When you have a question about process automation that needs a short answer, let us know with #WishIknew and #Visaya! We’ll reply with a #WishIknew post. It’ll give a quick explanation, then some related articles, videos, or reviews if you want to know more.

I wish I knew what flow measurement is!

Okay, this question is pretty basic, but I realized recently that we still didn’t have an answer for that here! So why not clarify this standard Google question? After all, we want to help our general audience as well as our engineer friends.

Firstly, for our non-engineers, I’ll give an example of flow in your daily life. Secondly, I’ll get into some technical details to complete your  understanding of the topic itself.

Okay, let’s use your home as an example. You have a water supply that you use to wash your dishes, take showers, and other stuff, and you pay based on how much water you use, right? Basically, the water company tallies your monthly use with a flow meter.

image of flow meter water usage
Image of Finansalbilinc

For instance, if you want to take a shower but haven’t turned it on yet, then you have zero flow. When you turn the valve to let the water flow, the stream of water increases up to the maximum of the valve. The water flow meter installed in the main pipe in your home measures that flow for as long as you have the tap open. And that data goes with the rest of your water use to totalize all the water consumption of your home.

You can have different working principles to measure flow, but we can get into those later. Also, you can have a flow meter for gas consumption that can use different methods too.

The technical explanation

Technically, flow is a quantity of fluid or gas passing through a known area  in a specific period of time. We also have two types of flow, volumetric and mass flow.

Volumetric flow:  When you have a volume of fluid passing through an area in a unit of time. We measure volumetric flow in units such as cubic meter per second and hour (m³/s, m³/h) or liter per second and hour (l/s, l/h).

Qv = v x A

Qv = volumetric flow

v = flow velocity

A = cross-sectional area


Qv = V/t

Qv = volumetric flow

V = volume

t = time

Mass flow: When you have a mass of fluid or gas passing through a pipe during a certain unit of time. We measure mass flow by kilogram per second and hour (kg/s, kg/h).

Qm = ρ x v x A

Qm = mass flow

ρ = density

v = flow velocity

A = cross-sectional area

Qm = m/t

Qm = Mass flow

m = fluid mass

t = time

We have several articles here on Visaya that explain the different principles we use for the electromagnetic flow meter, Coriolis flow meter,  vortex, and others.

And here we have a colleague of mine, Walt Boyes. He talks more about flow measurement in this video:

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