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24 bit delta sigma IC EVM

May
Genius 9880 points
Other Parts Discussed in Thread: ADS1235, ADS1232

Hi,

Customer want to display 1,00,000 counts of load cell value with digital output module of 24 bit delta sigma IC.

Do we have such model the can meet this requirement?

Thank you in advance.

Regards,
Maynard

  • 0
    TI__Guru** 113765 points

    Hi Maynard,

    The ability for high resolution will depend on several factors.  Primarily this will depend on the sensitivity of the load cell (expressed in mV/V), the excitation voltage, the gain applied, and the noise-free resolution of the ADC.  I would recommend that you point the customer to a couple of resources.

    The first resource is a new guide TI recently published as A Basic Guide to Bridge Measurements.  The guide gives general information as well as several possible application circuits.

    The second resource is the Analog Engineer's Calculator.  There is a drop-down menu under the Data Converters selection where you can select Bridge Sensor + ADC.  Here you can enter in the pertinent information and depending on the actual resolution required you can see which devices might be applicable.  If you select a device and if the indicators are all green, then the device is a possibility.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Genius 9880 points

    Hi Bob,

    Thank you for the information, please see response from customer.

    "My load cell will produce 35mV Full scale signal : Based on your experience can you please arrive to nearest solution"

    Regards,
    Maynard

  • 0 in reply to May
    TI__Guru** 113765 points

    Hi Maynard,

    Unfortunately this is not much information to go on.  I need to know the specifics of the load cell such as capacity, sensitivity (mV/V), and excitation voltage that will be used at the very least.  Then there is system information such as how fast does the measurement need to be.  Devices such as the ADS1232 or ADS1235 may work, but 100,000 counts is not trivial and there are many factors that need to be considered to achieve that level of scale resolution.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Genius 9880 points

    Hi Bob,

    Just received response from customer, please see details below.

    We have already informed that our loadcell produce 35mV Full scale output to what capacity it is designed and all parameters checked on 5 1/2 digital meter and found at par to our design : so we need 24 bit delta sigma IC that we can display 1,00,000 weigh
    In case if u need further information please inform us

    Regards,
    Maynard

  • 0 in reply to May
    TI__Guru** 113765 points

    Hi Maynard,

    To be able to achieve a high degree of resolution you need to consider more than just the voltage measurement of the load cell output.  To get the most stable response you need to also consider the reference voltage and to make the overall measurement ratiometric.  Normally a load cell is not given an output voltage expressed simply in mV.  The load cell is basically a Wheatstone bridge where the output of the bridge is expressed in mV/V (or mV per V) of excitation for the rated weight output to reach full-scale.  To get the 35mV output from the load cell, there is some excitation voltage.  The output of the load cell is a differential voltage, but for the ADC the voltage output must also be within the input range of the ADC.  So the differential output voltage may be 35mV, but the common-mode output of the bridge is 1/2 of the excitation voltage.  For example, if the load cell is excited by 10V, the common-mode output of the bridge is 5V (10V/2) which would be outside of the input range for the ADC if the ADC is powered by 5V or less.

    It would appear that the customer does not have a full understanding of the measurement and how to achieve best performance.  Please refer the customer to the original links I provided in my first response.  You can also suggest that either the ADS1232 or ADS1235 may work given the limited information they have provided.  Also, 1,00,000 is not a valid number.

    Best regards,

    Bob B