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Re: water well depth
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Steve,

Have you tried just using a clamp on ammeter to measure the current being drawn
by the pump during a pump cycle to verify that the current changes as you
theorize?

--
James T. White



Re: water well depth
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Classic oilfield technique.  Extremely precise
measurments can be made if you use helium instead
of air/nitrogen and if you carefully compensate
for the temperature and density of the gas.

Probably not practical for a 800 foot water well
without the capillary tube.

Re: water well depth

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Just be careful what plastic tube you use (and you would have to weight it
so
it didn't float when full of air).  If it is 200 feet under the water, the
pressure
in the tube is close to 100psi (about 1/2 pound per food) -- some of your
lighter plastic tubing will pop at that kind of pressure.  If my quick
calculations
are correct, a 200 foot air column 1/8 inch in dia displaces about 4 pounds
of
water so you would require a 4 or 5 pound weight on the end of the little
tube
so it would sink to the bottom with air in it (this does not take into
account the
weight of the tube, but I do know most of the plastic tubes I have played
with
will float quite well if full of air).

mikey




Re: water well depth
snipped-for-privacy@hotmail.com says...
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If your well is like mine, it pumps into a pressure tank---the pressure
in which varies from 40 to about 75 PSI as the tank fills.  That
change in head pressure  is equivalent to  a change in water level of
about  60 feet.     To get rid of  that changing addition to the
energy needed to lift the water, you have to make your measurement
at the same point in the tank filling cycle.

If this is an irrigation well, your head pressure will  vary with
the number and type of sprinklers.  


What type of resolution do you need?  825 feet is a pretty
deep well, and a 1% power sensor may be difficult to
build.  This is especially true in light of possible line
voltage fluctuations.

When you pump a lot of water,  you should expect the water
depth in the well to  go down unless the aquifer is very
porous.
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Mark Borgerson



Re: water well depth
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With most pumps the throughput varies with the presure, so you also have to
measure the flow. The heigth will be  power/flow, corrected for the
(changing )efficiency of the pump.

Wim



Re: water well depth
On Tue, 25 Jan 2005 19:19:22 -0800, Steve Calfee

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The problem is that a solution should work relatively quickly, but
also work for several years of the wells life. We have had some really
creative suggestions, but no real solution. Lots of experiment
required. Some of you H/W analog types must have alternatives. I would
think that between water, non-water, pump power, head pressure, water
flow etc. there must be some method of telling how far down in a hole
water is sitting.

The next time I have the "really expensive well riggers" out, I could
ask them to drop something into the well. Is a simple wire enough? If
you have a wire with a heavy weight on it (to get it to the bottom)
can you tell the distance to the water? I don't like the usual
suggestions as "drop a pebble" or "make an ultrasound pulse" or "blow
through a straw into the well bottom". I don't dislike them because
they are not possible, just they are not sustainable (dropping
1,000,000 pebbles fills the well) or "automate able" or just custom to
one particular well construction technique.

Well maybe that is why there is no commercially available product?

Thanks for the ideas, ~Steve



Re: water well depth


I don't like the usual
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Steve, sorry to hear that we've not provided you with a solution.. I
guess you got what you paid for.

On the other hand, I've actually looked into this quite a bit. I went so
far as to talk to a couple of municipal engineers (something you could
have done for yourself, btw) as well as the local USGS engineers that
track water tables in my county. My local county uses pressure
transducers permanently installed at the bottom of the well.

The "straw blowing bubbles idea" is used regularly in commercial wells,
but I guess I'll have to tell these folks that you've determined that
this technique is neither sustainable or automatable.

I guess you'll just have to drag your butt out to the well every so
often and lower a string until you hit water.

  - jim

Re: water well depth

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Jim, I actually got lots of useful ideas and good brainstorming on how
to solve an apparently difficult problem. I got some pointers to web
sites that were interesting, even if I had visited some of them in the
past. I guess in that sense this has been a valuable and interesting
thread at least to me.

No one of us can be expert in all phases of embedded systems work and
sometimes someone will have run into a solution in the past. A
commercially available solution will usually show a way to solve the
problem and probably be cheaper than a doit yourself solution. Not as
much fun though.

It appears that if I want the solution, I will have to actually do
some work and tests. Soon as I get the round tuit!

Thanks everyone for the ideas!

Regards, ~Steve



Re: water well depth

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Sometimes a very rare device these round tuits. ;>

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Re: water well depth

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They work best if used with a henway ...



Re: water well depth

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Could be.  Another reason may be that there is no use for the answer to
the question, "What is the current depth of the water?"  I suspect that
practical answers are usually classified as "enough" and "not enough."
The former requires no action and the latter requires either a new well
or a deeper well, in which case, you'd hire a pro who would employ a
very basic method:  drill deeper and then test flow rate, i.e. test for
sustained flow rate and pressure.  There's not really much science
involved in well-drilling.

Still, it's an interesting engineering question, and I've had some fun
thinking about it and reading other answers.  I have a well, too, and I
might just experiment with the sonar approach if I get some time and the
inclination.

Another approach briefly occurred to me, but it won't actually work
without modification.  If you aimed a laser at a slight angle down the
well casing, the water surface would reflect the light.  By measuring
the angle and the distance between the incident and reflected beams, you
could use a little bit of trigonometry to determine the depth of the
water.  Unfortunately, with the very nearly 90 degree incident angle and
the poor reflectivity of water, this approach wouldn't actually work
very well if you could get it to work at all.  But if you ever decide to
monitor a mercury well, let me know.  ;-)

Ed


Re: water well depth


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Actually, municipalities (sp?) are very interested in monitoring water
levels in wells. Given historical data from each well, they can make
decisions about:
    1) Water use restrictions
    2) Which wells to pump from
    3) Capacity planning (i.e. building permits )
etc etc. To some extent, a homeowner could even decide in a dry year
that they might have to abandon watering the lawn/garden for the sake of
taking a shower and fire suppression.

Hmm, a mercury well... I'll let you place the sensor ;-)

I do like your idea though. I'd also be concerned about vibrations on
the water's surface when the pump was running, and the miniscus where
the power feed and water pipe entered the water column.


FYI. Once engineer I spoke with about this said he'd seen an ultrasonic
measuring device once, but that it required pulling the pump out of the
well, as the wires/pipes interferred with the device. Handy for
"inspection wells", but not for in-service wells.

  - jim

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Wells are a deep subject, it seems.  I thought that the wells that were
used to monitor water table level were not homeowner wells but wells
drilled just for the purpose of monitoring.  In that case, I think there
would be somewhat different requirements, but maybe ultimately similar
techniques.

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Actually, such a well wouldn't be as dangerous as you might think.  With
the surface 100 meters below, there shouldn't be too much mercury vapor
at the surface.  ... so you can place the sensor.

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There's still the basic problem that water doesn't reflect light that
well.  My calculations (based on Fresnel's law) say that you'd only get
about 2% of the light back, so if you start off with a little class IIIa
laser pointer (less than 5mW), you'd get less than 100uW at the sensor.
  Fortunately, wells tend to be very dark, so maybe you could use a
sensitive photodiode circuit perched at the rim of the well.

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That makes sense.  I think that the most practical is probably the "drop
a weight and measure the line" technique, but it's a lot more fun to
mess with lasers.  :-)

Ed


Re: water well depth



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I suppose, for a monitoring well, one could float a mirror on the
surface of the water to achieve a 'better' reflection ;-)

  - jim

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Somehow I doubt that the borehole is a straight line for 800 feet
or so.  It probably wiggles back and forth, or maybe even
corkscrews.  This will interfere with the light path.

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Re: water well depth

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Not necessarily.  Another cause of the level dropping during pumping
is that too much iron or calcium has deposited itself on the screen
that sits below the pump.  You don't need a new well, but you do need
to clean the screen.


-Robert Scott
 Ypsilanti, Michigan
(Reply through this forum, not by direct e-mail to me, as automatic reply
address is fake.)

Re: water well depth

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There are commercially available products, here

http://www.globalw.com/products/levelsensor.html

Which does up to 250' of water comes with up to 500' of cable for example

Bit expensive for what it is and in your application the expensive vented
cable for barometric compensation would be an overkill.

Personally I would look for a robust industrial absolute pressure sensor
with a 2  wire 4..20mA interface. Then worry about what kind of cable to
use to take the strain and survive down a well for 20 years, and how to
seal between cable and sensor.



Re: water well depth
I've homebrewed a system similar to the GlobalW one referenced here
recently.
Although I am on a well, it was more a 'head scratching' experiment than for
real use. It did require opening the wellhead up and dropping the sensor
into the water though, something that the OP has ruled out. Too bad, this
worked well for me.
Consisted of a diff press xducer/microcomputer/4 wires. You MUST compensate
for the local ambient air pressure else your numbers are wrong......
Another micro at the top of the well did the datalogging.The whole thing ran
off one 6 volt battery for about 2 years.
J




Re: water well depth


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Atmospheric pressure is about 32 feet of water and varies by about 2 feet.

If you are trying to monitor water level in an 800 foot  well over a season
2 feet of noise from atmospheric pressure variation is irrelevant.



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If you're going to do that you have a whole new situation.  For
example, you need only pass a wire down (and back) with a high
temperature coefficient of resistance.  (only one direction needs
that wire)  Pass current through it, and you can measure volts and
amps.  The part immersed will not change temperature significantly,
but the part exposed will.  Once more, calibrate.  You should
expect an exponential approach to the steady state.

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