Measuring cistern water level

[debequechute]

General specs:

 3400 gallons (two 1700gal poly tanks connected side-by-side)

 Buried in-ground about 6' below surface

 4" PVC fill tube down to 1' below top of tanks where it has a tee to connect both tanks.

 Tanks are about 7-8' high which would make for about 3-4psi at the bottom when full.

My initial thought was to snake a pressure sensor on a wire down the 4" pipe to the bottom of one tank and read it out electronically. Having a hard time finding one that will work in that environment. I'm also unsure about what kind of wire to use in the event of insulation failure. I don't want something corroding down there.

Any other ideas?

[woodnmetalguy]

Well, my cistern gravity feeds into the basement of the house, where I pressurize a tank with a jet pump.  Since the cistern and the basement are about the same depth below ground, I plumbed a clear sight tube into the line, and by opening a valve the water rises in the tube to match the level of the water in the cistern, so I can check the level from the comfort of the basement and go out and turn on the windmill if necessary.  During the winter we generally run the windmill for a day or two about every three weeks to keep the level up.

Another idea might be to have a rod with a float on the bottom extending above ground from the cistern itself.  As the water level lowers you could see the top of the rod descending and could judge when you need to run your pump to replenish the supply.  Small chance of debris getting around the rod, but with a reasonable fit I wouldn't think it would be a big problem...

-- Dave

[Nando]

Pressure sensor with stainless steel wiring with TEFLON.

Expensive after thought indeed, specially due to the T/

Maybe a minor job to open the ground and separate the T to allow vertical drop of other type sensors.

How is the water retrieved from the tanks.

I did one where the retrieving piping attached to both tanks had a T with a pressure sensor -- all depends how the system is built, give more information.

Regards

Nando

[Drives]

http://www.levelworks.com/PDF-BlueRibbon/BC1000.pdf#search='birdcagepressuresensor'

I've used these on a couple of water and waste water plant retrofits.  They work well, but may be too expensive for your taste.  Good Luck.

[debequechute]

Some good ideas there, thank you. I've been searching on this for hours and have more or less settled on the Freescale/Motorola MPX5050GP 0-7.25PSI sensor available at Digikey for $19:

 http://tinyurl.com/494t5

From the looks of this it should be possible to drop a tube down to the bottom of the cistern with a weighted end and leave the sensor topside. If it works out I'll post back results. My only real concern is temperature of the air in the tube changing with ambient/water temperature which will change the pressure in the tube. I'll have a temperature sensor topside, so I should be able to detect these fluctuations during periods of constant water level and calibrate my micro accordingly.

[farmerfrank]

In industry the transmitter is left on top or even remotely up to hundreds of feet away. A small air line goes to the bottom of the tank with just a very small trickle of air going through it. The sensor measures the air pressure which is in direct correlation to the depth of the liquid. This eliminates having to run any wires to the field and leaves the transmitter in a handy atmosphere out of the elements.

[mkseps]

Do you remember as a kid, blowing bubbles with a straw in a glass of soda or water?  Well, if the water in the glass was one foot high, it would take exactly 0.433 lbs of pressure before the bubbles would be ejected from the bottom of the straw.  If you place a sturdy tube down to the bottom, possibly copper, then run a poly tube to wherever inside your house.  Inside the house, you will place a 'T' and a schader tire nipple.  This you will attach to a hand tire pump.  The other side of the 'T' is attached to a pressure gauge like 0-5 psi.  If the tank is 8 ft. high and is full, the pressure gauge will read: 8x0.433=3.5 lbs.  What you do is gradually pump the poly line until the pressure no longer increases.  This tells you that air is escaping the down pipe inside your water tank.  If you can't find a low pressure gauge, you can fabricate one out of poly tubing with a small resourvor on the bottom of the verticle tube, putting in some coloring to make the water level more visible.

Gene

[georgeodjungle]

i use home made swimming pool alarms with leds.

ther's some good web sites out tharrr.

cost about $1 to make, for each level.

[Godfried]

There is a great and easy way to get a gauge for your already build cistern or water tank. Works on any cistern, is cheap, reliable and really easy to install.

It tells you the water level in inches and meters, and requiers no batteries.

check this link:

www.cisterngauges.com

Godfried