water well depth

Robert Scott wrote: past the "pit-less adapter"

It's "pittless". I don't know the origin/etymology of the term

That sounds like the best idea yet, provided the delivery pipe is continuous and regular, and doesn't cause too many losses so that you can't hear the reflections. Those pipes are usually plastic, with long lengths coupled, and those couplers might foul the scheme.

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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

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

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

Steve Calfee wrote: I don't like the usual

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

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

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

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.)

There are commercially available products, here

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.

... snip ...

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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Hi group,

First off, I am not an embedded engineer but have been in software for the last 2 decades plus. Just getting interested in embedded now. Haven't seen an active well in a couple of decades as well where I stay.

But I just thought of this - can someone see if it will work ? My criteria were simple and cheap enough - what that means to each reader, and whether practical, may vary !

Let's have a weight that is heavy enough to drop with the dropping well water level but light enough to float on it's surface. Have a light fishing line connected to it and wound up on a spool. The spool needs to be tensioned such that it takes up slack without lifting the float off the water.

The reel is mounted on a screw threaeded rod. Now, the end of the rod will move in one direction or the other as the float drops or rises and rotates the reel. Can we not then have some form of measurement of how far the rod end is from a fixed point ? Or alternatively, a device that simply tracks the turns made by the reel from when the float was initially dropped from the ground level ? Both of these measurements should give a fairly accurate water level reading i think.

Just a thought.

Harnek

In furtherance to my earlier response I have found this interesting site from a company who produce off the shelf borehole monitoring solutions. I won't claim that they are in your budget.

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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

[...]

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.

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.

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.

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

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

- jim

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.

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

Hi Steve,

Well, the echo method would be sustainable and long-lived. Pretty much maintenance free if you use good parts that don't corrode easily. Some of our early ultrasound designs are still in use, to the point where the chassis paint starts to wear off.

An idea for the cable: What if you mounted a pressure transducer at the end? Then you would exactly know where your water level is, including dynamics such as detecting a slow-down of refill through the rock formation fissures. Of course, you would have to have a non-fatigue and chemically neutral guide wire in parallel so your cable doesn't sag over time. And nothing that can leach out and contaminate your water. You might be able to lower it all the way to the pump if that's safe.

Regards, Joerg