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Forum Thread Details
  • State Verified Answer
  • Replies 38 replies
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  • temperature
  • temperature sensor
Related

Temperature sensor accuracy

ntewinkel
ntewinkel over 1 year ago

Hi all,

I have two temperature sensors near each other, outside. In the winter I was using one to keep track of the nectar temperature in a hummingbird feeder, but I just left it hanging there for the summer.

Here is the typical result:

image

The top line is a dht11 or could be 12. It includes pressure and humidity. The bottom line is a ds18b20 in a metal tube.

Both are digital, but one is nearly always about 1 or 2 degrees higher than the other. Generally it’s fine to give me a close enough idea of what’s going on, but I think I should be more accurate when looking at the freezing point.

Do I need to calibrate them? How would I go about doing that? Ie, what can I trust as a proper baseline? I don’t have access to any really guaranteed kind of thermometer, I think. Thinking 

Thanks in advance for any wisdom you can send my way!

-Nico

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  • dougw
    dougw over 1 year ago +5 verified
    If they are waterproof you can stick them in a slush of ice and water to get a zero degrees reference. If they aren't waterproof you can put them in a plastic bag in the ice/water mix. If they can take…
  • beacon_dave
    beacon_dave over 1 year ago +5 verified
    Comparing data sheets it looks like the accuracy of the DHT11 is ±2°C whereas the DS18B20 is ±0.5°C It will be interesting to see what your testing shows.
  • wolfgangfriedrich
    wolfgangfriedrich over 1 year ago in reply to dougw +4 verified
    During the ice-water test, you have to be careful not to touch the ice-cubes. They are still colder than zero degC. I learnt this during a thermocouple roadtest.
Parents
  • ntewinkel
    0 ntewinkel 11 months ago

    Here’s my ice bath setup. I’m using an insulated little lunch box type cooler, with a yogurt tub in it that holds the ice water. Under it and on both sides are ice pack, and I tossed in a frozen bottle of water.

    image
    closed up it holds the temperature really well.

    image
    image
    I adjusted the sensor readings on the server side (node red). It’s a bit of a cheat but it’s specific to that sensor and that sensor only reports to the one server. And, at least at the zero mark, they are both reliably reporting the same zero temperature for hours.

    • image
      Not sure what will happen as the temperature goes up, but that is close enough. Next I’ll have to print a separate enclosure for the bme280 so the warmth of the chip won’t affect it.
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  • battlecoder
    0 battlecoder 11 months ago in reply to ntewinkel

    That's great!

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  • battlecoder
    0 battlecoder 11 months ago in reply to ntewinkel

    That's great!

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