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HDC2022: Is the drift caused by organic gases permanent?

Nan Zhang
Intellectual 1890 points
Part Number: HDC2022

Hi team，

     During the assembly process, hdc2022 is inevitably exposed to some organic gases (such as benzene), causing the drift. The customer found that when using the 80°C internal heater for 4 hours, the humidity reading of the HDC2022 remained at 20%.

    Here are the questions:

Q1. is the '20%' caused by organic gases permanent drift?

Q2. is the 20% drift stable during whole test?   For example, the actual humidity is 20%, HDC2022 humidity will read 40%.  The hdc2022 humidity measurement value is always the actual humidity plus 20% during the test.

Q3.Can we calibrate 20% with the internal registers?  If yes, would the calibration decrease the range of humidity test? For example, we can set -20% to calibrate the 20% to make output as 0%,but the range would be from 0%-80%. Would this happen?

YOURS

NAN

  • 0
    TI__Expert 4855 points

    Hi Nan,

    1) If the 20% RH offset could not be removed by running the heater for an extended period of time, then yes it is likely permanent. Is it possible at all for Benzene and other volatile organic compounts (VOCs) to either be removed from the assembly process, or to at least minimize the HDC2022's exposure time & the Benzene/VOC concentration? The best way for the customer to proceed is to limit or remove the HDC2022's exposure to contaminants as much as possible.

    2) Have you or the customer checked more that 1 RH condition? Different contaminants can cause different changes in the HDC RH error profile so I cant say for certain whether this is a flat RH offset across RH, or a changing offset with changing ambient RH (RH gain). If the customer could, try measuring at 20% and 60% ambient conditions, those points can provide guidance on whether its a flat RH offset or an RH gain change.

    3) RH offset can be corrected with the internal registers, and yes I believe doing so will constrain the range to 0% to 80%. The Humidity Offset Adjustment register with address 0x09 can apply a flat offset to the RH readings. However, there is no way in the internal registers to correct for RH gain. The only way to correct for RH gain would be to test a sample of the drifted devices at several different RH setpoints with a reference (ideally all these drifted parts perform roughly the same). Then make a table of differet offsets for the customer to apply programmatically. This only works of course if the RH gain & offset are predictable, and the customer has a reasonable understanding of the RH environment the HDC2022s are being used in.

    So in summary, please find out from the customer if they have a flat RH offset or RH gain, and see how they can limit the chemical exposures in the assembly process. They should not be using board cleaners on or near the HDC2022, and the HDC2022 should be installed as the very last step in the assembly process.

    Best regards

    -Alex Thompson