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What will a digital voltimeter do if.....?

I am trying to figure out which resistors I have are good and which are bad. I am using a digital voltimeter. Some have no continuity, some just show resistance without continuity. What will a digital voltimeter display if I have a good resistor?

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  • ryo_samaryo_sama Member Posts: 18
    Hie.
    The digital voltmeter shuld be displaying the Ohm value of the resistor, the value shuld filcker only on the lowest digit or so.
    It sounds to me like your problem is how you are conecting to the resistor. Im gessing that you are holding it against the probes with your hands, or somthings to that effekt.
    The best way is to use some sort of gripper at the end of the probes. If you don't have enything like that try putting the resistor on your desk and holding the ends of the resistor down, hard, with the probes. The point is to have a continues connection.
    Hope this helps... :-)

    : I am trying to figure out which resistors I have are good and which are bad. I am using a digital voltimeter. Some have no continuity, some just show resistance without continuity. What will a digital voltimeter display if I have a good resistor?
    :

  • ibyiby Member Posts: 323
    : I am trying to figure out which resistors I have are good and which are bad. I am using a digital voltimeter. Some have no continuity, some just show resistance without continuity. What will a digital voltimeter display if I have a good resistor?
    :

    Do yourself a favour and buy a working multimeter.
    Last time I was in electronic store they were selling
    for $10 and up.

    If you want to check resistors using voltmeter
    (eh!?... whatever...), then you must put them into
    a circuit. You will need one known resistor,
    one battery (1.5V cell will do) and calculator.
    Since digital voltmeters have quite high input
    impedance (10-20 MOhm), we can simplify the
    formula by dropping correction factor out.
    Put both resistor in series and connect to battery.
    If you put meter across unknown resistor and measure
    voltage V, and battery voltage is Vb, and KNOWN
    resistor is R, you can calculate the value of unknown
    resistor by:

    Rx=V*R/(Vb-V)

    The background of this calculation is simple if you know
    Ohms and Kirhoff's laws:

    I=Vb/(R+Rx) ==> (R+Rx)*I=Vb

    V=I*Rx ==> I=V/Rx

    Combinig the two you get:

    (R+Rx)*V/Rx=Vb ==> (R+Rx)/Rx=Vb/V

    R/Rx=Vb/V-1 ==> 1/Rx=(Vb-V)/V*R







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