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Improve case design for DHT22 Sensor

martinjuhasz

Hi Community,

 

i'm working on a multisensor based on an ESP8266 with multiple components/sensors including an DHT22 attached to the outside of the housing (see picture).

 

Sadly the sensor is giving me incorrect results from +1/2° depending on the outside conditions. I noticed that it's the case itself that has some effect on the temp reading. When increasing the space between the DHT and the case about 2-3cm the readings are fine. Having just a narrow gap between the case and the sensor results in a slightly warmer reading, so the case itself is emitting some warmth.

 

I tried putting in multiple venting holes into the case and also removed the top plate (as in the picture) but without any noticeable improvements.

Does anybody have an idea how i could improve my case design to include the DHT sensor somehow without having it heated up by the other components itself? Hardcoding some subtraction from the actual reading is no option for me, as this inelegant and also the increase in temperature from the case varies depending on the outside condition.

 

image

 

Thanks for any tips on this!

  • 0

    Martin,

     

    from the Aosong Electronics Co., Ltd specification:

     

    "DHT22 should be mounted at the place as far as possible from parts that may cause change to temperature"

     

    While the statement is loosely translated, it does make a good point.  If possible isolate the sensor from any potential heat sources (insulation around the source of heat).  Another possible solution would be to use a small (very small) fan to circulate air in the enclosure.  Circulating ambient airflow might limit the effect of any local heat rise.  Be careful to not have the sensor in the direct airflow as that might decrease the temperature too much.

     

    Good luck,

    Gene

  • 0

    There are a couple of things you can try.

    1. Insulate the area of the main case that is close to the sensor - this will minimize the heat flow and allow the external surface to be closer to ambient temperature. Perhaps a little pad of weather stripping foam on the inside of the case would help.
    2. Decrease the outer surface thermal resistance to ambient temperature. You can conduct ambient temperature (from a place of good ambient temperature) to the area where you want to measure it using a copper or aluminum plate.

    If you use both of these methods, you should be able to get much better measurement performance.

  • 0 in reply to dougw

    This is a good advise. If you ever go with option 2 I'd like to add that I would test both materials and see which one fits best. Copper is better at heat transfer than aluminum, but is not very good at releasing the heat, which may end up increasing your temperature readings in the short term, this is one of the reasons why hybrid Cu-Al heat-sinks are popular.

  • 0 in reply to dougw

    Thanks for this aleady. Speaking of option 2, how would you advice me to apply the plate? Not to sure about where to place that plate. Between the sensor and the outer case? and then extend it somewhere offside the case?

  • 0 in reply to martinjuhasz

    Just think of it as a constant temperature surface - it should go between your sensor and a place where the temperature is correct.

    You want as much insulation as possible between your sensor and the incorrect temperature.