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Original question:

ADS112C04: Please help to check the setting for PT100 3-wire RTD

ADS112C04: Temp Accuracy over 1°C

Jerry Liao
Prodigy 40 points
Part Number: ADS112C04
Other Parts Discussed in Thread: ADS124S08

Tool/software:

Hi Ti Partners,

I found out during the temperature test below question.

1. When my device is placed in an environment of 10~-40°C, there will be an error of more than 1°C when measuring temperature. The lower the ambient temperature, the larger the error (measuring range -40~200°C)

2. When my device is placed in an environment of 20~85°C, it will not exceed 1°C.

I have some question about "RTD calculator" table (My design is 3W RTD, and setting table as below pic. )

1.  What's "accuracy type" condition define about typical & maximum? 

2.  What errors does system accuracy contain? (ex:Rref,IDAC...)

3. If viewed at maximum, the test error seems to be within expectations? If there are any suggestions to improve the error to within 1°C?(It seems to me that the Rref is currently adjusted to 2000 ohm and the TCR should be below 20 ppm.)

  • 0
    TI__Expert 8130 points

    Hi Jerry,

    I will take a closer look at this and get back to you early next week.

    Best Regards,

    Angel

  • 0 in reply to Angel Rodriguez de San Miguel Bermudez
    Prodigy 40 points

    Hi Angel,

    Any update about this topic?

    Jerry.

  • 0 in reply to Jerry Liao
    TI__Guru 52586 points

    Hi Jerry Liao,

    All of the detailed accuracy information is shown in the "Design" tabs, I have copied the one that I see below.

    You can see how all of the accuracy calculations are made using these tabs

    Let me know if this answers your questions

    -Bryan

  • 0 in reply to Bryan Lizon86
    Prodigy 40 points

    Hi Bryan,

    Thanks for your feedback.

    I have below question, please help explain & confirm.

    1. What conditions does accuracy type refer to? (RTD temperature, IC temperature, voltage combination...)

    2. My understanding of system accuracy includes Gain error, RREF accuracy/offset, voltage offset, RTD resistance offset, and IDAC error. Is this correct?

  • +1 in reply to Jerry Liao
    TI__Guru 52586 points

    Hi Jerry Liao,

    Answers to your questions:

    Jerry Liao said:
    What conditions does accuracy type refer to? (RTD temperature, IC temperature, voltage combination...)

    All specifications (except for RREF error) are taken from the ADC datasheet. For example, the typical / max gain error for the ADS124S08 is shown in the image below

    When you select "maximum", you are selecting the maximum or worst-case values to be used in the accuracy calculations. When you select "typical", you are using the typical values that you would see from each device

    Jerry Liao said:
    My understanding of system accuracy includes Gain error, RREF accuracy/offset, voltage offset, RTD resistance offset, and IDAC error. Is this correct?

    The accuracy calculations provided in the spreadsheet include the error factors shown in the image below. These do not include IDAC error since we expect the measurement system to be ratiometric, where the IDAC error is seen equally in the inputs and reference, thereby cancelling out

    -Bryan