Ultrasonic Flow Meter Explained | Working Principles
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⌚Timestamps:
00:00 - Intro
00:54 - Ultrasonic flow meter
01:20 - Physical principles
02:00 - Mechanical principles
02:49 - Electrical principles
03:16 - Dynamics
05:16 - Design considerations
06:40 - Applications
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There are many types of process flow meters:
- Coriolis mass flow meters;
- Positive displacement flow meters, such as turbine meters;
- Volumetric flow meters, like the ultrasonic flow meter, just to name a few.
Each type of flow meter operates on different physical, mechanical, and electrical principles.
In this video, we will explore the working principles for Ultrasonic flow meters. We will demonstrate how a simple physical property, sound, can be used to measure the rate of flow of a fluid moving in a pipe.
Ultrasonic flow meters measure the volumetric flow of the fluid, that is, the number of gallons or liters per unit time.
Ultrasonic flow meters require the use and understanding of some basic physical, mechanical and electrical principles that allow ultrasonic flow meters to accurately measure flow rate over a wide range of flow conditions.
Here are a few examples of using basic physical, mechanical, and electrical principles to measure the flow rate using an ultrasonic flow meter:
1) When fluid flows through a pipe, it flows in one direction at a velocity that is influenced by many factors, such as temperature, pressure, fluid viscosity, and pipe size.
2) Sound waves move through a fluid based on the transmission of vibrations through the fluid. These mechanical oscillations between molecules of the flowing fluid are passed to adjacent molecules, thereby transferring the wave to those adjacent molecules.
3) An ultrasonic flow meter generates sound waves using a rapidly vibrating piezoelectric crystal. These special ceramic crystals deform when an electric current is applied. By rapidly changing the electrical signal, the crystal will deform in one direction, and then in the other, causing a high-frequency wave to be generated.
An ultrasonic flow meter consists of at least one sensor and transducer pair. Each member of the pair can act both as a transmitter and a receiver.
- When in transmit mode, an oscillating electrical current creates a vibration in the piezoelectric crystal, and an ultrasonic wave is sent through the flowing fluid.
- When in receive mode, an ultrasonic wave passing through the fluid creates vibration in the piezoelectric crystal, and an electrical impulse is generated.
A pulse that travels from the upstream element to the downstream element, or with the flow, takes less time to make the trip than the pulse returning in the opposite direction, or against the flow. The difference in this time of flight between the two pulses is directly proportional to the flow velocity.
Since the volumetric flow rate is equal to velocity times the cross-sectional area of the pipe, which is fixed at the flow meter, this measurement yields the flow rate. This type of ultrasonic flow meter is appropriately named a time of flight flow meter.
In order to eliminate differences in the flow profile across the pipe, additional pairs of sensors are added to ensure an accurate measurement. Each pair of transmitter and receiver forms what is called a chord.
There are many different ways that the sensors are mounted in a time of flight ultrasonic flow meter.
- The sound wave pulses can travel directly from transmitter to receiver or the pipe wall can be used to reflect the sound waves.
- The sensors can be wetted, or built into the wall of the flow meter such that the sensors contact the fluid. Or the sensors can be strapped to the exterior of the pipe, where the sensors do not contact the fluid. The non-contact sensors are not quite as accurate.
Ultrasonic flow meters are an excellent choice for high-pressure, high-flow applications.
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I was literally waiting for an ultrasonic flowmeter video.
Thanks realspars.
Hope you enjoyed it!
Thank you Realpars
Concise, precise and informative
Thanks a lot!
Just as usual, amazing job!
Thank you, Daniel!
Perfect educational video for me. Thank you for sharing.
Glad you enjoyed it!
Great video. Very informative and easy to understand. You have gained a subscriber!
Awesome, thank you!
Thank you for useful contents
Our pleasure!
Very information video respect full real pars. Ultrasonic video
Big thanks!
Very useful clip, thank you for sharing
Glad it was helpful! You're very welcome.
Thank you! This is awesome!
Glad it was helpful!
Thank you!!
No worries!
Thanks RealPars
You're very welcome, Bitebo!
Thanks real pars. Very good
Always welcome!
Thanks for your transfer knowledge
It's our pleasure
very informative thanks real pars make more videos on instrumentations
Thanks for your support, Asad!
Excellent video.
Thank you very much, Jeff!
Great!
Fantastic job
Thank you very much!
Great explanation given thanks sir
Always welcome!
Perfect
Proud to be your subscriber.Thanks for this video.. 👍 Grabbing ease of learning in your videos..
Thanks a lot, Logesh! Great to hear
Great video...Can you make such an informative video on multi phase flow metering (with electrode and gamma ray source) principles??
Hi Ali!
Thanks for your comment and your suggestion. I will pass this on to our course developers!
Thanks for sharing and happy learning!
I remember beta gauges from the 80's. Nasty, dangerous things...
Thank you
You're welcome!
Great
Thanks I'm addicted to your uploads I don't miss any
Glad to hear that!
Thanks
Our pleasure!
As usual excellent work. Can anyone tell please:
In which case, (for gases) we have to measure " mass flow rate" and in which case we will have to measure "volumetric flow rate"?
Thanks.
If you know the fluid you are measuring, and if you know the temperature and pressure that it is at, then you can always convert between mass flow rate and volumetric flow rate. You can measure either, bring the measurement into the process supervisory computer, and convert there if needed.
I suppose in a mixing scenario where you are metering the proportion of one material to another. Basically, so many pounds of this, to so many pounds of that. But for gases?
Like Alexander said, adding a temperature sensor (as well as some math) will give you your mass. One exception to this is for steam. For most applications you can count on what its temperature is going to be, and just plug that number in.
Or so says the ABB rep that sold me my meters... :)
@@MrWaalkman Thanks for your kind reply.
For gas turbine, mass flow rate is measured but for domestic consumption, it's volumetric flow rate.
I may be wrong.
Thanks.
@@alexandernorman5337 Thanks for your kind reply. Keep it up.
@@cck1496 You're welcome of course!
When it comes to (natural) gas meters, I'm familiar with the Roots style (positive displacement), Diaphragm (bellows) meter (which IMHO are pretty cool as to how they work), and turbine gas meters (not positive displacement).
What they all have in common is that you can get a temperature compensating drive for your meter's dial to correct for changes in measurement due to temperature. These gauge faces are (usually? always?) painted red. And you will see both flavors out in the wild (some municipalities choosing not to use compensation. Most seem to). So either way you are correct. :)
Some random rambling follows...
You also can usually install a pulser such as the "Pulsimatic" transmitter which will give you a pulse for a given volume passed through the meter (like one pulse per 10 cubic meters of gas). The standard setup on these is a C-form contact block which can be ordered instead with an A-form contact block. It will last much, much, longer with the A-form contact block. I would know, one of my assignments at Schneider Electric was to intentionally break things to see how long they would last in the field. Great assignment! I had no problem causing the C-form contact block to fail, but I never managed to make the A-form one break. My other assignment at Schneider was in Okinawa, which was pretty nice too. :)
And occasionally you will see "shadow" meters installed when a facility is concerned that the utility's meter in not functioning properly. The opposite is true as well. Utilities have fake transformer cans that can house a meter to see if a homeowner or business owner is stealing power from the utility.
When it comes to metering Liquified Natural Gas (LNG) or Liquified Propane Gas (LPG), it's a completely different animal. LPG has a Centipoise of .1 (for reference, water has a Centipoise of 1, making it 10 times more viscous than LPG). Which makes metering and pumping LPG a bit of a bear to do.
how would you compare these to thermal mass flow meters for compressed air flow measurement?
Since most gas flows of this type are small, thermal mass flow meters have the advantage of a smaller footprint than ultrasonic flow meters. For flow rates in the l/min realm, thermal mass flow meters are the only viable option. Ultrasonic flow meters typically require entrained solids to be useful in gas applications, and for compressed air, that is not acceptable.
Ultrasonic flowmeters have one outstanding advantage in that you can temporarily mount them to existing pipes. This means that you can make measurements on all of your piping with just one meter. This saves a ton of money compared to installing a flowmeter per pipe.
The downside is that (in my experience) the external ultrasonic flowmeters are a bit finicky to set up. But that can be said for a number of flowmeters. When it comes to metering, there are lies, damn lies, and flowmeters.
And ultrasonic flowmeters also require 10x - 15x of straight pipe before the flowmeter and 5x of straight pipe past it. But this is a typical requirement for most other types of flowmeters as well.
What this means is that if your pipe is 2" in diameter, then you will need 20" to 30" of straight pipe ahead of the meter, and 10" past it. Not a big deal when your pipe diameter is small, but try it on some 60" pipes (ductwork) sometime. :)
Very good information. Keep it up.
Thank you for your comments on ultrasonic flowmeters. These "clamp-on" type flowmeters have a wide range of applications, especially for processes where it is either too difficult to physically install an in-line flow meter type or the process is not amenable to in-line metering. Upstream and downstream pipe runs are considerations that cannot be overlooked, especially if you want to have the best measurement accuracy. Again, great comments, and thank you for supporting Realpars!
Well, you don't need to meet that requirement you cite for straight pipe. You need to meet that to achieve the highest accuracy. But if you only need to be within ~5% then you can work with a lot less.
@@alexandernorman5337 Not according to almost every installation guide that I have ever read. Coriolis meters don't need straight pipe IIRC, nor do wafer mags and possibly positive displacement meters, but pretty much everything else does. And if your upstream bends are not on the same plane then you need even more straight pipe.
And I don't know if I agree with the 5% inaccuracy limit, that would likely depend on the type of flowmeter more than anything else. And the brand of meter makes a difference of course, some being better than others. I've definitely seen worse than 5%.
I do know that the thermal flowmeters that we installed in place of the wafer mag meters didn't have the 10x, 5x "smoothing" zones and performed very poorly. But the application allowed for a 50% error without causing any process problems (we just needed to know that material was flowing, we didn't really care what the actual flow rate was). And these meters were all over the place. Any given instant you might see a 50% change in flow. But for our purposes they did just fine.
The thermal flow meters were *very* attractive because they were completely smooth on the inside without any obstructions whatsoever. Because we were running paint through the meters we had to be careful not to create a place for "dirt" to accumulate. "Dirt" in this case is paint shop slang for paint clumps. Not actual dirt. Basically we didn't want goobers to form and plug up the robots. We also have to keep the amount of "shear" to the paint at a minimum. Shear breaks down the paint affecting the finish. So positive-displacement meters such as Roots type meters are out as well. Flow straighteners are a no-no too.
DP, vortex, and turbine meters would have contributed to dirt. Coriolis was too expensive, and we didn't have enough room for ultrasonic meters. So thermals it was.
The thermal meters fit in where the mags once were, with some changes to the plumbing of course, as well as sacrificing the straight flow requirements. But it all fit within the allotted equipment space.
But so be it. If nothing else engineering is a game of compromises...
So why replace the wafer mags? They were purchased without fully considering what the properties of the materials were that were going to be running through the meter. The meters were there for measuring the flow of paint as well as solvent that was being circulated through the tanks to the robots and then back to the tanks. It turns out that the paint that we were planning on using was non-metallic (as well as the solvent of course), so all 37 wafer mags showed "Empty pipe?" on each meter when running.
Wafer mag meters, or at least these wafer mags, require metallic particles to function. So 37 brand new wafer mags in the dumpster.
@@realpars You're welcome! And it's always a treat to see a new video show up. :)
Its Great video, more informative ..we need paint flow detect device. We take trail on Keyence FD_Q , it sense hardener and thinner only. Paint flow quantity not detect. Pls suggest any other flow that's sense flow quantity & control flows of paint.
Look for a doppler us flowmeter.
I enjoyed the video. I have a question.
Looking at the path that ultrasound crosses, it seems to pierce the wall twice in the middle. By the way, can ultrasound penetrate a blocked wall?
My experiment showed that ultrasound couldn't penetrate the wall.
So I wonder if ultrasound can pass through obstacles.
There are two types of ultrasonic flow meters: wetted and external. Wetted meters do not need to transmit through pipe walls, so they are more accurate than external (or wrap around) sensors. Sound waves can penetrate metal pipe walls pretty well. It is the same as hearing a conversation in the next room through a thin room wall.
Whats a good one for reading water consumption wireless?
Thank you for asking such a valid question, which many others have also raised. However, I must maintain the same response I've provided previously. Without specific details about your application and not being part of your technical team, regrettably, I'm unable to offer a precise answer. Nevertheless, I can certainly offer you a link to the manufacturers, providing an opportunity for further exploration and deeper understanding related to your learning objectives.
www.keyence.com/about-us/corporate/ www.omega.com/en-us/ www.emerson.com/en-us/automation/measurement-instrumentation
Happy learning!
Can i get a video on how analog input are processed in PLC analog card.??
Thanks for the topic suggestion, Pravin!
I will definitely go ahead and forward this to our creator team.
Happy learning!
I see you reply to almost every comment so I'm going to take my chances and ask you something. I'm learning a lot from your videos but I am still not sure what is the best type of flow meter is for my case and I would appreciate if you could help me.
I want to measure the volumetric flow of water through a 3/4 or 1" pipe for a potable water vending machine I am planning to build. See Watermill Express as an example. Which type of flow meter do you think would be the best choice for this case? I know turbine flow meters would probably work well but (leaving the cost factor aside for a moment) is the ultrasonic even better? Is it more accurate?
or is there any other better option
A turbine meter is the most compact and easiest to install for this application. A small clamp-on ultrasonic flow meter can also be used fairly easily, but is not as accurate as a turbine meter. Both have pulse outputs which will require an interface card, which is typically small and not expensive. A compact magnetic flow meter could be used, as long as the conductivity of the water is greater than about 10 microsiemens/cm or so (depends on the specific flowmeter).
You seem to suggest that turbine meters are positive displacement. They are not. They are inferential meters or velocity meters
They usually have a limited viscosity range enhanced with helical rather than straight blades.
Ultrasonic meters, multichord, can handle fluids with viscosities as high as 4000 cst.
What you didn't explore but rather simply brushed over to say this was why you had multichord Meyers, I'd that the sound wave transits from transmitter to receiver and is influenced by the fluid velocity. Should that not be " mean fluid velocity"?.
It would have been helpful to. Explore the relationship between the measured transit time difference and laminar flows, transitional flows and turbulent flows.i would have expected to that swirl would have some effect. Not discussed.
However, a good basic explanation. Tks.
Jon, you are correct. Turbine meters are velocity meters in their principle of operation. However, they do share the property of positive displacement meters in that a single revolution is equated to a specific volume of fluid flow, albeit for a turbine meter this volume is calculated from the fluid velocity instead of a chamber volume.
As this is an introductory video to ultrasonic flow meters, we did not get into the details of differences in sound profiles through laminar and turbulent flow streams or the meaning of mean flow velocity. Ultrasonic meters are nearly linear in response in turbulent flow ranges, but in laminar or transitional flow ranges, special conditioning sections upstream of the meter are required.
how do ultrasonic flow meters perform on curved pipes?
Ultrasonic flowmeters need a straight run of pipe to work accurately. Bends in pipes tend to distort the flow patterns and can lead to void spaces as the fluid makes the bend. Both of these issues can degrade the flow signal. Typically, a straight run of 10 pipe diameters upstream of the meter and 5 pipe diameters downstream of the meter will provide a steady and consistent flow pattern to allow for accurate measurement.
There are Electromagnetic flow meters from Siemens that has a Venturi shape inside. And they claimed it could be placed just about 1 meter before the curve.
Maybe there are something like that for ultrasonic flow meters.
Are ultrasonic meters able to flow bidirectionally?
No. The ultrasonic transmitter is positioned to send sound waves in the direction of flow, and the receivers are a few pipe diameters downstream of the transmitter.
Is it more accurate then Coriolis?
Coriolis flowmeter measures mass flow rate, ultrasonic flow meter tells velocity of flow. If you wish to find mass flow rate from ultrasonic flow meter, you need know density of the fluid which is temperature dependent. so unless you have compensation techniques it cannot give accurate reading
@@ashwinmurali1911 im asking for comparison of accuracy for volumetric flow rate between these two
Coriolis is considered the "Gold standard" for mass metering. Not necessarily for flow.
As for volumetric flow, according to sciencedirect:
"The Coriolis meter will oscillate at a specific frequency depending upon the density of the fluid in the flow tubes. ... With proper calibration, the density of the drilling fluid can be determined from the frequency. Mass flow rate is density times volume, so the volume rate of flow can be accurately determined."
So your flow measurement is only going to be as good as your density calculation.
@@MrWaalkman thank you sir. Thats the problem that we have with our application, we're using Coriolis to measure flow rate but once the fluid is not homogeneous, we're not getting accurate flow rate. That's why i wanted to know if the ultrasonic flow meter is more accurate for using in our application.
@@fahmietalife Yes, I would think so. Coriolis (like any other meter) is great for what it does well, but in this case it sounds like it was a poor choice. This is where a good meter rep is your friend. Try to pick a rep who sells a lot of different meters or your "perfect" meter will be the one that his company makes. ;>
What are you metering, and do you have a Reynolds number for it?
How are ultrasonic meter calibrated?
Ultrasonic flowmeters are typically calibrated gravimetrically, by collecting water flowing through the meter at different flow rates into a collection tank. Because the gain of the meter usually varies with % of maximum flow rate, 10-20 calibration points from 0 to 100% are measured and the gain (correction) factor is calculated at each point to develop a curve. This only needs to be done periodically (every 1 - 2 years), more often for dirty or coating fluids.
hi why dont you make a pcs7 course on siemens
We do have an Introduction to PCS7 course that is available through subscription on the Realpars.com website! It includes network, hardware, and program configuration as well as WinCC graphic development using a simple process example. There is also an extension to the WinCC course for PCS7 that includes writing C-language routines to int4eract with the graphics.