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HDC3020: When humidity is measured in a constant temperature and humidity chamber, the error becomes larger.

Manabu Hashimoto
Prodigy 60 points
Part Number: HDC3020
Other Parts Discussed in Thread: HDC3022

When humidity is measured in a constant temperature and humidity chamber, the error becomes larger.

When the HDC3020 is placed in a constant temperature and humidity chamber to measure humidity, the lower the humidity, the larger the error.
*There was almost no error for temperature.

Measurement Procedure:
1) Put HDC3020 and Assmann Psychrometer into the constant temperature and humidity chamber.
2) Change the humidity in the order of 25°C/30->10->30->50->70->90->70->50->30%RH.

Measurement results:

Chamber 30 10 30 50 70 90 70 50 30
Assmann 28.9 6.5 28.5 50.7 71.8 92.8 71.1 49.7 28.3
HDC3020 32.1 9.9 31.4 53.3 73.1 93.0 73.2 53.3 31.6
Error 3.2 3.4 2.9 2.6 1.3 0.2 2.1 3.6 3.3


A few days later, when we checked the readings of the HDC3020 and the Assmann Psychrometer in the room, the error was 0.1% at 25°C/60%RH humidity.
Is there anything I should pay attention to when measuring humidity in a constant temperature and humidity chamber?
*We waited 20 minutes after the humidity in the thermostatic chamber reached the set value before recording the measured value.
*The HDC3020 was not housed in a case and the sensor board was left bare for the measurement.

  • 0
    TI__Genius 9720 points

    Hello,

    With the information that you provided, your testing approach is correct. In regards to determining the reason for error, I have some questions.

    1. Can you describe your assembly process? What is your soldering process? Are there any potential chemical contaminants? How are you cleaning your board?
    2. How are you storing the devices?
    3. What is the distance between the HDC3020 and your reference point you are measuring?
    4. What is the RH accuracy of that reference?
    5. Waiting 20 minutes after the humidity in the thermostatic chamber is an appropriate time length, but how are you confirming stability?
    6. Have you tested multiple HDC3020 devices?

    Answer as much as you can. The more details you provide, the better I can assist you. Refer to the HDC3020 User Guide for guidance for storage and handling guidelines.

    https://www.ti.com/lit/ug/snau265c/snau265c.pdf?ts=1690491590819&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FHDC3020

    Best Regards,

    Meredith McKean

  • 0 in reply to Meredith McKean
    Prodigy 60 points

    Thank you for your reply.

    >1. Can you describe your assembly process?
    We have already told the component mounters to be careful about potential chemical contaminants, but when we asked them again, we received the following response.

    >What is your soldering process? Are there any potential chemical contaminants?
    Not compliant with JEDEC J‑STD‑020. Although it uses its own process, there is no concern about contamination.

    >How are you cleaning your board?
    Not cleaned.

    >2. How are you storing the devices?
    It is stored in a Static Shielding Bag 1000.
    documents.staticcontrol.com/.../Static_Shielding_Bag_1000_Series.pdf

    >3. What is the distance between the HDC3020 and your reference point you are measuring?
    It is about 10 cm horizontally from the air supply port of the Assmann Psychrometer. the height is the same.

    >4. What is the RH accuracy of that reference?
    The dry bulb and wet bulb thermometer accuracy of the Assmann Psychrometer is 0.2°C. This value is substituted into the humidity conversion formula.
    Also, when the Assmann psychrometer was compared with other companies' hygrometers, the error was within 1.0% RH.
    www.rotronic.com/.../hygropalm-hp21-handheld

    >5. how are you confirming stability?
    Data was acquired from the device at 1-second intervals and visually confirmed as a line chart in real time.

    >6. Have you tested multiple HDC3020 devices?
    I tested 7 HDC3020s and 1 HDC3022 simultaneously and all had similar results.

  • 0 in reply to Manabu Hashimoto
    TI__Genius 11985 points

    Hi Manabu,

    Thank you for answering these questions. One more thing to try that could fix the issue is running the heater on the parts. If you run the on-chip heater on each device for a couple minutes (until the temperature rise saturates), that may bake out excess moisture and potential contaminants, and possibly correct the RH errors you are seeing. So please try running the heater, and then recharacterizing the devices with the up-down sweep as you did before.

    While you run the heater, I will follow up with my test and validation team to see what we can do to help find the root cause.

    Thank you

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 60 points

    thank you for your reply.

    I understand about the heater.
    Please understand that my reply will be delayed due to the software modification, the test in the constant temperature and humidity chamber, and the summer vacation.

  • 0 in reply to Manabu Hashimoto
    TI__Genius 11985 points

    Thank you for the update, take the time you need. Please do let me know if using the heater is helpful once your tests are concluded.

  • 0 in reply to Manabu Hashimoto
    TI__Genius 11985 points

    Hi Manabu,

    While you are working on trying to use the on-chip heater, I have three additional requests. Can you please look at the sensor area of the HDC3020s and see if there are any scratches, smudges, or debris inside the cavity? Scratches or signs of contamination could be the root cause of the sensor behavior. Can you also confirm that these devices are soldered, and not tested loose in a socket? Lastly, can you please also read the NIST ID bytes 0 through 5 and report them back to me? With the NIST ID byte values we can see if these particular devices had any problems in production. The commands to read the NIST ID bytes are listed at the bottom of table 8-3 in the HDC302x datasheet.

    Thank you

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 60 points

    thank you for your reply.

    1) on-chip heater
    The power pin of the sensor is connected to the I/O pin of the MCU, and the current can only flow up to about 20mA, so I couldn't get it to work well.
    - Quarter Power : 36.5°C maximum
    - Half Power : 40.4°C maximum
    - Full Power : 38.7°C maximum
    So I didn't test it in a constant temperature and humidity chamber.

    2) look at the sensor area
    It looks like there are no scratches.

    3) devices are soldered
    The device is soldered.
    No sockets are used.

    4) NIST ID (Bytes 5 4 3 2 1 0)
    HDC3020 (7 devices)
    - 76 B8 81 7C 01 16
    - 76 B9 81 7C 01 16
    - 76 BA 81 7C 01 16
    - 76 BB 81 7C 01 16
    - 76 BD 81 7C 01 16
    - 76 BE 81 7C 01 16
    - 76 BF 81 7C 01 16
    - 76 C8 81 7C 01 16
    HDC3022 (1 device)
    - 26 6E C7 65 05 17

    What do you know with all this information?

  • 0 in reply to Manabu Hashimoto
    TI__Genius 11985 points

    Manabu,

    With the NIST ID bytes we can track the production information for this material to see if there were any problems or clues as to why your devices are behaving this way. Thank you for trying to run the heater on these devices, did that provide any improvements to your RH readings? Also, are these devices a representative sample of all the HDC302x parts you have? Do they all show this positive RH offset and negative RH gain? Or are these outliers from a larger set of devices that perform correctly?

    I will give this NIST information to our test engineers to see if they can find an explanation for this behavior. 

    Thank you

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 60 points

    thank you for your reply.

    1) did that provide any improvements to your RH readings?
    Even with the heater, the temperature did not rise to 125°C, I have not tried it assuming it is not effective in decontamination.
    Is it possible to remove contamination even if the temperature rises only to 40°C?
    I have to rent a chamber to test it, so I can't test it very often.

    Also, I modified the circuit board by cutting a pattern so that the current could flow up to 100mA, but the maximum temperature was only 75°C.
    - Quarter Power : 40°C maximum
    - Half Power : 56°C maximum
    - Full Power : 75°C maximum

    2) are these devices a representative sample of all the HDC302x parts you have?
    7 HDC3020's and 1 HDC3022's are all the devices I own and all of them show abnormal values.

    3) Do they all show this positive RH offset and negative RH gain?
    yes. all the same.

    Chamber 30 10 30 50 70 90 70 50 30
    Assmann 28.9 6.5 28.5 50.7 71.8 92.8 71.1 49.7 28.3
    HDC3022_0 32.1 9.9 31.4 53.3 73.1 93.0 73.2 53.3 31.6
    HDC3020_1 31.9 9.6 31.0 53.1 72.7 92.4 72.9 53.1 31.5
    HDC3020_2 31.9 9.5 31.0 53.2 72.8 92.7 73.1 53.2 31.5
    HDC3020_3 32.2 9.8 31.2 53.4 72.9 92.6 73.1 53.3 31.7
    HDC3020_4 32.2 9.9 31.4 53.4 73.0 92.7 73.2 53.4 31.8
    HDC3020_5 32.0 9.6 31.1 53.3 73.0 92.7 73.2 53.2 31.6
    HDC3020_6 31.9 9.6 31.0 53.2 72.8 92.5 73.0 53.2 31.6
    HDC3020_7 32.1 9.6 31.2 53.1 72.8 92.6 73.1 53.2 31.7
    Error_0 3.2 3.4 2.9 2.6 1.3 0.2 2.1 3.6 3.3
    Error_1 3.0 3.1 2.5 2.4 0.9 -0.4 1.8 3.4 3.2
    Error_2 3.0 3.0 2.5 2.5 1.0 -0.1 2.0 3.5 3.2
    Error_3 3.3 3.3 2.7 2.7 1.1 -0.2 2.0 3.6 3.4
    Error_4 3.3 3.4 2.9 2.7 1.2 -0.1 2.1 3.7 3.5
    Error_5 3.1 3.1 2.6 2.6 1.2 -0.1 2.1 3.5 3.3
    Error_6 3.0 3.1 2.5 2.5 1.0 -0.3 1.9 3.5 3.3
    Error_7 3.2 3.1 2.7 2.4 1.0 -0.2 2.0 3.5 3.4
  • 0 in reply to Manabu Hashimoto
    TI__Genius 11985 points

    Manabu, 

    Thank you for this detailed information. Our test engineers weren't able to find any test production issues with these parts or signs of why these parts are out of spec for you, so I think the best way forward is for you to submit these devices to TI as a customer return. That way I can get my hands on them and test them in my RH chamber.

    You will have to submit the return through this website: https://www.ti.com/support-quality/additional-information/customer-returns.html

    Please include as much information about the failure mechanisms and the system as possible. Here is what we will need:

    • Board schematic & layout
    • Bench test schematic (how you tested these parts)
      • Since these are humidity parts that are sensitive to soldering and rework, I will likely need to test these parts on the boards they are already one, so any help making that easier for me is appreciated
    • All your measured values (the table you included is very good, any extra data you can provide like your reference readings or temp values would be great as well)
    • Clear description of the problem (please summarize what you have told me throughout this thread and include any additional information)
      • Please also include any potential chemical contamination information, whether by you or the assembly house. Even something as simple as board cleaner can significantly change the RH accuracy so making sure we know exactly what these 8 parts were exposed to is critical
    • How many systems show failure?
    • How many systems were tested?
      • Please also include some information on your RH reference as well

    Please submit this as soon as you can. I will help support testing these parts once the return is processed.

    Thank you

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 60 points

    thank you for your reply.

    I shipped the package today.

    Should this discussion be closed?
    Is it better to leave it open?

  • 0 in reply to Manabu Hashimoto
    TI__Genius 11985 points

    Thank you for shipping the parts, I am going to everything I can to try and solve ths for you. Let's leave the thread open for now, I may need to reach you quickly for additional questions.

  • 0 in reply to Alex Thompson
    Prodigy 60 points

    Understood.
    Thank you very much.