How Flow Meters Work

There are many types of flow meters
available for use in industrial automation. Depending on the product to be measured, whether it be liquid or gas, some basic principles apply to how the meters work. If you enjoy these videos, be
sure to click the like button and subscribe so you don’t miss any future videos. Let’s take a Magnetic Flow Meter or mag meter. The measured liquid must be water based or conductive. This makes the mag meter a
great choice for waste water or process water that is considered fouled or dirty. Mag meters are volumetric meters
that have no moving parts. This is ideal for those areas where you wouldn’t want to be
exposed to the measured liquid while working on the meter. The way a mag meter works is based on
a formula called Faraday’s formula. Firstly, again, the liquid must be conductive. A voltage is measured that is dependent
on the average velocity of liquid times the strength of the magnetic field times the length of the conductor (this is the distance between the electrodes). This is all that wonderful science stuff, you know like E=m × c 2. It’s
Einstein’s theory of relativity. We’ve all heard of or seen the equation. Many of us don’t know what it means however, the people that do
know how to use the equation have used it to for both benefit and detriment, eg: the atom bomb. We don’t need to know Faraday’s
formula to use a mag meter. We don’t necessarily even need
to know what that formula is, we just know that whomever invented the mag meter used the formula to produce a signal voltage
that can be measured by your automation process. While mag meters work based on Faraday’s formula, other flow meters work in different ways. For instance, a mechanical
flow meter has some moving, internal parts which may not
fit with specific applications such as dirty water that carries large particles that may cause damage or obstruct the internal parts. The mechanical flow meter has
a rotational device inside such as a paddle wheel or a propeller. Liquid flowing through a pipe causes
the rotation of the internal paddle, which creates a flow rate that is proportional
to the rotational speed of the internal paddle. The mechanical flow meter is
easier for laymen to understand. Peddling a bicycle slowly moves you slowly, while pedaling quickly will move you much faster. Direct correlation between how fast the pedals rotate (therefore wheels) and how fast you go down the road. No formula needed, just pedal faster, move faster. Same principle as the internal paddle, the faster it is rotating, the more flow
going through the pipe which in turn, sends a graduated signal to your PLC. That’s the simplified version
but there are other factors that the manufacturer takes care of for you. Piping size, water temperature, etc, all go into a formula that will
correlate the rotational speed with a unit measurement such as gallons per minute. Yet still, there are other types of flow meters. There’s vortex, which measures vortices, essentially, a sensor tab will bend and flex
from side to side as the vortex passes. The bend and flex action will
then produce an output frequency that is proportional to volumetric flow. There are also ultrasonic flow meters. The principle behind these meters is that an ultrasonic signal is transmitted downstream or in the direction of the flow while
another signal is transmitted upstream. The delta or differential time is used
to calculate the velocity of the liquid. That velocity is then used to calculate
the volumetric flow through the pipe. As you can see, there are many types of
flow meters for various applications. You don’t really need to know the
formulas and science behind the scenes but hopefully we have given you some
idea of how a flow meter works. make sure that you head over to to find even more training material for
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37 thoughts on “How Flow Meters Work

  1. @realpars do you have the Advance PLC course on udemy website?
    i want to purchase it from udemy..

  2. I wish I found much earlier. I wasted so much money trying to learn programing which was not working. But at realpars, you learn programing and a lot more about automation in general which are relevant as well. Otherwise you go in the field and realize knowing programing alone is not enough. I have acquired more knowledge here that I am able to technically hold automation conversations.

    Keep up the good work

    We need some more videos on level 9 please.

  3. Thank you very much
    Question !! Have you disable the monthly subscribe in Realpars?
    I'm really interested to watch your professional courses asap

  4. _____ gives the flow rates as well as the totalised flow.
    (a) rotating disc flow meter
    (b) flow nozzle
    (c) ultrasonic flow meter
    (d) none of above

  5. One thing to remember is that most flowmeters measure velocity and compute the flow rate based on the square footage of the flowtube. That is to say, the meter ASSUMES the flowtube is completely full and there are no bubbles in the media being measured. Easier for gasses than liquids. Most flowmeters also have a minimum velocity they need to see before they start reading flowrate. Therefore, even though they say they have a range of zero to something, it’s actually some number above zero to something.

  6. I have a question…
    If I want to calibrate PT
    For example
    PT-1234 having a range (25 to 50mmwc) how can I check into 4 to 20mA.

  7. Amazing video! Regardless of your experience, you have to have a subscription with RealPars. About a 120 dollars a year.

  8. These flowmeters are used very much in water transfer in the oilfield . I have 12 years in the oilfield and honesty the digital ones suck bad !!!

  9. Thought i'm gonna find Turbine,Positive dispacement ,and Coriolis meters in the video .. but thanks anyway .. greetings from the Oil training institute of Baghdad/Iraq ??

  10. hi there i would like to ask you i deal with digital flow meter in my work it changed its reading from real number to hexadecimal number for example from 97834567 to 1005E08 how could know the real number should i use conversion from hexa to decimal ?

  11. Ohhh………… I remember having to replace a meter once. I was supposed to instruct another work buddy and take the lead in that operation. Job was done but up until today I was really confused how the hell is that thing going to measure flow. It was the magnetic one. Just a straight hole through the whole thing. Yeah dont expect anyone whether above or below us to know everything lol. Thankfully a lot of stuff are idiot proofed so we just need to lizard brain them to completion and hope things work. Thanks for the video. Now thats one thing I can get off my mind.

  12. can we use mechanical flow meter at the inlet and outlet of a water tabk to measure the daily discharge? pls reply

  13. Which one is suitable for acid process and can be reduce, increase the flow rate, calibration option and all

  14. Absolutely useless.. Maybe a LITTLE useful for empty headeds but for someone who knows a little about science this video is utter crap

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