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HOW TO SHORT THE OP-AMP'S INPUTS TOGETHER ?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Minh Thanh, Sep 7, 2017.

  1. Minh Thanh

    Minh Thanh New Member

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    This is first time that I heard " Short Inputs " .It 's terrible to me . I dont know how to short it . Could you help me about this, ?. Please you illustrate by picture so that I can understand it clearly . I attached a photo below . Thank you !
     

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  2. AnalogKid

    AnalogKid Well-Known Member

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    Depends on the context. Why are you being instructed to short the inputs together? Shorting the inputs together will not damage anything, but it usually is not a good idea. If this is for some kind of performance/noise test, what is the test?

    Also, are you sure they don't mean to short the input to ground?

    ak
     
  3. Minh Thanh

    Minh Thanh New Member

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    Just to calibrate the circuit, first short the inputs together and adjust the offset potentiometer to obtain 0-mV output from the LM351.
     

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  4. dave

    Dave New Member

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  5. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    PS: It's stupid design. Shorting the input may not even work in this case.

    PH probe basics: https://www.omega.com/Green/pdf/pHbasics_REF.pdf
    and http://www.ti.com/lit/an/snoa529a/snoa529a.pdf

    I'd actually use any resistor > 10 meg ohms for the PH input. Shorting can conceivable make the OP amp go full scale.

    LM351 Datasheet: http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00000453.pdf

    PH is just one of those applications that a typical OP-amp won;t work well. It's also where guarding should be used at the inputs. Ib (Input bias current) is temperature sensitive. It's also a board where the board should be cleaned thoroughly and not touched afterwards.

    The reference electrode is your best calibration. You should have a second reference too,
     

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