Most weather stations of an official nature, seem to come with the louvered Stevenson screen. Osengr.org has a shield of a different configuration. I think I've run across searches which acknowledge that people here have at least seen what I am talking about.
But, for those that don't, there is a horizontal section of pipe (white) where the sensors go, and then at either end there is a 45 degree elbow with a section of pointed to the ground, and there is one (or two) fans drawing air through the pipe.
I don't believe the person at osengr.org claims to have invented this, but it has been a while since I read things carefully.
Whether a person gets "white" pipe or not, I really don't think the white pipe is "white" enough. I think it is a good idea to find a paint with a very white titanium dioxide pigment, and paint the outside with that. And this might be a yearly maintenance issue. I've raindrops sit on a very white painted railing for more than 1 day in bright sunshine. A good white absorbs very little sunshine. And my "days" are much longer than most people, since I am closer to the N pole.
In any event, what I am thinking of is to have a 4 inch pipe inside of a 6 inch pipe (with the bends at either end, so a fussy assembly problem). At the inlet end, have a 6 inch T (vertical leg pointing down), so that a person can "cap" the outer "plenum" . There is to be a 4 inch fan pushing on the inlet which protrudes past the cap, and a 4 inch fan sucking on the exhaust. There is a 6 inch fan on the T inlet. All fans are 4 wire (PWM control).
The centre (horizontal portion) might be a bit longer than most people would use. Near the "beginning" of the 4 inch horizontal section, would be the RH sensor. Then there is to be an array of temperature sensors. Some of the temperature sensors will be inside capsules. The capsules will be small. What would be nice (I think) is to find small titanium capsules, as stainless steel and most plastics are lousy at conducting heat.
If you have seen a Differential Scanning Calorimeter (DSC), I think you will catch what I am doing. The 3 organic "goat" acids have phase changes at useful temperatures (Caprylic - C8 16.7C; Capric - C10 31.6C; Caproic - C6 -3.4C), there are other materials which could be used as well.
Each capsule is a cylinder, with the two flat ends horizontal. The active region of the temperature sensor is near the bottom. A "heater" is attached to the bottom of each capsule. Each capsule contains a known amount of something. Most should be materials with a phase change in the temperature range of interest. There should be two of a material that has no phase change in the temperature range of interest (a wax?). There should be one of these NULL capsules at the inlet end (alongside an un-capsuled sensor) and one at the end.
The capsules should be arranged so that the lower phase change temperatures are towards the inlet end.
The idea is, that if the unshielded temperature probes are for example indicating a temperature of -3.6C (which means the Caproic acid capsule should be frozen), we can send a few Joules of heating to that capsule to get the Caproic acid just above the phase change temperature, and then we follow the cooling curve through the phase transition.
There are lots of details in doing this. The fan speed has to not change during the test. The unshielded air inlet temperature sensor should not change. And probably others.
Measuring temperatures or RH with an Arduino has been done a lot. This kind of thing will need a RPi to run things. I never looked, can a person compile a real-time kernel for RPi?
But the idea is to sample temperatures something like every 15 minutes. So, at some times of the day, the temperature measuring system may insert a heating cycle to an appropriate sensor to catch the cooling cycle. How many Joules to inject will vary with what the temperature is for any given sample.
I have no doubt most people would think this too much. For those that don't, is it possible? Will it allow me to calibrate the system of temperature probes?
