porject|Build a voltmeter| accuracy in opamp

Discussion in 'Homework Help' started by Saar Boaz, Apr 18, 2017.

  1. Saar Boaz

    Thread Starter New Member

    Apr 18, 2017
    5
    0
    hellow and thank you for reading.
    i got project assiment to develop a voltmeter that can mesure voltages in the range of 10mv-10v with 5% accuracy.
    i had allready built a design that works in theory, but in the lab things become real.
    i will be glad for your apinion if i should drop the case or not.
    in one stage of the design i need to :
    1. Amplify a really small signal 10 time: (10mv-0.0995v) signal should be amplified to (100mv -0.995v).
    2. i need to lower a signal by 10 : (1v-10v) signal should be lowerd to (100mv -1v).
    in order to do so im using 741 op amp, the problem is the accuracy of the 741 and the accuracy of the resistor.
    i have upload 3 images , each one shows a different signal the should be lowered/amplified .
    another file contain the hole design in multisim.
    fill free to download/ check my design .
    any suggestion would be welcomed.
    thank you very mutch saar.
     
  2. bertus

    Administrator

    Apr 5, 2008
    18,587
    3,598
    Hello,

    The LM741 is a bad opamp for this.
    The offset will give large faults as you have measured in the low input selection.
    Better look for an other opamp with better specifications.

    Bertus
     
  3. Saar Boaz

    Thread Starter New Member

    Apr 18, 2017
    5
    0
    can you specify some models you think will be better?
     
  4. crutschow

    Expert

    Mar 14, 2008
    20,041
    5,638
    Where do you buy electronic parts?
     
  5. Saar Boaz

    Thread Starter New Member

    Apr 18, 2017
    5
    0
    i do not, i recive from the university.
    but if you think i should take somthing preticular i can buy it..
     
  6. bertus

    Administrator

    Apr 5, 2008
    18,587
    3,598
    Hello,

    You could ask fo a LT1055 or LT1056, those have an offset of 0.5 mV max, as the LM741 has an offset of 6 mV max.
    If you can not get this opamp, you can try to compensate the offset with the circuit in the LM741 datasheet:

    LM741_offset_compensation.png

    Bertus
     
  7. Saar Boaz

    Thread Starter New Member

    Apr 18, 2017
    5
    0
    thank you very mutch' i will use thouse OP-AMP
     
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