Question on capacitor working

Discussion in 'The Projects Forum' started by prana, May 13, 2011.

  1. prana

    Thread Starter New Member

    May 13, 2011
    3
    1
    Hi Guys,

    Am trying to develop a circuit where am trying to get an approximate idea of distance by capacitive sensing. I have seen few products where a sensor ring (completely of steel) acts as a capacitor plate and its distance from a steel plate surface is tracked. There is no electrical connection to the steel plate. However, my question is how can just a single ring act as a capacitor. A capacitor can be formed only when 2 plates with a dielectric in between is given an AC vltg. Just not able to understand.
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Welocome,
    have a read of this attachment
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
    Hello,

    This page of the EDUCYPEDIA will give you several links on Capacitive sensors

    Bertus
     
  4. prana

    Thread Starter New Member

    May 13, 2011
    3
    1
    Not too useful guys :(
     
    strantor likes this.
  5. jerseyguy1996

    Active Member

    Feb 2, 2008
    206
    9
    I'm not sure if this is too simplistic for you but I learned a lot about implementing a capacitive proximity sensor by watching this:

    http://www.youtube.com/user/nerdkits#p/u/7/euv8ZLgPh8A

    I built my own which uses a slightly different software implementation here:

    http://www.youtube.com/user/jg1996business?feature=mhee#p/a/u/0/zbBPf3Xncdw

    Regarding your comment above, is it possible that the steel plate shares a common ground with the circuit in which case I don't think it would need a wire connection?
     
  6. prana

    Thread Starter New Member

    May 13, 2011
    3
    1
    No the system works even if i put my hand under the ring (due to the conductive nature of human skin) .. so dont think a separate ground is required.
     
  7. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
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    Its not due to the conductive nature of human skin. Capacitive sensors work when the electric field is broken by anything, even plastic. I just set one up yesterday that looks through a piece of plexiglass to determine the presence of plastic pellets on the other side. This is possible by adjusting the sensitivity of it, so that the electric field is just strong enough to make it through the plexiglass. This is all outlined in the unuseful PDF I posted.
     
    Last edited: May 14, 2011
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