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HDC2022: vacuum and offset in sensor readings

Aivaras Sakauskas
Intellectual 1410 points
Part Number: HDC2022
Other Parts Discussed in Thread: TMP116

Hi,

Customer is pulling almost a full vacuum and are putting the board in a vacuum chamber and decreasing the pressure down to below 1 psia. Then after holding the vacuum for seconds or minutes, we pump air or gas back into the chamber. 

Then later, they expose the board to high temp and high humidity conditions. While the chamber is ramping up temperature and humidity, the humidity sensor has a large offset (+ 15%RH). they have plenty of data from other boards with HDC2022 that does not have this +15%RH so we are trying to identify the root cause of the issue and have highlighted this vacuum event as one potential area of investigation.

Now the datasheet mentions that exposing the device beyond the recommended 20%-80% RH can cause shift in sensor readings. Can you please provide some feedback if you have seen something similar before? Are the devices damaged? are such tests recommended? How long is the expected recovery time? etc...

Thank you for your support!

Aivy

  • 0
    TI__Expert 3270 points

    Hi Aivy,

    Thank you for posting to the Sensing forum. 

    Is there a temperature reference in the chamber? If so, is the device temperature the same as the reference? 

    Regards,
    Pavani Tenneti

  • 0 in reply to Pavani Deepthi Tenneti
    TI__Intellectual 1410 points

    Hi Pavani,

    I have asked the questions. In the meantime there is an update below.

    Update,  further testing has narrowed the issue down a bit. We no longer think that is directly related to the vacuum testing.

    We are exposing the humidity sensor to -30° and -40°C and then returning the sensor to room temperature. In later testing, the humidity sensor clearly as an offset as we increase in temperature. The data sheet discusses this a bit.

    Is there a firmer specification on what exactly is meant by “prolonged operation”? Does prolonged operation mean 10 minutes? 1 hour? 1 day?

    With sensors that have this offset, what is the recommended method for removing this offset? This a critical issue.

    Please let me know additional details about removing the offset as soon as possible.

    Thanks 

    Aivy

  • 0 in reply to Aivaras Sakauskas
    TI__Expert 3270 points

    Hi Aivy,

    What is the humidity in the chamber/room when the device temperature changes from -30 to 25? It might be close to the dew point temperature and it could potentially condense on the device. 

    If it is condensing, I would recommend baking and rehydrating the device. After baking and rehydrating, re-measure the temperature and humidity to see if the error has improved. 

    Regards,
    Pavani Tenneti

  • 0 in reply to Pavani Deepthi Tenneti
    TI__Intellectual 1410 points

    Hi Pavani,

    There is TMP116 located very close to the HDC2022 on the PCB. We believe that the cold temperature exposure test is causing the issue, but the issue is appearing during high temperature, high humidity testing. 

    The delta between the two temperature readings during the high temp, high humidity test is less than 2°C (1st plot below). The second plot shows the humidity sensor railing out at 100%RH, despite the expected max %RH level of ~90%RH.

     

    First plot: X-axis is Hours, Y-axis is Delta Temperature (°C)

     

    Second plot: X-axis is hours, Y-axis is %RH

    Thanks

    Aivy

  • 0 in reply to Aivaras Sakauskas
    TI__Expert 3270 points

    Hi Aivy,

    Can you confirm if the devices were exposed to any of the chemicals on page 5 of this document?

    Also, have you tried baking and rehydrating the devices?

    Regards,
    Pavani Tenneti