Hi,

I'm thinking of making a magflow type flowmeter,
could someone tell me what sort of voltage i could expect from tap-water.
This would not be high velocity, just sort of tap-half-on sort of speed.

I am thinking of using reasonable strength permanent magnets,
or one magnet if i can find or make a suitable magnetic path.

John

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I don't know what you're talking about.

Please post a link or schematic.

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the basic concept of MagFlow is application of the law said that if you move a conductor in a magnetice field, an EMF will be generated in the conductor.

In MagFlow concept, water used as the conductor.

Is that clear

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We used magflow meters at the refinery I use to work for. They were pretty expensive, required two external coils at 90 degrees, driven with an AC current source around the pipe carrying the fluid, with sensor coils opposite the driving coils. It also was somewhat picky to the fluid being measured, pure water being one of the fluids it was not very good at detecting, if my memory serves me right. I think it required a minimum of some level of ions in the process fluid to measure well, but it has been awhile. We used it mostly to measure acid flows as the fact that a magflow meter requires no taps or other direct contact with the process fluid in the pipe, it was safer for personnel and the environment.

The cheapest solution I can think of for your application would be a flow switch. Here is a E-bay listing I just called up:

flow switch, Electrical Test Equipment, Manufacturing Metalworking items on eBay.com

Lefty

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Hi Hero,

A 'magflow' type flow device, is probably one of the simplest type of flowmeter
its possible to conceive, which can give a proportional electrical signal.

In a simple form, a magnetic field surrounds a plastic pipe, a connector on each
side of the pipe like a rivet makes a connection through the pipe onto the flow,
and forms the output terminals, the flow through the pipe bridges between the
connections, and the flow produces an emf across the two rivets.

Disadvantages:
The flow has to be of a conductive fluid.
Bubbles can upset the reading.
I think the output is very low and has to be amplified.
Ones i have seen have always had large coils to make the external magnetic field,
but these days of relatively strong permanent magnets, it may be possible to use
permanent magnets for the field.

Breifly, if the lines of magnetic force are vertical, above and below the pipe,
then the connectors would be placed either side, and the flow between the
connectors would essentially be the "conductor cutting magnetic lines" as 'aljamri'
has said.

I will try to draw a small diagram to illustrate.

Hope this is Ok, John

Attached Images

Mag Unit.jpg (24.3 KB, 13 views)

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one more important thing is that the unit has to be made from insultor materials, otherwise the two electrods will be shorted. and Grounding the unit is of great important otherwise the noise will spoil the generated emf.

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Hi aljamri,

After much internet searching, and perusing the web for information at great length
i was able to narrow down the sort of voltage output i can expect from one of
these units.

It would appear to lie somewhere between zero and infinity.

My own guess is that it would probably be more than a hundredth of a volt,
and unlikely to be as much more than a quarter of a volt.

However, since you tell me that unless i earth it properly,
" ... the noise will spoil the generated emf. "
So it would appear my guess was optimistic, and maybe the output would be far
less than i thought.

Maybe a few thousandths of a volt ?

You would think this information could easily be found on the internet.

Regards, John

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sorry for not answer long time. for your question the answer is yes, the out put emf is of low and quality that required a separate unit to filter, reshape and amplify it into a useful signal, this is the case if you need a relible accurate signal.

What you are trying to do? a flow rate meter or flow switch ( Flow / No Flow ) ?

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