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Controversial schematic symbol

Discussion in 'General Electronics Discussion' started by tedstruk, Jul 11, 2018.

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  1. tedstruk


    Jan 7, 2012
    Now here I go again.
    The capacitor symbol is a widely used and important part of the diagram. It consists of a bar seperate from another bar, and often has (the following is as I learned it DIY study and research); A straight bar, with a curved bar on the opposing side.

    A barred line on schematics usually represents a block such as a diodes direction where the arrow designates the signal , or flow. but the way I learned it was that there is one exception to the rule, and that is the capacitor. In that case, it represents a cell terminal in a multi-cell battery(a type of capacitor), or a terminal on the positive side of the circuit and the curved line representing the negative side of the circuit.

    NOW there are lots of symbols for capacitors! two straight bars, the straight bar and curved bar, the straight and curved bar with a + sign on it, and of course the multiple, two sized straight bar symbol, indicating the cells in the battery.

    Usually....(in my opinion..not so good!)
    The cap is installed with the straight bar toward the flow, kind of like a stopper that has to charge, before it fires.
    and that means the curved line goes toward the grounded or
    "where the -(negative) side of the capacitor connects".ie. an antiquated polarized electrolytic type

    Now the teaching of the schematic symbol art is lost in all home made circuits and they are fading fast.

    I have a set of 0.1uf caps in my schematic. They are both straight bars with curved bars, but no + sign on them.
    Am I to presume that the straight bar is the + positive connection of the capacitor, and curved bar the - negative ?

    Or am I to assume that in power electronics, this is moot, arbitrary, and not warrenting any further discussion?

    I am asking this because I have run into this same misnomer every time I build something electronic. and it bothers me everytime....

    When I trust myself, it usually works. when I trust the taught diagramatic symbology of the electronical sciences, it fails.
    IDEAL? man I didn't even get past batteries and capacitors yet!

    how, can this be fixed so that our best techs don't blow the caps up in their faces?
  2. Minder


    Apr 24, 2015
    I believe what you are referring to is non-polarized capacitors, IOW they work with both polarity.
    One of the main reasons for this difference in marking is in HF or radio circuitry where the capacitors are use for de-coupling.
    The curved bar end goes to ground connection, this connects to the outer foil of the cap, this ensures that the outer foil of the cap is also close to the ground connection in a capacitive sense.
    In many simple LF or slower digital circuitry, it is not so important.
  3. kellys_eye


    Jun 25, 2010
    Electronic schematic symbols follow one of three standards:

    IEC (British)
    IEEE (American)

    and whilst there are similarities between some, there are also some (glaring?) differences too. Ideally, any schematic is drawn using ONE standard (try not to mix standards!) and the symbols readily available from the 'standards site'.
  4. Minder


    Apr 24, 2015
    Pretty much the same as the use of the Ground/Earth/Chassis/Logic common symbols.
    Very Rare to see the correct one used.:(
  5. FuZZ1L0G1C


    Mar 25, 2014
    I have a book of full schematics and circuit-snippets where there should be a polarized capacitor, instead the (submitter?) of the circuit has failed to indicate this.
    While not wanting to slander or defame the author or publishers, this smacks of laziness in drawing and post-editing.
    The two equal-width and thickness parallel bars would lead an inexperienced hobbyist to believe these are NP caps.
  6. shrtrnd


    Jan 15, 2010
    The way I was taught (40 some years ago), you are correct in your assumption.
    The straight bar is the positive, and the curved bar is the negative.
  7. jorgen


    Jul 28, 2018
    Curious question. I first learned to read schematics via the Oct 1960 edition of Electronics Illustrated.

    In those days, the majority of publications used the curved and straight bar to represent capacitors. It was simply the accepted symbol de jure (if electrolytic, the straight bar got the '+').

    Of course, in those days HTZ wasn't yet an accepted unit of measure either, so we all referred to frequency as CPS (cycles per second).

    If you are curious about 'old school' electronics, here's a link to EI from 10/1960:
    Last edited: Jul 29, 2018
  8. Minder


    Apr 24, 2015
    As in post #2 it was also used for non-polarized caps to indicate the terminal (outer foil) that should be grounded in R.F. decoupling, valve circuits etc.
  9. jorgen


    Jul 28, 2018
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