# rjs3273

Member Since: October 17, 2013

Country: United States

## Profile

http://www.kandrsmith.org/RJS/

• I have been really impressed with this sensor. I did not believe they could possibly deliver the datasheet’s quoted accuracy at this price. You can spend thousands on a lab-grade hygrometer and they still only claim 2% accuracy. How can this do it for \$10? So I tried to test and compare six of them for my myself. I do not claim to be an expert or that this experiment is flawless, but if anyone is interested my write up is at http://www.kandrsmith.org/RJS/Misc/calib_dht22.html These are just the results I got for my devices. At the level of errors I am seeing, the fault could just as likely be in my experiment as in the devices themselves.

I still do not really believe the 2% absolute accuracy claim from 0-100%, but they are amazingly good for the price and come surprisingly close to that. The maximum errors I have measured are about 6% RH, with typical errors of 2-3% RH. I see quite a strong temperature dependence of at least 2% RH over the temperature range I have tested so far but am still working on that. I have not done any long term tests, but on timescales of a few weeks I find repeatability in the range 0.5-1% RH.

• Yes, I think that is part of the reason why the powers-that-be keep trying to discourage use of terms like “1000-year event”, but it is so much easier to say and sounds cooler than either 0.1% or 693 year event.

To tristan, maybe it is just me, but I find it much easier to look at probabilities like this from the other side. Instead of what is the chance of it happening, what is the chance of it not happening. For the 0.1% event, there is a P=0.999 probability it will not happen this year. Chance it will not happen this year AND not happen next year is just 0.999 x 0.999. Not happen three years in a row is 0.9993. The point TomC is making is that 0.999693 is about 0.5 so after 693 years the thousand year event in some sense becomes “likely”.

RJS (Another Boulder resident. Yesterday I just got the house heating back on after the flood.)

No public wish lists :(

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