Depth of water sensing 1

[alternety]

I would like to monitor the water depth in well. Maximum depth is 500" and minimum is 0'.

I have been thinking pressure sensor but everything I have found is quite expensive packaged sensors.

Any ideas on other ways to monitor depth or sources of something I can use for a sensor in a 500' well.

 

[dhwilliams]

Mount a pulley wheel above the well. Wrap a couple of turns of rope around it. Suspend something that floats on one end of the rope and something that sinks on the other such that when one is at the top the other is at the bottom. As the float moves up and down with the water level, count the number of turns of the pulley wheel. With the right choice of pulley diameter you could either count the turns with a mechanical or electrical up/down counter or arrange to turn a pointer by using gears driven by the pulley.

 

[alternety]

Thanks. An interesting idea but I think there may some implementation issues. First of all the pipe, power wire, and safety cable are not necessarily tightly clustered or even in the center of the 6" shaft and they may interfere with the "sensing" cable. I am also not sure how to arrive at a float that would fit and work with the sinker while 500' of rope changes sides of the pully. I will mull this over.

I really only get one chance if I need to attach anything to the pump end if I am going to try that. I have to hire big equipment to take the pump in or out. I have to do this in the next two weeks.

Thanks again for your idea.

 

[melone]

How accurate do you have to be? On my home sump pump, I have 2 wire that sense the water level. If sensor 1 gets wet, then it turn on the sump. If sensor 2 gets wet, then it sounds an audible alarm. Perhaps, if you only need a couple of differnt key water levels, then something like that might work. The nice thing about that implemenation is that the sensors can get mounted to the side of the well, and should not interfere with the readings.

Just a thought.

 

[alternety]

As I noted I need 0-500'. I am not turning on a pump, I want to monitor well performance.

 

[melone]

I think you missed the whole point! If you are simply trying to see if the water level has reached certain level (like 100', 250', 375' and 400'), you can simply place water sensors at the different levels. However, if you need to know the level to 0.000001mm, this solution won't work. So I must ask the same question again, how accurate to you need to be?

 

[alternety]

Yes, sorry, I did miss the point.

Note to self: don't post while attention is elsewhere.

I would like to see 10'. Less would be nice. I want to log and analyze the draw down rate over an extended period of time to determine probable long term reliability.

The pump will operate at about 2 GPM. If the recharge rate is less than this I will see a drawdown in the well level. I want to be able to see how fast the well is emptying. In normal operation the pump will not necessairly run for a long time and if I have a large granularity I will not easily see early trends in supply.

A bit of background. I am concerned because this will be the only water supply. The well was difficult. 605' of solid rock produced slightly less liquid than I can with my kidneys and a six pack (well maybe a 12 pack). Brought a guy 300 miles to apply high pressure water to fracture the rock. This injects a large amount of water in the process. Subsequent "proving" of the well did not seem to me to extract the amount of water injected. I am also concerned about short and long term trends because I have no idea where the water is comming from. It is unlikley to be an aquifer based on the materials brought up by the drill. I could have a real problem and not find out for a while. I am just trying to placate my paranoia.

 

[Modemman]

Lateral thinking!

It seems to me you have put the cart before the horse! Use dowsing rods to find out if there is water and what depth it's at. This presupposes you know how to douse or can track down your local water divining expert. Don't laugh at the technique it really works, I have used it to locate sewers.

The only measurement techniques that will solve your problem otherwise are ultrasonic sensors and down hole pressure sensors and you are talking about expensive bits of kit for your depth.

Can you drop a smallbore pipe down the hole? 500 ft of even smallbore pipe is going to weigh some, but if you attach a pressure sensor at the top end then via a tapping introduce compressed air until you can detect air bubbling up to the free surface of the well. Shut off the air supply and the pressure remaining will give you the depth of water. 32 feet for every atmosphere (14psi). Temperature aand atmospheric pressure variation may give you some problem but to get the accuracy you require it may be good enough. This should continue to work without any further attention

Good Luck!

 

[alternety]

In point of fact, the dowser ($175 US) said at the exact center of where we drilled there would be 20 GPM at 135'.

 

[melone]

Or place the pulley/float assembly in a tube and poke lots of hole in to allow water to fill the tube. Then the previous solution might work....

 

[nbucska]

use the tube as a whistle : blow on it and measure
the frequency

<nbucska@pcperipherals.com>

 

[adc]

Assumming that the pump starts at a certain pressure, either or a combination of the following indirect measurements might work. After the motor inrush current and interia of the column are past: 1. measure the current drawn by the motor, 2. measure the flow rate.

Of course there is the problem of calibration. However, the pump manufacturer may have some data available. Get one point at installation with a float and a lonnng piece of twine. At mimimun you should be able to see long term trends.

 

[Chuckles159]

To measure the depth you are going to have to put down a small diameter tube the entire depth of the well, right down to the bottom. Maybe a 1/8&quot; diameter brass tube. Before you put it down, you are going to have to seal the top end with a pressure sensor. In the 70s I used the National LX1600 but I don't think this is available any more. Motorola have the MPX series sensors now.
It is important that the top of the tube be sealed before it goes down the well as the amount of water forced up the tube will increase the air pressure in the tube in proportion to the depth. If the seal is lost, your calibration will be lost.
However, you will have to calibrate the depth sensor empirically but by looking at the spec sheet for whatever sensor you use, and knowing the length of tubing you will be able to calculate from the air pressure, the depth of water. Higher air pressure = higher water level.

 

[buzzp]

Suggestion: if your going to monitor electrical parameters to determine if the well is 'dry' or not, monitor the power to the motor not just the current. The power is much more linear with head pressure vs. current. If the supply voltage remains constant as well as the frequency, then monitoring the power to the pump motor could, theorhetically, tell you the head pressure. There is down hole pressure monitoring equipment. I have installed some on large submersible pumping equipment. They generally failed rather quickly since the signal was piggy backed on the main current carrying conductors feeding the motor. Check out

http://www.centrilift.com

Good luck

 

[nbucska]

Use an open-ended piece of symmetrical TV cable and
measure the reflection time.

<nbucska@pcperipherals.com>

 

[hacksaw]

water water everywhere nor any drop to drink,
water water everywhere and all the boards did shrink...

sounds like you've discovered the joys of having your own well...

surprized that hydrofrac was used.


depending on your well size, pick up a cheap video camera and drop it down the hole, it should reach terminal velocity pretty quickly, when you hear the splash you can tell where the water level is +/-.

 

[alternety]

I have had the joy of owning a well several times before. But never to this level of sheer enjoyment. One failed well pump yielded my wife (a longer story) so they are not all bad.

I could also compress a Rolls Royce to 6&quot;, put an insulating layer around it and stick it down the well. It would probably reach the water. Using a simple continuity sensor to detect grounding of the RolaR-probe through the well water I could determine depth.

Using an automated 500' derrick to support the RolaR-probe, I could include a feedback loop to raise and lower the RolaR-probe to track levels.

 

[MMurphy]

Take a look at

http://www.consiliumus.com/Metritape.htm#Product_Selection

 

[Steventyj]

I like the motor monitoring idea, however here is a different, unrealistic idea:

Heat the air above the column of water in the well. Put a thermistor in the bottom of the well and in the output water at the top of the well. Calculate the temperature difference and from that determine how long the water was travelling in the pipe exposed to the warmer air.

Steven

 

[alternety]

I have been able to get the current vs pumping lift from the manufacturer. I do not have it for the full range needed, but a reasonable subset. Per the manufacturers spec, current is largely independant of applied voltage, so current in a leg (3 phase) is a reasonable measure of lift height.

The next most suitable solution would probably be a tube with a pressure sensor at the top of the well. The detail on this would require a presure fitting and pressurizing after installation. With 500 feet of tube it is probably impractical to seal it before installation. Eventually air would be absorbed by the water in the tube so external pressurization would also be necessary. Not a problem to implement, but monitoring current is easier.

Thanks for all of your suggestions, both thoughtfull and spurrious.