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[on:]

Hi

I put together Arduino nano and temperature/humidity sensor DHT11 using DHT11 library..
DHT11 humidity should work in range 20%-90% RH.
I am getting 27%RH at 21 Celsius -dry but ok.. but when i increase temperature to 40 degrees of Celsius i get result 4% RH ..
Sensor is in the sealed box with two ventilators..
...even if i put inside wet towel i still don't get more than 11% RH

do i have problem with sensor or with understanding the physics??

thanks

[Reply #1 on:]

Hi dragot,
Can you supply links to the DTH11 library your talking about, post your code using the 'Insert Code' # button and a picture/diagram of how you have the DTH11 wired up please. This will make it a lot easier to help you.

[Reply #2 on:]

The DHT11 sensors are not the most accurate, DHT22 scores better. Both are discussed at regular intervals on this forum, and an often heart advice is "calibrate"

[Reply #3 on:]

I am getting 27%RH at 21 Celsius -dry but ok.. but when i increase temperature to 40 degrees of Celsius i get result 4% RH ..
Sensor is in the sealed box with two ventilators..
...even if i put inside wet towel i still don't get more than 11% RH

do i have problem with sensor or with understanding the physics??

Physics. RH is a measure of how much water there is in the air compared to the maximum amount of water that the air can hold. The amount of water that air can hold increases with temperature. The tables at http://en.wikipedia.org/wiki/Vapour_pressure_of_water describe how the saturation vapour pressure of water (i.e. how much water air can hold) varies with temperature, and from that you can work out whether a drop from 27% to 4% from 21C to 40C is reasonable.