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Load cell interface

Discussion in '8051/8951' started by Ttushar487, Jan 12, 2016.

  1. Ttushar487

    Ttushar487 New Member

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    I am using load cell which has very low output voltage so i decided to use AD524 but i can not understand how to use it
    and according to pin diagram pin no 6 which is for reference so what to connect to this pin
     
  2. JimB

    JimB Super Moderator Most Helpful Member

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  3. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    If you require unipolar output from the AD524, connect Vref pin to 0V, else connect to +Vref.
    Post your circuit diagram so that we can give a better answer.
    E
     
  4. dave

    Dave New Member

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  5. Ttushar487

    Ttushar487 New Member

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    Thank you sir,
    we get it. But its out put is too high its around 12v for full load and we are interfacing it to pic16f877a so it is possible to connect it direct
     
  6. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    You cannot directly connect a 12V input signal into a PIC, it will damage the PIC,
    You could use a resistive potential divider.
    PLEASE post your circuit.
    E
     
  7. Ttushar487

    Ttushar487 New Member

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    Thank you sir,
    we are testing this circuit on brad board.so we are not able to send circuit . please tell me can we use other ic instead of AD524 for better responce
    thank you
     
  8. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Post the schematic of your circuit.
     
  9. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi 487,
    Do you mean a faster response or better amplifier gain?
    Tell us about your project, what is it expected to do.?
    E
     
  10. Ttushar487

    Ttushar487 New Member

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    Thanks Sir,
    we are making conveyor check weight system.
    and we want to measure weight of box (60 box per min)
    box weight around 520 gm
    we are using load cell Which has 20ms setting time
    and output voltage 2 mv
     
  11. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi,
    The AD524 has a very fast settling time, see image.
    It will not present a problem at a weighing rate of 1/second.
    The L/C settling time is typical at 20mSec.
    Your main problem will be the conveyor mechanics.

    Assuming your L/C is specified as 2mV/V of excitation, when using a 10Vdc excitation, that is 20mV for Full Scale output.
    If you are using a PIC with a 5V supply and its internal 5V reference, you require a gain of 5V/0.02V = 250.
    Use a Vref on the AD524 of 0V [ that is assuming you are using a dual power supply to power the AD524]

    E
     

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  12. Ttushar487

    Ttushar487 New Member

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    Thanks sir,
    but we are using two load cell in this project so how to add signal of both load cell
     
  13. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Hi,
    Its common practice to wire two L/C's in parallel, it helps if you try to get both L/C's subject to an equal loading.
    Look at this attached pdf file.
    E
     

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    Last edited: Jan 12, 2016
  14. Ttushar487

    Ttushar487 New Member

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    Thank you sir
    But sir we are not able to amplify load cell out put
    how to amplify it to get desired out put
     
  15. alec_t

    alec_t Well-Known Member Most Helpful Member

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    See post #2. Read the datasheet.
     
  16. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    That is the function of the AD524.
     
  17. Ttushar487

    Ttushar487 New Member

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    Thank you sir,
    we use ad524 for amplification we set gain of it to 250 by setting RG t
    but i cant understand where to connect pin no (4,5,15,14)of ad524
    (input null,input null,output null,output null)
     
  18. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    hi 487,
    You should produce a simple circuit drawing of the project, showing what you have connected to the AD524.

    It is difficult to help you if we cannot see what you have already done.
    Look at figure #47 . page #19 of the datasheet, it shows the NULL on pins 14/15 and the NULL on pins 4/5.
    It shows two 10K pots on these pins, that are used to NULL out any 'offset' errors in the AD524 and its circuitry.
    OK.?
    E
     
    Last edited: Jan 15, 2016
  19. Ttushar487

    Ttushar487 New Member

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    Thank you sir,
    i send circuit diagram of it from that we get 1.25v with 0 input please send me circuit diagram
     

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  20. alec_t

    alec_t Well-Known Member Most Helpful Member

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    The image is too small. Post a larger, clearer one showing all component values.
     
  21. Ttushar487

    Ttushar487 New Member

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    Thank you Sir
    We send you new image of circuit
    we use AD524 but we cant get desired out put
    for 0 input we get 1.25 output instead of 0v
    Sir please tell me what to do
     

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