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ADS124S08EVM: ADS124S08EVM

vadim piskun
Expert 2250 points

Part Number: ADS124S08EVM
Other Parts Discussed in Thread: ADS124S08, ADS1261, ADS1261EVM

Hi 

ADS124S08EVM  is connected to GUI, but I do not get any data in data analysis window. If i click refresh/sync I have "Write failed " message bottom left 

thanks vadim

 

  • 0
    TI__Guru** 113765 points

    Hi Vadim,

    If you try to collect data at the default settings you need to wait for the collection to complete or you will crash the GUI and will need to restart the GUI and repower the EVM.  The default setting is 20sps and the analysis client defaults to 2048 samples.  So the time required for collection is 102 seconds.  Before collecting data try either a faster data rate or change the analysis client to use a much smaller sample size.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Expert 2250 points

    Thanks Bob!

    I changed the data collected to 20 and connected PT100 https://www.adafruit.com/product/3290

    per user guide. I hold the sensor in my hand and collect the data. But the data is not changing.

    thanks vadim

  • 0 in reply to vadim piskun
    TI__Guru** 113765 points

    Hi Vadim,

    What I see here is negative full-scale.  Most likely this is due to either a misconfiguration of the ADS124S08 or a miswiring of the sensor.  There are built-in scripts for various sensor types including RTD and explanations on how to configure the 3-wire RTD in the EVM user's guide.

    The RTD measurement is ratiometric with a high-side reference.  A complete current path is required for the the reference to be valid.  The reference resistor is 1k and with the current set to 1mA, the reference voltage should be 1V and not 2.5V on the data analysis window.  When making ratiometric measurements it is best to use the codes instead of volts display as the output code is proportional to the reference resistor.

    It is also required that the internal reference be enabled even though it is not used for the conversion.  The IDAC current sources require the internal reference to establish the desired current.

    You may also find A Basic Guide to RTD Measurements useful as it more clearly describes the various measurement methods.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Expert 2250 points

    Hi Bob,

    I am using this script. I set ref voltage to 1 it did change the scale, still negative and the voltage still does not change with time when I warm the sensor with my hand. I used this sensor with a similar board from ADI and the sensor works properly, has 109 Om at room temperature. Pin 1 J7 measure 1.2V Pin 3,4 measure 1.12V. The status of LED D1 green, D2 blinks green while collecting data, D3 is red. What does D3 red indicate? All jumpers set according to fig 2 of user guide. What else can i check?

    thanks vadim

  • 0 in reply to vadim piskun
    TI__Guru** 113765 points

    Hi Vadim,

    It appears that the EVM is working.  The D3 LED just let's you know that the START pin is pulled high for continuous conversions.  Based on your description you may have the RTD connected incorrectly.  The actual measurement channel is AIN1/AIN2.  So the RED wires should connect to J7-2 (A2) and J7-4 (A0).  The WHITE wire should connect to J7-1 (A1).  J7-4 should be about 2V (with respect to AGND) if wired correctly.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Expert 2250 points

    Thanks Bob!

    It was indeed miswiring and now it works fine. I have another board to try ADS1261EVM. For ADS124 i had to download some plug in software, but it looks for this board i could not find a similar plug in, so when i connect ADS1261 i have empty registers.

    Thanks vadim

  • 0 in reply to vadim piskun
    TI__Guru** 113765 points

    Hi Vadim,

    Go to this page: https://www.ti.com/tool/ADS1261EVM

    And select the circled device package for download:

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Expert 2250 points

    Thanks Bob,

    Both boards are working now. I need to build an external board to accommodate for Rref and Rbias and two diodes. Chapter 10.2 of  ADS126x provides detailed procedure for RTD 400 Ohm sensor design. I am wondering if i can use Rbias=Rref=1000Ohm, I =1000uA , PGA= 4 and other parameters as in ADS124 for pt100, will the result be correct for PT100 with ADS1261 as well? 

    vadim

  • +1 in reply to vadim piskun
    TI__Guru** 113765 points

    Hi Vadim,

    There are various ways to connect an RTD to the ADC.  I would suggest that you review A Basic Guide to RTD Measurements to see the various possible circuits.  The ADS124S08EVM uses a high-side reference in its application circuitry.  If you connect up the ADS1261EVM in the same way you should be able to see similar results using the same configuration settings.

    As this thread topic is changing, please start a new thread for any ADS1261 related questions.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Expert 2250 points

    Thanks Bob!

    vadim