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Regarding AC value in mutimeter

Discussion in 'General Electronics Discussion' started by alpha001, Mar 12, 2011.

  1. alpha001

    alpha001

    2
    0
    Mar 12, 2011
    Recently i was checking a laptop charger when i noticed that it showed around 45 V AC when i checked it using multimeter(by keeping it at 200 V AC range). It worked perfectly and so did all the other chargers i checked - giving the same value. DC voltage is around 19-20 V as expected. So should multimeter not show ZERO AC voltage,:confused:? After all the charger is supposed to provide pure DC.
     
  2. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    I take it you measured from pole to pole at the plug, and not from pole to ground (or yourself).
    The simplest/cheapest multimeters are lacking the ability to discriminate DC from AC, they require a pure sine AC when in AC range if they're to show correct figures.
    They incorporate very simplified measuring circuits and can't be used to measure ripple voltages (unless you put a (0.1uF) capacitor in series with them).
     
  3. alpha001

    alpha001

    2
    0
    Mar 12, 2011
    so u mean if i use a high-end multimeter it will not show this error?Right now i checked this website http://www.ladyada.net/learn/multimeter/voltage.html (check last para), i think they are using pretty good multimeters.I want to know WHY we can't measure accurately.
     
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