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A Question about ultrasonic range meters

Discussion in 'Electronic Design' started by Sara, Jul 14, 2006.

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  1. Sara

    Sara Guest

    Dear friends,
    I'm working on a project for measuring the level of liquid in a tank
    with ultrasonic sensors.
    In this project i need a measurement resolution about 1mm and the
    maximum range of measuring is about 4m.
    First I want to know if resolution depends on the frequency of the
    sensor or the electronic circuit that measures the time of going and
    returning of signal.
    Second I have found an article that has measured the level with phase
    shift with great resolution but the maximum range is 90cm.I will
    appreciate any information about this method and it's relation with
    resolution and the way one can extend the maximum range to 4 m.

    Thanks in advance
  2. Guest

    Have several sensors spaced 90cm apart, with a float switch on each so
    you can determine which sensors are not presently covered by liquid.
  3. John Fields

    John Fields Guest

    What's the liquid and what's the minimum range?
    It depends on both, as well as on the change in the velocity of
    propagation of sound through the medium, which in turn depends on
    the density and temperature of, and pressure on, the medium.

    Also, you don't mention whether you'll be measuring through the
    liquid or through the space in the tank above(?) it.
  4. I guess the range depends on whether the signal can
    travel in a tube or whether is is in the open.

  5. Joerg

    Joerg Guest

    Hello Sara,

    Both. Resolution goes up with frequency but your electronics must be up
    to snuff, especially if you want to extricate phase angles. Most likely
    you have to become very familiar with I/Q mixing and detection. Analog
    Devices and Mini-Circuits carry the relevant parts for that.

    Why was the range limited? What's the liquid? How do you focus the beam?

    Anyway, before you get too carried away with achievable resolution look
    at the fluid to be measured. I'd bet that it's ultrasonic properties
    will not be constant over pressure, temperature etc. Look closely at the
    sound velocity in it and how it changes with other parameters. This data
    isn't always published but can be measured.

    Then there is a whole other topic to ponder: Gas micro bubbles in the
    liquid. These will scatter the ultrasound signal no matter how good you
    focus the beam and influence the velocity of sound.
  6. Sara

    Sara Guest

  7. Sara

    Sara Guest

    Hello John,
    Thank you for your good information.

    The liquid in the tank is petrol or gasoline and the minimum range is
    I'm measuring the level of liquid through the air(the space above the
    liquid).I want ot know if it is possible to gain 1mm resolution with
    40khz ultrasonic sensor?The name of article is "Extending the accuracy of ultrasonic level
    meter" at : by P.Olmos.And also i found another article
    that is "Fast processing techniques for accurate ultrasonic range
    measurments"By B.Barshan which explained four methods for measuring TOF
    one of them is sliding-window which is exactly the thing I'm looking
    for.I will still appreciate more information or circuit for the method.
    Thanks a lot
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