Capacitor tolerance for oscillator

Discussion in 'General Electronics Chat' started by Jotto, Dec 28, 2011.

  1. Jotto

    Thread Starter Member

    Apr 1, 2011
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    Have a board that I need a 200pf 100v cap. Does the tolerance have to 1% or just go with the standard 5%? There is no tolerance marking.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    How can we answer your question if we don't know the purpose of the capacitor?:confused:
     
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
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    All together now, with feeling: post a schematic!

    Seriously though, it depends on the role of the capacitor (e.g. a coupling capacitor may not be so critical, a tuning capacitor in an LC oscillator may matter more).

    It also depends on what the oscillator is for - is its frequency critical?
     
  4. Jotto

    Thread Starter Member

    Apr 1, 2011
    159
    17
    There is no schematic available. They will not release one, proprietary equipment. No longer manufactured.
     
  5. Jotto

    Thread Starter Member

    Apr 1, 2011
    159
    17
    If I had one I would post it, all together now ....
     
  6. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    2,693
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    Stick a new cap in. See what happens.
     
  7. Adjuster

    Well-Known Member

    Dec 26, 2010
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    A photograph might help, at least to identify the physical type of capacitor used. For instance, compact ceramic types often have wider tolerances, polystyrene film or especially mica tend to be close tolerance.

    You did not say anything about the frequency of the oscillator, or how accurate it may need to be. Is this similarly unknown?

    A 200pF capacitor could well have a frequency determining function. If you do know the required frequency accuracy, and what class of oscillator this is,this may give you an idea of how accurate the capacitor might need to be. For instance, in an LC oscillator the frequency varies inversely as the square root of the tuning capacitance, of which which this capacitor may represent a greater or lesser fraction.

    In the end, in the absence of other data you may be advised to fit the closest tolerance device you can get.
     
    Last edited: Dec 28, 2011
  8. Adjuster

    Well-Known Member

    Dec 26, 2010
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    How very practical! It certainly beats trying to do a Sherlock Holmes act on a secret circuit.
     
    joeyd999 likes this.
  9. bertus

    Administrator

    Apr 5, 2008
    15,652
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    Hello,

    A lot of characteristics are depending on the materials used inside the capacitor.
    There are ceramic, foil, silver and electrolitic capacitors.
    This site will give you a heap of information on the capacitors:
    http://my.execpc.com/~endlr/index.html

    Bertus
     
  10. Adjuster

    Well-Known Member

    Dec 26, 2010
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    @Jotto: I'm sorry that I seem to have upset you by my comments about the difficulty of answering enquiries where very little data is given. I am trying to answer such queries as I can these days, and I find the dearth of of information supplied in many cases frustrating.

    If you are subject to a confidentiality agreement, you might have thought to have made it clear at the outset that only limited information could be supplied. Alternatively, in the context of such an agreement, one might wonder if it was correct to make any mention of this issue in a public internet forum.

    I have to say however that in my turn I am quite upset by your PM.

    Perhaps it is better to say no more on the subject.
     
    Last edited: Dec 29, 2011
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