Dave,
thanks a lot for the document you have indicated to me.
I will read it carefully.
I noted that all the weather station here on the web and the control towers broadcast RH even if the temperature is below 0°C. All of them diclare a consistent RH. At this point I do not understand well. I must study a little bit more.
At the same time I am notice that my Oregon weather station gives a correct RH for negative temperature too.
The SHT15.BS2 program has a bug somewhere : I would like to know if someone solved it !
Please let me know... just in case you know a fix.
Thanks again Dave for the help.
73 !
Ambrogio
IW2FVO
North Italy


Quote Originally Posted by Dave View Post
iw2fvo, It is not possible to have this sensor or that equation to give you acurate results below freezing. Please read this artical: http://www.rhsystems.net/papers/RH_WMO.pdf. I have used a chilled mirror in the past for this type of measurement sampling air from a test chanber at - 20 F. However the type of sensor you are using is limited as far as humidity measurements and that is why the formula is not acurate below 0C.

Dave Purola,
N8NTA