water meter with accuray +-0.5% 1

[Keith1976]

Dear All;

Nowadays, the technology for water flow measurement is using Faraday's law (electromagnetic flowmeter) where the accuray can be +-0.25%.

But the challenge is the cost. It is extremely expensive if we want to have size 1/2 inches for residential use. It is applicable and acceptable only for bulk meter.

With recent technology, is there any way to produce water meter with maximum o.5% tolerance at cost around US$50. Considering nowadays so many theories and science invented.

The sky is the limit, isn't it? The fact that water is incompressible may be the foundation for such meter.

Regards,
Keith

 

[BigInch]

Water is not incompressible and also changes specific volume with temperature. From 18ºC to 30ºC water changes density by 0.5%, so to be accurate, your meter would have to be temperature compensated too. Not impossible, but adding a bit more expense to your $50 price tag. The real problem is that on a commercial scale the additional accuracy you want to have cannot be justified by the very small cost of the additional tiny volumes of water you hope to measure.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[cloa]

I think Keith1976 is aiming to achieve less accuracy for less cost.

 

[hacksaw]

Magmeters require special electrodes for clean water, so you may have a further problem in a half-inch size that again translates into cost. It also has low velocity limits unless you get special signal processing...another win-win solution for the seller, oops..

Most water depts, sell water on a volume basis, just like most fuel pumps, open season on the buyer is not only the wall street maxim

 

[Keith1976]

You are right, BigInch;

Water will expand and shrink upon temperature change.

Here is the situation, within a district of residential, for the district meter, I use 8inches MAG8000, nicely installed and the reading is excellent. But at the end of the month, the totalizer from the district meter is 30%higher than the total m3 paid by the resident. Well, pipe leakage may be another suspect. But using vane rotary meter with 10 years old may give the water suppliers wrong (and losing money) reading.

My investigation shows that the existing residential meter cost is around US$25. If we can have a meter with 0.5% accuracy (for 10 years), the water supplier company is willing to buy this new meter.

I am sure that in the future 1m3 of water loss is big deal to everybody.

Keith

 

[moltenmetal]

If you don't want to miss the low, trickling flow events entirely, you're stuck with positive displacement I'm afraid. Every electronic technology for continuous flow measurement has a minimum flow cut-off- too little turndown to serve in the capacity of a water paymeter.

What's wrong exactly with the nutating disc meter?

 

[BigInch]

Many water systems all around the world leak up to 30% or more. Instead of making the customer pay for the last 0.00000025%, wouldn't your efforts be better spent FIXING LEAKS? Excuse the shouting, but that absolutely makes me CRAZY!

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[hacksaw]

It is a bit unusual to have a 30% error like that without un-documented branch connections or leaks.

An 8" line is running about 1 millivolt at 1000 gpm peak flow and less than 0.2 mv below 200 gpms, what sort of a user meter are your using (turbine, PD, etc.)? The mag meter error increases exponentially at low flows less than 1 ft/s.

You also need to examine the signal conditioning at the magmeter, grounding, signal averaging etc.

 

[BigInch]

That's how they know the leakage rate. What gets billed out is 30% to 40% of what went in.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[vpl]

Of course, your problem might be something like this....
Doesn't matter how accurate your water meters if someone doesn't install one.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[jmw]

In the UK I think it is around 25% loss through leakages, on average. Part of the problem is the old distribution system and lack of investment. Then too the pipework has been vulnerable to earth movement such as during droughts.
In the UK it used to be the 1942 water act or something similar that defined the required accuracy and that was based on "equable" measurement. In other words what was actually metered had to fairly represent the total amount used.

There is no compulsion to have a meter. The consumer could opt for paying a water rate which is an amount based on the property size and occupancy. Then too the potable water metered is used as a basis for determining the cost of sewage treatment and disposal. The consumer has the choice as to pay according to the rateable value of the property or the amount used though most new properties do have water meters installed as a matter of course.

There is a lot more to it than simply the meter accuracy and as BigInch says, it doesn't matter to the water company how much is lost so long as they make a profit and that means, quite rightly, that the amount billed is calculated to cover costs which includes wastage.

In the UK and especially in the south of the country, indirect plumbing is used. This is a hangover from the Napoleonic war scares; it was feared that if the French invaded they would disrupt water supplies and hence each property had a cystern or gravity tank which provided a reserve of water. The tank is kept full using a float valve which results in a trickle flow as the valve starts to close. Hence in the UK (and Europe) the preferred water meter is the oscillating piston type. More expensive than nutating disc it has a wider flowrate range and is better at low flows.
It also tends to maintain its accuracy better over the long term and over the course of the working life its accuracy will change in a typical manner from over positive to under positive so that over time it should average out; ie it isn't simply the absolute accuracy but the long term equable measurement.

One of the most important aspects of domestic water meters is the installation cost and especially the labour costs and a key factor is the first time failure rate. Here the nutating disc meter would win out because it has better dirt handling capability but since the preferred meter for other reasons is the rotary or oscillating piston meter, the meter design is often modified to try and compensate for the initial start up problems where entrained dirt is flushed through the meter.

In short there are a lot of factors that have to be considered and the rotary piston meter takes a lot of beating especially with indirect plumbing systems but in the US it is the nutating disc meter that is preferred and makes a good fit to the conditions, expectations and regulations.




JMW

http://www.ViscoAnalyser.com

 

[Keith1976]

BigInch;
The reason that the developer needs to find the leakage is becuase they want to save money for future investment, i.e replacing all steel pipe with HDPEpipe. HDPE pipe can give you 0 leakage theoritically.

Hacksaw;
30% leakage is equal to US$50,000/month in my situation. Assuming we can reduce to 20% (which is achievable, neighbouring residential area has proved it), we have 'extra cash' of US$ 15,000++ monthly. It is large amount in country like Indonesia where salary can be US$200(two hundred)/month for a fresh graduate engineer

Furthermore, Lyonesse from French is one of the main operators (the other is Thames from UK) in Jakarta. Their water loss is around 55%. This is "acceptable" due to the illegal tapping.

Technolog Cello datalogger and Siemens MAG8000 can be a good solution for the district metering. But I still can't find the solution for the residential/individual meter. Hopefully the dream will come true.

 

[jmw]

A new water meter requires a great deal of investment.
I have put forward a new mechanical positive displacement meter design which combines the best features of the nutating disc meter and the rotary piston meter to a couple of the major meter manufacturers.

I claim for my design that it should be more accurate, wider ranging quieter (meter noise is something to be avoided) and with good dirt handling capacity and probably at nutating disc meter prices (we won't know the truth of any of these claims until it can be prototyped) but the reply was that it (or any new meter) would cost about $1milion to put into production.

Now there is probably an element of truth in this but I suspect it is more likely that "if it ain't broke, don't fix it".
No one has challenged my claims for the design but the reluctance is to do anything that will obsolete the existing designs and why? probably because there is not too much wrong with them.

It may seem ideal to have a non invasive meter such as mag meters, fluidic meters, US etc. and I have seen a number of these designs touted as the best thing since sliced bread for domestic metering only to see them come to nought. Of course, mechanical meters have a great attraction that they are energy abstractive - they are powered by the flow. Non-intrusive generally means power supplies or batteries...we are a long way from energy harvesting and ultimately that energy is derived from pumping energy anyway.

Of course, there are many reasons why newer and better doesn't always win the day. I once worked on a project with the then new single straight tube mass flow meter in an application where no other meter had proved successful and I was confident of some nice business when it proved to do all that was expected of it.
Unfortunately, the client said thanks but keep it under your hat" (confidentiality clause invoked). They wanted to know if it could be done in case they were required to do it by the regulators but were content for the regulators to believe it could not be done and therefore not require metering.

I live in hopes that I will one day see my meter adopted but I need a new strategy before that happens.



JMW

http://www.ViscoAnalyser.com

 

[Keith1976]

JMW;

I appreciate and admire people with dream like you.

I do not intend to ask for a copy of your design, but if it is fine with you, can I ask a few question with regard to your design:

1.what is the accuracy? at least on paper according to your calculation

2. how can you claim that your design is good in handling dirt? if it is really good, the accuracy will remian the same for how long? again, just acoording to your calculation.

3. in Indonesia, I dont think it will cost US$ 1 million to put into prototype. Noise is not an isssue either where the teenager can have illegal racing without proper muffler on their bike

keith

 

[jmw]

Kieth1976,
Generally, accuracy is required to be compliant with the domestic water meter regulations and there are a several accuracy classes. Piston and disc meters usually being the more accurate as positive displacement meters compared to inferential meters such as the single and multi-jet meters.
SO the question is, why is a better meter accuracy required for a domestic meter?

Accuracy for my design is speculative as it must be until it can be verified empirically.

The best I can say is that understanding the factors that contribute to accuracy both initially and over time, and by comparing the designs, I know that my design potentially is better than either the nutating disc or the rotary piston meters and it may be that that could be traded into better accuracy or better long term life or any other feature that is prioritised. (PD meters are obviously capable of much higher accuracies than water meters e.g. for fiscal metering but the question is how is it to be achieved and at what cost?).

It is not simply a case of looking at the geometry and tolerances, if it were then there would be no significant theoretical difference between disc and piston meters. In reality a range of factors must be considered including accuracy over time.

Accuracy changes over time and use... some meters tend to wear in and others to wear out. Rotary piston meters tend to have better wear characteristics than disc meters.

If we had an ideal meter then the meter would be perfectly accurate over an unlimited flow range.
However, they must have working tolerances which means that some fluid slips through the tolerances unregistered.

The higher the pressure drop, the greater the slip flow.

Nutating disc and rotary piston meters have different mechanisms and the effects of wear are different.

For example, as a disc meter wears the change is progressive but in a rotary piston meter, as it initially wears, there some compensation - the loading on the guide roller increases with higher flow rates for a nutating disc meter but decreases for a rotary piston meter - the guide roller is necessary to control the tolerances and is more necessary at low flows in a piston meter and at high flows in a disc meter. In the piston meter, at high flows centrifugal forces take over but for the disc meter here is no radial freedom of movement due to the hub bearing but there is a tipping effect not so evident in the piston meter.

Wear is also influenced by peak pressure drop during the meter cycle and that is influenced in part by port design.

The ultimate best design depends on tolerances and materials and these have an evolutionary component to them:

The Kent "bomb" meter was one of the first to exploit a new manufacturing method.

Unlike industrial meters, there is no calibration adjustment, the calibration is determined by the meter's swept volume and the standard reduction gear train in the register assembly.
Until that time PD meters were assembled and components fitted by skilled craftsmen and were thus very labour intensive.
What Kent did was to simply assemble the meters with as manufactured components with no skilled fitting and test them.
In the Kent bomb meter, any meters that failed the calibration test were were stripped down and all the parts marked with a spot.
If, when the failed meter is disassembled a part already has a spot signifying that it has previously been found in a failed meter, it is given a second spot.
If a part was found with two spots, then the engineers would examine that batch of parts and look for deviations from the mean manufacturing tolerances etc.
In this way they not only ensured they brought together all the optimum components and identified any problem component batches they were also able to progressively optimise the component specifications.

What I mean to say is, there are a lot of factors to consider and also one has to consider the accuracy under test has to represent the performance of the meter over a long period of time.

My meter design exploits different design features to optimise performance by reducing slip flow generally, reducing peak pressure drops and hence also reducing wear and log term wear effects.

An easy question to answer is about dirt handling.
It will be seen that the flow path around the nutating disc meter is more favourable to dirt handling partly because the ports are in the outer chamber surface and dirt is "centrifuged" out of the chamber and partly because the disc edge sweeps the chamber surface with little opportunity to trap solids in the working tolerances.

In a rotary piston meter, on the other hand, the ports are in the top and bottom plates of the chamber and there dirt would tend to flow over the chamber wall surfaces where the piston skirt "rolls" or slides in a manner far more likely to trap the dirt in the tolerances.
Also, the dirt has to move radially inward to reach the chamber ports due to the port location.

Usually the problem is from larger particles which most frequently are present during the initial start up.
The nutating disc design is less vulnerable to such particles which are usually voided quite quickly and only rarely expected to cause a problem.

One solution would be to fit a filter but while a coarse filter is OK to screen out the few larger particles, a finer screen would trap finer particles in greater quantities and require cleaning i.e. labour. Modern rotary piston meters include slots scored in the piston skirt outer surface to allow particles to be swept through from the inlet to outlet by being carried in the slots rather than trapped in the clearance(the nutating disc meter clearance does not significantly change and the edge sweeps the chamber wall, the rotary piston tends to move radially outward at higher flows closing the tolerances which, while a benefit for long term accuracy has a negative in that it increases the vulnerability to dirt particles between the piston outer surface and the chamber wall).

So my design exploits the positive features of both meters to obtain good wear factors, good dirt handling and good long term accuracy.

Undoubtedly, with very precise manufacturing controls even the domestic water meter could have better instantaneous accuracy but at what price? Long term performance? higher reject rates during manufacture? ore dirt handling vulnerability?

The estimated cost to put into production is based on more complex component geometry (though no more or less components than the nutating disc or piston meters) which may require more time and more tool iterations to get right. However, the figures were given to me by a major global water meter manufacturer. It might be therefore that they:
a) multiplied the costs by the retooling not for one factory but several
b) overestimate because they don't want to obsolete their current designs... and they could probably be sure of similar thinking with other manufacturers.

But I would tend to agree that manufacturing costs would be better in Indonesia or Sri Lanka and I would guess that if you were thinking of a single factory probably not nearly so great to tool up either.


JMW

http://www.ViscoAnalyser.com

 

[jmw]

PS
mechanical meters depend on a fixed gear train to a mechanical register. This means the performance must be linear over the operating range.
Electronic meters do not need to be linear, just repeatable as the signal processing can linearise the results.
Today's water meters have to do much more than previously and this includes remote reading e.g. pulse transmission, drive-by radio telemetry etc.
This means that modern water meters could use electronic registers that are energy scavenging (you have the nice mechanical rotation of the moving element) and could therefore have individual calibration which can be automatically performed.
If we are going down this route then any mechanical meter will provide much better accuracy and very affordably.

JMW

http://www.ViscoAnalyser.com

 

[Keith1976]

Hi JMW;

Thanks for the in-depth information. I personally think about electronic meter. As long as it is repeatable.

May be free flow whre by there is magnet outside the pipe that will update the register. IC is very cheap nowadays.

Keith

 

[jmw]

Research has been ongoing for a good many years but I only recall discovering one manufacturer of a no-moving parts water meter and that link is dead but a search did reveal this one which is new to me:

http://www.tagmeter.com/gb/dommeter.html

but I rather suspect it is a conventional mechanical meter with electronic sensing and integral valve... not quite what we are looking for.
The meter I was thinking of was "Fusion" and a search turned it up (it is fluidic device and I was aware of some work being done on fluidics about 15-20years ago... one of the major utility meter companies... and this is apparently now produced by a wing and a prayer type of company:

http://www.water-waste-environment-marketplace.com/details.asp?cid=9046

It is easier said than done and evidently difficult to get a satisfactory meter with the right performance at the right price.


JMW

http://www.ViscoAnalyser.com

 

[jmw]

PS Elster Kent (the makers of the Kent Bomb) do do magentic meters but as you can see, they are expensive.
One is tempted to suggest that if they could make a domestic version they would... but they may not want to obsolete the conventional designs.
We shouldn't neglect customer resistance to new technologies.
After all, the rotary piston meter has been around from about the 1860's and the nutating disc about as long.

JMW

http://www.ViscoAnalyser.com

 

[jmw]

Having said that, Siemens seem to be achieving the technology but at what price?

http://www.accessinstrumentation.co.uk/PDFs/siemens_MAG8000.pdf

I guess though, that you will have found these already and have investigated them.
Another fluidic is the Severn Trent meter:

http://www.edie.net/news/news_story.asp?id=11733

Mag:

http://www.krohne-downloadcenter.com/dlc/TD_OPTIFLUX2070_en_080411.pdf

JMW

http://www.ViscoAnalyser.com