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B Can someone help me find a method to measure water level in a tank

  1. Aug 10, 2017 #1
    At the outset I am a novice in physics. i have constructed a rain water storing tank with a capicity of 1,20,000 litres. I propose to seal the tank so that there is no light penetrating inside the tank. My question now is how do I measure how many feet of water is left inside the tank? Can someone suggest a simple way? Thank you in advance.
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  3. Aug 10, 2017 #2


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    Do you mean without opening the tank? The simplest way by far would be to have the ability to open at least a small area at the top of the tank and stick in a long rod that darkens in water and then take it out and see what length is dark.

    Absent that, you're going to have to have a float and some electronics including a transmitter. Seems like a lot of unnecessary work/cost.
  4. Aug 10, 2017 #3
    Clear plastic tubing run vertically up the outside of the tank. The bottom of the tube is connected low in the tank (for example, tee it into the outlet pipe). Tube level = tank level.
  5. Aug 10, 2017 #4
    thank you for your replies.
    yes i want to measure without opening the underground water tank. Measuring with a stick is my last resort if nothing works out.
    probably a float tied to a string which comes out and some way to measure...with a scale outside with the same height of the tank?
    Is this possible? if so how?
  6. Aug 10, 2017 #5
    Can you please explain how the float and transmitter can be used?
  7. Aug 10, 2017 #6


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    Yell into the top and time the echo? [better -- measure the tone of the resonant frequency]
    Drop some yellow dye in, wait and measure the concentration that comes out?
    Put a barometer onto a boat and have it phone home?

    If one is going to suck the water out of the tank, it should be possible measure the suction required to draw it up and obtain a depth reading from that information.
    Last edited: Aug 10, 2017
  8. Aug 10, 2017 #7
    Sorry, I missed the "underground" part of the description. I'd go with the stick; that's how they do it at the gas station.

    What are you going to do with the water and how are you going to get it out of the tank?
  9. Aug 10, 2017 #8
    there is going to be a submersible motor to pump the water out to the overhead tank.
  10. Aug 10, 2017 #9
    How deep is the tank?
  11. Aug 10, 2017 #10


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  12. Aug 10, 2017 #11
    the tank is 7 feet deep. 23feet ×26feet length and breath.
    Last edited by a moderator: Aug 13, 2017
  13. Aug 11, 2017 #12
    A $5 ultrasonic sensor and an Arduino is what you need. All you need at the tank is a 5v supply, which I'd do with batteries for this. Just turn the Arduino on to take a reading and off when you're done, should last years. Mount the ultrasonic sensor inside the access hatch pointing at the surface of the water and write about 20 lines of code.

    You could play around with an RF relay back to the house, but I'd be more tempted to just use a simple 7-segment digital display right at the tank. If you build a little shelter it should be good down to around -10C.

    I won't tell you how to do it here - lots of code and tutorials online:


    Whole thing should cost less than $30.
    Last edited: Aug 11, 2017
  14. Aug 11, 2017 #13


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    Water is a pretty good conductor. You can put a set of contacts along the length of a stick (plastic and smeared with silicone to shed water) and 'measure' the resistance between each one and the bottom contact. The 'measurement' can consist of an LED, a suitable resistor at each division, all powered by the same battery. The dry contacts would not cause their LEDs to light and the wet ones would. It would be a very simple Bar graph. Ten LEDs would give you a measurement in tenths of the depth. If there is a problem getting enough current to light a LED then a transistor switch at each contact would do the trick. Natch, you would only turn on the battery when you wanted to see the level.
    Not as sexy as an ultrasonic machine but cheaper (probably). Having said that, you can buy ultrasonic tape measures fairly cheap'
  15. Aug 13, 2017 #14
    just a note of caution - I experimented with water sensing in a small outdoor irrigation system a while ago. I was plagued by corrosion caused by unwanted electrolysis (over months of time). So if you use direct contact electrodes, do design to use a really low voltage (suggest no more than a few tens of millivolts), and don't leave it running when not in use.

    I had some success with a little low-current oscillator dumping its output into a piece of insulated wire running from top to bottom of the water tank. I monitored the current draw from the battery which went up as the water level rose, increasing the capacitance on the oscillator output. Required a light twin cable which doubled as power supply and signal cable. But that needed calibration and wasn't ultra-precise.
  16. Aug 13, 2017 #15


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    . . . . . or AC?
  17. Aug 13, 2017 #16


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    I think this idea by @jbriggs444 is a good one. Can you run an ABS tube (about 1-2" ID) from near the bottom of the water tank up to where you can work with it? Can it be a straight tube, or would it need to be curved? If straight, just use an audio tone generator and sensor to find the resonance of the tube from the water's surface to the top of the tube. You could do that with a cellphone app, probably...
  18. Aug 13, 2017 #17

    jack action

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    This is my favorite kind of float gauge:


    The middle twisted blade (1-turn) is connected to the dial indicator and it turns as the float goes up and down. Usually found on gas tank for small vehicles like snowmobiles or lawn tractors.
  19. Aug 28, 2017 #18
    I didn't spend time on AC direct contact sensors - I went to capacitive ones instead. However, while AC would prevent measurement errors due to electrolysis polarising the system, I wonder if it would actually prevent the corrosion rather than simply making it symmetrical? Perhaps a higher frequency would be more effective than a lower one?

    I think (not being a chemist) , and supported by some experiments in a different context - that if the voltage is low enough ( say under 50 mV - the lower the better), it is too low to cause electrolysis and one should get consistent reading without inducing corrosion. That might be a very simple way of doing it. But I've not tried that as a moisture sensor.
  20. Aug 29, 2017 #19


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    You can buy ultrasonic gauges with a remote display for home heating oil tanks. Some even have an alarm that goes off of the level drops too quickly indicating oil theft or leakage.
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