Measure very low dc voltage using oscilloscope help!

Discussion in 'The Projects Forum' started by Kih, Mar 7, 2012.

  1. Kih

    Thread Starter New Member

    Nov 3, 2011
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    Hi everyone !
    I have a circuit which only has two 1ohm resistors in series. And I use a dc power supply to apply a 1mv voltage on them.
    and then I measure the voltages across the two resistors using the 2 leads of an oscilloscope. The results displayed in the screen is noisy.
    (with the lead connected to the hv side and the black clip connect to the lv side )
    And then I apply 50mv to the circuit. Voltage measured Channel 1 is about 30mv and the voltage from channel 2 is quite low(only around 400uV and is not stable). However when I inverse the connection of the lead of the channel 2 (lead---lv, clip----hv),the voltage apperas on the screen are about 25mv of CH1 and -25mV of CH2.....

    I cannot figure out what happen. I think the way i do the measurement is wrong. and maybe I need to amplify the samll dc voltage ?

    Please give me some advices please ! Thanks !:confused:
     
  2. #12

    Expert

    Nov 30, 2010
    16,248
    6,744
    You have a bad scope probe. They tend to get loose at the connector that plugs into the scope.
     
  3. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
    488
    You can measure 400uV with an oscilloscope?

    What probe (10:1, 1:1 and model) and oscilloscope are you using and what's the input divider set to?
     
  4. Kih

    Thread Starter New Member

    Nov 3, 2011
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    0
    yeah i changed a probe and the results are much better.
    And I think my breadboard is not good
     
  5. Kih

    Thread Starter New Member

    Nov 3, 2011
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    0
    the 400uV is the number calculated by the oscilloscope....and the number jumps between different values....

    now I want to use my dc power supply to apply a small voltage to my measurement circuit and then apply a voltage to activate my op-amp to amplify the small dc voltage across it. The dc power supply has outputs as +6, -6, GND, +25, COM, -25.
    what is the proper way to connect the power supply and the oscilloscope ?
    I did this: (+6)----circuit------(-6), (-6)---GND----Com,
    (+25)---Op-amp---(-25),
    Op-amp output-----probe of oscilloscope
    COM----Clip in the probe
     
  6. Kih

    Thread Starter New Member

    Nov 3, 2011
    10
    0
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