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grid capacitance sensor??

Discussion in 'Electronics Homework Help' started by r4w_tsuk, May 31, 2012.

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  1. r4w_tsuk

    r4w_tsuk

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    May 31, 2012
    does anyone know how to make a grid capacitance sensor? or where is it available?? id like to use it for my thesis topic to measure cooking oil quality.. need some help please..
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
  3. r4w_tsuk

    r4w_tsuk

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    May 31, 2012
    yup i've read this before.. i wonder if it is available to be bought? or do i have to make this myself..? thanks
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I don't know, sorry.

    Harald
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    For your thesis... I'd make one.

    I guess the issue will be making the whole thing "food safe", and that is likely to be a larger issue than actually making a sensor.

    edit: although a quick google of "food safe capacitance sensors" yields a significant number of results that you could follow up on.
     
  6. r4w_tsuk

    r4w_tsuk

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    May 31, 2012
    thank you very much sirs, i would accept more helps and inputs.. future thanks..
     
  7. CocaCola

    CocaCola

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    Apr 7, 2012
    Last edited: Jun 21, 2012
  8. r4w_tsuk

    r4w_tsuk

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    May 31, 2012
    just like that sir?? i just wanna make sure.. thanks
     
  9. CocaCola

    CocaCola

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    Apr 7, 2012
    Yeah, pretty much capacitive sensors are interwoven grids, or two paths near each other.... You will see a lot of DIY capactive sensors that are just grid work on a PC board...

    For example...

    http://web.mit.edu/imoyer/www/portfolio/easyset/index.html
     
  10. r4w_tsuk

    r4w_tsuk

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    May 31, 2012
    do we need to supply voltage for this sensor?? because when we submerged it to different usage of oils the reading doesnt change.. thanks.
     
  11. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    This kind of sensor is passive, meaning that it needs some excitation (needs to be stimulated somehow). The capcitive sensor works on the principle of changing the capacitance in reaction to the medium it is immersed. So you need to measure the capacitance somehow.
    There are different ways of measuring the change in capacitance. You coulkd for example
    - use a capacitance meter
    - use the sensor as part of an oscillator and evaluate changes in the oscillator's frequency
    - use the capacitor as the timing element in a monoflop and measure teh monoflop's time constant
    - etc. etc.
     
    Last edited: Jan 18, 2013
  12. r4w_tsuk

    r4w_tsuk

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    May 31, 2012
    we immersed it with different kinds of oil but we get the same reading on the LCR meter. We are hoping that it will change depending on the quality of oil. How do we excite it? what do you suggest we do?
    thank you sir
     
  13. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    As long as the dielectric constant of the different types of oil is similar, you won't find a noticeable difference in capacitance. As this article shows (referenced before), you will see adifference in capacitance if the dielectric constant of the oil changes. In that case the degradation of the oil with time changes the dielectric constant. This is used as an indicator fopr the quality of the oil.

    Also: Whatever method you use, make sure the capacitance of the sensor is a noticeable percentage of the capacitance of the whole setup. If the sensor's capacitance is small, but the setup (wires etc) has a high capacitance, any change in capacitance of the sensor will be seen proportionally smaller on the meter.
    2 Examples:
    1) Assume a sensor capacity that is 50% of the capacity of the whole test setup. If the capacity of the sensor changes by 10%, the whole setup's capacity changes by 5%. You should be able to measure that.
    2) Assume a sensor capacity that is 10% of the capacity of the whole test setup. If the capacity of the sensor changes by 10%, the whole setup's capacity changes by only 1%. This will be difficult to detect.
     
    Last edited: Jan 18, 2013
  14. r4w_tsuk

    r4w_tsuk

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    May 31, 2012
    thanks for the inputs sir.. this will really help us..
     
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