Flow meters work by measuring the amount of gas, liquid, or steam that passes through or around its sensors. While they all do the same thing, there are many ways to do it – hence the many flow meter types to choose from. This article helps you choose which one you need to deliver accurate and repeatable measurements for specific applications, whether for general research, process control, or monitoring.

Flow meters measure either mass or volume. In a volumetric flow meter, the flow (Q) equals the cross section of the pipe (A) times the velocity of the fluid (v):  Q = A * v

And for things like chemical reactions, combustion, or buying and selling gases, you need the mass flow rate. So in a mass flow meter, the mass flow (ṁ) equals the volumetric flow rate (Q) times the fluid density (ρ): ṁ = Q ∗ ρ

Picomag Smart electromagnetic flowmeter with wireless remote access
in the shop from 480 €

Flow Meter Types

Capillary thermal mass flow meter

Thermal heat transferring between gas in a very small tube (the capillary) and a set of sensors indicates the gas mass flow.

Immersible thermal mass

More thermal heat, but this time transferred from a heated sensor immersed in the flow.

Vortex shedding flow meter

Another sensor immersed in the flow, but this one uses vortices and a computed fluid density to measure volumetric and/or mass flow.

Transit-time ultrasonic flow meter

On the other hand, this one can sense flow speed from the outside of the pipe with ultrasound, so no immersion necessary. 

image of Transit-Time Ultrasonic
Courtesy of Sierra

Applications for various flow meter types

So what and how will your flow meter measure?

  • Gas, liquid or steam?
  • Very large flows or only small flows?
  • High or low temperature or pressure conditions?
  • Simple or complicated pipe layouts?
  • Costly products that need precise measurement?

Some flowmeters work better when measuring different things.

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