DHT22 sensor calibration

Thread Starter

kalasas28

Joined Apr 28, 2024
1
Hello, since my circuit and code is finally working i've decided to test it out.First i've tried to compare humidity data from dht22 and from my digital clock who's also capable of measuring humidity.I don't have possibility to create accurate environment, so i've compared my clock and dht22 in a room conditions and in a lunchbox sprayed with water.While temperature data is almost simillar humidity data between those two are way off.In a room condition dht22 show about 15% more humidity than my clock while in a lunch box clock showed about 70% humidity.This is the reading when dht22 was in a lunchbox.As you can see there was a time when i opened the box, since humidity dropped.But when i closed it after a while humidity rises by approximately 0.2-0.4 each time data is sent, and i have a feeling it would keep going untill 100%, but i dont have time to test it out.I feel like dht22 needs calibration although it needs to be tested in different environments which i dont have tools for that.Even though clock measurements also might be not so accurate i trust it more than dht22.How could i calibrate my sensor with household stuff,or maybe there are better sensors which would not require calibration?


Humidity: 92.70%
Temperature: 26.10°C
Humidity: 92.80%
Temperature: 26.10°C
Humidity: 92.80%
Temperature: 26.00°C
Humidity: 92.60%
Temperature: 26.00°C
Humidity: 84.00%
Temperature: 26.00°C
Humidity: 78.00%
Temperature: 25.90°C
Humidity: 68.00%
Temperature: 25.90°C
Humidity: 64.20%
Temperature: 25.90°C
Humidity: 63.50%
Temperature: 25.80°C
Humidity: 63.80%
Temperature: 25.80°C
Humidity: 70.00%
Temperature: 25.80°C
Humidity: 74.20%
Temperature: 25.80°C
Humidity: 77.50%
Temperature: 25.80°C
Humidity: 80.10%
Temperature: 25.80°C
Humidity: 82.10%
Temperature: 25.80°C
Humidity: 83.60%
Temperature: 25.80°C
Humidity: 84.90%
Temperature: 25.80°C
Humidity: 85.90%
Temperature: 25.80°C
Humidity: 86.70%
Temperature: 25.80°C
Humidity: 87.40%
Temperature: 25.80°C
Humidity: 88.00%
Temperature: 25.90°C
Humidity: 88.50%
Temperature: 25.90°C
Humidity: 88.90%
Temperature: 25.90°C
Humidity: 89.30%
Temperature: 25.90°C
Humidity: 89.70%
Temperature: 25.90°C
Humidity: 90.00%
Temperature: 25.90°C
Humidity: 90.20%
Temperature: 25.90°C
Humidity: 90.50%
 

MrChips

Joined Oct 2, 2009
31,088
Humidity sensors are not exactly precision devices. If you can get accurate measurements within ±2% then you're doing well. In other words, you can throw away the 2 decimal places.

Also, humidity sensors are less accurate below 10% and above 90% RH.

There are two ways to do RH calibration.

1) Standard salts
For example, common salt NaCl in a jar will give 75%RH @25°C
https://www.engineeringtoolbox.com/salt-humidity-d_1887.html

2) Dewpoint measurement
You can use a wet bulb/dry bulb measurement to determine dewpoint.

Then use a psychrometric chart to determine the RH.
https://www.engineeringtoolbox.com/docs/documents/816/psychrometric_chart_29inHg.pdf

RH vs wet-dry bulb temperature
https://www.engineeringtoolbox.com/...e_humidity_wet_dry_bulb_temperature_deg_C.pdf
 
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