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Original question:

ADS124S08: Can I use the ADS124S08 to acquire several PT100 RTD?

ADS124S08: How to configure 4 sensors to be acquired simultaneously at 1ksps

Arjun R K
Prodigy 50 points
Part Number: ADS124S08
Other Parts Discussed in Thread: ADS131E04, ADS124S06, ADS1261, ADS1220

Tool/software:

i have 4 bridge-based sensors to which current is programmed through iDAC and differential output from each sensor has to be acquired simultaneously. Is there any example code for this. Most of the code are only for single sensor acquisition. How can i program to get high sampling rate as well without causing inter channel overlapping.

  • 0
    TI__Mastermind 47630 points

    Hello Arjun,

    The ADS124S08 will not support simultaneous sampling of multiple inputs; there is only a single ADC inside the device along with a multiplexor to allow connection to multiple inputs, and only 1 input at a time can be read.

    You can either use 4 ADS124S08 devices (or the lower channel count ADS124S06), or move to a multi-channel ADC device that has multiple ADC cores inside, such as the ADS131E04. 

    https://www.ti.com/product/ADS131E04

    This device has 4 individual ADC cores, supports simultaneous sampling, includes PGAs, and samples up to 64ksps per channel. However, the ADS131E04 does not include internal iDACs for bridge excitation and would need to be added external.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Prodigy 50 points

    How can I multiplex the channels so that I can acquire multiple sensors at 1ksps. is there any pseudocode or sample code for that.

  • 0 in reply to Arjun R K
    TI__Mastermind 47630 points

    Hello Arjun,

    I want to confirm your expected measurement speed requirements.  Do you want to measure 4 bridge sensors every 1ms?  In this case, using a single ADC with multiplexor, such as the ADS124S08, would require the conversion rate to be 4ksps, which the ADS124S08 cannot support due to settling time of the internal digital filter.

    The maximum practical speed of the ADS124S08 when measuring multiple channels will be about 2ksps, or 500sps per each of the 4 bridge inputs.

    Regards,
    Keith

  • 0 in reply to Keith Nicholas
    Prodigy 50 points

    Will that problem be resolved if the digital filter is disabled?

  • 0 in reply to Arjun R K
    TI__Mastermind 47630 points

    Hello Arjun,

    The ADS124S08 is a delta-sigma ADC and requires the internal digital filter.  There is no option to disable the internal filter.  If you need to read 4 channels in 1ms or less, then you will need to use a higher speed ADC, such as the ADS1261.  

    Or, you can use 4 separate ADCs; 1 for each bridge measurement.  In this case, a lower cost option instead of the ADS124S06/08 is the ADS1220.

    Regards,
    Keith