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Capacitance Meter or LCR

Discussion in 'Electronic Design' started by shayan, Feb 25, 2005.

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  1. shayan

    shayan Guest

    Hello every one, Can i measure the continuous variation(with frequency
    above 10 kHz) in the capacitance and dielectric constant of a fine
    capacitor with capacitance meters or LCR's? Please introduce me a web
    link for these instruments.
     
  2. google make them, for example
    http://my.integritynet.com.au/purdic/lc-meter-project.htm#circuit-osc

    martin

    "An eye for an eye makes the whole world blind"
    Gandhi
     
  3. Chris

    Chris Guest

    Hi. First off, I believe you're possibly talking about D (dissipation
    factor) instead of "dielectric constant".

    Second, your question provides insufficient data to expect an
    intelligent answer. I mean, this is the nuculer age, and these are the
    internets, but honestly, you might want to put a little more effort
    into it.

    Please introduce us a question (all your base are belong to us?) which
    includes:

    * What, specifically, are you doing? Trimming a cap with a laser,
    tweaking a variable cap with a screwdriver, motion control from
    determining the variable capacitance of two sliding conductor plates
    with an air dielectric, or what? There is actually more than one
    reason to continuously measure a variable capacitance. I've run across
    these and more in my day.

    * What kind of measurement accuracy do you need?

    * What is the "fine capacitor"? They're all fine. What capacitance
    value or range? In pF, nF, or uF please.

    * What does "above 10 KHz" mean? Capacitance can be measured at many
    frequencies, and you'll have to be more specific. What's the
    frequency, Shayan? (Dan Rather's going to have a lot of time to ponder
    that one ;-)

    * Do you have a requirement for a test voltage? How about a DC bias?
    If so, what are they?

    * What do you mean by "continuous"? Once a second? Twenty times a
    second? A purely analog measurement which gives a continuous analog
    output without any updating, like some of the old General Radio meters?
    This goes back to the question of what you're doing here.

    * What kind of output or interface do you need? A 4-digit LCD on a
    handheld LRC meter? How about GPIB, or do you require a handler
    interface or an analog output voltage? Some combination of these?

    * What kind of fixturing do you have, or are you building it? Do you
    have an idea what the impedance of your fixturing is at the specified
    frequency? (If you think this is picky, you should know that for low pF
    measurements, the fixturing is sometimes the part of the project that
    requires the most engineering work, and if there's automation involved,
    you can easily be pulling your hair out trying to get good
    measurements.)

    * Last, but not least, how about a price range? If you want something
    for less than $2.95 USD, set up a 555 with a 9V battery, and infer
    capacitance from frequency. Prices for real solutions aren't cheap.
    Whether it's possible in your price range is dependent on answers to
    the above questions.

    I'm not trying to be harsh, because you may just need a little more
    help than most OPs. But the solution to your problem might be fairly
    expensive, and you wouldn't want to waste time on an instrument that
    won't do the job for you. If you don't know the answers to these
    questions, please ask around and find out.

    Look forward to hearing from you.
    Chris
     
  4. shayan

    shayan Guest

    Hi Chris. Tank you for your kindness and answering to my request.
    Indeed I'm a chemical engineer and I want to use a special capacitor
    for measuring the variation of dielectric constant in a fluidized bed.
    A fluidized bed is column in which air or another fluid is entering
    from bottom and fluidized the fine particles (5 to 500 micrometer)
    exist in the column.
    By variation in the particle concentration in the capacitor volume its
    dielectric also changed. If we could measure this changing in
    dielectric with a high sampling rate, we could calculate the particle
    concentration using convenient equations. But the traditional LCR's
    have not enough measurement speed (minimum 2 ms) and we want the
    sampling frequencies above 5 kHz (measurement speed below 0.2 ms).
    By which type of capacitance meters can I do this?
     
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