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Best sensor for my application

Discussion in 'Electronic Basics' started by gtslabs, Apr 1, 2005.

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  1. gtslabs

    gtslabs Guest

    I want to measure the distance a glass hydrometer bulb drops over time
    in a solution of suspended solids. This distance is only about 4
    inches. Since I can not modify the hydrometer bulb dramatically I
    thought I could add a drop of metallic paint on the top tip. Then I
    want to measure the distance from a fixed point to the top of the
    bulb/metallic paint. My resolution needs to be about 1 mm. I am
    looking to collect the data with some type of acquisition system.

    What is the best type of sensor that could measure the vertical
    distance assuming the bulb might float form side to side about 1 inch

  2. Bob Masta

    Bob Masta Guest

    I wonder if you could constrain the hydrometer to stay on-axis
    and use an LVDT (Linear Variable Differential Transformer).
    This is a standard way of measuring linear displacements,
    consisting of an iron core that moves in a tube with a winding
    on each end. An AC excitation signal is coupled between
    the windings, with the percent of coupling proportional to
    the core displacement.

    In your application, you'd have to allow for the weight of
    the core affecting the hydrometer depth, but this should
    be pretty straightforward. This isn't as elegant as the
    massless optical approach, but has the advantage that
    you might be able to do it with an off-the-shelf sensor.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
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