In my empirical observations experimenting with a dht22 temperature / humidity sensor, I have come to the conclusion that they are most definitely for INDOOR USE ONLY! Any time I placed one outside, they quickly max out at 99.9% humidity, and don’t recover until I dry them out, and place them indoors. I have ordered a HTU21D-F sensor to replace the dht22 in my rf propagation / humidity experiment.
The dht22 does work pretty well indoors. I took over 14K samples over a 30 hr period and got clean results.
The temperature is in red and the humidity in green. For most of my data logging projects using a pi, I sore the results in CSV format. I used perl’s CSV database functions to query results and create graphs. This is the sql query I use on the to csv tables to get the above graph:
select data.index, data.temp, temp_humidity.humidity from data outer join temp_humidity on data.index = temp_humidity.index