MCP617 op amp problem

Discussion in 'The Projects Forum' started by mah, Jan 27, 2014.

  1. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
    2
    i used MCP617 to amplify 0-8 millivolt signal from sensor the non inverting amplifier is working well with a signal larger that 1.5 mv but for less that that value the output is bigger that expected i tried 0.8 mv but the output using total gain 106V/V was 129 mv , i don't know if my op amp is not sensitive with this value or it need enhancements .
     
    Last edited: Jan 27, 2014
  2. BobTPH

    Active Member

    Jun 5, 2013
    782
    114
    What is the input offset voltage of the opamp? I suspect that is is comparable to the 1.5mV you have as input.

    Bob
     
  3. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
    2
    its input offset voltage is ±150μv , very small .
     
  4. BobTPH

    Active Member

    Jun 5, 2013
    782
    114
    Not very small compared to your signal of 800uV. The offset is definitely going to cause inaccuracy at that level.

    Bob
     
  5. LvW

    Active Member

    Jun 13, 2013
    674
    100
    mah - why not measuring the output dc level for zero input (grounded!)?
     
  6. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
    2
    I have already done this step and the output was zero:)
     
  7. LvW

    Active Member

    Jun 13, 2013
    674
    100
    I do not believe that it wa really "zero" - however, perhaps you couldn`t measure with more accuracy.
    What about resistor tolreances?
    Perhaps you should give us some real values rather than simply stating "bigger than expected"?
     
  8. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
    2
    sorry there was disconnected wire the output is alternating between 9mv and 10.5 mv for zero input , now iam measuring .4 mv input signal with gain 441 the output is 0.51 v . what is the solution now ? i need accurate measurement.
     
    Last edited: Jan 28, 2014
  9. LvW

    Active Member

    Jun 13, 2013
    674
    100
    "...output alternating" ?
    What does this mean? Oscillating? Slowly changing?

    How did you measure 400µV at the input? Opamp connected yes/no?
    What are thr resistor values?
    What is the internal source resistance?

    You should show us the COMPLETE circuit with parts values and power supply. Otherwise no help possible.
     
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