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HDC1080: Accuracy issue with humidity sensor

Katrina Barnes1
Prodigy 70 points
Part Number: HDC1080

I currently have 3 custom circuit cards that have the exact same layout and are being tested on the same lab bench, but are all reading different RH values.  One is reasonable at 45% (agrees with an external RH sensor), another reads 61% and the last reads 70%.  Can you please give me some pointers as to where I should look for issues?

Thanks,

Katy

  • 0
    TI__Expert 5695 points
    Our support team will contact you shortly.
  • 0
    TI__Expert 5145 points
    Hi Katy,
    Have the parts been soldered following the procedure described in the product datasheet on page 18?? Could you please also double checks if there is any contamination on the surface of the sensing elements?
    Please let us know.
    Best regards,
    Carmine
  • 0 in reply to Carmine Iascone
    Prodigy 70 points

    Carmine,

    I directed our technicians to replace the sensor, taking care to protect the window from contamination and also not to surpass the max soldering temp of 260 degC.  This seemed to have worked, but now the sensor is drifting down significantly (-10%).  Any idea what would cause drifting?  Also, what can be used to properly clean the sensor?

    Thanks,

    Katy

  • 0 in reply to Katrina Barnes1
    Prodigy 70 points

    Some additional information on this issue--I have multiple sensors with this issue.  One has drifted all the way from 44% RH at the start to 17% after about 1 hour.  I looked at the I2C data and that looks good, verified the calculation is correct, verified there is not a power issue or excessive heat in the area. 

  • 0 in reply to Katrina Barnes1
    TI__Genius 13650 points
    Hello Katrina,
    this sounds like the sensors have been damaged by contamination. Please verify that they have been assembled with no-clean solder (see section 8.3 in the datasheet), and no chemicals have been used to clean the sensors.
    While the issue you are describing appears to be a contamination issue, it may still be worth checking if you observe a temperature difference between the devices. A difference in temperature measurement, for example by heat transfer from a nearby processor to the sensor, affects the %RH measurement.
  • 0 in reply to Ben Kasemsadeh
    Prodigy 40 points

    What kind of effect would contamination have? Is it always a positive offset? Is it a fixed offset?

    I have a similar problem as Katrina: 4 PCBs sitting on the same bench, reading a correct temperature. However I'm getting completely different RH readings. External meter says approx 49%RH and the 4 boards read anywhere between 40-60.

    Also, this gets worse with time: leaving the board on for a long time (days) makes the problem worse. The sensor has a cutout around it on the PCB to avoid temperature bleed - if any - from other components.

    Could it be that I run the heater on a regular basis (30 seconds every 4 hours-ish)? (The spec says there's a heater, but doesn't explain when/how often we should run it)

    Thanks!

    ML