the water. These meters are not ideal with a low flow of water.

Vortex flow meters

These meters use vortices shed from a sensor immersed in the flow. Vortices are forces of nature. In vortex flow meters, a sensor tab flexes from side to side as each vortex flows past. It produces a frequency output in direct proportion to the volumetric flow rate. Multivariable vortex flow meters can measure up to five process variables with one process connection. These are volumetric flow rate, density, pressure, mass flow, and temperature. These meters are great on very large pipes.

Magnetic flow meters

By using a magnetic field, magnetic flow meters measure the speed of a fluid flowing in the pipe to measure volumetric flow. Faraday’s Law of Electromagnetic Induction is vital here. This Law states that there is voltage generation when liquid flows through a magnetic field. More voltage gets generated when the fluid flows quicker. The voltage generated and the movement of the water are proportional to each other. Electronics process the voltage signal into the volumetric flow rate. These meters are accurate on an intermediate level only. They are not suitable for custody transfer applications.

Choosing the best type of water flow meter depends on why you need one. Each flow meter is ideal in their unique ways.

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