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HDC2080: In same environment, getting difference in Temp and Hum readings from multiple HDC2080

Vivek Roy
Prodigy 110 points
Part Number: HDC2080

Hi,

We are using HDC2080 to monitor temp and RH of environment.

We place multiple units, having HDC2080 in a canopy after proper calibration.

Initially we found that the max difference in temp is approximately 0.5 degC and in RH, its 1%.

But after 5 days, we found that the difference in temp was increased to 6 degC and in RH, more than 10%.

Please help us to to find the root cause and its resolution.

  • 0
    TI__Mastermind 27535 points

    Hi Vivek,

    Thank you for your post.

    Are all of the HDC2080 devices reporting similar offsets? Have they been exposed directly to condensation of some kind, or any of the chemicals listed in our storage and handling guidelines?

    Also, what reference are you using to determine the temperature and humidity offsets?

    Best Regards,
    Brandon Fisher

  • 0
    Prodigy 110 points
    Hi Fisher,

    Please see the answer of queries.

    1. Are all of the HDC2080 devices reporting similar offsets? No, in some cases, the diff is less and in some cases its high, max diff we observed is 6 degC in Temp and in RH, its apx 10.

    Have they been exposed directly to condensation of some kind, or any of the chemicals listed in our storage and handling guidelines? No, we are not using any chemical. 

    Also, what reference are you using to determine the temperature and humidity offsets? We have standard reference instruments (thermometer and hygrometer, both are analog) and placed along with the devices. After 10 minutes, we noted the analog values, calculate temp & Rh offsets for each unit and written the same into HDC2080.

    Please let me know if you have any other questions.

    Regards

    Vivek Roy



  • 0 in reply to Vivek Roy
    TI__Mastermind 27535 points

    Hi Vivek,

    Vivek Roy said:
    No, we are not using any chemical. 

    In the past we have seen chemicals mistakenly applied to the sensors during routine cleaning of the surrounding environment, so the chemicals could have been applied inadvertently. Please ensure that no one would have mistakenly cleaned your test fixture. 

    Vivek Roy said:
    We have standard reference instruments (thermometer and hygrometer, both are analog) and placed along with the devices. After 10 minutes, we noted the analog values, calculate temp & Rh offsets for each unit and written the same into HDC2080.

    Good, it sounds like you are using the right instruments to assess this. Sometimes 10 minutes in a new environment is not enough for precision humidity sensing instruments to completely settle, but I would not expect that to produce an error of 6%.

    How long after assembly did you wait to calibrate the sensors? There will always been a period (roughly 24-48 hours days) after assembly where the HDC sensors read below the expected RH value. If you calibrated the sensors before the polymer had a chance to "rehydrate" after assembly there is a chance that their settling has caused your offset point to shift.

    Best Regards,
    Brandon Fisher

  • 0
    Prodigy 110 points
    Hi  Fisher,

    Thanks for the prompt response.

    I checked with our production team and they shared that at present no chemical compound has been used to clean the pcb boards.

    How long after assembly did you wait to calibrate the sensors? The units were manufactured 15-20 days back and ran for several hours. After that we took all those units and started the process.

    There will always been a period (roughly 24-48 hours days) after assembly where the HDC sensors read below the expected RH value.  Ok, we can wait for 48 hrs after manufacturing and before doing calibration. But we also want to know if the sensors need to power up during that period or power-off condition is also fine. 

    Request you to suggest us some steps, so that we can reduce the %error within an acceptable limit.

    Again, yesterday we noticed another problem. In one separate unit we did calibration. After calibration the Temp value was around 27 degC and RH 45. After 5 minutes, we noticed temp value changed to around 33 degC, but no change in RH. You can see the following log message at every 1 sec interval. Then we read the calibration value and found that temp calibration changed to 0xF9. Then we re-calibrate again and ran. After 5-7 mints, problem occured again and found temp calibration value changed to 0XF9 again. Please help us to resolve it. 

    TEMP: ,27.42,RH: ,44.99
    TEMP: ,27.41,RH: ,45.02
    TEMP: ,27.41,RH: ,45.03
    TEMP: ,32.90,RH: ,45.01
    TEMP: ,32.90,RH: ,45.04
    TEMP: ,32.91,RH: ,45.00
    TEMP: ,32.88,RH: ,44.98
    TEMP: ,32.88,RH: ,45.00
    TEMP: ,32.90,RH: ,44.97
    TEMP: ,32.90,RH: ,44.89

    Regards
    Vivek Roy


  • 0 in reply to Vivek Roy
    TI__Mastermind 27535 points

    Hi Vivek,

    You configuration register being corrupted makes me think that you are experiencing the same issue that was discussed in this thread: https://e2e.ti.com/support/sensors/f/1023/p/879641/3260547#3260547.

    You can follow the suggested answer at the bottom of that thread (i.e. either operate at 1.8V, or use the i2C command sequence listed in that answer). That should prevent the offset register value from changing. 

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    Prodigy 110 points

    Hi Fisher,

    Thanks for sharing the document. I will go through it and update you.

    I have another query and need your suggestion. In few sites, where we will install our devices, the environment is not good.

    Device may face the presence of NH3 in Air and ppm will be changing, 0 to 30 ppm range, not constant at any point.

    1. Do you think it will create any problem in HDC2080? any possibility of damage or drift?

    2. If there is a possibility of drift in temp and RH value, how much percentage and in which direction (increase or decrease)?

    3. If there is a drift , then how much time it will take to compensate the drift, after removing the device from bad environment?

    Regards

    Vivek

  • 0 in reply to Vivek Roy
    Prodigy 110 points

    Hi Fisher,

    Waiting for your reply.

    Appreciate if you can share the answer of my queries as early as possible.

    Regards

    Vivek

  • 0 in reply to Vivek Roy
    TI__Mastermind 27535 points

    Hi Vivek,

    Vivek Roy said:
    1. Do you think it will create any problem in HDC2080? any possibility of damage or drift?

    We do not have data specific for various concentrations of NH3 (i.e. measurements for 0 30 ppm concentrations), but our testing with common cleaning solutions found that many do result in a positive offset in humidity sensors. Typical atmospheric concentrations of ammonia would be fine, but with your exact range of PPM it is hard to say.

    Vivek Roy said:
    2. If there is a possibility of drift in temp and RH value, how much percentage and in which direction (increase or decrease)?

    Depending on the exact chemical, the exposure time, and the concentration, you may see shift anywhere from 0% to 20% RH. 

    Vivek Roy said:
    3. If there is a drift , then how much time it will take to compensate the drift, after removing the device from bad environment?

    Not all chemically induced offsets are reversible, but for those that are, typically a bake (85 - 100C for 24 Hours), followed by a resting period will help correct some of the offset.

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    Prodigy 110 points

    Hi Fisher,

    Actually we are using our device in public urinals where in some cases the ammonia concentration in the air is about 7-8 ppm ( As you might have known Public urinals when not cleaned properly can generate Ammonia odour).  Hence to check the effect of ammonia on our device we introduce ammonia of 15 ppm on the device.    

    If HDC 2080 can work in that environment without any issue that would solve our problem.

    As regards the drift is concerned we shall check if baking at 85-100 deg resolves the issue.

    Regards,

  • 0 in reply to Vivek Roy
    TI__Mastermind 27535 points

    Hi Vivek,

    Your explanation makes sense and I believe an exposure test to 15ppm Ammonia is the correct path to take. 

    If you encounter any more issues or have any more questions feel free to ask. 

    Best Regards,
    Brandon Fisher