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hotman1107
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Join Date: Jun 2009
Location: norway
Posts: 2

How to Choose a Flowmeter

06/28/2009 10:16 PM

We need flowmeters to measure water flow (pure water in galvanized steel or PVC pipes) during inspections on solar thermal systems either for swimming pools or domestic hot water).but I have no idea of what kind of flowmeters I should use .doppler flowmeter or ultrasonic flowmeter ? how to decide ?
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holger
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Join Date: Jun 2009
Posts: 2
#1

Re: is ultrasonic flowmeter ok ?

06/28/2009 11:43 PM

I have used ultrasonic flowmeter before and they normally worked well as long as you have a good enough run of straight pipe and no air pockets and no big particles in the liquid . pipe should be full of liquid when working .as for doppler flowmeter ,I didn't use it before .
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longruncn
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Join Date: Jun 2009
Location: P.R.China
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Good Answers: 1
#2

Re: is ultrasonic flowmeter ok ?

06/29/2009 4:00 AM

There are several questions before selecting flowmeter .

  • Is the pipe full? All ultrasonic flowmeters require that the pipe is full of liquids. There are some work around with partially full pipe, but by no means you will get good results.
  • Does the liquid have particles more than 200ppm and particle size larger than 75um (the number may be different for different manufacturers)?
    If yes, use Doppler. Otherwise, consider transit-time.
  • Does the liquid temperature fall into the transducer temperature range?
  • Press range in the pipe (if you select wetted transducer)?
  • High accurate the measurement should be?
    In general, multi-path is higher than single path, flow cell is better than insertion, and insertion is better than clamp-on. However, if you have on-site calibration facility, the story will change.
  • Do you want to easily move the flowmeter around?
  • What output signals you need? What functionalities you want?
    Analog? Digital? RS232? Data logger?
  • What are the safety requirements?
  • Pipe size range? Pipe material? Lining?
  • Flow rate range?
  • Enough straight pipe length?
    In order to guarantee the result accuracy, it is normally recommended to have 15 times of pipe diameter straight pipe run at the measuring site. If there is a pump or valve on the upstream, the straight length should be increased.
  • The financial budget.

The above questions seem overwhelming if this is the first time you are looking for an ultrasonic flowmeter. Please do not be scared. Most likely, a simple clamp-on transit time handheld flowmeter or wall-mount flowmeter will suit your application. If not, please feel free to contact us for detailed suggestions.www.ultrasonicscn.com
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gsuhas
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#4
In reply to #2

Re: is ultrasonic flowmeter ok ?

06/29/2009 11:27 PM

Hotman will cancel his plans looking towards the list of questions you asked!

Jokes apart. The answers to all these are necessary.

Normally pipe will be full. It is the criteria for almost all types of flowmeters. This is because, what actually flowmeter measures is the velocity, and then does the mathematics to give you flow rate. If pipe is not full, it does not understand that and assumes that the pipe is full and gives multiplication of velocity and the cross sectional area of water flowing.

Ultrasonics need some particals in the liquid, but magnetic flowmeters does not need any particals.

Magnetic will need much less straight lengths than all other types. It is accurate to 0.25% of actual flow (not the full scale. Try to understand the difference between accuracy with respect to actual flow and accuracy with respect to full scale flow)

On site calibration to the accuracy is almost impossible thing practically.

Type of outs are available with almost all types of flowmeters.

But if your intention is just to meter the quantity to some 1 to 2%, simple water meters available in the market is good enough.
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Steve Melito
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#3

Re: How to Choose a Flowmeter

06/29/2009 4:29 PM

Take a look at this page from GlobalSpec, the company that powers CR4.
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Anonymous Poster
#5
In reply to #3

Re: How to Choose a Flowmeter

06/30/2009 8:24 AM

Based on my experience and costing, mostly all major water industries,desalination plant & metro water they are using magnetic flow meter.
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Anonymous Poster
#6

Re: How to Choose a Flowmeter

06/30/2009 1:59 PM

We need flowmeters to measure water flow (pure water in galvanized steel or PVC pipes) during inspections on solar thermal systems either for swimming pools or domestic hot water).but I have no idea of what kind of flowmeters I should use .doppler flowmeter or ultrasonic flowmeter ? how to decide ?

As long as the pipe is full and larger than 2" size, use a Clamp-On Transit Time Flowmeter available from almost every large manufacturer of Flowmeters. Go to Global Spec

Good Luck
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hotman1107
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Join Date: Jun 2009
Location: norway
Posts: 2
#7

Re: How to Choose a Flowmeter

07/02/2009 1:43 AM

I 've decided to have a try with transit-time clamp on ultrasonic flowmeter . Thanks for all your information !
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Users who posted comments:

Anonymous Poster (2); gsuhas (1); holger (1); hotman1107 (1); longruncn (1); Steve Melito (1)

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