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Circuit to trigger an alarm on water level change

Discussion in 'Electronic Design' started by [email protected], Aug 3, 2007.

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  1. Guest

    I have a water tank where I want to get an alarm when the water level
    change, up or down, based on to wires going from top to bottom in the
    tank as sensors.
    I have found a circuit on the web to trigger alarm on a certain water
    level, but not one that triggers on change in water level.
    I want the circuit to be simple with as few components as possible
    more that accurate.
    I also have living organism in the tank so the voltage on the sensors
    to be as low as possible.
    Can anybody point me in the right direction?
    Than you.
  2. Pressure sensor in bottom, PIC
  3. Guest

    I forgot to say that that prssure sensor is not an option, I need to
    use two paralell wire sensor. - Any idea?
  4. Bruce Varley

    Bruce Varley Guest

  5. Keith Sloan

    Keith Sloan Guest

    How about putting a square wave signal ( IC555 ) on the bottom wire and
    monitoring then other wires with a PIC processor.

  6. MooseFET

    MooseFET Guest

    How fast is the change? Would it be ok if the system ignored very
    slow changes?

    Signal --> High Pass Filter ---> Window Comparitor

    If you need it to react to even very slow changes, the high pass
    filter can be a bit of a problem. If yu don't want to use a PIC, you
    can use a DAC and a counter.
  7. Gary Tait

    Gary Tait Guest

    wrote in
    You have two tasks.

    1: Get a linear electronic value of the level in the tank.

    2: Sample the signal collected in step 1, and compare with a previous
    sample. Based on the outcome, you would have a signal of a change in
    either direction, or a stable value.
  8. MooseFET

    MooseFET Guest

    It doesn't truly have to be linear.
  9. Guest

    Jesus just weigh the damn thing.
  10. But Jesus walked on water, so things may happen.
  11. John B

    John B Guest

    Probably because it's a homework question!!!

    The OP hasn't said whether the 'organism' lives in fresh or salt water.
    That makes a huge difference to the sensitivity of a two-wire sensor.
    How about a float running up and down the two wires with a linear Gray
    code graticule attached. I guess it depends on how much space there is
    above the tank. Ah, his supervisor won't have thought of that method
    will he.
  12. Capacitive sensor on outside of tank. I'm assuming glass or plastic
  13. D from BC

    D from BC Guest

    Change in water from rain, leaks and fish jumping out...

    So call it level A and level B and A-B is the water level change.

    So... I guess the circuit sets Level A to be at the water surface..

    But the level A set point should change so that a difference can be
    monitored beginning at any tank level.

    Level A
    |\/\/\/\/\/\/\/\/ water
    Level B
    D from BC
  14. Rich Grise

    Rich Grise Guest

    If you have access to the outside of the tank, use a sightglass with
    a ball and an array of optical sensors?

    A pressure sensor at the bottom?


    Good Luck!
  15. Rich Grise

    Rich Grise Guest

    Use platinum wire, and have a reference sensor to tell you the
    conductivity of the fluid in general. Then just measure the resistance.

    Good Luck!
  16. Rich Grise

    Rich Grise Guest

    How do you intend to account for movement of the critter?

    Good Luck!
  17. Jasen Betts

    Jasen Betts Guest

    use insulated wires and measure the capacitance between them (perhaps
    use 0.1" pitch ribbon cable and measure between odd and even numbered

    what counts as a change in level?

  18. Guest

    I have done some measurement on the sensor and found that the
    resistans is from 200Ohm to 1KOhm.
    I need to have a trigger if it drops 50 Ohm within 10 sec. time. - An
    increase in ohm is not important after all.
    I also cheked that I can use a measurement voltage of up to 1,5V
    without disurbing the living organism.

    Anybody have an idea of a simple circuit, without too many components,
    that can solve this?

    I found a circuit on the Velleman web that may be used as a starting

  19. Fred Bloggs

    Fred Bloggs Guest

    I don't know what's best for your incompletely described situation. You
    need some kind of precision to detect 50 ohms out of 200 to 1000. LEDs
    make good voltage references. You could do something like this with a
    "dual single supply" operational amplifier. Select R1 for about 10mA
    through a 1.5V red reference LED:
    View in a fixed-width font such as Courier.

    .. V+
    .. |
    .. +-----------------+--------|<|---.
    .. | 1N914 |
    .. [R1] |
    .. | | ----
    .. | |\ | | |
    .. +--------|+\ | |\ | |
    .. | | >--+--[100k]------------|-\ | |
    .. red --- .---|-/ | | | >--+--> | |
    .. LED ~ \ / | |/ [51] .----+--|+/ | -- --
    .. 1.5V --- | | | |+ |/ |
    .. | +----o o-+--[100k]----' === [100k]
    .. | | || |47u |
    .. | [1.5k] Rx +--------'
    .. | | |
    .. | | [10k]
    .. | | |
    .. '----+-------------+-------------'
    .. |
    .. ---
    .. gnd
  20. Fred Bloggs

    Fred Bloggs Guest

    Never mind, I don't like that circuit, it has practical problems...
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