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Water sense with AC Signal - Cutoff Design

Meir Yeru
Prodigy 50 points

We want to build an circuit of water cutoff

Controlling of water pump motor that adding\stop adding water to a container
The water container maid of metal and the signal in the water should be AC Signal (square 5V)
The body of the container connect to GND

I have only one Entrance\inlet to the container so with the AC signal
I should also fit the AC Signal to the water and also sense the present's of the water
(We must use AC signal)

Another issue - I need design sensitivity of water that my probe feel's (sense) 20Kohm\50Kohm\100Kohm
with AC signal that fitting probe sense

I thought of some idea's
like Voltage divider with the water resistance
or current flow measurement - when my fitting probe (AC Signal) close circuit with the water to container body (GND)

Of course we are using MCU with ADC to measure analog signals

Please suggest more ideas how can I over come that problem
Measure the present's of the water and sensitivity to water resistance

Thanks in advance

Mayer

  • 0
    TI__Intellectual 1385 points

    Hello Mayer,

    I have a few alternative water level measurements methods I am looking into.  I think that these methods might be a better alternative to low-current sensing.  What is the power budget for the solution?

    Regards,

    Jamieson Wardall

    Sensing Applications

    Texas Instruments

  • 0 in reply to Jamieson Wardall
    Prodigy 50 points

    Hello Jamieson,

    The budget of the solution is around 30-50$ max

    We also sense preset of water in the container using AC Signal

    And that probe (AC Signal) should sensitivity to water quality (water resistance)

    I am very Appreciate your help - Hear more ideas 

    Regards,

    Meir

  • 0 in reply to Meir Yeru
    TI__Intellectual 1385 points

    Hello Mayer,

     

    I am still working on alternatives and have looped in others on your design. 

    Pure water is an excellent insulator and it’s the ions in the water that conduct.  This is the biggest issue with doing a current measurement as the water resistance will vary depending on the free ions (purity of the water).  We could design a complicated measurement system to account for the variation but I want to eliminate other more simplified methods first. 

    Regards,

    Jamieson Wardall

    Sensing Applications

    Texas Instruments

  • 0 in reply to Jamieson Wardall
    Prodigy 50 points

    Hello Jamieson,

    As you said

    I did an experiment of putting 8Vpp Triangular signal in the water

    and measure the voltage divider between 400kOhm resistor and free mineral water (Distilled water)

    I saw on the scope that the voltage divider is "working"
    but the voltage drop on the water is decreasing 
    look like that water resistance is decreasing

    We cannot work with that

    Any suggestion can be very helpful

    Regards,

    Mayer

  • 0 in reply to Meir Yeru
    TI__Intellectual 1385 points

    Hi Mayer,

    Have you looked into some type of ultrasound or proximity sensor  to measure the distance of the water to the top of the tank?

    Regards,

    Jamieson Wardall

  • 0 in reply to Jamieson Wardall
    Prodigy 50 points

    Hi Jamieson,

    I have no room to put ultrasound or proximity sensor 
    It's generator tank - I have only small Entrance\inlet in the generator to put there a prob of metal

    Regards,

    Mayer