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ADS1262 - 4 wire bridge measurement

Alan Fleming
Prodigy 40 points
Other Parts Discussed in Thread: ADS1262, REG104

Hi,

I have recently acquired your ADS1262EVM and would like advice on the best way to connect multiple electronic scale sensors to the EVM. I have seen reference to ratiometric connection in the reference manual but was unable to get a response based on section 2.6.2 in SBAU206.I was however able to measure output using the bridge with 5V excitation however this seems to be a noisy option.

Thank you.

  • 0
    TI__Mastermind 44600 points
    Hi Alan,

    Welcome to the TI E2E Forums!

    If you're using the ADS1262EVM in a single supply configuration, I would recommend exciting the load cell(s) with the 5V analog supply (+Excitation = AVDD; -Excitation = GND). Then the load cell outputs could connect into any two differential input pairs.

    To make the measurements ratiometric, you would either wire AVDD & GND back into a reference input (such as AIN0 & AIN1)
    OR
    without any additional wiring, configure the ADS1262's reference MUX to select the analog supply as the reference source.

    You should be able to connect up to 4 or 5 load cells this way (5 if you don't dedicate an input pair as a reference input). I believe the REG104, which generates the AVDD supply on the MMB0, will be able to supply sufficient current to excite five 350-Ohm load cells.

    Best Regards,
    Chris
  • 0 in reply to Christopher Hall
    Prodigy 40 points
    Hi Chris,
    Thank you for the welcome and useful advice. I have a few more questions:
    1. How would you suggest connecting 6 - 8 load cells - External mux maybe or use two EVMs?
    2. Is the chop function useful for reducing noise in this configuration?
    3. Will a suitably sized capacitor between the load cell outputs help reduce noise?
    4. Are there situations when you would recommend to not use ratiometric measurement?
    Kind regards,
    Alan
  • 0 in reply to Alan Fleming
    TI__Mastermind 44600 points

    Hi Alan,

    1. Yes, you'll either need an external MUX or an additional ADC to increase the channel count. Note that the effective data will decrease as you increase the number of MUX channels.
    2. Chopping averages 2 samples; therefore, noise is reduced by a factor of sqrt(2). Additionally, chopping reduces ADC offset and offset drift.

    3. Not by much, and it can significantly slow down your effective throughput due to increased settling time. The ADC's digital filter will provide the bulk of noise filtering. See the ADS1262 Excel calculator for a calculation of the digital filter's effective noise bandwidth: http://www.ti.com/lit/zip/sbac137
    4. Not that I know of...ratiometric connections remove the excitation voltage error; noise performance is also improved because the input and reference noise tend to cancel.

    Best Regards,
    Chris