Resistor values

Discussion in 'General Electronics Chat' started by Webby, Aug 25, 2008.

  1. Webby

    Thread Starter Active Member

    Jun 15, 2008
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    0
    Hi, with a simple series circuit with lets say 3 resistors in order to work out the individual resitor values do i have to isolate them from the circuit so iam actually testing an individual component?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    If you are seeking the value of an unknown resistance, Ohm's Law provides a way to calculate the resistance if you can obtain the voltage and the current associated with that resistance.

    To get the voltage dropped across the resistor you can use a voltmeter. To get the current associated with the resistor you will need to disconnect one end of the resistor and insert an ammeter. With these two measurements you should be able to apply Ohm's Law to calculate the resistance.

    hgmjr

    PS. Of course, if you have to lift the resistor to insert an ammeter, you can use an ohmeter to make the measurement directly.
     
  3. Webby

    Thread Starter Active Member

    Jun 15, 2008
    66
    0
    Thanks Super Moderator, what if the circuit has been disconnected from its power supply would i still have to undo the resistors from the circuit board to measure there values?
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    In this case, since there is no voltage applied to the unknown resistor, you would need to disconnect the resistor and use an ohmeter.

    hgmjr
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Yes, because other components may be in parallel with the resistor and cause a faulse measurment.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    If the case of three resistors in a simple series circuit is true, the only condition necessary to let you measure each resistor with an ohmmeter is to open the path to a voltage source. With the current path open, there is no problem reading each resistor while still in circuit.

    This is very easy to demonstrate with three resistors and an ohmmeter.
     
  7. Webby

    Thread Starter Active Member

    Jun 15, 2008
    66
    0
    Hi, thanks for the feed back appreciate your support how could i measure the resistors while still in circuit? beenthere can you explain please?
     
  8. rezer

    Member

    Aug 26, 2008
    10
    1
    beenthere is correct. You do not have to disconnect the resistors if it is a simple series circuit. Just disconnect one side of the source. Simply connect your meter leads across the component in question. Make sure it is set to read resistance. They will usually have an omega symbol (Ω).
    Are you just curious about how to do this or do you have a resistor that you can't read?
     
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