A Brief Discussion of the Different Fluid Flow Meter Types

A flow meter is used for measuring the flow rate of either gas or liquid substances. The measurement applications used for flow vary along with requirements in engineering. It is a very simple device that can prove to be useful in a variety of industries. This is why development of flow meters has been consistent.

As technology progresses, the flow meter also continues to advance. For example, we now have a digital flow meter aside from the simple, no-nonsense ones. Additionally, there are also different types of flow meters, particularly for fluid like gas and liquid.

To be able to determine which flow meter is best for your needs, it is important to know some basics of every fluid flow meter type.

The Different Kinds of Fluid Flow Meters

flow meter

Fluid flow meters are quite varied in principle and function. Below are the most popular ones.

Positive Displacement or PD Flow Meter

This meter uses rotors that are precision-fitted in measuring the flow of process fluid. It moves automatically when fluid motion is present and then stops as soon as there is no more fluid motion.

A PD floor meter has different types: the oscillating piston (also called rotary piston), the nutating disc, reciprocating piston; and various types of bi-rotors like the oval gear, gear, and helical gear. Positive displacement flow meters are good for non-abrasive fluids (i.e. printing ink, lubrication oils, vegetable fat, animal fat, heating oils, and polymer additives, among others).

The Ultrasonic Doppler Flow Meter

This meter is used to measure the flow of blood that sends out sound to the flowing blood. Its name is inspired by Austrian Christian Doppler, who was a physicist and mathematician. Doppler became famous because of his principle, the Doppler Effect or Doppler Shift, which stated that a wave’s observed frequency is dependent on the observer and source’s relative speed.

Described as a volumetric flow meter, the Ultrasonic Doppler is able to assess certain abnormalities in the flow of blood, especially in the veins and major arteries.

Thermal Flow Meters

This meter utilizes a sensing element that is heated. This heat is directly in proportion to the rate of mass flow. The thermal flow meter’s accuracy level is largely dependent on the actual process’ reliability of calibrations, as well as changes or differences in pressure, heat capacity, temperature, fluid viscosity, and flow rate, among others.

The Electromagnetic Flow Meter


Aside from the mechanical flow meter, the electromagnetic flow meter is also common and popular. This meter is also known as “electromag.”

In the electromagnetic flow meter, the metering tube has a magnetic field and follows the Law of Electromagnetic induction or Faraday’s Law. The law predicts the manner of interaction between a magnetic field and an electric circuit in producing an EMF or electromotive force.

This meter needs water or any conducting fluid in addition to a pipe surface that’s electrically insulated. Thus, it is best used for electrically conductive dirty liquid or wastewater applications.

An electromagnetic flow meter does not have moving parts.

The Turbine Flow Meter

There are a lot of designs for turbine flow meters, but all cling on to the principle that when fluid flows into a pipe and acts on a turbine’s vanes, this will result to the turbine rotor spinning or rotating. It will spin as the liquid goes by the blades. Movement is automatically detected and this leads to the generation of electrical pulses.

In order to get the flow, the spin rate is measured.

The Vortex Flow Meter

This meter is commonly and significantly utilized in applications for steam measurement, especially since it is ideal for both liquid and gas applications. There are three vortex flow meter components:

– bluff body in the flow meter bore

– sensor for detection of vortex and to creation of an electrical impulse

– a circuit for signal amplification

The vortex flow meter is also called an oscillatory flow meter or vortex shedding flow meter.

Differential Pressure Flow Meters

The best examples for this meter are Venturi tubes, flow nozzles, variable area rotameters, and orifice plates. In measuring fluid, the differential pressure flow meter makes use of the Bernoulli’s equation, which states that pressure or potential energy decreases as fluid speed increases.

The Variable Area Flow Meter (Rotameter)

Imagine a plastic or glass tube that has a large top end. Inside it, there is what you call a metering float. This float can move freely inside the glass tube. This float rises because of the fluid flow. This is the operating premise of a rotameter.

Coriolis Flow Meter

This meter is considered one of the most accurate. In fact, its turndown rate is estimated at over 100:1. Used to measure mass like liquids and gases, this meter follows the Coriolis Effect in measuring the mass amount.

These are just some of the types of fluid flow meters. Studying them further will help you find the right one you need in no time.