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HDC3020EVM: Drift calibration

Yishan Chen
Prodigy 720 points
Part Number: HDC3020EVM
Other Parts Discussed in Thread: HDC2010, HDC3020, HDC2010EVM, , HDC1080

Hi,

My customer evaluated HDC2010 and HDC3020 using EVM at the same time.

They found the consistency of HDC2010 is good but HDC3020 is bad. You can check with the following picture.

It seem there are some drift both in temperature and humidity.

I know we have solution to deal with humidity but what about temperature?

HDC2010： Two group, both use HDC2010EVM,Blue and Red is temperature, yellow and green is humidity.

 

HDC3020:Two group, same configuration

Customer said the HDC3020 group 2 have more offset compared to the HDC2010.

I think we should calibrate HDC3020 group 2 because it seems have some DC offset here.

Do you have any advise?

Yishan Chen

  • 0
    TI__Expert 5670 points

    Yishan,

    Thank you for finding this. I will have to look into on why these HDC3020EVMs are offset and not consistent with each other. My guess is that there may be an issue with the HDC3020 group 2 part from the factory before it is placed on the EVM. But I will look into this.

    To solve the immediate problem, yes please write a temperature and humidity offset using the GUI into the HDC3020EVM group 2 board. Normally, a higher temperature value will cause RH to drop, but when programming the temp offset register, that change won't affect RH. So you will need to program an offset for both temp and humidity to have the group 2 board match the group 1 board.

    Thanks

    -Alex Thompson

  • 0 in reply to Alex Thompson
    TI__Prodigy 720 points

    Hi Alex,

    Any update from you? Thank you

    Besides, I want to know if we have the humidity offset, are there must be temperature offset at the same time? Do they(offset) have any relationship?

    We can run the algorithm to determine the humidity offset, but how do we know temperature offset？

    Another question is do we have any material about how to design the mechanical case of HDC3020?

    Thank you.

    Yishan Chen 

  • 0 in reply to Yishan Chen
    TI__Expert 5670 points

    YIshan,

    Normally RH does depend on temperature, so as temperature increases RH decreases. However when programming the offset regsiters, there is no tied relationship. So you can adjust each one independently. If you want to be safe, I would start with temperature first, verify the offset you apply to temp does not affect RH, then apply the RH offset.

    There is no algorithm to determine temperature offset in HDC3020, because the temperature result isn't going to drift like RH will (technically it does drift slowly over time like any temp sensor but that drift is very small and isnt dependent on environment like RH). The way to determine your temp offset would be to compare it to a calibrated reference, or another trusted temperature sensor. Since you have other EVMs like the HDC2010 that you trust, I would use the difference between the HDC3020EVM and the HDC2010EVM as your offset.

    This document here is an older app note mainly pertaining to the HDC1080 family, but its recommendations on how to enclose an HDC device are still valid for HDC302x:

     snaa297a.pdf

    Thanks

    -Alex Thompson

  • 0 in reply to Alex Thompson
    TI__Prodigy 720 points

    Hi Alex,

    Thank you.

    Another question is could we use one PC to sample multiple data rails using HDC3020EVM？ How do we set the software and hardware? Gui and I2C address.

    Yishan Chen

  • 0 in reply to Yishan Chen
    TI__Expert 5670 points

    Yishan,

    Yes you can connect two EVMs at once on the PC with HDC3020EVM. I would plug in one EVM, launch the GUI, confirm connections and readings. Then in a separate window, open another instance of the GUI and plug in the second EVM. Each GUI window will read from 1 EVM. This is what worked for me.

    Thanks

    -Alex Thompson