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HDC1000: Drift and offset questions

Tim Zwirs
Prodigy 10 points
Part Number: HDC1000
Other Parts Discussed in Thread: HDC3020, HDC1010

I have two questions about this product (HDC1000). The first one is regarding the electrical characteristics, the second about the long term drift effects. I've already contacted customer support but they suggested to post a forum question so here we are. I hope one of you can help me with this.

In the datasheet the following point is written down: (7) Recommended humidity operating range is 20% to 60% RH. Prolonged operation outside this range may result in a measurement offset. The measurement offset will decrease after operating the sensor in this recommended operating range.
Would someone be able to more accurately define prolonged? What should I think of this? What would be the "negative" effects after 1 minute above 60%RH, and what for 1 hour, 1 day, 1 week, 1 month, 1 year. And what period do I need to think of when I read "offset will decrease after operating the sensor in this recommended operating range"? Does it behave proportionally with the definition of prolonged? For example, 1 day above 60% creates an offset, and it needs another day to recover?

The second question is about the long-term drift. On the datasheet, it says long-term drift is 0,5%/Year, Under which conditions does this happen? and does it drift faster if the product operates in an environment where the RH is between 40-80% with peaks of 95%? In that case what %/Y would I more likely have? Would I be able to get an estimation?

Links to the product:

HDC1000 data sheet, product information and support | TI.com

HDC1000 Low Power, High Accuracy Digital Humidity Sensor with Temperature Sensor datasheet (Rev. C) (ti.com)

  • +1
    TI__Genius 13085 points

    Hi Tim,

    Thanks for reaching out. To address your first question, I agree that "prolonged" is vague, and not quantified. I would not expose the HDC1000 to RH conditions above 60% for more than 1 hour. RH drift can occur quickly as the sensing polymer locks in moisture in very humid environments, especially in early generation humidity devices like the HDC1000. The "negative effects" would be RH drift, which means that the device will start to show a higher RH value than is actually present. For example, if the RH in the room is actually 50%, a HDC1000 with significant RH drift could read 60%. All polymer-based humidity sensor ICs will face this problem to some extent, but HDC1000 is an older device is more vulnerable to RH drift than newer devices in our portfolio.

    The HDC1000 should recover proportionally when left at ambient conditions like you suggest, but to caution you, RH drift can become permanent (especially on these old HDC devices) if the exposed RH condtions are extreme (>80%) and for a continuous period of time (usually more than 1 week) since the moisture can get so saturated into the sensing polymer that returning the device to ambient room conditions wont evaporate the excess moisture completely.

    For long term drift, this spec refers to the drift that will occur even if the device is never used outside of ambient room conditions. The HDC1000 will definitely drift faster in the conditions you have listed, where RH can easily exceed 60%. I would expect in that case you would have RH drift levels of around 10%RH. 

    Hence, if you are considering a TI humidity sensor for a new design, I strongly recommend you dont use HDC1000. Instead, you should look at HDC3020. HDC3020 is more accurate, is more drift resistant, and will be able to be used in the RH conditions you have listed.

    Thanks

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 10 points

    Hi Alex,

    Thank you for your quick response. We have implemented this sensor around 6-7 years ago in our sensors that were used inside office buildings to measure the RH. Last summer we experienced a week of high humidity with levels of around 90% outside. After a while the sensors started to measure a post processed RH of 100%. There have probably been more of these summers in the past 6 years, so long-term drift would also account to this problem partially. In any case we could expect the same behaviour again next year so I'm glad we are aware of the cause of the issue and can anticipate on that.

    We are currently using the HDC1010 which seems to be more sufficient for our practices according to its datasheet. However, I will suggest looking into the HDC3020 for any future hardware updates. Thank you for your advice, it's much appreciated.

    Kind regards, Tim