Do you want to know more about flow meters ?

Flow meters work by measuring the amount of gas, liquid, or steam that passes through or around its sensors. But while flow meter sensors work in many ways, they all need to do the same thing – deliver accurate and repeatable measurements for the specific application, 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 () equals the volumetric flow rate (Q) times the fluid density (ρ): ṁ = Q ∗ ρ


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

image of capillary flow meters
Courtesy of Sierra

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

image of Immersible Thermal Mass
Courtesy of Sierra

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

image of Vortex Shedding
Courtesy of Sierra

Transit-time ultrasonic – 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


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.

  • Thermal mass flow meters can precisely measure mass flow of gases from low to high flows.
  • Vortex meters are ideal for measuring liquid and steam flows at high temperatures and pressures.
  • Ultrasonic meters work well in liquids when you want to avoid pipe cutting or shutdown.
  • Older technologies such as differential pressure, positive displacement, and turbine meters also have their places.

Original article here.

Author: Scott Rouse, Product Line Director @ Sierra Instruments

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