Just found out about the Citizen Weather Observation Program (CWOP) hosted by NOAA. The have a wealth of data that I am working my way through. In particular the previous project logs show my concern with accuracy for wind speed and relative humidity. It turns out that those concerns were well placed as they are difficult things to accurately quantify.
From their information and other sources I have decided that I need to make this station in a way that allows aspirated temperature and humidity measurements. My own experiments show that in the gulf coast U.S. (and other equatorial areas), humidity above 80% is common and becomes a real problem for nearly all "membrane" type electronic humidity sensors. For that reason I am developing an aspiration method that will allow for three simultaneous sensors:
- Electronic digital temperature & humidity sensor
- Dry bulb digital temperature sensor
- Wet bulb digital temperature sensor
Having a wet bulb system really adds to the complexity, but seems unavoidable if reliable low cost humidity measurements above 80% RH are needed. On the other hand, the wet bulb system falls short of design goals for very dry (less than 15%) areas like deserts and for RH measurements below freezing. My hope is that the membrane sensor will fill in those weaknesses.
My current plan is to use common PVC fittings for the aspiration system because I don't want to take the time to learn enough 3D software to model it for 3D printing.