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shred / dustycase

3D printed frame for a Particulates Sensor
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DHT22 temperature reading is too high #1

Open shred opened 6 years ago

shred commented 6 years ago

There are reports that the DHT22 temperature is about 3°C higher than a temperature measured by other outdoor thermometers.

It seems that the sensor is too well isolated inside the case, and not sufficiently surrounded by the air inside the wind tunnel.

A solution may be to place the sensor as close to the outside of the air inlet as possible, or even outside of the case.

mrueg commented 6 years ago

I'm seeing this issue as well. It seems to be worse on the position of the optional BMP and not a static offset.

"Real" temperature 19.80
DHT22 temperature 23.20
BMP180 temperature 24.90

The increased temperature of the BMP180 is probably due to the fact that it's in the top part of the case where the heat of gets stuck.

mach0 commented 5 years ago

it seems that the BMP180 is showing a higher temperature anyway, see: http://www.kandrsmith.org/RJS/Misc/Hygrometers/calib_many.html

but still there should be more airflow inside the case. Has anyone a solution for that?

shred commented 5 years ago

Thank you for the link!

The BMP180 was meant to be a barometer sensor only, with an added thermometer as bonus. The DHT22 was supposed to be the main sensor.

I must confess that I am somewhat disappointed of the DHT22's accuracy in the printed frame. I was hoping that the air taken in by the particulates sensor was sufficient for accurate temperature and humidity readings, but it turned out that the temperatures are always about 3°C too high, and the humidity is adapting to changes very slowly.

I was contacted by someone who planned to put the DHT22 outside of the case, but never heard back about the results.

The DHT22 doesn't look very weather proof to me, so I prefer to keep it inside the case anyway. Maybe it should be mounted closer to the outside of the intake pipe? Maybe it's also a problem that its back and its sides are covered by the printed frame, which may work as a thermal insulation.

I am also pondering about removing the DHT22 altogether, and replacing it with a BME280 (combined thermometer, hygrometer, and barometer) that is mounted as close to the outside as possible.

However I can't do much about it at the moment, as the 3D printer I have access to is broken. :cry: