Instrumentation Amplifier with LM324

Discussion in 'Homework Help' started by Mangrio, May 21, 2010.

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  1. Mangrio

    Mangrio Thread Starter New Member

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    Will anyone help me about the Instrumentation Amplifier with LM324 IC.... I have made a circuit with this IC but it is not resulting as it to be :(

    also needed help in resistor combination in above circuit.

    I have made this design

    [​IMG]
    Last edited: May 21, 2010
  2. t_n_k

    t_n_k AAC Fanatic!

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    The LM324 probably isn't that fantastic a choice to serve as an instrumentation amplifier. It's not surprising the circuit doesn't perform as you hoped.

    Posting your circuit schematic would enable a better understanding of your setup & thereby assist forum members in making suggestions for improving your circuit.

    OK - see the circuit now!
    Last edited: May 21, 2010
  3. Mangrio

    Mangrio Thread Starter New Member

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    i have posted the diagram, please consider it.
  4. t06afre

    t06afre AAC Fanatic!

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    Have you tried www.wikipedia.org they have some usefull info on this topic. Could tell us why it is not working and post the exact schematic for your application. Also what is the range of your input voltage
  5. bertus

    bertus Administrator Staff Member

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  6. Audioguru

    Audioguru New Member

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    Maybe your circuit doesn't work because it has no power supply.
    Please show if its power supply has dual polarity and the voltage.

    The LM324 works poorly above only 2kHz. It is very noisy. It has crossover distortion.
  7. Mangrio

    Mangrio Thread Starter New Member

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    I have applied power in orignal circuit...
  8. Mangrio

    Mangrio Thread Starter New Member

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    then will you please tell me that what IC i use for IA,

    I have to just design a simple instrumentation amplifier (IA) for class work with any range. it just only give right the output.

    will you suggest me something else plz.
  9. t_n_k

    t_n_k AAC Fanatic!

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    Try searching for "AN31 op amp collection".

    Section 3 has some examples of 'practical' differential input instrumentation amp circuits. You'll note for instance that 0.1% tolerance resistors are routinely used for the critical components.
  10. Audioguru

    Audioguru New Member

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    Datasheets for instrumentation amplifier ICs explain why their excellent matching of opamps and resistors produces results that are much better than you can make with separate parts.

    There are many high gain intstumentation amplifiers on the web made by students that are made with separate parts and they do not work!.
    Maybe if yours has a low gain then it will work about as well as a piece of wire.

    You still do not show a power supply for your opamps and whether it has a single polarity or a dual polarity.
    You also do not show the input AC and DC voltages.
    You also do not explain what is wrong with the output of your circuit.
  11. t06afre

    t06afre AAC Fanatic!

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    If you look at tis document on http://www.national.com/ds/LM/LM124.pdf at page 16 you will see a schematic just like yours. You can build an Instrumentation Amplifier with your Lm324. It will not be the best one. But good enough if you want to study the principals. If you have problem with your circuit I guess something not done correct.
    By NOT giving all the details we have asked for you are only wasting your own time. If you had given us the details we have asked for. Your problem would have been solved now. But this is your call.
  12. Audioguru

    Audioguru New Member

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    The instrumentation amplifier in the datasheet for the LM324 uses the much better and more expensive LM124A instead of the ordinary LM324N. The resistors must be well matched.
  13. Mangrio

    Mangrio Thread Starter New Member

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    well at last I have tried to get complete help from Wikipedia and electronics workbench...



    schematic diagram on wiki
    [​IMG]

    Wikipediasuggested ICs for this amplifier are these...

    "Examples include AD620, MAX4194 and INA128."

    I have use [AD620]

    pin configuration of AD620
    [​IMG]

    and its data sheet
    http://www.analog.com/static/imported-files/data_sheets/AD620.pdf

    ......................

    now my schematic diagram on workbench according to data sheet and Wikipedia..

    [​IMG]


    Function Generator & Oscilloscope setting before starts
    [​IMG]


    RESULT:-

    just straight line on oscilloscope.... :(

    [​IMG]
  14. bertus

    bertus Administrator Staff Member

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    Hello,

    The AD620 IS an complete instrumentation amplifier.
    Take a look at page 14 of 20 of the datasheet you present.
    There is a comparison between the AD620 and a homebrew instrumantation amplifier.

    Bertus
  15. Mangrio

    Mangrio Thread Starter New Member

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    dear LM 124 and Lm 324 has same datasheet... so they can be called substitute of each other ... thats why I have used LM324 at the place of lm124.
  16. Audioguru

    Audioguru New Member

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    The LM124 is selected for better spec's. The LM124A is selected for the very best spec's. But it is not a good quad opamp because it is very old and it is made for low supply current.
    An LM324 has very poor spec's.

    Where can you buy resistors that are matched to 0.02% like the ones inside an AD620A instrumentation amplifier?
    Where can you buy an LM324 that has its opamps matched as well as the opamps in an AD620A?

    Why did you make a differential amplifier with three AD620 instrumentation amplifiers but did not use a resistor to set the gain of each one? Why didn't you use a single AD620A instrumentation amplifier instead?
  17. Mangrio

    Mangrio Thread Starter New Member

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    unfortunately i couldn't find the AD620 here in my city's shops.
  18. Mangrio

    Mangrio Thread Starter New Member

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    I have to just make it for my class work , whatever i.e; poor result or something it has....

    please help me to design this with lm324.
  19. bertus

    bertus Administrator Staff Member

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    Hello,

    As I told you, did you have a look at page 14 of 20 of the AD620 datasheet?

    [​IMG]

    Bertus

    Attached Files:

  20. JoeJester

    JoeJester AAC Fanatic!

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    Mangrio,

    Post a screen shot of your original non-working simulation. The original schematic has no errors and while it is not up to contemporary standards, it does work.
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