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How can we get full Data range (0 - FFFFFF) in ADS1256

Yashpal Patel49892
Expert 1835 points
Other Parts Discussed in Thread: ADS1256

Hi,

We are using ADS1256 in our project to measure loadcell data.

We are attaching the schematic of loadcell with instrumentation amplifer for input of ADS1256 in differential mode(AIN0 - AIN1).

by using this configuration we have getting the data code from 0 to 7FFFFF, what we have to do for get the data code in full range (0 - FFFFFF).

Regards

Dharmendra

Hi,

 

 

 

  • 0
    TI__Guru** 113765 points

    Dharmendra,

    The ADS1256 is a differential input device, where the measurement is the voltage of AINP relative to AINN.  Your load cell is a bridge device with the output with no load centered at about AVDD/2.  If the load cell output polarity is connected to the  ADS1256 inputs with the same polarity, then the range of the load cell will move in the positive direction.  What you are asking is a way for the output to move in the negative and positive direction.  This becomes a tricky thing to do, as now you would have to shove the no load state of the load cell so that it would read negative full scale.  At least two problems arise doing this.  First of all it becomes very tricky to calibrate and take measurements, especially if you tare the scale.  The second problem is the circuit will have additional noise by creating the offset which will most likely cost you more than the LSB you gain by extending the range.  In might be a better idea to maximize your system performance by minimizing noise sources.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Expert 1835 points

    Hi,

    Thanks.

        We are getting noise free only 15bits. So We want to increase the data Range.

    Have you any idea for get loadcell Output from -10mv to +10mv or is there any way which can convert 0 to +10mv loadcell output to -5V to +5V in our given Circuit.or any method in the Software to get the Full scale reading from 0 to FFFFFF for input 0V to +5V with ref 2.5V.

     

    With regards

    Dharmendra

  • 0 in reply to Yashpal Patel49892
    TI__Guru** 113765 points

    Dharmendra,

    As I said earlier, if noise is your problem, then adding more noise isn't going to help as basically you want to offset and gain up your signal.  It would be a much better choice to reduce your system noise.  This can be done through improved PCB layout, improved filtering at the input stage, and reduction of noise in the reference and excitation sources.  You can also improve noise and drift performance by making the measurements ratiometric, where the reference and excitation voltage sources are common.  Unfortunately the ADS1256 will not allow a 5V reference.  Another option might be to increase the excitation voltage, but you have to make sure that the bridge output remains within the common mode input range of the ADS1256.  This might be difficult to do with your gain stage.  There may be some digital processing that can be done with your processor, but this will reduce the throughput rate.

    So, find your noise sources and reduce them.

    Best regards,

    Bob B