How Do Flow Meters Work - Flowmeter Types And Principles

Posted by Adrian Hardmann

The need to measure the flow rate in a pipe or tube has many aaplications for individuals and in business. Generally, gases and liquids need to be measured. there are two ways to do this. The volumetric flow rate is a measure of the volume of the medium by time. The mass flow rate is a measure of the mass of the medium by time.

Flow meters can be used in many ways. Some of these ways apply to individuals, like the peak flow meter that measures lung capacity and can help asthmatics to know if an attack is likely to occur.

Other than that, flow meters are used in many industries, like the food processing industry, water management, semi conductor fabrication and many others. This article will give a brief overview of how flow meters work.

Flow meters are generally classified by the principal that governs their operation or possibly by their applications. For instance, mass flow meters measure the flow rate of a medium in terms of it’s mass.

One example of a principle governing the name of a meter is the Coriolis flow meter. It uses the Coriolis effect to determine the mass of a fluid passing through two vibrating tubes or pipes. The idea being that by understanding the change in the characteristics of the wave patterns in the vibrating tubes, you can correlate the flow rate of the substance passing through.

Ultrasonic and Doppler shift flow meters also use the changes caused to sound waves to correlate a rate of flow for the medium passing through the meter.

In the case of the ultrasonic flow meter, two transmitters of ultrasonic sound waves are placed at the ends of a pipe where the measure is to take place. Each transmitter sends a pulse of sound.

The ultrasonic waves are recorded by receivers at opposite ends of the pipe. One wave is sent in the direction of the flow of the liquid to be measured. The other wave is sent in the opposite direction to the flow.

Provided some information is known about the type of pipe used and a few constants for the liquid or gas, then the flow rate can be determined from the time difference of each wave.

Doppler shift flow meters also use waves to determine the flow rate. They work on the principle that a sound wave that bounces off a moving particle in the medium has it’s frequency and amplitude changed. By determining the change in these dimensions, the flow rate of the medium can be determined.

A more traditional type of flow meter is the variable area flow meter that uses a float in a calibrated tube. When a substance passes through the tube, the float is displaced by the flow.

By taking the reading from the calibrated tube an indication of the flow rate can be determined. This is the principle of the peak flow meter used for lung capacity and asthma.

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