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'[EE] Measuring water flow rate'
2011\04\06@212548 by M.L.

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Hello all,
I'm looking for insight on measuring water flow rate inexpensively. I
know about various methods, but one-off solutions are fine for what
I'm trying to accomplish.
I was thinking measuring differential pressure drop would be the
easiest way, but differential pressure sensors are quite expensive.
Any ideas?

-- Martin K

2011\04\06@213229 by Josh Koffman

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On Wed, Apr 6, 2011 at 9:25 PM, M.L. <spam_OUTmTakeThisOuTspamlkeng.net> wrote:
> I'm looking for insight on measuring water flow rate inexpensively. I
> know about various methods, but one-off solutions are fine for what
> I'm trying to accomplish.

I'm guessing this is in a pipe? How large? What's the projected flow?
What kind of accuracy do you need?

Just a few questions to get the ball rolling (or water flowing).

:)

Josh
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completely foolproof is to underestimate the ingenuity of complete
fools.
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2011\04\06@213615 by Marcel Duchamp

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On 4/6/2011 6:25 PM, M.L. wrote:
> Hello all,
> I'm looking for insight on measuring water flow rate inexpensively. I
> know about various methods, but one-off solutions are fine for what
> I'm trying to accomplish.
> I was thinking measuring differential pressure drop would be the
> easiest way, but differential pressure sensors are quite expensive.
> Any ideas?
>

To choose an appropriate method, fill in the blanks:
a) max/min flow rates?
b) required accuracy?
c) low cost means max price < ?
d) fresh water, salt water, waste water?
e) any harmful chemicals present?
f) temperature range of flow?
g) ease of installation/replacement?
h) reliability? (just curious about the flow or do your fish die if it's wrong?
i) ??

2011\04\06@232002 by RussellMc

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> I'm looking for insight on measuring water flow rate inexpensively.

"Rate" may mean volume per second or velocity. The former is more
rigorous but the latter not unknown.
Mass rate may also be used.

{Quote hidden}

- In a pipe / In an open channel.

- Flow can be assumed to be constrained by gravity to bottom of pipe
or channel  / no assumptions on where flow is is allowed

- Flow cab be partially obstructed / greatly obstructed / may not be

- Large / moderate / some / no pressure drop allowed at measuring point.

Orifices, notches and weirs with head and/or pressure change or level
are easy and time honoured and may not be appropriate.

Propellors and similar allow inferred flow.

Positive displacement systems allow great accuracy.

Ultrasonic systems and correlation systems allow obstructionless flow.

....

2011\04\07@021957 by Sergey Dryga

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RussellMc <apptechnz <at> gmail.com> writes:

>
> > I'm looking for insight on measuring water flow rate inexpensively.
>
> "Rate" may mean volume per second or velocity. The former is more
> rigorous but the latter not unknown.
Linear velocity, at least for pipe flow is a non-descriptive term by itself..  Is
it an average velocity, velocity in the center or at a certain distance from
pipe walls?  For a round pipe, linear velocity at the wall will be 0, in the
center ~2x average velocity (volumetric rate/cross-section area).  This, of
course, assume newtonian liquid such as water and a laminar flow.
Probably better description is volumetric flow and pipe geometry, at least
cross-section.
On the other hand, I might be smoking my microfluidics weed and be completely
wrong about the macrofluidic flow.  This brings us to already described set of
questions.

Sergey Dryga
http://beaglerobotics.com

2011\04\07@035110 by cdb

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:: 'm looking for insight on measuring water flow rate inexpensively

Define inexpensive, Futurlec have a range of 3 pulse flowmeters starting at $8.00 and ending at $12.00 (US).

Colin
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2011\04\07@042350 by RussellMc

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> > "Rate" may mean volume per second or velocity. The former is more
> > rigorous but the latter not unknown.

> Linear velocity, at least for pipe flow is a non-descriptive term by itself.

Och aye!
That was embodied in  " ... the former is more rigorous ... " along
with a few other things as well :-)

> Is it an average velocity, velocity in the center or at a certain distance from
> pipe walls?  For a round pipe, linear velocity at the wall will be 0, in the
> center ~2x average velocity (volumetric rate/cross-section area).  This, of
> course, assume newtonian liquid such as water and a laminar flow.

Occam opines that Newton doesn't seem to have any of his fluids about
in most real situations.
It get's quiet by the walls, but there oft seems to be quite a lot of
stuff tearing past.

If you use eg a "propellor" for velocity measurement it will add it's
own "law" to what it tells you and you'll probably need a custom form
of weed to be sure of getting it right as eg depth varies, prop dia
other than full pipe dia leads to differences, fluid density may
matter, entrained solids too, ... .

> Probably better description is volumetric flow

perhaps something like

> ... "Rate" may mean volume per second ...

No?

> This brings us to already described set of questions.

?
Points a - i didn't address this.
fwiw

Occam opines that George Box had the right idea (misquoting):

"All models are wrong. Some models are useful".


R

2011\04\07@074835 by M.L.

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On Wed, Apr 6, 2011 at 9:25 PM, M.L. <mspamKILLspamlkeng.net> wrote:
> Hello all,
> I'm looking for insight on measuring water flow rate inexpensively. I
> know about various methods, but one-off solutions are fine for what
> I'm trying to accomplish.
> I was thinking measuring differential pressure drop would be the
> easiest way, but differential pressure sensors are quite expensive.
> Any ideas?
>
> --
> Martin K.
>


I sent this email quickly last night then realized that I didn't
specify anything. I want to measure the flow rate of potable water in
a (<1" diameter) pipe. The temperature may be 55 - 90F and the static
pressure is whatever normal household municipal water is. I'm thinking
it's between 35 and 65 PSI.

It doesn't have to be easy to install. I've got full control over all
the plumbing here (there's a joke in there somewhere.)

This is for an experimental gray water heat exchanger device I have
going. I appreciate the responses.
-- Martin K

2011\04\07@083927 by Spehro Pefhany

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At 07:47 AM 4/7/2011, you wrote:
{Quote hidden}

Here's a really cheap one (maybe already mentioned from another supplier?)
http://www.seeedstudio.com/depot/water-flow-sensor-p-635.html?cPath=6&zenid=594b89701c7a2015a13064b67aed4f44

I don't see any approvals on it, BTW, so if it blows out and floods
your house while you're away for a long weekend, your insurance might
not be 100% cooperative.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
EraseMEspeffspam_OUTspamTakeThisOuTinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2011\04\07@084134 by IVP

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> This is for an experimental gray water

Martin,

some years ago when the council were to start charging for
grey water, someone came to me with an impellor fitting
inside a water pipe. I was meant to do a little PICcing so
the grey water could be measured but he never followed
through

ISTR the impellor was either iron or had iron embedded in
it and the PIC was to record the rpm with a Hall Effect sensor

Although we didn't get to a prototype I don't recall any
unsolved issues. The impellor had semi-circular vanes, like a
butterfly valve, so it fitted closely into a round pipe and only a
very slow trickle was not measurable. I think there was some
discussion about a reservoir holding such a slow trickle and
letting it go at a certain weight/volume so it would move the
impellor

There was also the related question of how full the pipe would
be at the impellor and what effect that would have on the rpm.
If memory serves there could have been some sort of vertical
reservoir which released the water through a hole of smaller
diameter than the pipe, so that the calculation was based on time
as well as rpm. ie the water pressure and duration of this 'jet'

Fine on paper theory but we never got to find out how well it
would have worked. Water volumes and drainage of sink vs
bath vs shower for example, size of a reservoir etc

Jo

2011\04\07@084620 by cdb

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:: This is for an experimental gray water heat exchanger device I have
:: going. I appreciate the responses.

As I mentioned in my post,

This may do the job for you US$10.90. http://futurlec.com/Flow_Sensor.shtml

"
1.5 to 25.0 L/min Hot and Cold Water Flow Sensor
Just arrived our new range of digital flow sensors, these units are ideal for use in water conservation systems, storage tanks, hot water systems, irrigation systems and much more. The sensors are solidly constructed and provide a digital pulse each time an amount of water passes through the pipe. The output can easily be connected to a microcontroller for monitoring water usage and calculating the amount of water remaining in a tank etc.

This flow sensor is suitable for a standard 1/2" pipe and can be easily inserted into a standard piping system. A wide supply voltage can be connected to the unit. The unit is constructed of long-life polymer and is suitable for outdoor mounting. These easy to connect units are ideal for use in environmentally friendly household water management systems.



Part Code: FLOW25L0
Pricing Features
Flow Rate 1.5 - 25.0 liter/min Digital Output Fitting for 1/2" Pipe Suitable for Hot and Cold Water Systems Open Collector Output Water Temperature: 0 - 80oC Supply Voltage: 2.4 - 26V
"
Colin

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2011\04\07@112316 by Sergey Dryga

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RussellMc <apptechnz <at> gmail.com> writes:

>
> > > "Rate" may mean volume per second or velocity. The former is more
> > > rigorous but the latter not unknown.
>
> > Linear velocity, at least for pipe flow is a non-descriptive term by itself.
>
> Och aye!
> That was embodied in  " ... the former is more rigorous ... " along
> with a few other things as well <SNIP>
> If you use eg a "propellor" for velocity measurement it will add it's
> own "law" to what it tells you and you'll probably need a custom form
> of weed to be sure of getting it right as eg depth varies, prop dia
> other than full pipe dia leads to differences, fluid density may
> matter, entrained solids too, ... .
> Next time I need flow measurement I will ask you for the custom weed form.  Last
year I was involved in a project where the "pipe" was 100 micron tube.  We
measured flow optically, by tracking suspended particles (about 1 micron
diameter), and by NMR (nuclear magnetic resonance).  I did not think NMR would
be applicable to the OP question.  Need some pretty uniform magnets and highly
specialized (read expensive) electronics.  IIRC, frequency shift of NMR signal
was <10 Hz with center frequency about 70 MHz.  
During the project I also saw a nice demonstration of "newtonianness" of
different liquids: e.g. water - newtonian, blood - not.

Sergey Dryga
http://beaglerobotics.com

2011\04\07@123140 by M.L.

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On Thu, Apr 7, 2011 at 8:46 AM, cdb <@spam@colinKILLspamspambtech-online.co.uk> wrote:
>
>
> :: This is for an experimental gray water heat exchanger device I have
> :: going. I appreciate the responses.
>
> As I mentioned in my post,
>
> This may do the job for you US$10.90. http://futurlec.com/Flow_Sensor.shtml
>

Colin,
That looks like it may do the job fairly well. I will probably buy a
few and let everyone know how well they work.
Thanks.

-- Martin K

2011\04\07@125049 by M.L.

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On Thu, Apr 7, 2011 at 11:22 AM, Sergey Dryga <KILLspamsergeyKILLspamspamdryga.us> wrote:

> Next time I need flow measurement I will ask you for the custom weed form.  Last
> year I was involved in a project where the "pipe" was 100 micron tube.  We
> measured flow optically, by tracking suspended particles (about 1 micron
> diameter), and by NMR (nuclear magnetic resonance).  I did not think NMR would
> be applicable to the OP question.  Need some pretty uniform magnets and highly
> specialized (read expensive) electronics.  IIRC, frequency shift of NMR signal
> was <10 Hz with center frequency about 70 MHz.

I had thought of many possible Rube Goldberg style ideas, but my
primary objective is to figure out the efficiency of my heat
exchanger, not to test flow rate.
Paddle wheels and propellers are pretty common in this arena, but this
is the first I've heard of NMR for flow rate.

--
Martin K.

2011\04\07@130557 by Denny Esterline

picon face
>
> I sent this email quickly last night then realized that I didn't
> specify anything. I want to measure the flow rate of potable water in
> a (<1" diameter) pipe. The temperature may be 55 - 90F and the static
> pressure is whatever normal household municipal water is. I'm thinking
> it's between 35 and 65 PSI.
>
> It doesn't have to be easy to install. I've got full control over all
> the plumbing here (there's a joke in there somewhere.)
>
> This is for an experimental gray water heat exchanger device I have
> going. I appreciate the responses.
> --
> Martin K.
> --

Ok, looks like you've gotten more than a few good suggestions about
flow meters, hard to argue with the $10 option. :-)

But as far as gray water heat exchangers goes.... there's plenty of
people before you:

http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13040

-Denn

2011\04\07@130733 by RussellMc

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> I had thought of many possible Rube Goldberg style ideas, but my
> primary objective is to figure out the efficiency of my heat
> exchanger, not to test flow rate.
> Paddle wheels and propellers are pretty common in this arena, but this

For REAL creativity you need Heath Robinson.
Rube was just a beginner.

New Zealand exports iron-sand to Japan.
This is pumped as a water slurry to tankers moored offshore, the water
is discarded overboard and the sand is retained.
Flow measurement was wanted.
The material is very abrasive and dense and in-line obstructions were
"unwelcome".
The solution, implemented by the Auckland University (now decades ago)
was to use auto correlation of electrical signals in the iron sand
offset by a known distance. Time to peak autocorrelation gave flow
velocity. Newtonianness, flow profile and more no doubt gave them lots
of fun.


2011\04\07@132907 by Sergey Dryga

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M.L. <m <at> lkeng.net> writes:

> I had thought of many possible Rube Goldberg style ideas, but my
> primary objective is to figure out the efficiency of my heat
> exchanger, not to test flow rate.
> Paddle wheels and propellers are pretty common in this arena, but this
> is the first I've heard of NMR for flow rate.
> NMR was for a very specific application, and flow rate measurement was a side
benefit.  The application was detection of individual bacteria, labeled with
magnetic material.  Besides, it's a bit hard to put a paddle wheel inside of a
100 micron tube.  
BTW, I am all for the Rube Goldberg or Heath Robinson style ideas, especially if
it is for fun, not for a commercial application.
It was a good question and a lot of good answers.  I can see some applications
in my future where I will need to measure flow in 1/2 - 1 inch pipes, I will
keep this discussion in mind.
Sergey Dryga
http://beaglerobotics.com

2011\04\07@134443 by Gary Crowell

picon face
It sounds like you've found a solution, but with talk of impellors and
vanes, I wanted to drop one other term into the discussion: nutating disk.
http://www.engineersedge.com/instrumentation/nutating_disk_displacment_meter.htm

Gary

On Thu, Apr 7, 2011 at 6:36 AM, IVP <RemoveMEjoecolquittTakeThisOuTspamclear.net.nz> wrote:

{Quote hidden}

>

2011\04\07@144309 by M.L.

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On Thu, Apr 7, 2011 at 1:05 PM, Denny Esterline <spamBeGonedesterlinespamBeGonespamgmail.com> wrote:
> Ok, looks like you've gotten more than a few good suggestions about
> flow meters, hard to argue with the $10 option. :-)
>
> But as far as gray water heat exchangers goes.... there's plenty of
> people before you:
>
> http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13040
>
> -Denny

Had I thought I invented something new, I wouldn't have shared it with
all of you folks!
Certainly there's nothing new about a water-water heat exchanger. I
just want to put a figure on how much energy I'm reclaiming at
present.
My heat exchanger is a single-walled design, which although it is
perfectly safe, is probably not "legal." The potable water is of
significantly higher pressure than the gray-water, thus there can
never be any accidental contamination. It's also an order of magnitude
less expensive than the double-wall designs that use a 4" diameter
copper pipe for the drain water.

There's more to the system, and I hope to put up a web page to show
some pretty graphs and things.

-- Martin K

2011\04\07@155012 by Carl Denk

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In the USA, that likely would require a backflow preventer of some type by the EPA via your local water supplier. There are some rather stiff fines for non-compliance I believe. There is then an annual inspection required that costs ~$60. I have an 8000 gallon cistern (tank) and collect all roof rain water. We use the water for washing, bathing. At the kitchen sink there is a separate faucet for the city water for potable purposes. The remainder of the house can be either roof or city water with a switchover that is impossible to cross connect, and yet a reduced pressure backflow preventer is required.

On 4/7/2011 2:42 PM, M.L. wrote:
{Quote hidden}

>

2011\04\07@160907 by Bob Blick

face
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> This may do the job for you US$10.90.
> http://futurlec.com/Flow_Sensor.shtml

Just looked at the data sheet for the biggest one - looks pretty
nonlinear especially at low flow rates and is very dependent on mounting
position.

And accuracy only +- 10 percent at mid to high flow rates.

But the price is right.

Bob


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                         love email again

2011\04\07@163405 by M.L.

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On Thu, Apr 7, 2011 at 3:50 PM, Carl Denk <RemoveMEcdenkspamTakeThisOuTwindstream.net> wrote:
> In the USA, that likely would require a backflow preventer of some type
> by the EPA via your local water supplier. There are some rather stiff
> fines for non-compliance I believe. There is then an annual inspection
> required that costs ~$60. I have an 8000 gallon cistern (tank) and
> collect all roof rain water. We use the water for washing, bathing. At
> the kitchen sink there is a separate faucet for the city water for
> potable purposes. The remainder of the house can be either roof or city
> water with a switchover that is impossible to cross connect, and yet a
> reduced pressure backflow preventer is required.
>


I'm not actually using the water for anything other than it's waste
heat. It only goes down the drain.

I've lived in a few houses that were designed with cisterns in the
basement. It always seemed like a logical idea, but they were always
empty and converted to dry storage space.
-- Martin K

2011\04\07@182731 by Carl Denk

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The concern is the possibility of liquid, including any water that might not meet potable (drinking) water standards into the city water main (system). Although your other water pressure is low, if there is a water main break at a lower level than your equipment, a vacuum could happen, drawing the other liquid into the system. This can also happen for a variety of other causes including a pump or it's power failure.
en.wikipedia.org/wiki/Backflow_prevention_device
http://www.watts.com/backflowprevention

On 4/7/2011 4:33 PM, M.L. wrote:
{Quote hidden}

>

2011\04\08@021136 by Ruben Jönsson

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> > As I mentioned in my post,
> >
> > This may do the job for you US$10.90.
> http://futurlec.com/Flow_Sensor.shtml
> >
>
> Colin,
> That looks like it may do the job fairly well. I will probably buy a
> few and let everyone know how well they work.
> Thanks.
>
I had a quick look at the technical information:

Supply voltage: 2.4 - 26 Vdc
Supply current: Typical 2.8 Amps, maximum 8.0 Amps. Ouch!!!

/Ruben

==============================
Ruben Jönsson
AB Liros Electronic
Box 9124, 200 39 Malmö, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
EraseMErubenspampp.sbbs.se
==============================

2011\04\08@035046 by Richard Prosser

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2011/4/8 Ruben Jönsson <RemoveMErubenEraseMEspamEraseMEpp.sbbs.se>:
{Quote hidden}

But the one with the display runs off 2 x AA batteries.

Maybe the 8amp rating is the contacts or something But Some are open
collector output??

RP

2011\04\08@045806 by cdb

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:: Supply current: Typical 2.8 Amps, maximum 8.0 Amps. Ouch!!!

Supply current : typical 3.0mA, maximum 6.0 mA

That's for the 1.5 to 25.0 L/min hot cold water version.

Colin
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