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AD7794/AD7795

Hi all ;

I would like to design a loadcell reader and pressure reader; in   our old control card we used to use AD7705 ; but now I think AD7794/95 is better ; it is six channels ;

I confused about which one is the 24bits resolution 94 or 95?

other question ; I will use 4 channels to read loadcells and 2 channels just connect a displacments sensor ( POT variavle resistance) ; would be that a problem ? Any suggestions for other IC or anything ?

Regards

Assaad 

  • Hello Assaad,

    the AD7794 is a 24-bit part and the AD7795 is a 16-bit part. This is the only difference between the parts. Both parts have the same pinout and functionality.

    Four loadcells and 2 displacement sensors can be connected to the AD7794. For the loadcells, the loadcells need to be connected in parallel. I would recommend a ratiometric configuration. So, the excitation voltage to the loadcell is used as the reference to the ADC. This minimises errors in the system.

    Are the displacement sensors excited from a current source or a voltage source. Since you are using all 6 channels of the AD7794 as analog inputs, you will not have access to the on-chip excitation currents. If you wish to use the excitation currents, then you would need to use a second AD7794 or even an AD7793 (a 3-channel version of the AD7794) so that the excitation currents can be accessed.

    Regards,

    Mary.

  • Hello Marry ;

    Thank you for your helpful reply; I will go on  with AD7794.

    I will use it like this ;

    laod cell 1 = AN1+ and AN1-  .

    laod cell 2 = AN2+ and AN2-  .

    laod cell 3 = AN3+ and AN3-  .

    laod cell 4 = AN4+ and AN4-  .

    for displacment sensors;

    displacment 1= output(middle pin) to AN5+  and AN5- to GND .

    displacment 2= output(middle pin) to AN6+  and AN6- to GND.

    for displacment sensors i will voltage excited. the load cells and displacment will be excited by +5Vdc and same source to REF+.

    I hope there is no problem with this configurations; could you confirm please ?

    ALso ; Could you help me to get samples from Analog Devices for AD7794 , please?

    Regards

    Sami .

  • Hi Sami,

    the configuration that you plan to use is fine.

    If you go to

    http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7794/products/product.html#ppa_print_table

    you can order AD7794 samples on line.

    Regards,

    Mary.

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